État des populations naturelles de rainette faux-grillon boréale (Pseudacris maculata) et stratégies de réintroduction en milieu aménagé

Abstract

The boreal chorus frog (Pseudacris maculata) is a threatened species in parts of Canada. A significant decline in its occupancy has been noted over the last 20 years in the Montérégie region of Québec, Canada. However, the size of these populations is unknown. Limited information is available on the reproductive dynamics of this species, which hinders the planning of conservation actions such as reintroduction.
To fill these gaps and adequately prepare for the first reintroduction, we conducted a project targeting natural populations and larval development. Three populations of boreal chorus frogs were monitored during one breeding season to estimate their abundance and to identify the influence of environmental factors on call intensity. We also aimed to evaluate the effect of density and additional resources on larval development and survival in mesocosms, and to estimate the survival of metamorphs after reintroduction.
We found a quadratic relationship between the calling intensity and air temperature. There was a low occurrence of choruses of P. maculata. One of the three natural populations went extinct. In the other two sites, population sizes were estimated at 28 adults (95% confidence interval: [23,38]) and 10 adults (95% CI: [8,16]). Body condition of metamorphs was better at low larval density with additional litter in mesocosms. A total of 732 metamorphs were reintroduced into ponds constructed in Mont-Saint-Bruno National Park. Some reintroduced individuals were recaptured, but no survival estimation could be modelled due to the high incidence of tag loss.
This study highlights the precarious situation of the populations of P. maculata, which were once more abundant in southern Quebec. We showed that larval development in mesocosms is an effective strategy for rearing individuals for reintroduction. These data will help guide other amphibian reintroductions in protected environments.

Full text

© Aurore Fayard, 2022
État des populations naturelles de rainette faux-grillon
boréale (Pseudacris maculata) et stratégies de
réintroduction en milieu aménagé
Mémoire
Aurore Fayard
Maîtrise en sciences forestières - avec mémoire
Maître ès sciences (M. Sc.)
Québec, Canada

État des populations naturelles de rainette
faux-grillon boréale (Pseudacris maculata) et
stratégies de réintroduction en milieu aménagé
Mémoire
Aurore Fayard
Sous la direction de:
Marc J. Mazerolle, directeur de recherche
Vance Trudeau, codirecteur de recherche

Résumé
La rainette faux-grillon boréale (Pseudacris maculata) est menacée dans certaines régions du
Canada. Un fort déclin de sa probabilité d’occupation a été noté au cours des 20 dernières
années dans la région de la Montérégie au Québec, Canada. Néanmoins, les tailles de popu-
lations sont méconnues à cet endroit. Peu d’information est disponible sur la dynamique de
reproduction de cette espèce, ce qui entrave la planification d’actions de conservation telles
que la réintroduction. Pour combler ces lacunes et préparer adéquatement la première réin-
troduction, nous avons réalisé un projet visant les populations naturelles et le développement
larvaire. Trois populations de rainette faux-grillon boréale ont été suivies durant une saison
de reproduction afin d’estimer leur abondance et d’identifier l’influence de facteurs environ-
nementaux sur l’intensité des chants. Nous avions également comme objectif d’évaluer l’effet
de la densité et de ressources additionnelles sur le développement et la survie larvaire en
mésocosmes, ainsi que d’estimer la survie des métamorphes après réintroduction. Nous avons
trouvé une relation quadratique entre l’intensité du chant et la température de l’air. L’oc-
currence des chorales de P. maculata était faible. Une des trois populations naturelles s’est
éteinte. Dans les deux autres étangs, les tailles de populations moyennes ont été estimées à 28
adultes (IC à 95% : [23,38]) et 10 adultes (IC à 95% : [8,16]). La condition corporelle des méta-
morphes était meilleure lorsque la densité larvaire était basse, avec supplément de litière dans
les mésocosmes. Un total de 732 métamorphes a été réintroduit dans des étangs construits
au parc national du Mont-Saint-Bruno. Quelques individus réintroduits ont été recapturés,
mais aucune estimation de la survie n’a pu être modélisée à cause de la perte de marque.
Cette étude met en évidence la situation précaire des populations de P. maculata, qui étaient
autrefois plus abondantes dans le sud du Québec. Nous avons montré que le développement
larvaire en mésocosmes est une stratégie efficace pour élever cette espèce en vue d’une réin-
troduction. Ces données permettront de guider d’autres réintroductions d’amphibiens dans
des environnements protégés.
Mots-clés : dynamique de population, mésocosme, gestion adaptative, réintroduction, Pseu-
dacris maculata.
ii

Abstract
The boreal chorus frog (Pseudacris maculata) is a threatened species in parts of Canada. A
significant decline in its occupancy has been noted over the last 20 years in the Montérégie
region of Québec, Canada. However, the size of these populations is unknown. Limited infor-
mation is available on the reproductive dynamics of this species, which hinders the planning
of conservation actions such as reintroduction. To fill these gaps and adequately prepare
for the first reintroduction, we conducted a project targeting natural populations and larval
development. Three populations of boreal chorus frogs were monitored during one breeding
season to estimate their abundance and to identify the influence of environmental factors on
call intensity. We also aimed to evaluate the effect of density and additional resources on
larval development and survival in mesocosms, and to estimate the survival of metamorphs
after reintroduction. We found a quadratic relationship between the calling intensity and
air temperature. There was a low occurrence of choruses of P. maculata. One of the three
natural populations went extinct. In the other two sites, population sizes were estimated at
28 adults (95% confidence interval: [23,38]) and 10 adults (95% CI: [8,16]). Body condition
of metamorphs was better at low larval density with additional litter in mesocosms. A total
of 732 metamorphs were reintroduced into ponds constructed in Mont-Saint-Bruno National
Park. Some reintroduced individuals were recaptured, but no survival estimation could be
modelled due to the high incidence of tag loss. This study highlights the precarious situation
of the populations of P. maculata, which were once more abundant in southern Quebec. We
showed that larval development in mesocosms is an effective strategy for rearing individuals
for reintroduction. These data will help guide other amphibian reintroductions in protected
environments.
Keywords: population dynamics, mesocosm, adaptive management, reintroduction, Pseu-
dacris maculata.
iii

Table des matières
Résumé ii
Abstract iii
Table des matières iv
Liste des tableaux vi
Liste des figures vii
Remerciements viii
Avant-propos x
Introduction générale 1
Mise en contexte .................................... 1
Intensité des chants et facteurs environnementaux ................. 2
La rainette faux-grillon boréale ............................ 3
Situation de l’espèce à l’étude ............................. 4
Objectifs et hypothèses ................................ 5
1 Population size, call intensity, and larval development of boreal chorus
frogs (Pseudacris maculata) to orient reintroduction in created wetlands 14
Résumé ......................................... 15
Abstract ......................................... 16
Introduction ....................................... 17
Materials and methods ................................. 19
Data collection .................................. 21
Statistical analyses ................................ 24
Results ......................................... 28
Calling activity .................................. 28
Adult abundance ................................. 28
Tadpole development in mesocosms ....................... 29
Metamorph release ................................ 29
Discussion ........................................ 34
Conclusion ....................................... 37
Acknowledgements ................................... 38
Conflict of interest ................................... 38
Author contributions .................................. 38
References ........................................ 49
iv

Conclusion générale 50
Intensité des chants et taille des populations naturelles ............... 50
Stratégie d’élevage et de réintroduction ....................... 51
Perspectives du marquage des rainettes faux-grillon ................. 53
Limites de notre étude ................................. 54
Avenues de recherche .................................. 55
A Supplementary material for the article 61
A.1 Arrangement of the adult capture-recapture equipment and experiment in
aquatic mesocosms for the boreal chorus frog (Pseudacris maculata). . . . 61
A.2 Metamorph anaesthesia, capture-recapture details, and recapture sessions
of introduced boreal chorus frogs ........................ 65
A.3 Ordinal logistic regression model estimated by Markov Chain Monte Carlo
describing the calling activity of Pseudacris maculata ............ 69
A.4 Adult capture-recapture model and population size estimations from the
top-ranked model (Mt) .............................. 72
A.5 Number of emerged metamorphs and linear mixed-effects models describing
chorus frog rearing mesocosms with different density and leaf treatments . . 79
A.6 Population viability analysis on boreal chorus frog .............. 85
Bibliographie 93
v

Liste des tableaux
1.1 Number of boreal chorus frog metamorphs released according to site and date
of release in the Mont-Saint-Bruno National Park, Québec, Canada. ...... 33
1.2 Number of boreal chorus frog metamorphs recaptured in 2021 according to site
and session of recapture in the Mont-Saint-Bruno National Park, Québec, Canada 33
A.2.1 Result table of control, anaesthesia, and tagging of boreal chorus frog meta-
morphs. ........................................ 67
A.2.2 Date of recapture sessions of introduced boreal chorus frog juveniles accor-
ding to reintroduction site in the Mont-Saint-Bruno National Park. ....... 68
A.3.1 JAGS code used to conduct ordinal logistic regression models. ........ 69
A.3.2 Parameters of the explanatory variables describing the calling activity of P.
maculata in an ordinal logistic regression model estimated by Markov Chain
Monte Carlo. ..................................... 71
A.4.1 NIMBLE code used to estimate the population size of P. maculata...... 72
A.4.2 Model selection among three closed-population capture-recapture models
assessing capture probability and derived population size of boreal chorus frogs. 76
A.4.3 Output of the top-ranked data augmentation model based on WAIC values. 76
A.5.1 JAGS code used to conduct the binomial generalized linear model and linear
mixed-effects models. ................................. 80
A.5.2 Binomial generalized linear model estimating the probability of metamorph
survival as a function of tadpole density and leaf litter treatments with random
effect of mesocosm identity and a fixed effect of blocks. .............. 83
A.5.3 Parameter estimates of the linear mixed-effects model of P. maculata mass
at metamorphosis (g) at different tadpole density and leaf litter treatments
with random effect of mesocosm identity and a fixed effect of blocks. ...... 84
A.5.4 Linear mixed-effects model estimating P. maculata size at metamorphosis
(mm) as a function of tadpole density and leaf litter treatments with random
effect of mesocosm identity and a fixed effect of blocks. .............. 84
A.6.1 P. maculata life-history traits used as constants in the population viability
analysis. ........................................ 87
A.6.2 Combinations of scenarios tested by varying six factors of the population
viability model of P. maculata............................ 90
vi

Liste des figures
0.1 Rainette faux-grillon mâle (Pseudacris maculata). ................ 5
1.1 Localisation of study sites in Québec, Canada. .................. 20
1.2 Insertion of a PIT-tag on a female boreal chorus frog. .............. 27
1.3 Predicted probability of boreal chorus frog calling indices at breeding site BCV2
according to days elapsed since the beginning of the reproductive season in 2021
in southern Québec, Canada. ............................ 30
1.4 Predicted probability of boreal chorus frog calling indices according to air tem-
perature at breeding site BCV2 (a) and site IP013 (b) in 2021 in southern
Québec, Canada. ................................... 31
1.5 Predicted mean mass (g) of P. maculata at metamorphosis ±95% Bayesian
credible interval according to mesocosm treatments. ............... 32
1.6 Predicted mean size (mm) of P. maculata at metamorphosis ±95% Bayesian
credible interval according to mesocosm treatments. ............... 32
A.1.1 Arrangement of the minnow traps and wooden boards around three natural
ponds during the capture-recapture session for the boreal chorus frog. ..... 61
A.1.2 Installation of traps and geotextile fences for capture-recapture monitoring
of chorus frogs. .................................... 62
A.1.3 Twelve mesocosms at the Mont-Saint-Bruno National Park. .......... 63
A.1.4 Diagram of the arrangement of the randomised complete block experiment
in aquatic mesocosoms in Mont-Saint-Bruno National Park. ........... 63
A.1.5 Snapshot inside of a mesocosm, protected by wire mesh and window screen. 64
A.3.1 Predicted probability of boreal chorus frog calling indices at breeding site
BCV2 according to the occurrence of spring peeper choruses. .......... 71
A.4.1 Posterior distribution of population size Nunder the model Mtfor time-
dependent capture probabilities. .......................... 77
A.4.2 Mean abundance estimates (±95% credible intervals) of adult P. maculata.78
A.4.3 Mean capture probability (±95% credible interval) of adult P. maculata.. . 78
A.5.1 Emergence of P. maculata metamorphs introduced at the Gosner stage 26
into mesocosms. ................................... 79
A.5.2 Mean water temperature of mesocosms (+/- IC 95%) during the experiment
in mesocosms. ..................................... 79
A.5.3 Predicted mean survival of P. maculata at metamorphosis according to tad-
pole density and leaf litter treatments. ....................... 83
A.6.1 Simplified representation of the life cycle of P. maculata by distinguishing
three age classes. ................................... 88
A.6.2 Scenarios tested with density-dependence at larval stage (26= 64 combina-
tions) in natural populations. ............................ 92
vii

Remerciements
Ce travail n’aurait pas été possible sans la collaboration d’une équipe de passionnés.es, d’où
mes longs remerciements! En premier, j’aimerais exprimer ma gratitude à mon directeur de
recherche Marc J. Mazerolle. Je l’applaudie et le remercie pour cette opportunité ainsi que
pour l’intégration dans son laboratoire de recherche. Il est un des seuls qui étudie l’herpétologie
dans la province, ce qui est ô combien important pour promouvoir cette discipline au Québec.
Grâce à Marc j’ai aujourd’hui les outils nécessaires pour devenir une meilleure biologiste.
Je remercie mon co-directeur Vance Trudeau pour avoir été positif à 100% lorsque l’horizon
était noir ; à Jeffrey Ethier, un grand chercheur et allié, sur qui j’ai pu prendre exemple à de
nombreux moments.
Pour essayer de sauver une mini grenouille sur qui ont met tant d’espoir, j’ai dû faire face à
certains dilemmes. Au Québec, j’ai compris qu’avec de belles personnes, une bonne commu-
nication, et une énergie positive on était capable de beaucoup. C’est dans cet état d’esprit
que j’ai réussi à faire passer les côtés pénibles, les doutes et les angoisses rencontrées. J’ai été
épaulée par des femmes incroyables, expertes et inspirantes : Sophie Tessier, la plus souriante
et enthousiaste des personnes que je connaisse sur la planète, ainsi que l’équipe du parc na-
tional du Mont-Saint-Bruno, notamment Nathalie Rivard, sans qui ce projet n’aurait pas vu
le jour au départ. Odile Colin, maman attentionnée des rainettes faux-grillons, qui m’a cha-
leureusement intégrée au Biodôme de Montréal sans hésiter. Émiko Wong et Karine Bédard,
deux vétérinaires hors pair, qui sont clairement à l’image du métier dont je rêvais enfant (en
mieux). Elles inspirent chaque jour de nombreux jeunes tout en se multipliant 100 fois par
jour pour les animaux ! Bien évidemment je remercie tous les employés.ées du Biodôme de
Montréal et plus particulièrement Gheylen Daghfous, ainsi que tous les bénévoles curieux qui
sont venus m’aider sur le terrain.
Un grand merci à Lyne Bouthillier du Ministère des Forêts, de la Faune et des Parcs (MFFP),
qui a su réunir toute l’équipe rainette virtuellement et retrousser ses manches maintes fois pour
gérer ce gros projet, tout en prenant soin de faire le lien entre tous. Je remercie également
Simon Bellefleur et Yohann Dubois, tous deux au MFFP pour leur soutien logistique et
technique au cours de ce projet.
Bien sûr, je n’oublie pas mes chères aides terrain, qui ont mis les mains dans la bouette,
traquant les rainettes faux-grillons sous toutes leurs formes, Michelle Nadeau, sans qui j’aurais
viii

craqué de fatigue beaucoup plus souvent. Je te remercie de questionner mon travail et de
t’obstiner sur les débats philosophiques de la science ! Merci à Katrie Marsan, une stagiaire au
top, Kirstin Laviolette-Lachance, une naturaliste infatigable. Finalement je tiens à remercier
l’Université Laval, et mes collègues de laboratoire Clara, Robin, Pierrick, Joëlle, William,
Anaïs et Jeanne pour leur support moral. Une pensée particulière pour Hugues, mon guide
et soutien de vie, sans qui je n’aurais pas osé me lancer en recherche.
ix

Avant-propos
Ce mémoire de maîtrise en sciences forestières de l’Université Laval intitulé « État des po-
pulations naturelles de rainette faux-grillon boréale (Pseudacris maculata) et stratégies de
réintroduction en milieu aménagé » est rédigé selon le format « par article ». Le corps du mé-
moire est composé d’un article rédigé en anglais dont je suis l’auteure principale. Les autres
parties du mémoire incluant l’introduction et la conclusion générales du mémoire sont rédigées
en français.
L’article scientifique contenu dans ce mémoire, intitulé « Population size, call intensity, and
larval development of boreal chorus frogs (Pseudacris maculata) to orient reintroduction in
created wetlands » sera soumis à l’automne 2022 à la revue scientifique « Animal Conser-
vation ». Les coauteurs sont : Vance Trudeau (Université d’Ottawa), qui a mis en place le
projet et aidé avec toutes les étapes de production de l’article, Émiko Wong (Biodôme de
Montréal) et Sophie Tessier (parc national du Mont-Saint-Bruno), qui collaborent au projet
de réintroduction de la rainette faux-grillon et qui ont aidé à la rédaction de l’article, et
Marc J. Mazerolle (Université Laval), qui a participé tout au long du projet, autant dans les
analyses statistiques que dans la rédaction de l’article. Cet article comprend deux volets. Le
premier apporte des connaissances sur la dynamique des populations naturelles de la rainette
faux-grillon boréale pendant la reproduction. Ceci a guidé le deuxième volet, qui présente
la réintroduction de l’espèce en milieu aménagé. Cette réintroduction s’inscrit dans le projet
« Développement d’un programme d’élevage et de réintroduction de la rainette faux-grillon
de l’Ouest », qui a débuté en 2018 et qui se poursuivra jusqu’en mars 2024. Ce dernier est
financé par Environnement et Changement Climatique Canada (ECCC) et par le Ministère
des Forêts, de la Faune et des Parcs (MFFP). Les partenaires sont le MFFP, l’Université La-
val (Québec), l’Université d’Ottawa (Ontario), le Biodôme de Montréal, le parc national du
Mont-Saint-Bruno géré par la Société des Établissements de Plein Air du Québec (SÉPAQ),
Nature-Action Québec et les municipalités de Longueuil et Boucherville.
x

Introduction générale
Mise en contexte
La dynamique des populations décrit les processus démographiques déterminant les varia-
tions temporelles d'effectifs et la persistance à long terme des populations naturelles (Sæther
et al.,2013). À travers l’étude de la structure d’une population, c’est-à-dire le comportement
reproducteur, l’âge, le sexe-ratio ou bien le développement physiologique, nous améliorons
nos connaissances sur les espèces. L’écologie des populations est également un axe majeur
de la conservation de la nature (Williams et al.,2002). Cette discipline apporte des éléments
clés qui guident la rédaction de plans de conservation pour des espèces en péril, ainsi que les
actions proposées, telles que la planification d’une translocation (Dee Boersma et al.,2001).
Les données démographiques existantes peuvent servir à anticiper le devenir des populations
étudiées (Guisan et Thuiller,2005). Ces informations devraient former la base sur laquelle les
actions de gestion sont construites (Michaels et al.,2014). Le partage des résultats obtenus
par les chercheurs, comme les facteurs qui influencent la démographie d’une espèce, permet-
trait d’ajuster ou d’orienter rapidement les actions prises sur le territoire par les gestionnaires
(Botsford et al.,2019). C’est le cas des outils de gestion adaptative qui proposent de mettre
en pratique les résultats de la recherche dans un processus continu en collaboration avec les
gestionnaires (Salafsky et Margoluis,2003;Williams,2011;Keith et al.,2011). Une accélé-
ration du processus de partage des connaissances entre les communautés scientifiques et les
acteurs est nécessaire dans le contexte actuel où la biodiversité décline à une vitesse inédite
(Barnosky et al.,2011).
Les amphibiens sont mondialement menacés (Alford et Richards,1999;Reading,2007;Al-
lentoft et O’Brien,2010). Les familles d’amphibiens avec le plus grand nombre d’espèces en
déclin rapide sont les Bufonidae, les Leptodactylidae et les Hylidae (Stuart et al.,2004). Les
principales menaces pour les amphibiens sont la perte ou la dégradation de leur environne-
ment (Gibbs,2000;Matthews et al.,2013;Stuart et al.,2004). La fragmentation des habitats
naturels entrave la connectivité fonctionnelle entre les populations, ce qui les isole et les fragi-
lise en faisant émerger, par exemple, des problèmes génétiques (Cushman,2006). Les actions
possibles sont la restauration ou la création de nouveaux habitats, qui sont couramment uti-
lisées en Amérique du Nord pour les translocations d’amphibiens (Brown et al.,2012;Shulse
et al.,2010;McPherson,2015). Cependant, la restauration de ces habitats naturels n’est pas
1

toujours possible, ce qui amène à créer de nouveaux habitats connectés qui sont moins à même
d’être dégradés ou fragmentés (Semlitsch,2002). Les zones protégées constituent des sites de
réintroduction sûrs, qui limitent la menace de la pression anthropique (Bowler et al.,2020).
Ces nouveaux sites doivent de préférence être proches des sites naturels de l’espèce, afin de
réunir des conditions similaires à ces sites (Langridge et al.,2021).
Chez une grande quantité d'espèces d'amphibiens, les traits démographiques sont très va-
riables d'une population à une autre (Cayuela et al.,2021,2022a;Morrison et Hero,2003).
Par exemple, chez le sonneur à ventre jaune (Bombina variegata) le temps de vie varie du
simple ou double selon l'environnement occupé par les populations, tout comme la valeur de
l'élasticité de survie adulte (Cayuela et al.,2022b). Ces données sont spécifiques à chaque
espèce et sont souvent incomplètes pour éclairer les décisions de gestion, telles que la mise
en captivité de spécimens pour leur patrimoine génétique, la translocation, ou bien l’élevage
pour la reproduction hors du milieu naturel (Michaels et al.,2014;Schad,2007). Il est donc
important de prioriser les suivis des populations sources sur le long terme (Muths et Dreitz,
2008). Une des méthodes fréquemment utilisée pour suivre le taux de fréquentation et le
succès reproducteur des populations est l’enregistrement des chants des anoures.
Intensité des chants et facteurs environnementaux
De nombreuses espèces d’amphibiens se reproduisent à une période spécifique de l’année, ca-
ractérisée par des chants produits en groupes que l’on appelle des chorales (Vitt et Caldwell,
2013). Ces chants sont produits par les mâles adultes pour attirer les femelles, mais aussi pour
défendre leur territoire (Vitt et Caldwell,2013). Ils sont donc plus facilement détectés que les
femelles, qui passeraient plus de temps hors de l’étang (Dorcas et al.,2009;Regosin et al.,
2003). La présence et l’intensité des chants chez une espèce peuvent être influencées par des
facteurs sociaux et environnementaux (Brooke et al.,2000;Steelman et Dorcas,2010). L’inten-
sité de chant d’une espèce d’anoure à un même site peut être affectée par les chants d'autres
anoures. Par exemple, les mâles d’une même espèce se synchronisent en chantant pendant
les pauses de chants d’autres espèces (Schwartz et Freeberg,2008). La saison de reproduc-
tion des amphibiens est régulée par la température, qui peut affecter la fréquence des chants
d’accouplement des mâles (Brinley Buckley et al.,2021;Ethier et al.,2021). Chez certaines
espèces du genre Pseudacris, l’activité du chant est positivement corrélée à la température
(Saenz et al.,2006;Steelman et Dorcas,2010). Une reproduction précoce peut être observée
lors des hivers plus chauds chez la grenouille des bois Lithobates sylvaticus (Benard,2015),
ou bien lors d’années sèches chez la rainette faux-grillon (Pseudacris maculata) au Colorado
(Corn et Muths,2002). Il existe également un effet de saisonnalité dans le comportement
des chorales chez les amphibiens. Steelman et Dorcas (2010) ont observé que l’activité de P.
crucifer et P. feriarum était négativement corrélée au jour de l’année, qui est le manifeste
d’une reproduction dite « explosive ».
2

La rainette faux-grillon boréale
Ce projet se concentre sur la rainette faux-grillon boréale (Pseudacris maculata, Agassiz, 1850)
classée dans la famille des Hylidae. La dénomination « maculata » vient du latin « tacheté »,
car le corps de la rainette est recouvert de points ou de lignes. Elle possède des petites
ventouses aux doigts, sa peau ventrale est granuleuse et sa couleur varie du brun au gris olive,
pour un poids d’environ 1 g (Rodrigue et Desroches 2018, Figure 0.1). Le terme « boréale » est
probablement lié à sa limite de distribution nordique, allant jusqu’à la Baie-James (Rodrigue
et Desroches,2018). Une des problématiques majeures qui touche actuellement les populations
de P. maculata au Canada est la perte de ses habitats, particulièrement les zones humides
temporaires, en raison de la densification humaine et du réchauffement climatique (ERRFGO,
2019;ERRFGO, 2010,Bouthillier et al. 2022). Au Québec, 14 à 28% des milieux humides
servant à la reproduction de l’espèce ont disparu entre 2004 et 2009 (ERRFGO, 2010). Cette
espèce se trouve au rang de priorité mondiale (G pour global), désignée comme abondante
et stable par NatureServe. Par contre, à l’échelle provinciale (rang S pour subnational), les
populations des Grands Lacs/Saint-Laurent et du Bouclier canadien (GLSLBC) sont désignées
en péril. En effet, Pseudacris maculata a été évaluée au fédéral par le COSEPAC en 2008.
L’espèce est entrée en 2010 dans l’Annexe 1 de la Loi sur les Espèces en Péril (Environnement
Canada,2015). Au Québec, le gouvernement provincial l’a inscrite en 2001 « vulnérable » au
titre de la Loi pour les Espèces Menacées ou Vulnérables (ERRFGO, 2019).
Depuis les études génétiques de Moriarty-Lemmon et al. (2007), les quatre sous-espèces de
Pseudacris triseriata (Wied-Neuwied, 1838) ont obtenu le statut de quatre espèces distinctes
(ERRFGO, 2019). Au Québec, Pseudacris triseriata est absente, car sa distribution se limite
du centre-ouest de New York jusqu’à l’extrême sud de l’Ontario. Grâce à des analyses récentes
d’ADN mitochondriaux, l’étude de Rogic et al. (2019) a confirmé que les populations du
Québec appartenaient à l’espèce Pseudacris maculata, et non à Pseudacris triseriata. Elles
auraient divergé il y a 9,5 millions d’années (Moriarty-Lemmon et al.,2007). Cependant,
les noms communs n’ont pas encore été officiellement changés dans les plans officiels et les
populations du sud du Québec conservent leur statut de protection. Nous reconnaissons qu’il
existe des travaux en cours qui remettent en question l’identification de P. maculata pour les
populations du sud du Québec. Toutefois, nous utilisons dans ce mémoire le nom commun
rainette faux-grillon boréale, ou tout simplement rainette faux-grillon pour désigner l’espèce
à l’étude.
Parmi les 21 espèces d’amphibiens du Québec, la rainette faux-grillon boréale est la plus
petite espèce d’anoure (moyenne longueur museau-cloaque = 2,5 cm, Environnement Canada,
2015). P. maculata est une des premières espèces d’anoures à se reproduire au printemps
(Dodd,2013). Les deux paramètres qui déclencheraient le réveil des rainettes faux-grillon
sont la température et la quantité de neige restant au sol (Corn et Muths,2002). L’espèce
est extrêmement difficile à observer en raison de sa petite taille et de sa coloration, même si
3

elle reste active jour et nuit pendant la saison de reproduction qui ne dure que deux à trois
semaines (Kissel et al.,2020;Whiting,2004). La reproduction est observée dans les milieux
humides temporaires de faibles superficies (moyenne de 0,27 ha; Gagné,2010), et de faibles
profondeurs (Ouellet et al.,2009;Ouellet et Leheurteux,2007). Bien que la distance maximale
de dispersion des individus semble être de 600 m, l’espèce ne possède pas une grande capacité
de déplacement (Dodd,2013;Bouthillier et al.,2022). Les adultes restent en moyenne entre
20 et 50 m de la zone humide durant la période de reproduction (Dodd,2013;Whiting,2004;
Smith,1983).
Situation de l’espèce à l’étude
Dans la région administrative de la Montérégie, dans le sud du Québec, les effectifs des popu-
lations de l’espèce ne sont pas connus (ERRFGO, 2019). Pourtant, modéliser les changements
de taille des populations est un moyen d’évaluer rapidement la santé d’une population (Brown
et al.,2014;Collen et al.,2011). Au Québec, les biologistes observent un déclin de l’occupation
et de l’intensité des chants de la rainette faux-grillon depuis 1994, bien qu’elle était autre-
fois commune dans le sud de la province (Daigle,1994;Bonin et Galois,1996). Selon une
évaluation à dire d’experts, les cotes de viabilité des occurrences calculées dans le plan de
rétablissement de 2019, les populations de la rainette faux-grillon sont en « bonne situation »
dans seulement 17 mentions sur 71. Les 56 populations restantes sont listées dans les catégo-
ries « situation précaire ou mauvaise », « disparue » ou « données insuffisantes » (ERRFGO,
2019).
Chaque année depuis 1999, des inventaires sont menés par les équipes du Minisitère de la Forêt,
de la Faune et des Parcs (MFFP) du Québec, ainsi que par l’association citoyenne Ciel et Terre
selon un protocole de points d’écoute, qui a été standardisé en 2010. Ces organismes attribuent
une cote de chant aux sites visités durant la période de reproduction (Daigle et al.,2011;
Bouthillier et al.,2015;Picard,2015). Ces données permettent de documenter les changements
d’occupations, dans la limite où la cote de chant est basée uniquement sur le chant de mâles.
Néanmoins, ces initiatives ne permettent pas d’étudier la dynamique des populations ni de
quantifier le recrutement (COSEPAC,2008;Environnement Canada,2015;Picard,2015).
Des lacunes existent aussi concernant les facteurs favorisant la survie de P. maculata au stade
larvaire, ce qui complique l’estimation du taux d’émergence dans les populations naturelles
(Ethier et al.,2021). La survie des larves peut être fortement dépendante de la densité de
têtards présents dans les mares temporaires (Burgman et al.,1993;Caswell,2001;Brannelly
et al.,2019;Labadie et al.,2017). Une étude exploratoire sur la densité-dépendance chez les
amphibiens et les reptiles indique que trois espèces du genre Pseudacris :P. nigrita,P. ornata,
ainsi que P. regilla, ont une croissance démographique dépendant de la densité au niveau de
la population (Leão et al.,2018). Plus récemment, la densité-dépendance s’est avérée être
un phénomène commun dans la régulation du taux de croissance des sous-populations, et des
4

populations (Cayuela et al.,2020). Cependant, il est parfois complexe de savoir à quel stade de
vie cette dépendance agit sur les amphibiens (Kissel et al.,2020). À la lumière de ces lacunes et
du statut précaire des populations de la rainette faux-grillon boréale au Québec, une initiative
de reproduction en captivité et de réintroduction a été développée par le MFFP, la Société des
établissements de plein air du Québec (SÉPAQ), le Biodôme de Montréal, l’Université Laval
et l’Université d’Ottawa. La captivité permet d'optimiser le nombre de survivants durant la
translocation en évitant les risques externes tels que les maladies, ou l’assèchement précoce
du milieu humide (Griffiths et Pavajeau,2008;Crockett et al.,2020;Lewis et al.,2019).
Les individus des populations sources sont maintenus en captivité en attendant la fin des
travaux de restauration, ou pour contrôler la phase de reproduction, et ainsi réintroduire de
nouvelles populations (Muths et al.,2014;Kendell,2002;Klop-Toker et al.,2016;Duarte
et al.,2017). Le présent projet de maîtrise s’insère dans cette initiative et s’intéresse aux
effectifs des populations naturelles ainsi qu’à la survie larvaire.
Figure 0.1 – Rainette faux-grillon mâle (Pseudacris maculata) capturée en 2021, Aurore
Fayard ©.
Objectifs et hypothèses
Ce projet comporte deux volets. Le premier cible les populations naturelles pendant la période
de reproduction, alors que le deuxième cible le développement larvaire. Les objectifs du pre-
mier volet de cette étude étaient de quantifier l’influence des facteurs environnementaux sur
l’intensité des chants de la rainette faux-grillon boréale pendant la saison de reproduction, et
d’estimer l’abondance des populations dans trois étangs abritant de grandes populations selon
les cotes de chants élevés documentées depuis au moins 20 ans. Ces données permettront de
quantifier les tendances de ces populations et de formuler des recommandations de gestion.
5

Plusieurs études ciblant Pseudacris maculata ont montré que la présence et l'intensité des
chants peuvent être influencées par des facteurs environnementaux. Par exemple, la date du
pic d'activité de sa reproduction dépendait de la quantité de neige restant au sol (Corn et
Muths,2002). La saison de reproduction de cette espèce semble régulée par la température,
qui peut affecter la fréquence des chants d'accouplement des mâles (Brinley Buckley et al.,
2021;Saenz et al.,2006).
Les hypothèses associées au volet ciblant les populations naturelles étaient les suivantes :
1. L’intensité des chants de P. maculata lors de la reproduction est influencée par certains
facteurs environnementaux.
2. En raison de la réduction du nombre de sites occupés par l’espèce en Montérégie, les
chorales de P. maculata sont moins fréquentes pendant la période de reproduction que
les chants d’individus isolés.
Le deuxième volet se concentre sur les premières étapes du programme de réintroduction de
P. maculata, qui a pour but de créer de nouvelles populations dans des étangs aménagés.
Ces étangs se trouvent dans un espace naturel protégé ce qui permet d’écarter sur le long
terme la plus grande menace qui pèse sur cette espèce, soit la dégradation ou la destruction
de son habitat (ERRFGO, 2019;ERRFGO, 2010,Bouthillier et al. 2022). Il est important
de combler les lacunes existantes sur le développement larvaire de la rainette faux-grillon
afin d’optimiser le succès de réintroduction en milieu naturel. Le stade larvaire semble être
densité-dépendant pour plusieurs espèces d’anoures selon la littérature (Burgman et al.,1993;
Caswell,2001;Brannelly et al.,2019;Labadie et al.,2017). La présence de litière forestière
dans l’étang peut être un refuge et une source de nutriments pour les têtards (Dodd,2010;
Jowers et Downie,2005). Nos objectifs étaient d’évaluer l’effet de la densité et de la présence
de litière forestière sur la survie et le développement larvaire de P. maculata, mais également
la survie des juvéniles après la réintroduction. Les hypothèses associées à la survie et au
développement larvaire étaient les suivantes :
1. La survie, la masse et la taille des métamorphes dépendent de la densité larvaire.
2. La présence de ressources additionnelles influence la survie et le développement larvaire.
6

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Williams, B. K., J. D. Nichols, et M. J. Conroy. 2002. Analysis and management of animal
populations. Academic Press.
13

Chapitre 1
Population size, call intensity, and
larval development of boreal chorus
frogs (Pseudacris maculata) to
orient reintroduction in created
wetlands
Aurore Fayard1, Vance Trudeau2, Émiko Wong3, Sophie Tessier4and Marc J. Mazerolle1
1Centre d’étude de la forêt, Département des sciences du bois
et de la forêt, Université Laval, Québec, QC G1V 0A6, Canada.
2Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
3Biodôme de Montréal, Espace pour la vie, Montréal, QC H1V 1B3, Canada.
4Parc national du Mont-Saint-Bruno, Saint-Bruno-de-Montarville, QC J3V 4P6, Canada.
14

Résumé
La conservation des espèces en danger passe par un travail collaboratif, permettant de regrou-
per les connaissances et les savoirs des chercheurs et gestionnaires. Cependant, la planification
des actions de protection peut être freinée en absence d’informations clés sur la dynamique
des populations de l’espèce cible. La rainette faux-grillon boréale (Pseudacris maculata) est
menacée dans certaines parties du Canada. Pourtant, il existe peu de données sur la taille
des populations, les facteurs influençant sa reproduction et le recrutement. Pour combler ces
lacunes et préparer adéquatement la première réintroduction, nous avons réalisé un projet
visant les populations naturelles et le développement larvaire. Trois populations de rainette
faux-grillon boréale ont été suivies durant une saison de reproduction afin d’estimer leur abon-
dance et d’identifier l’influence de facteurs environnementaux sur l’intensité des chants. Nous
avions également comme objectif d’évaluer l’effet de la densité et de ressources additionnelles
sur le développement et la survie larvaire en mésocosmes, ainsi que d’estimer la survie des
métamorphes après réintroduction. L'un des trois étangs n'a pas été fréquenté par l'espèce, et
l'occurrence de chorales de P. maculata dans les deux autres étangs était faible. La taille des
populations des deux populations restantes était estimée à 28 adultes (intervalle de confiance
à 95% : [23,38]) et 10 adultes (IC à 95% : [8,16]). La probabilité de survie des larves n’a
pas différé entre les traitements. Cependant, les métamorphes provenant des traitements à
faible densité étaient de plus grande taille et avaient une masse plus importante que ceux
provenant des traitements à forte densité, indépendamment de la présence de litière. Au to-
tal, 732 métamorphes ont été réintroduits dans des étangs construits au parc national du
Mont-Saint-Bruno. Quelques individus réintroduits ont été recapturés, mais aucune estima-
tion de la survie n’a pu être modélisée en raison d’une perte importante des marques. Cette
étude souligne la précarité des populations de P. maculata autrefois plus abondantes dans le
sud du Québec. Nous avons montré que le développement larvaire en mésocosme était une
stratégie efficace pour élever des rainettes faux-grillon avant leur réintroduction. Ces données
contribueront à optimiser la réintroduction d’amphibiens en milieu aménagé.
Mots-clés : taille de population, suivi acoustique, gestion adaptative, réintroduction, Pseu-
dacris maculata.
15

Abstract
The conservation of endangered species requires extensive collaboration, bringing together the
knowledge and expertise of researchers and conservation managers. However, the planning of
protection actions can be impeded if data on the population dynamics of the target species are
lacking. The boreal chorus frog (Pseudacris maculata) is threatened in some parts of Canada.
Yet, there are scarce data on population size and the factors influencing its reproduction. To
fill these gaps and adequately prepare for the first reintroduction, we conducted a project
targeting natural populations and larval development. Three populations of boreal chorus
frogs were monitored during one breeding season to estimate their abundance and to identify
the influence of environmental factors on call intensity. We also aimed to evaluate the effect
of density and additional resources on larval development and survival in mesocosms, and to
estimate the survival of metamorphs after reintroduction. One of the three ponds was not
frequented by the species and the occurrence of choruses of P. maculata in the other two
ponds was low. The population size of the two extant ponds was estimated at 28 adults (95%
confidence interval: [23,38]) and 10 adults (95% CI: [8,16]). The probability of tadpole survival
did not vary among treatments. However, metamorphs from the low-density treatments were
larger and had a greater mass than those from the high-density treatments, regardless of litter
presence. A total of 732 metamorphs were reintroduced into ponds constructed in Mont-
Saint-Bruno National Park. Some reintroduced individuals were recaptured, but no survival
estimation could be modelled due to the high incidence of tag loss. This study highlights the
precarious situation of the populations of P. maculata, once much more abundant in southern
Québec. We showed that larval development in mesocosms is an effective strategy for rearing
chorus frogs before reintroduction. These data will contribute to optimise the reintroduction
of amphibians in constructed environments.
Keywords: abundance estimate, acoustic monitoring, adaptive management, reintroduction,
Pseudacris maculata.
16

Introduction
Population dynamics describe the demographic processes that determine the temporal varia-
tions in population size and the long-term persistence of natural populations (Sæther et al.,
2013). The study of variables influencing population structure, such as reproductive beha-
viour, age, sex ratio, or physiological development improves our knowledge of species. Acqui-
ring data on threatened species is a priority but entails budgetary and logistical challenges
(Miller et al.,2006;Martin et al.,2018;Ewen et al.,2012). Population ecology is also a major
focus of nature conservation (Williams et al.,2002) and provides key elements in developing
conservation plans for species at risk (Dee Boersma et al.,2001). Using existing demographic
data, we can anticipate the future of populations (Guisan and Thuiller,2005). These data are
species-specific and are often incomplete to inform management decisions, such as transloca-
tions (Michaels et al.,2014). This information should form the basis on which management
actions are built (Michaels et al.,2014). Sharing results obtained by researchers, such as the
factors that influence a species’ demographics, would allow for rapid adjustment or direction
of actions taken by managers (Botsford et al.,2019). Improving the knowledge transmission
process between research and management is necessary in the context of biodiversity loss
(Barnosky et al.,2011).
Biodiversity is declining at an unprecedented rate, especially among amphibians (Alford and
Richards,1999;Reading,2007;Blaustein et al.,2010). The primary threats to this group are
the loss and degradation of their environments (Gibbs,2000;Matthews et al.,2013;Stuart
et al.,2004). Fragmentation of natural habitats hinders the functional connectivity between
populations, isolating them and making them more fragile by causing, for example, genetic
issues (Cushman,2006). Possible actions include restoration or creation of new habitats,
which are commonly used in North America for amphibian translocations (Brown et al.,
2012;Shulse et al.,2010;McPherson,2015). However, restoration of these natural habitats is
not always possible, leading to the creation of new, connected habitats that are less likely to
become degraded or fragmented (Semlitsch,2002). Protected areas provide safe reintroduction
sites, limiting anthropogenic pressures (Bowler et al.,2020). Human activities are responsible,
along with climate change, for the degradation of amphibian habitats. Among the families
most affected by these threats is the Hylidae, the third family with the greatest number of
rapidly declining species of amphibians (Stuart et al.,2004).
Knowledge on Hylidae, with more than 870 known species to date, is limited (Faivovich et al.,
2005). Consequently, we lack data concerning their phenology and the environmental factors
that influence them (Ethier et al.,2021). Similarities in the life history traits of the genus
Pseudacris have been reported by Ethier et al. (2021). Examples include small size combined
with good camouflage in their environment, iteroparity, high mortality in early life stages, and
large aggregations of adults during breeding in early spring . Finally, calls are temperature-
dependent in the genus Pseudacris (Brinley Buckley et al.,2021;Saenz et al.,2006). On the
17

other hand, gaps remain regarding the factors favouring survival of this genus to the larval
stage, making it difficult to estimate the rate of emergence in natural populations (Ethier
et al.,2021). Larval survival may be highly dependent on the density of tadpoles present in
temporary pools (Burgman et al.,1993;Caswell,2001;Brannelly et al.,2019;Labadie et al.,
2017). A density-dependence review on amphibians and reptiles indicates that three species
of the genus Pseudacris :P. nigrita,P. ornata, as well as P. regilla have density-dependent
population growth (Leão et al.,2018). However, long-term studies are lacking to build a
complete picture of the survival of life stages of each species of the genus Pseudacris (Ethier
et al.,2021). Survival of tadpoles or metamorphs in the wild is rarely estimated, making
an assessment of reproductive success difficult (Ethier et al.,2021;Luja et al.,2015). This
information scarcity hinders the conservation and management efforts of Pseudacris species,
such as the boreal chorus frog in parts of its range.
The boreal chorus frog Pseudacris maculata (Agassiz, 1850) is classified as abundant and
stable by IUCN (Baillie et al.,2004). However, the species is listed as imperilled by Nature-
Serve in Québec (Canada) and Michigan (USA) (Ethier et al.,2021). Indeed, the province
of Québec protects the species since 2001 under the Act Respecting Threatened or Vulne-
rable Species (R.S.Q.,c. E-12.01). In contrast, the Committee on the Status of Endangered
Wildlife in Canada has listed the populations of the Great Lakes, St. Lawrence, and the
Canadian Shield as vulnerable under the Species at Risk Act in 2010 (ERRFGO, 2019 ;Envi-
ronnement Canada 2015). The number of breeding sites occupied by the species in southern
Québec, Canada, has decreased mainly due to habitat loss (ERRFGO, 2010;ERRFGO, 2019 ;
Dubois-Gagnon et al. 2021). Between 2004 and 2009, 14% of the species’ breeding sites disap-
peared in the Montérégie region (Environnement Canada,2015). Despite the alarming status
of the species in recent decades, the population size of the species in the northern portion of
its range has never been estimated.
The objectives of the present study were 1) to evaluate factors influencing the calling intensity
of the species, 2) to quantify the population size of breeding populations of boreal chorus
frogs, and 3) to estimate the influence of density-dependence and supplemental resources on
larval survival and development, as well as metamorph survival. Because the breeding season
is described as short and explosive, we predicted that the calling intensity of P. maculata
depends on environmental factors. Following the recent decline of boreal chorus frogs in our
study area, we predicted that the chorus occurrence was less likely than the calls of a few
individuals during the breeding period. Concerning density-dependence, we proposed that
survival, mass, and size of metamorphs depend on larval density. Forest litter at the bottom
of a pond can be a refuge and a source of nutrients for tadpoles (Dodd,2010;Jowers and
Downie,2005). Therefore, we predicted that the presence of additional resources influences
survival and larval development.
18

Materials and methods
Study area and focal species
The study area is located in the administrative region of Montérégie, in southern Québec
(Canada), and encompasses the cities of Boucherville (45°35’34” N, 73°26’12” W), Longueuil
(45°31’43" N, 73°25’53" W) and Saint-Bruno-de-Montarville (45°32’46" N, 73°20’33" W, Fi-
gure 1.1). The study area spans the sugar maple-bitternut hickory, which benefits from a
mild climate (Ministère des forêts, de la faune et des parcs, 2020). For more than 30 years,
the Montérégie has experienced one of the highest demographic growths in Québec, with
a population density of approximately 166 inhabitants/km2(Ministère de l’Économie et de
l’Innovation, 2021). This strong demographic pressure led to important urban development.
More than half of Montérégie is covered by agriculture, 45% of which consists of intensive row
crops dominated by corn, soya beans, and wheat cultures (ECCC and MDDELCC,2018).
Wetlands constitute only 6% of the landscape in this region, of which 72% are less than one
hectare in size in urban areas, with a low percentage of shallow water wetlands compared to
swamps, forested bogs, or marshes (ECCC and MDDELCC,2018;Beaulieu et al.,2013).
Natural ponds
We selected three natural ponds with a known historical presence of the boreal chorus frog
during the last 20 years assessed from call surveys (Daigle et al.,2011). These sites, hereafter
called IP013, BCV2, and TM199 have approximate areas of 900 m2, 1500 m2and 9000 m2,
respectively (Figure 1.1). These temporary wetlands are filled in spring from melting snow
and rainfall, and dry completely by midsummer. These ponds are located within 3 km of each
other, at an altitude of 29 to 33 m, between 60 and 300 m from busy roads (IP013 being the
closest). The canopy over the ponds is open, surrounded by trees or shrubs such as White
ash (Fraxinus americana), Trembling aspen (Populus tremuloides), Slippery elm (Ulmus ru-
bra), and Riverbank grape (Vitris riparia). The main aquatic plants are Softstem bulrush
(Schoenoplectus tabernaemontani), Pennsylvania smartweed (Persicaria pensylvanica), Rice
cutgrass (Leersia oryzoides), Narrow-leaved cattail (Typha angustifolia), as well as Retrorse
and Blunt broom sedge (Carex retrorsa and C. tribuloides).
Constructed ponds
Four wetlands were constructed in 2017 specifically for the needs of P. maculata in the Mont-
Saint-Bruno National Park, by the Ministère de la faune, de la forêt et des parcs (MFFP) and
the Société des établissements de plein air du Québec (SÉPAQ) in 2017. The ponds measured
16 x 25 m and were established in existing agricultural ditches. They were constructed with
20% bank slopes to maximise aquatic vegetation regeneration and to facilitate the emergence
of tadpoles following metamorphosis (Trottier-Picard and Bouthillier,2021;Bouthillier and
19

Reyes,2018). Two of these constructed ponds were selected for the reintroduction of boreal
chorus frogs, separated by 250 m (ponds SQ83 and SQ22, Figure 1.1). Manitoba maple (Acer
negundo, L.), Goldenrod (Solidago sp.), Reed canary grass (Phalaris arundinacea, L.), and
Broadleaf cattail (Typha latifolia, L.) are the main plants found on these two sites (Mont-
Saint-Bruno National Park data). Selective tree cutting was conducted within ten metres
of the pond edges to maintain the canopy open over the ponds. A drainpipe with a valve
was installed in each pond to control the hydroperiod and ensure that the water level was
between 30 cm and 40 cm in the spring, with a subsequent decline in water level in midsummer
(Bouthillier and Reyes,2018).
Study species
Among the 21 species of amphibians in Québec, the boreal chorus frog is the smallest species of
anuran (mean snout-vent length = 2.5 cm, Environnement Canada,2015). P. maculata is one
of the first anuran species to breed in spring (Corn and Muths,2002;Dodd,2013;Rodrigue
and Desroches,2018). Breeding sites consist of small temporary wetlands, mostly located in
old agricultural depressions, surrounded by annual crops (average of 0.27 ha ; Gagné,2010;
Environnement Canada,2015). Adults remain on average 20–50 m from the wetland during
the breeding season (Dodd,2013;Whiting,2004;Smith,1983).
Figure 1.1 – Localisation of study sites in Québec (A) and the Montérégie region (B). The
map in C shows natural ponds located in the city of Boucherville with black dots and the
pond located in the city of Longueuil with a blue dot. Constructed ponds in orange colour
are part of the national park in the city of Saint-Bruno-de-Montarville.
20

Data collection
Calling activity
We deployed an automated acoustic recorder with one analogue Micro-Electro-Mechanical
Systems microphone in the three natural ponds and the three created ponds under study
(AudioMoths 1.2; Hill et al.,2019). Recorders were set at 1.5 m from the ground level from
4 April – 4 May 2021 and recorded a sound clip of 5 minutes (.wav format, 48 kHz sam-
pling rate with 16 bits per sample) every hour of the day during the breeding period of the
boreal chorus frog. Loggers also measured air temperature at each recording. Following the
retrieval of the acoustic loggers, we listened to each file and we scored the maximum calling
intensity in each recording according to the standard three-point North American Amphibian
Monitoring Program index (Weir et al.,2005) : (0) absence of calling activity ; (1) up to two
or three unique individuals, with mostly non-overlapping calls, (2) overlapping calls but still
allowing to distinguish individuals, and (3) full chorus consisting of overlapping calls with
non-distinguishable individuals.
Adult abundance
We used a capture-mark-recapture design to collect data at our three natural sites (Royle
et al.,2005;Dodd,2010). We installed drift fences along the perimeter of each wetland :
BCV2, IP013, and TM199 (Willson and Gibbons,2010;Caldwell,1987;Greenberg et al.,
1994). The fences were 90 cm high and consisted of black silt fencing made of geotextile, the
bottom 20 cm of which was buried in the ground. Fences were held erect with wooden stakes
spaced at 3 m intervals (Figure A.1.1,A.1.2,Whiting 2004). A continuous fence surrounded
BCV2 and TM199 sites (Willson and Gibbons,2010). The third site (IP013) was partially
enclosed due to its large area relative to the two other sites (Chelgren et al.,2008). Plastic
minnow traps (43 cm long ×23 cm diameter, with a 48 mm square mesh and a 22 mm
entrance hole) were placed on the outside and the inside of each fence at 10 m intervals
(Adams et al.,1997;Swartz and Miller,2018). Each trap contained a wet sponge to retain
moisture. We also placed artificial spruce cover boards (25 cm ×30 cm ×2 cm) outside the
fences (Figure A.1.1,A.1.2).
Sites were visited twice a day (at 0800 and 2000) from 4 April to 29 April 2021, spanning the
entire breeding season of the species. During the visits, the traps and artificial refuges were
checked and 2–5 observers patrolled the perimeter of the wetland to locate individuals. We
captured individuals by hand or with a dip net. Capture sessions lasted 1–3 person-hours,
depending on the chorus frog activity. Each captured individual was handled with powder-free
nitrile gloves. At the end of the breeding season, portions of fences were dismantled to allow
free movement around the ponds and minnow traps were removed.
Individuals were anaesthetised by immersion in a solution of 1 g/L of MS-222 buffered to a pH
21

of 7.0 with sodium bicarbonate. Once anaesthetised, individuals were measured to snout-vent
length, sexed, and weighed to the nearest 0.001 g (Ohaus, Dundas, Canada). We tagged frogs
with a passive integrated transponder (8.2 mm long ×1.4 mm diameter, 0.03 g, PIT tag
mini HPT8 Biomark, Boise, USA). We used surgical microscissors to make a 5 mm incision
on the right dorsal surface of the individual at the level of the hind limbs (Ferner,2007,
2010;Ousterhout and Semlitsch,2014). The insertion point of the tag was sealed with a
medical adhesive (VetBondTM ) to avoid tag loss (Figure 1.2). Measurements and the surgical
procedure took less than five minutes. Following PIT tag implantation, the individual was
reanimated in a clean freshwater container and remained under observation for 12–24 hours
before being released at its capture site.
Captive breeding
Veterinarians and technicians from the Biodôme de Montréal initiated captive breeding of the
boreal chorus frog in the laboratory. Adult males and females from natural populations were
primed with a GnRH-A solution (0.04 µg/g GnRH-A given in 10 microlitres/g body weight)
and kept separate in containers filled with flooded sphagnum moss (23 ×15.5 ×17 cm).
Twenty-four hours later, males and females were intraperitoneally injected with a hormone
mixture called AMPHIPLEX (0.4 µg/g GnRH-A plus 10µg/g metoclopramide given in 10
microlitres/g body weight), and put together in breeding basins. This mixture is a combina-
tion of a gonadotropin-releasing hormone (GnRH) agonist and a dopamine antagonist, which
provoke a surge release of luteinizing hormone from the pituitary gland (Trudeau et al.,2010,
2013). This spawning induction protocol has been validated by several studies for different
frog species (Trudeau et al.,2010,2021;Melvin and Trudeau,2012).
Females laid a total of 3,076 fertilised eggs in controlled conditions between 10 and 21 April
2021 (mean eggs/clutch : 482, Ethier J. and Colin O., unpublished data). After hatching,
tadpoles developed in plastic containers filled with 8 L of water. Some of these tadpoles
were transported on 14 May 2021 to conduct the mesocosm experiment below, whereas the
remaining tadpoles stayed at the Biodôme de Montréal until they reached metamorphosis.
Tadpole development in mesocosms
We conducted a common garden experiment in twelve mesocosms in the Mont-Saint-Bruno
National Park, fewer than two kilometres away from the constructed ponds (Figure 1.1).
Mesocosms consisted of plastic cattle watering tanks measuring 63 ×95 ×79 cm (Rubbermaid
®maximum capacity of 378.5 L) and were distributed in three randomised complete blocks.
Each block consisted of a line of four mesocosms spaced 0.5 m apart (Figure A.1.3). In a given
block, each mesocosm contained one of four treatments based on two fully crossed factors,
namely tadpole density and leaf litter. We considered two levels of tadpole density within
the range reported for natural populations of P. maculata : (1) : 0.1 tadpole/L (Whiting,
22

2010), (2) : 1 tadpole/L (Earl et al.,2012;Hossack et al.,2017;Whiting,2010). The leaf
litter treatment consisted in adding 150 g of deciduous leaves, mainly maple (Acer sp.) and
birch (Betula sp.) in mesocosms to provide additional food resources and foraging habitat
(Earl et al.,2012). This amount is within the range found in other studies on tadpoles in
mesocosms (Williams et al.,2008;Stoler and Relyea,2011). Thus, each mesocosm in a given
block received one of the following treatments : (1) low tadpole density without leaf litter, (2)
low tadpole density with leaf litter, (3) high tadpole density without leaf litter, and (4) high
tadpole density with leaf litter (Figure A.1.4).
All mesocosms were filled with 180 L on 16 April 2021, one month before the introduction of
tadpoles. We added 179 L of tap water and 1 L of filtered water collected in the created ponds
to inoculate each mesocosm with micro-organisms and promote algal growth. We collected live
aquatic bryophytes (Fontinalis sp.) from the created ponds and added 30 g of these plants to
each mesocosm. Each mesocosm was protected with a mosquito screening to avoid colonisation
of other aquatic organisms and a chicken mesh fixed at the top to avoid disturbance by
mammals (Figure A.1.5). On 14 May 2021, 1118 tadpoles from the Gosner stage 26 (1960)
were randomly selected from six clutches housed at the Biodôme de Montréal. These tadpoles
were distributed among the 12 experimental mesocosms according to the treatments. We
divided the tadpoles from the six clutches equally in each mesocosm. We added eight cork
bark pieces (8 ×4 cm) and green plastic garden fences (10 ×4 cm mesh) in each mesocosm
to prevent the drowning of individuals as they reached metamorphosis (Figure A.1.5).
Mesocosms were visited initially every 2–3 days to monitor pH, water quality, and tempe-
rature. To supplement food for tadpoles, we added 5 mL of phytoplankton and 5 mL of
zooplankton (Reef ®, Seachem Laboratories, Madison, USA) to each mesocosm weekly until
the end of the experiment. As soon as we detected the first metamorphosed individual (pre-
sence of a tail stub, called metamorphs hereafter ; Gosner stage 45, 1960), mesocosms were
monitored daily. Between 9 June and 27 July 2021, we collected the emerging metamorphs.
Individuals from the same mesocosm were housed in the same terrarium (26 ×15 ×15 cm)
until their complete metamorphosis with the resorption of their tail. The experiment ended
when no more tadpoles emerged or remained in the water.
Metamorph reintroduction
After reaching metamorphosis, individuals weighing more than 0.07 g were marked with visible
implanted fluorescent alphanumeric tags (1.2 ×2.7 mm, Northwest Marine Technology Inc.,
Shaw Island, USA). Details of the marking procedure are available in Appendix A.2. Animals
were held under observation for 1–6 days and fed with Drosophila hydei. On the day of
release, animals were transported in terrariums (23 ×15.5 ×17 cm) on a wet moss substrate.
Individuals were released at dusk on the wet pond bank, within the inner perimeter of the
drift fences at the two created ponds.
23

Once all the introductions for the season were completed, we conducted a capture-recapture
study to follow individual survival. Three recapture sessions were performed one week apart,
on different dates for the two ponds (Table A.2.2). Some individuals from the Biodôme de
Montréal were released unmarked before recaptures were undertaken. Upon recapture, we
noted whether the individual was marked or unmarked, and measured its snout-vent length
before releasing it within the outer perimeter of the fence (Park et al.,2021). The traps and
portions of the fences were removed on the last day of the study to allow juvenile dispersal.
Although our objective was to estimate juvenile survival, a significant number of tagged
metamorphs lost their tag (Table 1.2), which unfortunately invalidates the assumption that
there is no tag loss when applying capture-mark-recapture models. For this reason, we only
present descriptive statistics for the recapture of juveniles.
Statistical analyses
Calling activity
Because the call index of P. maculata was on an ordinal scale, we used ordinal logistic re-
gression to model the response variable as a function of the explanatory variables (Agresti,
2002;Gelman and Hill,2007). This model is based on the cumulative logits to estimate the
probability of observing a score Sof level ≥jin recording i. Call indices 2 and 3 were com-
bined due to sparse data, yielding a total of 3 score levels i.e., level 1 no calls, level 2 a few
individuals heard, and level 3 overlap or chorus of boreal chorus frogs. Air temperature, linear
and quadratic effects of days elapsed since the start of the breeding season (4 April 2021), and
the interaction between air temperature and site were included in the model (equation 1.1).
The site and presence of noise disturbance during recordings were added as binary variables
(equation 1.1). Lastly, anthropogenic noise disturbance (airplanes or cars for more than 30
sec per recording), the presence of a chorus of Pseudacris crucifer, and disturbance from wind
and rainfall were incorporated as independent binary variables (equation 1.1). The call index
of lowest intensity was used as the reference level for the response variable. We formulated the
model in a Bayesian framework where each score Swas drawn from a categorical distribution,
with a probability Pij :
Sij ∼Categorical(Pij )
logit(Pij ≥Sij ) = β1·Sitei+β2·Temperaturei+β3·Daysi+β4·Days2
i+
β5·Sitei·Temperaturei+β6·Humani+(1.1)
β7·cruciferi+β8·Windi+β9·Raini−β0j,j=1, 2
Vague prior distributions were used for all parameters. We assumed uniform priors for the
intercepts U(-5, 5), and normal prior N(µ=0,σ2=1000) for the slope of explanatory
variables. Parameters were estimated with Markov chain Monte Carlo in JAGS 4.3.0 with R
using the jagsUI package (R Core Team,2020;Kellner,2019;Plummer,2003). Five chains
24

were run with 75,000 iterations each, including a burn-in period of 50,000 iterations, and one
observation was saved every 25th iteration. We assessed the convergence of the chains based on
the Brooks-Gelman-Rubin statistic, Monte Carlo error, trace plots, and posterior density plots
using package coda (Plummer et al.,2006). The model fit was evaluated using a posterior
predictive check based on the Hosmer-Lemeshow test statistic modified for ordinal logistic
regression as well as the Le Cessie and van Houwelingen test statistics based on smoothed
residuals (Hosmer et al.,1997). The complete JAGS code to run the analysis is in Table A.3.1.
Adult abundance
We estimated the number of adults present at each site using closed population capture-mark-
recapture models (Otis et al.,1978;Williams et al.,2002). At each site, capture histories
were constructed for each individual sampled on the four sampling occasions (J), where a
sampling occasion corresponded to a period of five days. We used a parameterisation of the
model where p(capture probability) and c(recapture probability) were estimated directly
and shared between both sites, whereas N(abundance) at each site was a derived parameter.
Abundance represented all adults alive on each site during the sampling season (Royle and
Dorazio,2008;Kéry and Schaub,2012).
We used a Bayesian formulation of closed population models for individual covariates based
on parameter-expanded data augmentation (Tanner and Wong,1987;Royle and Kéry,2007;
Royle and Dorazio,2008). Data augmentation consists in adding an arbitrarily large number of
zeroes to the data set, representing individuals that were never captured (Royle and Dorazio,
2012). The model estimates an inclusion probability ϕand a binary latent variable ziindicating
whether a given individual iwas part of the population (Kéry and Schaub,2012). The sum of
the latent variable estimates the total number of individuals in the population. In our case, we
augmented the dataset of individuals captured at least once with an additional 500 potential
individuals never captured and built a model with site-specific inclusion probabilities (ϕBC V 2
and ϕIP 013 ). The true occurrence was modelled as a Bernouilli variable with zi∼Bern(ϕ),
where icould vary between 0 and M, the sum of the number of individuals captured and
those never captured.
Three candidate models were built featuring different structures on the capture probabilities :
(1) null model, i.e., p=cconstant through time, (2) time model, p1=c1,p2=c2, and p3
=c3, where detection varied for each capture occasion as a fixed effect, and (3) behavioural
model with p=c, i.e., capture and recapture probabilities were estimated separately and
were constant across time. For this analysis, we used a uniform U(0, 1) prior for pand c.
The three models were compared using the Watanabe Akaike Information Criterion (WAIC ;
Watanabe,2010), where the model with the smallest WAIC value indicates the model that
would best predict a replicate dataset with the same structure. Three chains were run with
35,000 iterations each, including a burn-in of 5,000 iterations. We saved one observation for
25

each 25th iteration. Parameters were estimated by MCMC in program NIMBLE within R
with the Nimble package (de Valpine et al.,2017,2021;R Core Team,2020). Model selection
was conducted with the package AICcmodavg (Mazerolle,2017,2006). The NIMBLE code to
replicate the analysis is provided in Table A.4.1.
Tadpole development in mesocosms
We used the number of emerged individuals in mesocosm jin a binomial generalised linear
model to estimate the probability of surviving to emergence (Ej) as a function of larval density
and leaf litter, as well as a fixed effect of blocks and a random effect of mesocosm identity.
We tested differences among the four combinations of tadpole density and leaf litter with
orthogonal contrasts, namely Treatment.1 (high density without litter vs high density with
litter), Treatment.2 (low density without litter vs low density with litter), and Treatment.3
(low density vs high density) :
yj∼Binomial(Nj,Ej)(1.2)
log Ej
1−Ej!=β0+β1·Treatment.1j+β2·Treatment.2j+
β3·Treatment.3j+β4·Block.2j+
β5·Block.3j+δID.mesocosmj
We assumed vague normal priors, N(0, σ2= 100), for each slope of explanatory variables. The
random effect of mesocosm δID.mesocosm was drawn from a normal distribution with mean 0
and variance corresponding to σ2
ID.mesocosm, i.e., δI D.mesocosm ∼Normal(0, σ2
ID.mesocosm).
We investigated the effects of larval density and leaf litter on the size and mass of the chorus
frogs at metamorphosis with linear mixed effect models using a normal distribution, with a
fixed effect of blocks and a random effect of mesocosm identity. In the same way as above,
we tested differences among the four combinations of tadpole density and leaf litter with
orthogonal contrasts. Thus, our model was parameterised as :
µi=β0+β1·Treatment.2i+β2·Treatment.3i+β3·Treatment.4i+
β4·Block.2i+β5·Block.3i+δID.mesocosmi
(1.3)
Here, the response variable yifor individual iis drawn from a normal distribution with mean
parameter µiand variance σ2, i.e., yi∼Normal(µi,σ2). Again, we used vague priors for the
slope and variance parameters.
26

Parameters in the analyses of tadpole data were conducted in R using MCMC in JAGS
and the package jagsUI (R Core Team,2020;Kellner,2019;Plummer,2003). We ran five
chains with 10,0000 iterations each, including a burn-in of 50,000 iterations and saving each
fifth observation. We used the same convergence diagnostics as in the previous section and
checked the homoscedasticity and normality with residual plots. The JAGS code for these
analyses is available in Table A.5.1.
Figure 1.2 – Insertion of a PIT-tag on a female boreal chorus frog. The left image show the
insertion of the needle containing the tag. The right image was taken after the procedure,
once the incision was closed with a dot of surgical glue. The PIT-tag is visible inside the
female above the white line.
27

Results
Calling activity
We considered 31 recording days (4 April 2021 – 4 May 2021), covering the whole spring
breeding season of the species. Data were missing for 110 minutes at BCV2 (3%), 6 hours
at TM199 (9%), and 11 hours at IP013 (18%) due to equipment and battery issues. The
boreal chorus frog went extinct at the pond TM199, as we neither detected boreal chorus
frogs among the recordings nor captured individuals at the site. This site was excluded from
the analyses. More than half of the audio files from the pond IP013 did not feature boreal
chorus frog calls (call index 0 = 52%), whereas the pond BCV2 contained more detection
than non-detection of the target species (call index 0 = 34%). The most frequent call index
was 1 for both ponds. The percentage of recordings with call index 2 was very similar in both
ponds (BCV2 = 13% and IP013 = 12%). There were ten times more choruses (call index 3)
in the pond BCV2 compared to IP013 (8% versus 0.8%). In both ponds, choruses of spring
peepers (Pseudacris crucifer ) were heard in 16% of the recordings.
The ordinal logistic regression model used data from the two sites where P. maculata were
detected. Convergence diagnostics suggested that chains stabilised at similar values and that
chains were sufficiently long. The posterior predictive checks based on the Hosmer-Lemeshow
test statistic suggested lack-of-fit (P < 0.0001), although those based on smoothed residuals
suggested good fit (Score > 1,P=0.2894 ;Score > 2,P=0.4592). The call index at BCV2
was higher than at IP013 (Table A.3.2). There was a negative relationship between the call
index and the number of days elapsed since 4 April 2021 (Table A.3.2). The probabilities of
calling at scores 2 and 3 were highest during the first five days of the breeding season and
then decreased thereafter (Figure 1.3). By the seventh day after the start of breeding, the
probability of no calls (score 1) was over 0.50. The call index at both sites increased with
air temperature, but the relationship was stronger for BCV2 (Table A.3.2, Figure 1.4). The
probability of P. maculata calling (scores > 1) was lower under rain disturbance than without
any noise disturbance (Table A.3.2). Finally, the probabilities of boreal chorus frogs calling
at either scores 2 or 3 were substantially higher in the absence of P. crucifer choruses (Figure
A.3.1). However, call index values did not vary with wind and human disturbances (Table
A.3.2).
Adult abundance
We marked a total of 30 individuals in 2021 across the two sites where P. maculata was present.
Seventy-seven percent of individuals caught were males and the remainder were female. Hand
captures were almost as effective as traps for the 51 total captures (53% in minnow traps
versus 47% by hand). An average of two chorus frogs were captured per day. We observed
ten different capture histories for the 30 P. maculata adults captured at the two sites. In
28

summary, we recaptured seven individuals once, two recaptured twice, two recaptured three
times and finally, 19 individuals were never recaptured. We used capture histories of 22 unique
chorus frogs at BCV2, and 8 at IP013 in our models. Convergence diagnostics suggested that
chains were of sufficient length and stabilised to similar values (Figure A.4.1). The model with
time-dependent capture probability had all the support and we based our inferences on this
model (Table A.4.2). The population size estimated at BCV2 was 28 adults (95% CI : [23, 38])
and 10 adults at IP013 (95% CI : [8, 16], Table A.4.3, Figure A.4.2). Capture probabilities
on each site varied substantially among occasions, with the highest values during the first
occasion, coinciding with the first week of the breeding season (Table A.4.3, Figure A.4.3).
Tadpole development in mesocosms
A total of 561 tadpoles reached metamorphosis out of the 1,118 between 7 June and the end
of the experiment on 27 July 2021. The results of temperature and pH monitoring of the
mesocosms during the experiment are available in Figure A.5.2.
Based on convergence diagnostics, there was no evidence of issues or departures from model
assumptions. The fixed effect of blocks in the experiment was not significant in any of the
three analyses. Tadpole survival did not vary with larval density or leaf litter, with an average
probability of 0.46 across all treatments (Table A.5.2, Figure A.5.3). There was evidence of an
interaction between density-dependence and leaf litter on metamorph size and mass (Table
A.5.3,A.5.4). There was no effect of litter on body size and mass at high larval density,
but adding litter increased the mass and size of metamorphs in the low-density treatment.
Furthermore, metamorphs were larger and heavier when developing at low larval density than
at high density (Figure 1.5,1.6).
Metamorph release
Four amphibian species were heard and observed in the two constructed ponds at the Mont-
Saint-Bruno National Park : spring peeper (Pseudacris crucifer), wood frog (Lithobates syl-
vaticus), green frog (Lithobates clamitans), and American toad (Anaxyrus americanus). No
chorus frogs were detected at the two ponds before the reintroduction. We released a total of
732 metamorphs, including 203 reared to metamorphosis at the Biodôme de Montréal and 529
from the mesocosm experiment (Table 1.1). Seventy-seven percent of the released metamorphs
were tagged, regardless of their origin (mesocosms or Biodôme de Montréal, n = 566). The
remaining 23% either lost their tag or could not be tagged due to their low weight or because
of equipment malfunction (n = 166). We recaptured an average of eight individuals per CMR
session in both pond, and according to this average 47% of them were marked versus 52%
unmarked (Table 1.1,1.2). The average size of recaptured individuals was 11.34 mm (SD =
1.85 mm, n = 48), which is larger than the size of the metamorphs that emerged from the
mesocosms (9.06 mm, SD = 0.99 mm, n = 561). Of the recaptures in both ponds, 44% were
29

unmarked and 56% were marked (Table 1.2). Moreover, some fluorescent alphanumeric tags
were found on the ground close to the release area one week after release (Table 1.2).
Figure 1.3 – Predicted probability of boreal chorus frog calling indices at breeding site BCV2
according to days elapsed since the beginning of the reproductive season in 2021 in southern
Québec, Canada. Predictions are presented only for the BCV2 pond since the pattern was
the same for IP013. Dotted lines represent 95% credible intervals around predictions.
30

Figure 1.4 – Predicted probability of boreal chorus frog calling indices according to air
temperature at breeding site BCV2 (a) and site IP013 (b) in 2021 in southern Québec, Canada.
Dotted lines represent 95% credible intervals around predictions.
31

Figure 1.5 – Predicted mean mass (g) of P. maculata at metamorphosis ±95% Bayesian
credible interval according to mesocosm treatments.
Figure 1.6 – Predicted mean size (mm) of P. maculata at metamorphosis ±95% Bayesian
credible interval according to mesocosm treatments.
32

Table 1.1 – Number of boreal chorus frog metamorphs released according to site and date
of release in the Mont-Saint-Bruno National Park, Québec, Canada.
Site Date Number released
SQ83 10–16 June 2021 66
SQ83 17 June 2021 91
SQ83 20 June 2021 77
SQ83 22 June 2021 89
SQ83 25 June 2021 62
SQ22 25–28 June 2021 128
SQ22 1 July 2021 104
SQ22 4–9 July 2021 115
TOTAL -732
Table 1.2 – Number of boreal chorus frog metamorphs recaptured in 2021 according to site
and session of recapture in the Mont-Saint-Bruno National Park, Québec, Canada
Recapture site Capture occasion Tagged Untagged Tags found without individuals
SQ83 1 5 4 10
SQ83 2 4 7 1
SQ83 3 3 3 3
SQ22 1 5 3 1
SQ22 2 7 0 1
SQ22 3 3 4 2
TOTAL -27 21 18
33

Discussion
This study on natural populations of the boreal chorus frog showed a higher calling inten-
sity in the first week of April and when the temperature was above 7◦C. At the two sites
where the species was breeding, choruses were infrequent and were consistent with our low
estimates of abundances. We also showed that rearing tadpoles until metamorphosis maximi-
sed the survival of P. maculata larvae, requiring little monitoring and resources. Among the
rearing conditions tested in the mesocosms, low larval density and supplementation of leaf
litter produced the largest metamorphs. A large number of metamorphs were soft released,
which consists of keeping individuals under controlled conditions with a delay before com-
plete introduction into a new environment (Parker et al.,2012;Lepeigneul et al.,2014). They
were monitored during the first month of their introduction, however, tag loss precluded the
estimation of survival during the terrestrial stage.
Calling activity and natural population size
The calling intensity of the boreal chorus frog was influenced by environmental factors, such
as temperature and time elapsed since the beginning of the breeding season in both ponds,
validating our first hypothesis. We observed a period of cold weather on 21 April 2021, 17
days after the beginning of the breeding season for P. maculata. Snowfall was observed (5.3
mm of precipitation) and minimum temperatures dropped below 0◦C on 21–22 April 2021
(Environment Canada, 2021). After this event, the number of captures, as well as the number
of active males, decreased considerably and the season ended shortly thereafter. Male boreal
chorus frogs were more active when temperatures exceeded 7◦C, which is consistent with other
works on this species at other latitudes and elevations (Whiting,2004;Brinley Buckley et al.,
2021;Ouellet et al.,2009), as well as species in the same genus (Steelman and Dorcas,2010).
The peak activity of P. maculata occurred during the first week of the breeding season. The
probability of calling index 1 was highest at the beginning of the breeding season, decreasing
thereafter (Figure 1.3). This pattern was also observed for the species by Whiting (2004) and
Brinley Buckley et al. (2021). Furthermore, the highest average capture probability was also
recorded during the early days of the breeding season (Table A.4.3). Choruses of P. maculata
were rare, in contrast to choruses of P. crucifer. The latter interfered with the detection of
boreal chorus frogs (Figure A.3.1). This discrepancy suggests that spring peepers were more
abundant than boreal chorus frogs at our sites. /hlThis pattern was not observed by Whiting
(2004, Table 9, p. 70), which sampled one of the sites included in our own study. Chorus
frogs and spring peepers regularly occupy the same breeding ponds (Werner et al.,2009). The
observed higher chorus intensity in spring peepers compared to chorus frogs in our study is
consistent with the decline of the chorus frog over the past decades in the province of Québec.
Our results indicate that the population sizes of boreal chorus frogs studied at the three
sites are low. Indeed, one of the three sites with well-established populations of the species
34

went extinct. This supports the recent decline in occupancy of the species observed in the
Montérégie region (Dubois-Gagnon et al.,2021). In addition, the probability of calling indexes
2 and 3 was low during the breeding season in the ponds studied, supporting the low male
abundance in these populations. This result supports our hypothesis that P. maculata choruses
are less frequent during the breeding season than calls from single individuals. Corn et al.
(2011) used call indices to predict between 80 and 200 male boreal chorus frogs per pond in
Colorado. These estimates are much higher than the estimates for both sexes in our own study.
However, the population size and recruitment of this species can greatly vary between years
(Muths et al.,2018;Kissel et al.,2020). One of our natural sites (BCV2) was also studied
18 years earlier (Whiting,2004). We noted a sharp decline in population size in 2021 at this
site. Whiting (2004) reported 1,171 breeding adults in 2002, and 630 in 2003, with a sex ratio
biased towards males (60%) (see Whiting,2004, Tab. 9). The Whiting (2004) numbers are
based on raw captures. Nonetheless, the BCV2 breeding pond population between 2002 and
2003 was more than 30 times larger than our study at the same site in 2021.
The low population sizes at our natural sites could be associated with decreasing habitat
quality. The three natural study sites are surrounded by major roads, which limits the pos-
sibility of developments or connections between ponds to maximise reproduction and genetic
diversity (Cayuela et al.,2018). We observed that during spring, the road ditches overflowed
into one of the ponds (IP013). It may have helped fish migrate into the pond as some fish
species were caught in minnow traps, such as Central mudminnow (Umbra limi ) and Brook
stickleback (Culaea inconstans). Colonisation of breeding sites by fish decreases habitat qua-
lity for boreal chorus frog and increases the probability of extinction (Hecnar and M’Closkey,
1997;Hartel et al.,2007;Skelly,1996). Moreover, the prevalence of the amphibian chytrid
fungus Batrachochytrium dendrobatidis (Bd) has been confirmed in one of our ponds (BCV2)
by a positive PCR test, and is strongly suspected at the second site (IP013, Comité Québécois
sur la Santé des Animaux Sauvages Wildlife Health Intelligence Platform, Canadian Wildlife
Health Cooperative). This disease could be a factor in the decline of the species, although the
fungus has been present in Québec for more than 20 years (Ouellet et al.,2005).
Our study indicates that some natural populations of boreal chorus frogs in southern Québec
are too small to persist in the long term. We conducted a population viability analysis on the
species over a 25-year time step using much larger population sizes (A.6). It revealed that only
a quarter of the scenarios among the 64 led to an abundance as large as at the beginning of the
simulations, in addition to having a persistence probability of 0.8 and a positive average growth
rate. According to our results, the critical factor in avoiding early population extinction was
juvenile mortality of P. maculata (A.6, Figure A.6.2), which supports the work of Petrovan and
Schmidt (2019). The three natural populations we studied are among the last 71 occurrences
recorded in Montérégie (ERRFGO, 2019). Therefore, it will be necessary to continue the
population monitoring in subsequent years to determine the persistence of these three natural
35

populations of P. maculata. Current habitats are fragmented, which limits the potential to
colonise new, more favourable habitats. The construction of connected habitats in a protected
area could help preserve this species in southern Québec, by establishing new populations.
Tadpole development and metamorph release
We found a negative density-dependence and a positive effect of leaf litter on metamorph
size and mass, but no such effects on tadpole survival. The overall average survival of reared
tadpoles in our study was as high as the survival in some laboratory studies of the species
(Ethier et al.,2021). The size of metamorphs from the 0.1 tadpole/L density with litter was
close to the average size of P. maculata metamorphs reported by Amburgey et al. (2012),
which varied between 12 and 14 mm. However, the mass and size of high density reared
metamorphs were lower than those of metamorphs reared at low larval density, confirming
our original hypothesis. This result supports density-dependence effects on the size and mass of
amphibians during the larval stage, as also reported in previous studies (Boone,2005;Belden
et al.,2007;Brannelly et al.,2019). Several authors have shown that the size of a newly
transformed tadpole may impact juvenile and adult stage survival (Scott,1994;Brannelly
et al.,2019;Smith,1987;Semlitsch et al.,1988;Cabrera-Guzmán et al.,2013). Development
under high larval density can also compromise the immune system of metamorphs as well
as lower their lipid storage capacity (Scott,1994;Brannelly et al.,2019). Size and mass also
influences breeding success, as Pettus and Angleton (1967) found a positive linear correlation
between the size of the female and the number of eggs laid. It would be relevant to explore
new densities between 0.1 and 1 tadpole/L in mesocosms, to determine the threshold of larval
density beyond which body condition drops, as well as investigate the release of individuals
at the larval stage in the created ponds. We showed that additional resources such as leaf
litter mitigate the effects of density-dependence on larval development, but only at low larval
density. In fact, in the presence of litter a metamorph was on average 50 mg bigger and 0.9
mm larger than in the absence of litter (Figure 1.6,1.5). Burrow and Maerz (2021) and Stoler
and Relyea (2013) support the positive effect of leaf litter on larval development, which is
often used in mesocosm experiments to mimic a more natural environment (Semlitsch and
Boone,2010). The addition of leaf litter should therefore be considered for future rearing of
chorus frog tadpoles in mesocosms.
Marking with fluorescent tags did not appear to influence the short-term survival of boreal
chorus frog metamorphs during the first week before release (Table A.2.1,Swanson et al.,
2013). Unfortunately, the survival of juveniles after release could not be estimated due to a
tag retention problem. Almost half of the recaptured juveniles were untagged. Given the small
size of the VI alpha tag (2.7 mm long), the probability of its retention and readability varies
according to the expertise of the tagger and the size of the individual. Individuals lost their
tag from a few hours to two weeks after tagging (Osbourn et al.,2011). We could not close the
36

incision with surgical glue due to the tiny size of metamorphs, although other investigators
close the incision when using VI alpha tags on larger species (Courtois et al.,2013;McPherson,
2015;Donnelly et al.,1994). Despite the retention rate of VI alpha tags being similar to other
studies, it was impossible to determine if an individual recaptured without a tag had not been
marked or had lost its tag after release (McPherson,2015;Courtois et al.,2013;Heard et al.,
2008). Yet, the size of juveniles recaptured with a visible tag was significantly larger than
their size at metamorphosis (t = 6.51, df = 23, P < 0.0001), indicating growth.
The percentage of individuals recaptured after release is consistent with similar studies at-
tempting to estimate the short-term success of amphibian reintroductions. In the case of the
reintroduction of Pelophylax chosenicus, 6% of individuals were recaptured about a month af-
ter release, for an average of 4.66% per month (Park et al.,2021). According to Brannelly et al.
(2016), 4.83% of released Litoria verreauxii alpina individuals were recaptured on average six
months after release. Interestingly, during an attempted reintroduction of the boreal chorus
frog at Saint-Constant, Québec in 2016, biologists recaptured about 0.05% of the reintrodu-
ced individuals one year after release in 92 hours of search time (Doucet,2017). Improved
evaluation of the success of future reintroductions of P. maculata is needed, according to the
principle of a retroactive loop (Klop-Toker et al.,2016;Nichols and Armstrong,2012;Seddon
et al.,2007). One avenue would be changing the type of tags for metamorphs by using vi-
sible implant elastomers (VIE). If all released individuals are tagged, it would be possible to
estimate a post-release survival with a CMR model (Fouilloux et al.,2020). Because unique
marking with VIE tags is limited for small individuals, batch marks would be more effective
for metamorphs. A formal evaluation of tag loss in the longer term could be conducted with
a double-tagging study, for example, tagging individuals with VI alpha tags that enable indi-
vidual recognition combined with a batch mark using VIE. Another alternative would be to
reintroduce untagged metamorphs and monitor the following breeding season by CMR on the
surviving adults, since the retention of PIT tagging on P. maculata adults has been promising
in this study.
Conclusion
Our results suggest that the breeding season of the boreal chorus frog is short and depends
on air temperature. Male calls were predominantly low in intensity, and few choruses were
recorded. The abundances of the populations monitored in southern Québec were low and
their status would be of concern if future abundance estimates do not increase. We showed
that a collaborative project can be implemented in a short period to reintroduce a species
according to shared expertise to manage uncertainties. Temperature seems to have played an
important role in the intensity of boreal chorus frog calls, as well as the timing of activity,
which was greatest early in the breeding season. The species does not appear to be as abundant
as expected at sites previously described as having large populations. Two of the three study
37

sites were used as breeding sites by P. maculata, whereas the population at the third site
went extinct. The low abundance estimates of populations studied could be the result of a
bad breeding year for the species, but at this stage, we do not have enough information to
conclude on their situations. This study illustrated the value of rearing boreal chorus frogs
in captivity through metamorphosis before release. We found that larval development was
optimal in mesocosms with leaf litter supplementation and low larval density. The use of VI
alpha tags on recently metamorphosed individuals revealed issues of low tag retention at this
life stage.
Acknowledgements
We are grateful to L. Bouthillier, S. Bellefleur, as well as T. Montpetit, I. Picard, and Ciel
et Terre for sharing data from previous inventories. Y. Dubois, P. Charbonneau, and C.
Doucet provided logistic support. We also thank O. Colin, teams of the Biôdome de Montréal,
and of the Mont-Saint-Bruno National Park for their logistic support during fieldwork. All
animal manipulations were approved by the committee on animal care of Université Laval and
Université d’Ottawa, and the capture permit was delivered by the province of Québec. The
project benefited from financial and logistic support from Environment and Climate Change
Canada, the Ministère des forêts, de la Faune et des Parcs, the Biodôme de Montréal and the
Mont-Saint-Bruno National Park (SÉPAQ).
Conflict of interest
None declared.
Author contributions
MJM and VT conceptualised the idea and acquired funding for the project. AF, VT, and
MJM contributed to the conception and design of the study. AF acquired data by conducting
field sampling. AF and MJM contributed to data analysis and interpretation. AF, VT, EW,
ST, and MJM contributed to the writing and editing of the manuscript.
38

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Conclusion générale
Ce projet de maîtrise était composé de deux volets complémentaires. Le premier concernait
l’acquisition de connaissances sur les populations naturelles de la rainette faux-grillon bo-
réale, alors que le deuxième volet s’intéressait à l’impact de la densité sur le développement
larvaire et la taille et masse des métamorphes. Le suivi des populations naturelles et des tê-
tards jusqu’à la métamorphose a permis de compléter nos connaissances sur la dynamique
de reproduction de cette espèce. Ces informations étaient primordiales avant d’engager la
réintroduction de nouvelles populations de P. maculata en milieu protégé selon les priorités
du plan de rétablissement (ERRFGO, 2019 ;Environnement Canada 2015). Les objectifs du
premier volet étaient (1) de quantifier l’influence des facteurs environnementaux sur l’inten-
sité des chants de l’espèce pendant la saison de reproduction, et (2) d’estimer l’abondance
de populations naturelles de P. maculata, documentées depuis 20 ans comme abondantes.
Les objectifs du deuxième volet du projet étaient (3) d’évaluer l’effet de la densité et de la
présence de litière forestière sur la survie et le développement larvaire de P. maculata, mais
également la survie des juvéniles après la réintroduction. Nos résultats et recommandations
sont susceptibles d’aider d’autres programmes de réintroduction d’amphibiens.
Intensité des chants et taille des populations naturelles
Nous avons répondu au premier objectif en analysant les relations entre les facteurs environ-
nementaux et l’intensité des chants des rainettes faux-grillon boréales à l’aide d’enregistreurs
acoustiques. Nous avons observé une réponse significative de la fréquence des chants en fonc-
tion du temps et de la température dans deux étangs suivis. Ceci confirme notre hypothèse
selon laquelle l’intensité des chants de P. maculata lors de la reproduction est influencée par
la température, ainsi que par le temps écoulé depuis la fonte des neiges. L’espèce chantait da-
vantage en début de saison, lorsque les températures étaient supérieures à 7°C. Ceci confirme
le caractère explosif de la reproduction chez P. maculata (Corn et Muths,2002). Nous avons
également validé notre proposition selon laquelle les chorales de P. maculata sont moins fré-
quentes pendant la période de reproduction que les chants d’individus isolés. Nos estimations
montraient une occurrence des chorales remarquablement faible dans les deux étangs occupés
par l’espèce.
Afin de répondre au second objectif, nous avons estimé l’abondance des populations natu-
50

relles grâce à une étude de capture-marquage-recapture des adultes de rainettes faux-grillon
boréales. Notre étude était la première à estimer les tailles de populations de P. maculata au
Québec avec une technique prenant en compte la détection imparfaite. Les sites naturels à
l’étude sont connus depuis les années 1990s pour être fréquentés par la rainette faux-grillon
boréale et sont suivis chaque année depuis 1999 (Daigle,1994;Bonin et Galois,1996). Cepen-
dant, il n’y avait encore eu aucune estimation robuste de taille de population (Trottier-Picard
et Bouthillier,2021). Le protocole que nous avons décrit dans cette étude pourrait servir aux
gestionnaires et organismes qui inventorient cette espèce menacée, afin d’estimer les tailles
d’autres populations au Canada. Nos résultats soulignent le déclin de l’espèce par son absence
à l’un des trois étangs de reproduction, qui abritait autrefois une grande population. Nos esti-
mations de taille de populations sont considérablement faibles pour les deux sites utilisés par
l’espèce pour sa reproduction. En comparaison, Corn et al. (2011) estiment qu’entre 80 et 200
rainettes faux-grillon mâles fréquentent un étang en période de reproduction au Colorado,
ce qui est bien au-delà de l’abondance estimée dans notre étude. L’un de nos sites naturels
(BCV2) a également été étudié 18 ans plus tôt. Whiting (2004) avait compté 1 171 adultes
reproducteurs en 2002, et 630 en 2003, avec un sex-ratio biaisé en faveur des mâles (60%) (voir
Whiting,2004, Tab. 9). Les données de Whiting (2004) sont basées sur des captures brutes.
Néanmoins, la population de l’étang de reproduction entre 2002 et 2003 était plus de trente
fois supérieure à celle de notre étude sur le même site en 2021. En réponse à la pandémie de
la COVID-19 et à l’impossibilité de démarrer le projet sur le terrain en 2020, nous avons ef-
fectué une analyse de viabilité des populations afin de simuler la dynamique d’une population
naturelle de P. maculata selon plusieurs scénarios pour orienter les efforts de prélèvement
et d’introduction d’individus (Table A.6.1,A.6.2). Pour ce faire, nous avons synthétisé les
données empiriques sur le cycle de reproduction et la survie des différents stades de Pseu-
dacris maculata. Nous avons choisi de simuler des populations initiales de 200 individus sur
50 ans, et nous avons observé que certains facteurs comme la survie juvénile pouvaient avoir
un impact rapide sur les tailles de populations, jusqu’à atteindre l’extinction (Figure A.6.2).
Ceci appuie la proposition selon laquelle la sensibilité du taux de croissance aux variations de
survie larvaire et juvénile est élevée pour les espèces adoptant une stratégie de développement
rapide, telles que les Hylidae et certaines espèces de Ranidae et de Bufonidae (Petrovan et
Schmidt,2019;Cayuela et al.,2020). Finalement, selon les connaissances actuelles et sans co-
lonisation par des individus provenant de sites adjacents, la taille des populations naturelles
de P. maculata de notre étude ne serait pas suffisante pour se maintenir dans le futur.
Stratégie d’élevage et de réintroduction
Grâce à l’expertise du Biodôme de Montréal, les premières étapes du programme de réintro-
duction, soit la reproduction induite et l’élevage des rainettes faux-grillon, ont été exécutées
dans de bonnes conditions, assurant la survie des têtards lors de leurs premiers stades de
51

vie. L’élevage des têtards de P. maculata en semi-captivité dans des mésocosmes a bien fonc-
tionné. La température de l’eau dans les mésocosmes a varié au cours de la journée, avec au
plus chaud des valeurs de 27,5◦C relevées, ce qui a pu accélérer le développement des têtards
(Gomez-Mestre et al.,2010;Amburgey et al.,2012). Le traitement à haute densité larvaire
était 10 fois supérieur à la faible densité (1 têtard/L vs 0.1 têtard/L). Toutefois, cette diffé-
rence n’a pas influencé la survie des têtards comme le proposait notre première hypothèse.
Par contre, notre étude confirme l’hypothèse selon laquelle la taille et masse des métamorphes
diminue avec l’augmentation de la densité larvaire. La taille et masse des individus provenant
de basse densité avec litière forestière était meilleure que celle des individus élevés à haute
densité avec ou sans litière. L’ajout de feuilles mortes a eu un effet positif sur la taille et
la masse des métamorphes, mais seulement dans les traitements à basses densités. Les mé-
tamorphes plus corpulents auraient une probabilité de survie plus élevée au stade terrestre
que les métamorphes plus chétifs (Scott,1994;Brannelly et al.,2019;Smith,1987;Semlitsch
et al.,1988;Cabrera-Guzmán et al.,2013). La taille et la masse influencent également le suc-
cès de la reproduction, puisque Pettus et Angleton (1967) ont trouvé une corrélation linéaire
positive entre la taille de la femelle et le nombre d’oeufs qu’elle pond. Le développement
larvaire à haute densité pourrait également compromettre le système immunitaire des méta-
morphes, ainsi que de diminuer leur capacité de stockage des lipides (Scott,1994;Brannelly
et al.,2019). Il serait pertinent de poursuivre l’étude de l’effet de la densité larvaire sur la
taille et la masse en suivant les métamorphes réintroduits jusqu’au stade adulte. Cela nous
permettrait de savoir si le type de traitement a une influence sur la survie ou la reproduction
après réintroduction, et d’évaluer parallèlement le succès de la reproduction dans les étangs
construits (Strain et al.,2017). Cette densité-dépendance au stade larvaire devra être prise en
compte dans les prochains élevages de rainettes faux-grillons, dans l’optique de réintroduire
un nombre plus important de métamorphes avec de bonnes conditions corporelles au parc
national du Mont-Saint-Bruno.
Nous avons réintroduit plus de 700 métamorphes de P. maculata dans les étangs construits
au parc national du Mont-Saint-Bruno. Le marquage avec les étiquettes alphanumériques
fluorescentes (VI alpha tag) s’est avéré un mauvais choix à ce stade de vie en raison de la
perte des étiquettes sur les individus marqués. En moyenne, 47% des individus recapturés
étaient marqués pour 52% non marqués à chaque sortie de capture sur le terrain (Table 1.2).
Malheureusement, ceci a compromis l’estimation de survie selon les modèles classiques de
CMR, et nous n’avons pas pu atteindre cet objectif du projet. Toutefois, parmi les juvéniles
marqués et recapturés, nous avons pu confirmer que certains avaient survécu plus de trois
semaines après la relâche en milieu aménagé. De plus, leur taille était significativement plus
grande qu’à la métamorphose (t = 6.51, df = 23, P < 0.0001), indiquant une croissance.
L’introduction de nouveaux métamorphes ainsi que le suivi post-réintroduction devront se
poursuivre dans les trois prochaines années du programme afin d’évaluer le succès et d’assurer
le maintien des nouvelles populations de rainettes faux-grillons au parc national du Mont-
52

Saint-Bruno.
Perspectives du marquage des rainettes faux-grillon
Outre les résultats présentés dans ce mémoire, nous avons réussi à mettre en place deux
protocoles pour le marquage des adultes et des métamorphes de rainettes faux-grillon boréales.
Les opérations ne semblent pas avoir impacté leur survie. Premièrement, les adultes ont été
marqués avec des transpondeurs passifs intégrés (PIT tags). Les PIT tags sont de plus en plus
utilisés sur les amphibiens (Ousterhout et Semlitsch,2014;Connette et al.,2011). Cependant,
ce type de marque n’avait jusqu’ici jamais été utilisée pour cette espèce dans la littérature. Le
marquage en sectionnant des phalanges (toe clipping) a été grandement utilisé pour des projets
de capture-marquage-recapture sur les anoures (Smith et Green,2005), ainsi que sur la rainette
faux-grillon (Whiting,2004;Smith,1987;Muths et al.,2018;Corn et al.,1997). Toutefois,
cette méthode est depuis deux décennies remise en question pour des raisons éthiques, mais
également à cause de la limitation de combinaison unique que l'on peut obtenir par rapport à
un marquage par PIT-tag (Heard et al.,2008;May,2004;McCarthy et Parris,2004). Malgré la
petite taille des individus, nous n’avons pas observé d’effet limitant des PIT tags sur la survie
ou l’activité des adultes 48h après le marquage. De plus, plusieurs mâles ont été recapturés
quelques jours après le marquage en train de chanter. Une femelle gravide marquée au début
de la saison a également été recapturée deux semaines après le marquage, vraisemblablement
après avoir pondu ses oeufs. Le protocole que nous avons développé pour P. maculata pourrait
être utilisé par d’autres études portant sur des espèces du même clade (Ethier et al.,2021).
Deuxièmement, les métamorphes de P. maculata ont été marqués avec des VI alpha tags. Cette
étude est la première à adapter le processus de marquage à des individus de cette petite taille et
à évaluer la rétention de ce type de marque sur cette espèce dans le cadre d’une réintroduction.
Nous ne recommandons cependant pas la poursuite de l’utilisation des VI alpha tags sur les
juvéniles de cette espèce. Certains individus étaient trop petits proportionnellement au tag
(2.7 mm) pour être marqués. La taille moyenne de ces individus trop petits pour être marqués
était de 8.3 mm (sd = 0.5 mm, n = 105), le tag faisait alors un tiers de leur taille. À ce
nombre s’est rajouté des individus qui ont perdu leur tag après le marquage. Lorsque le tag
était inséré trop proche de l’incision, sa rétention était réduite (Osbourn et al.,2011). Nous
n’avons pas refermé l’incision à l’aide d’une colle chirurgicale, comparativement à plusieurs
études sur les VI alpha tags (Courtois et al.,2013;McPherson,2015;Donnelly et al.,1994).
L’utilisation de colle a été jugée dangereuse à ce stade de vie puisqu’elle est difficile à appliquer
avec précision sur les métamorphes. Ceci entraîne un débordement de la colle hors du point
d’incision ventrale, pouvant par exemple handicaper l’individu si la colle migre proche de ses
pattes (McPherson,2015). Une meilleure évaluation du succès des futures réintroductions de
P. maculata est nécessaire. Une avenue possible pour les prochaines années serait d’utiliser
des élastomères de couleur fluorescents (visible implant elastomer). Ces dernières pourront
53

être utilisées même sur les plus petits individus, car la quantité de peinture injectée peut
être ajustée. L’incision est microscopique, ce qui améliore la rétention sans colle chirurgicale
(Fouilloux et al.,2020). Cependant, une attention particulière devra être portée au risque
de migration de ces tags hors de la zone d’injection vers d’autres régions corporelles (Cabot
et al.,2021).
Limites de notre étude
Nous avons identifié certaines limites à notre étude. La qualité de l’écoute des chants d’anoures
peut facilement être médiocre à cause des bruits de fond produits par d’autres animaux, des
conditions météorologiques difficiles ou bien du bruit anthropique, causant un biais de détec-
tion (Lapp et al.,2021). L’écoute manuelle est également limitée par l’expertise et l’ouïe de
la personne en charge de les analyser. Nous avons observé que les chants de P. maculata de
faibles intensités se retrouvaient noyés parmi les chorales de P. crucifer, ou bien parmi les
bruits de véhicules sur les routes adjacentes. Ces interférences ont pu sous-estimer l’effet néga-
tif des bruits anthropiques sur les chants. Une étude sur Hyla arborea a mis en évidence qu’un
individu chantant seul serait plus affecté par le bruit de la route qu’une chorale (Lengagne,
2008). Il serait pertinent d’obtenir la fréquence de passages sur les routes à proximité des
étangs, et d’étudier plus spécifiquement sa relation avec les différentes intensités de chant de
la rainette faux-grillon (Caorsi et al.,2018). Autrement, l’automatisation de l’analyse des en-
registrements permettrait d’augmenter le nombre de sites de reproduction suivi. Pour cela, il
faudrait sélectionner des enregistrements où la rainette faux-grillon chante à plusieurs intensi-
tés différentes. Un algorithme d’apprentissage profond pourrait alors être entraîné à identifier
l’espèce dans les enregistrements, en remplacement d’une écoute manuelle (Xie et al.,2016;
Acevedo et al.,2009). Cependant, l’identification de chants avec interférence est également
problématique avec l’apprentissage profond, car il peut entraîner davantage de faux positifs
et faux négatifs.
Une autre limite de notre étude est de ne pas avoir été en mesure d’estimer le recrutement
dans les populations naturelles suivies. L’étude sur le long terme d’autres populations de P.
maculata indique que le taux de croissance d’une population, de même que la probabilité
de survie des adultes varient grandement d’une année à l’autre (Kissel et al.,2020). Ceci
laisse penser que de nombreux facteurs peuvent influencer le nombre d’adultes reproducteurs
dans le temps (Brinley Buckley et al.,2021). À l’avenir, il serait utile de poursuivre le suivi
de ces populations sur plusieurs années, et, lorsqu’au moins trois années de données seront
accumulées, d’appliquer un modèle de survie pour estimer la longévité de la rainette faux-
grillon boréale, toujours débattue dans la littérature (Ethier et al.,2021).
Une menace qui pourrait avoir contribué au déclin des populations de P. maculata observé
ces dernières décennies serait la chytridiomycose. Cette maladie est aujourd’hui une menace
54

mondiale pour les amphibiens (Rachowicz et al.,2005;Dejean et al.,2010;Vitt et Caldwell,
2013). La prévalence du champignon chytride des amphibiens a été confirmée dans l’un de nos
étangs (BCV2). En effet, un cas positif d’infection par la chytridiomycose a été confirmé par
un test PCR et vérifié via une nécropsie par le Comité Québécois sur la Santé des Animaux
Sauvages (CQSAS). La mort de l’individu aurait été causée par des lésions cutanées associées
au champignon Batrachochytrium dendrobatidis (Bd). Il s’agit à notre connaissance de la
première documentation de la chytridiomycose chez une rainette faux-grillon à l’état sauvage
au Québec (Wildlife Health Intelligence Platform, Canadian Wildlife Health Cooperative). Il
serait intéressant d’étudier plus spécifiquement l’incidence de cette maladie sur la dynamique
des populations naturelles de P. maculata. Par exemple, l’échantillonnage du champignon Bd
peut être fait selon un protocole d’ADN environnemental que l’on réalise sur un grand nombre
de sites de reproduction potentiels (Schmidt et al.,2013;Hyman,2012).
Avenues de recherche
Lors de notre analyse de viabilité des populations, nous avons identifié les éléments à prioriser
dans le programme de réintroduction de la rainette faux-grillon boréale (A.6). Les recomman-
dations pour le projet d’établissement de la population de l’espèce ont été de (1) réintroduire
au stade larvaire le plus avancé possible afin de maximiser le succès de réintroduction, et (2)
de déterminer la mortalité des juvéniles par une surveillance post-réintroduction pendant au
moins quatre ans. En effet, d’après notre analyse la survie juvénile joue un grand rôle dans
la persistance des populations. L’étude présentée ici a suivi la première recommandation, en
introduisant des métamorphes de rainette faux-grillon boréale. Selon la deuxième recomman-
dation, nous avons amorcé le suivi post-réintroduction, seulement nous n’avons pas pu estimer
une survie des juvéniles à court terme à cause d’un problème de rétention des étiquettes chez
les juvéniles.
La surveillance de la santé des populations naturelles de rainettes faux-grillon boréales doit
être effectuée dans le même sens que la surveillance de la dynamique des nouvelles popu-
lations (Sainsbury et al.,2017). Une attention particulière doit être portée à l’évolution du
nombre de cas de chytridiomycose dans les nouvelles populations réintroduites (Pessier et
Mendelson,2010;Ewen et al.,2012;Stockwell et al.,2008). Les métamorphes et juvéniles
auraient plus de risque d’être infectés que les adultes selon l’étude de Abu Bakar et al. (2016)
sur Litoria aurea. De plus, plusieurs prédateurs ont été fréquemment observés dans les deux
étangs construits pendant la recapture au parc national du Mont-Saint-Bruno, notamment la
grenouille verte (Lithobates clamitans melanota), la couleuvre rayée (Thamnophis sirtalis) et
la couleuvre à ventre rouge (Storeria occipitomaculata occipitomaculata). Ces différentes me-
naces constituent un risque d’échec de la réintroduction, et doivent continuer d’être surveillées
avec attention a posteriori d’une réintroduction (Muths et al.,2014).
55

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60

Annexe A
Supplementary material for the
article
A.1 Arrangement of the adult capture-recapture equipment
and experiment in aquatic mesocosms for the boreal
chorus frog (Pseudacris maculata)
Figure A.1.1 – Arrangement of the minnow traps and wooden boards around three natural
ponds during the capture-recapture session for the boreal chorus frog (Pseudacris maculata),
southern Québec, Canada
61

Figure A.1.2 – Installation of traps and geotextile fences for capture-recapture monitoring
of chorus frogs in one of the natural ponds (TM199). Early April 2021, southern Québec,
Canada. Hugues Terreaux de Félice ©
62

Figure A.1.3 – Twelve mesocosms at the Mont-Saint-Bruno National Park, Québec, Canada.
Figure A.1.4 – Diagram of the arrangement of the randomised complete block experiment
in aquatic mesocosoms in Mont-Saint-Bruno National Park, Québec, Canada.
63

Figure A.1.5 – Snapshot inside of a mesocosm, protected by wire mesh and window screen
attached to the container. Pieces of floating cork bark and plastic garden fence were added
into the water to create floating rafts for metamorphosed tadpoles.
64

A.2 Metamorph anaesthesia, capture-recapture details, and
recapture sessions of introduced boreal chorus frogs
Control marking test
We waited for the complete resorption of the metamorph tails before tagging (Gosner stage
46, 1960) which took 12 to 48 hours after emergence. A preliminary experiment was done to
assess the effect of tagging on 45 metamorphs : one-third were measured and weighed without
anaesthesia (control), one-third were anaesthetised, then measured and weighed without tag-
ging, and the last third were anaesthetised, measured, weighed, and tagged (Table A.2.1). All
metamorphs survived and recovered well. One of the 15 tagged metamorphs lost its tag about
six hours after tagging. The group of marked and anaesthetised individuals was released after
12 hours of observation in the reintroduction ponds, while the control group was marked 24
hours after the test before being released.
Anaesthesia and marking procedure
Each individual was anaesthetised by immersion in a solution of MS-222 at 0.4 g/L and
buffered to a pH of 7 with sodium bicarbonate. Once anaesthetised, the individual was weighed
(precision 0.001 g, OHAUS Scout ©SPX223, New Jersey, USA) and measured to snout-vent
length (SVL) to the nearest 0.1 mm using a Vernier caliper. A ventral incision of less than
2 mm was made on the lower left side of the individual with surgical scissors (Fisherbrand
TM High Precision Dissecting Micro Scissors, SDI13550, 12 cm). The individual was then
marked with a visible implanted fluorescent alphanumeric tag (1.2 x 2.7 mm, Northwest
Marine Technology Inc., Shaw Island, USA ; Courtois et al. 2013). After marking, individuals
were placed in a terrarium with natural moss for their reanimation. Individuals were kept
between 1 and 6 days in terrariums until their reintroduction and fed a few hours after
marking with fruit flies (Drosophila hydei).
Among the 561 metamorphs that emerged in mesocosms, 441 individuals were tagged. Seven
percent of them died after tagging before being released (n = 32). We also tagged 191 indivi-
duals from the Biodôme de Montréal that stayed in captivity until metamorphosis, and 18%
died after tagging before being released (n = 34). Across all origins, 60 metamorphs lost their
mark before being reintroduced to the constructed ponds, accounting for 11% of overall tag
loss (excluding dead bodies, n = 566). For these individuals, tag retention lasted from a few
hours to three days.
Recapture
Drift fences were installed at the created wetlands to intercept dispersing juveniles (Caldwell,
1987;Dodd and Scott,1994). These drift fences were combined with eight minnow traps
(43 cm long x 23 cm diameter, with a 48 mm square mesh and a 22 mm entrance hole) at
65

each pond to capture individuals. We added 20 artificial spruce cover boards (42 x 42 x 6
cm) between the water line and the fences on the ground. Individuals were released in the
two created ponds at dusk on the wet pond bank on the inner perimeter of the drift fences.
Each recapture session was accomplished in a single day, where sites were visited twice :
0800 and 2000. During the visits, 2–5 people checked the artificial refuges and patrolled the
perimeter, following the drift fences at the edge of the ponds to capture juveniles attempting
to cross (Doucet,2017). We captured them by hand. Capture sessions lasted 2–3 h depending
on the number of workers and the frog activity. Each captured individual was handled with
powder-free nitrile gloves to identify the tag and released immediately.
66

Table A.2.1 – Result table of control, anaesthesia, and tagging of boreal chorus frog meta-
morphs. Survival was 100%, regardless of the mesocosm treatment. The second column shows
the time in minutes until the individual is immobilised (fully anaesthetised).
date_tagging T_anaesthesia treatment group tag_ID retention dead
2021-06-11 01 :50 D180+F tagged X70 YES NO
2021-06-11 00 :51 D180+F anaesthesia N/A N/A NO
2021-06-11 N/A D180+F control N/A N/A NO
2021-06-11 01 :00 D180+F tagged X71 YES NO
2021-06-11 01 :30 D180+F anaesthesia N/A N/A NO
2021-06-11 N/A D180+F control N/A N/A NO
2021-06-11 01 :20 D180+F tagged X72 YES NO
2021-06-11 01 :00 D180+F anaesthesia N/A N/A NO
2021-06-11 N/A D180+F control N/A N/A NO
2021-06-11 02 :50 D18+F tagged X73 YES NO
2021-06-11 01 :20 D180+F anaesthesia N/A N/A NO
2021-06-11 N/A D18+F control N/A N/A NO
2021-06-11 01 :30 D18+F tagged X74 YES NO
2021-06-11 02 :30 D18+F anaesthesia N/A N/A NO
2021-06-12 N/A D180+F control N/A N/A NO
2021-06-12 00 :45 D180+F tagged X75 YES NO
2021-06-12 02 :45 D180+F anaesthesia N/A N/A NO
2021-06-12 N/A D180+F control N/A N/A NO
2021-06-12 02 :30 D180+F tagged X76 YES NO
2021-06-12 01 :30 D18 + F anaesthesia N/A N/A NO
2021-06-12 N/A D18+F control N/A N/A NO
2021-06-12 02 :15 D180+F tagged X77 YES NO
2021-06-12 02 :20 D180+F anaesthesia N/A N/A NO
2021-06-12 N/A D18+F control N/A N/A NO
2021-06-12 02 :20 D18+F tagged X78 YES NO
2021-06-12 02 :50 D18+F anaesthesia N/A N/A NO
2021-06-12 N/A D18+F control N/A N/A NO
2021-06-12 02 :15 D180+F tagged X79 YES NO
2021-06-12 01 :40 D180+F anaesthesia N/A N/A NO
2021-06-12 N/A D180+F control N/A N/A NO
2021-06-12 01 :40 D180+F tagged X80 YES NO
2021-06-12 01 :00 D180+F anaesthesia N/A N/A NO
2021-06-13 N/A D180+F control N/A N/A NO
2021-06-13 02 :30 D18+F tagged X84 YES NO
2021-06-13 3 :05 D18+F anaesthesia N/A N/A NO
2021-06-13 N/A D18+F control N/A N/A NO
2021-06-13 1 :15 D180+F tagged X85 NO NO
2021-06-13 2 :00 D180+F anaesthesia N/A N/A NO
2021-06-13 N/A D180+F control N/A N/A NO
2021-06-13 1 :45 D180+F tagged X86 YES NO
2021-06-13 2 :20 D180+F anaesthesia N/A N/A NO
2021-06-13 N/A D180+F control N/A N/A NO
2021-06-13 2 :15 D180+F tagged X87 YES NO
2021-06-13 2 :30 D180+F anaesthesia N/A N/A NO
2021-06-13 N/A D180+F control N/A N/A NO
67

Table A.2.2 – Date of recapture sessions of introduced boreal chorus frog juveniles according
to reintroduction site in the Mont-Saint-Bruno National Park, Québec, Canada.
Site Recapture occasion Date
SQ83 1 28 June 2021
SQ83 2 4 July 2021
SQ83 3 10 July 2021
SQ22 1 13 July 2021
SQ22 2 19 July 2021
SQ22 3 25 July 2021
68

A.3 Ordinal logistic regression model estimated by Markov
Chain Monte Carlo describing the calling activity of
Pseudacris maculata
Table A.3.1 – JAGS code used to conduct ordinal logistic regression models.
mode l {
# # it e ra t io n a cr os s e ac h o bs e rv a ti o n
for ( i i n 1 : n ob s ) {
## S c o r e is dr a w n from categorical d i s t r i b u t i o n w i t h p r o b a b i l i t y p
s co re [ i ] ~d c at ( p [i , ] ) # r eq u ir e s va l ue s > = 1
# # if r le v el s , o nl y r - 1 t h re s h ol d s a re r eq u i re d
p [i , 1] < - 1 - Q[ i ,1 ]
for ( r in 2 :( nlevels - 1 ) ) {
p [i , r ] <- Q[ i ,r - 1] - Q[ i , r ]
}
p [i , nlevels]<- Q[ i , ( nlevels - 1) ]
for ( r in 1 :( nlevels -1)){# o ne l e ve l l es s
## c [ r ] i s a n u n k n o w n c u t p o i nt f o r e a c h c a t e g o r y r
l og it ( Q[ i , r ]) <- beta. d ay *d ay [ i ] + beta. day2 *d ay 2 [ i ] +
beta. a i r *a ir [ i ] + beta. d is t ur b . p sc r *d i st u rb . p sc r [ i ] +
beta. d i st u rb . h um a n *d is t ur b . h um a n [i ] +
beta. d i st u rb . r ai n *d i st u rb . r a in [ i ] +
beta. d i st u rb . w in d *d i st u rb . w i nd [ i ] +
beta.site. BCV2 *B CV 2 [ i] +
beta. a i r . BC V2 *a i r [i ] *B C V2 [ i ] - c[r]
}
}
# # pr io r s f o r t h re s ho ld s ( i nt e rc e pt s )
for ( i in 1 :( nlevels - 1 ) ) {
dc [ i ] ~ d u ni f ( -5 , 5 )
}
# # so rt t h re s ho l ds ( i n te rc e pt s )
c[1:(nlevels - 1 ) ] <- sort( d c [ ] )
# # pr i or f or c om m on s l op e s
beta. d a y ~ d no rm (0, 0.001)
beta.day2 ~ d no rm (0, 0.001)
69

beta. a i r ~ d no rm (0, 0.001)
beta. d i st u rb . p sc r ~ dn o rm (0, 0.001)
beta. d i st u rb . h u ma n ~ d n or m (0, 0.001)
beta. d i st u rb . r ai n ~ dn o rm (0, 0.001)
beta. d i st u rb . w in d ~ dn o rm (0, 0.001)
beta.site. BCV2 ~ d no rm (0, 0.001)
beta. a i r . BC V2 ~ d no r m (0, 0.001)
# # od d s r a ti o
or . d a y < - ex p (beta. d a y )
or . day2 < - e xp (beta . d ay 2 )
or . a i r < - ex p (beta. a i r )
or . d i st u rb . p s cr < - e x p (beta. d is t ur b . p sc r )
or . d i st u rb . h u ma n < - e xp (beta. d is t ur b . h um a n )
or . d i st u rb . r a in < - e x p (beta. d is t ur b . r ai n )
or . d i st u rb . w i nd < - e x p (beta. d is t ur b . w in d )
or . site.BCV2 < - e x p (beta.site.BCV2 )
or . a i r . BC V 2 < - ex p (beta. a i r . BC V 2 )
# # Si m ul a te d at a f ro m m od el
for( i in 1 : n ob s ) {
s co r eS im [ i ] ~d ca t ( p [i , ] )
}
}
70

Table A.3.2 – Parameters of the explanatory variables describing the calling activity of
Pseudacris maculata in an ordinal logistic regression model estimated by Markov Chain Monte
Carlo. Summary statistics of the posterior distribution of parameters are presented with 95%
Bayesian credible intervals.
Mean SD 2.5% 97.5%
Intercept CI=1 -0.33 0.16 -0.64 -0.02
Intercept CI=2 and 3 2.21 0.18 1.86 2.56
Site BCV2 1.03 0.12 0.80 1.27
Air temperature 0.50 0.08 0.35 0.67
Day elapsed since April 4 -0.81 0.06 -0.93 -0.69
(Day elapsed since April 4)2-0.14 0.07 -0.28 -0.01
Site BCV2 : Air temperature 0.62 0.12 0.39 0.85
Human disturbance -0.06 0.15 -0.36 0.23
P. crucifer disturbance -0.88 0.18 -1.24 -0.53
Rain disturbance -1.07 0.29 -1.67 -0.52
Wind disturbance 0.05 0.18 -0.31 0.39
Figure A.3.1 – Predicted probability of boreal chorus frog calling indices at breeding site
BCV2 according to the occurrence of spring peeper (Pseudacris crucifer) choruses in 2021
in southern Québec, Canada. Predictions are presented only for the BCV2 pond since the
pattern is the same for IP013. Error bars represent 95% credible intervals around predictions.
71

A.4 Adult capture-recapture model and population size
estimations from the top-ranked model (Mt)
Table A.4.1 – NIMBLE code used to estimate the population size of Pseudacris maculata
in two natural ponds in Montérégie, Québec, Canada.
# # lo a d d a ta f r am e
load(" s e pa r at ed _c h _B CV 2 . R da " )
load(" s e pa r at ed _c h _I P0 1 3 . Rd a " )
# # da t a a u g me n ta t i on : t wo n a tu r al s i te s s e pa r at e d
yAug_BCV2 < - r b in d (history_BCV2 , matrix( 0 , ncol =ncol(history_B C V2 ) ,
nrow = 50 0 ) )
yAug_I P 0 1 3 < - r b in d (history_IP013 ,matrix( 0 , ncol =ncol(history_I P 01 3 ) ,
nrow = 50 0 ) )
# # pr e pa r at i on d at a
data_sites <-list(yaug_BCV2=as .matrix (yAug_B C V2 ) ,
yaug_I P 01 3 = a s .matrix(yAug_I P 01 3 )
)
c on st _s i t e s <-list( n t = ncol(yAug_B CV 2 ) ,
M_BCV2=nrow( yAug_B C V 2 ) ,
M_I P0 1 3 = nrow(yAug_I P0 13 ) )
# # in i ti a l v a lu e s
init s < - f u nc ti on ( ) list(z_BCV2 = r ep ( 1 , nrow(yAug_B C V2 ) ) ,
z_IP01 3 = rep( 1 , nrow(yAug_I P 01 3 ) ))
# Nul l model - - - - - - - - ----
M0 < - n imbl eC od e ({
# Priors
p~ du n if ( 0 , 1 )
# Sit e 1
o me ga _BCV2 ~ d u ni f (0 , 1)
# Likeliho o d s i t e 1
for ( i i n 1: M _B CV 2 ) {
z_B CV 2 [ i] ~d be rn ( o m eg a _BCV2)
for (tin 1 : n t ){
yaug_B C V2 [ i , t]~d be r n ( p. eff . B C V2 [ i , t])
p . eff. B C V2 [ i , t]<- z_B CV 2 [ i] *p
72

}#j
}#i
# Derived q u a n t i t i e s
N_BCV2 < - s um (z_B C V2 [ 1 : M_B C V2 ] )
# Sit e 2
o me ga _I P 0 1 3 ~ d un i f (0 , 1 )
# Likeliho o d s i t e 2
for ( i i n 1: M _I P0 1 3 ){
z_I P0 13 [ i ] ~d b er n ( om e ga _I P 01 3 )
for (tin 1 : n t ){
yaug_I P 01 3 [ i , t]~d be r n (p . e ff . I P 01 3 [ i, t])
p . eff. I P0 1 3 [i , t]<- z_I P 01 3 [ i] *p
}#j
}#i
# Derived q u a n t i t i e s
N_IP01 3 < - su m (z_I P0 1 3 [ 1: M _I P0 13 ] )
})
# Mo d e l d e t e c t i o n c st and r e c a p t u r e c s t - - - - - - - -
Mb < - n imbl eC od e ({
# Priors
o me ga _BCV2 ~ d u ni f (0 , 1)
o me ga _I P 0 1 3 ~ d un i f (0 , 1 )
p~ du n if ( 0 , 1 )
c ~ d un i f (0 , 1 )
# Likeliho o d s i t e 1
for ( i i n 1: M _B CV 2 ) {
z_B CV 2 [ i] ~d be rn ( o m eg a _BCV2)
# Firs t occasion
yaug_B C V2 [ i ,1 ] ~d be r n (p . e ff .BCV2[i ,1])
p . eff. B CV 2 [ i ,1 ] <- z_BC V 2 [ i] *p
# All subsequent o c c asions
for ( j i n 2: n t ) {
yaug_B C V2 [ i , j ] ~d b er n ( p . ef f . B CV 2 [ i , j ])
p . eff. B C V2 [ i , j ] <- z_B C V2 [ i ] *( (1 - y a ug _B CV 2 [i , (j - 1 ) ]) *p +
yaug_B C V2 [ i , (j - 1 ) ] *c)
73

}#j
}#i
# Derived q u a n t i t i e s
N_BCV2 < - s um (z_B C V2 [ 1 : M_B C V2 ] )
# Likeliho o d s i t e 2
for ( i i n 1: M _I P0 1 3 ){
z_I P0 13 [ i ] ~d b er n ( om e ga _I P 01 3 )
# Firs t occasion
yaug_I P 01 3 [i , 1] ~d be r n ( p. eff . I P0 1 3 [i , 1 ])
p . eff. I P0 1 3 [i , 1] <- z_I P0 13 [ i ] *p
# All subsequent o c c asions
for ( j i n 2: n t ) {
yaug_I P 01 3 [ i , j ] ~d be r n ( p. e f f . IP 0 13 [ i ,j ] )
p . eff. I P0 1 3 [i , j ] < - z_I P0 1 3 [i ] *( ( 1 - y au g _I P0 1 3 [i , (j - 1 ) ]) *p +
yaug_I P 01 3 [i , ( j -1 ) ] *c)
}#j
}#i
# Derived q u a n t i t i e s
N_IP01 3 < - su m (z_I P0 1 3 [ 1: M _I P0 13 ] )
trap.response < - c - p
})
# Mo d e l d e t e c t i o n t ime dependent as f i x ed effect --- - - - - -
Mt < - n imbl eC od e ({
# Priors
o me ga _BCV2 ~ d u ni f (0 , 1)
o me ga _I P 0 1 3 ~ d un i f (0 , 1 )
for(ti n 1: n t ) {
# f ix
p[t]~ du n if ( 0 , 1 )
}
# Likeliho o d s i t e 1
for ( i i n 1: M _B CV 2 ) {
z_B CV 2 [ i] ~d be rn ( o m eg a _BCV2)
for (tin 1 : n t ){
yaug_B C V2 [ i , t]~d be r n ( p. e f f . BC V 2 [ i ,t] )
74

p . eff. B C V2 [ i , t]<- z_B CV 2 [ i] *p[t]
}#j
}#i
# Derived q u a n t i t i e s
N_BCV2 < - s um (z_B C V2 [ 1 : M_B C V2 ] )
# Likeliho o d s i t e 2
for ( i i n 1: M _I P0 1 3 ){
z_I P0 13 [ i ] ~d b er n ( om e ga _I P 01 3 )
for (tin 1 : n t ){
yaug_I P 01 3 [ i , t]~d be r n (p . e ff . I P 01 3 [ i, t])
p . eff. I P0 1 3 [i , t]<- z_I P 01 3 [ i] *p[t]
}#j
}#i
# Derived q u a n t i t i e s
N_IP01 3 < - su m (z_I P0 1 3 [ 1: M _I P0 13 ] )
})
75

Table A.4.2 – Model selection among three closed-population capture-recapture models
assessing capture probability and derived population size of boreal chorus frogs (Pseudacris
maculata) sampled at two sites during 2021 in southern Quebec, Canada. Model M0is the null
model (p=care constant), model Mtrefers to time dependence (i.e., specific to each capture
occasion, p1=c1, . . ., pt=ct), and Mbdenotes the behavioral model which estimates pand
cseparately, both constant. Models were ranked based on the Watanabe-Akaike information
criteria (WAIC). Lower WAIC indicates a more parsimonious model.
Model K WAIC Delta WAIC WAIC weight
Mt10.77 191.25 0.00 1.00
M07.05 206.67 15.42 0.00
Mb10.21 214.90 23.65 0.00
Table A.4.3 – Output of the top-ranked data augmentation model based on WAIC values. N
corresponds to the abundance estimation of a population, ωis the inclusion probability with
which a member of the augmented data set is included in the population, and pcorresponds
to the capture probability on each occasion.
Mean Median SD 2.5%CI 97.5%CI
NBC V 228.15 27.00 3.91 23.00 38.00
NIP 013 10.41 10.00 2.07 8.00 16.00
ωBC V 20.06 0.05 0.01 0.03 0.08
ωIP 013 0.02 0.02 0.01 0.01 0.04
p10.47 0.47 0.09 0.29 0.66
p20.25 0.24 0.07 0.12 0.41
p30.40 0.40 0.09 0.24 0.58
p40.15 0.14 0.06 0.06 0.28
76

Figure A.4.1 – Posterior distribution of population size Nunder the model Mtfor time-
dependent capture probabilities. Red lines represent the number of individuals captured at
least once. The global data set including potential individuals was equal to M= 530 for this
analysis. The posterior mass of the population size was located well away from this upper
bound, indicating that the value of Mwas sufficiently high for data augmentation.
77

Figure A.4.2 – Mean abundance estimates (±95% credible intervals) of adult Pseudacris
maculata on two sites in 2021 in southern Québec, Canada.
Figure A.4.3 – Mean capture probability (±95% credible interval) of adult Pseudacris
maculata across capture occasions in 2021 on two sites in southern Québec, Canada.
78

A.5 Number of emerged metamorphs and linear
mixed-effects models describing chorus frog rearing
mesocosms with different density and leaf treatments
Figure A.5.1 – Emergence of Pseudacris maculata metamorphs introduced at the Gosner
stage 26 into mesocosms on the 13th of May, 2021 in Mont-Saint-Bruno National Park, Qué-
bec, Canada. Each bar corresponds to one day of emergence and colors indicate mesocosm
treatment. The peak of emergence lasted 19 days (from June 8 to 26), where an average of
24 tadpoles emerged per day. We also noticed three peak days where more than 35 tadpoles
emerged (June 14, 16, and 26). We observe that tadpoles from the litter treatments generally
emerged earlier than from the treatments without litter, regardless of larval density.
Figure A.5.2 – This figure shows the mean water temperature of mesocosms (+/- IC 95%)
during the experiment in Mont-Saint-Bruno National Park, Québec, Canada. During the
emergence peak, water varied from 17◦C to 25◦C. The water temperature of the mesocosms
recorded every three days ranged from 11.5◦C to 27.5◦C, with an average of 20.6◦C (sd =
3.5◦C). The pH values varied from 6.9 to 9, with an overall average of 7.4 (SD = 0.3).
79

Table A.5.1 – JAGS code used to conduct the binomial generalized linear model and linear
mixed-effects models.
# # ## B i no m i al g en e r al i z ed l i n ea r m od e l ( s u rv i va l ) # ## #
mode l {
# # P ri o rs ( no n - i nf o rm a ti ve )
beta 0 ~ d n or m (0, 0.001)
beta.treat1 ~ d no rm (0, 0.001)
beta.treat2 ~ d no rm (0, 0.001)
beta.treat3 ~ d no rm (0, 0.001)
beta.block2 ~ d no rm (0, 0.001)
beta.block3 ~ d no rm (0, 0.001)
# # ra n do m e ff e ct o f me s oc o sm
for( m in 1 : nm e so ) {
d el t a . me so [ m ] ~ d no r m (0 , ta u . m es o )
}
##SD of random effect
s ig m a . me so ~ d un if ( 0 , 10 )
t au . m es o < - p ow ( s ig m a . me so , - 2)
## likeliho o d
for( i in 1 : n ob s ){
s uc c es s [ i] ~db i n ( p [ i] , n [ i ])
l og i t ( p [i ] ) <- beta0 + beta .treat1 *t re at 1 [ i ] +
beta.treat2 *t re a t2 [ i ] +
beta.treat3 *t re a t3 [ i ] +
beta.block2 *b lo c k2 [ i ] +
beta.block3 *b lo c k3 [ i ] +
d el t a . m es o [ m e s oN u m [ i ]]
}
# # de r iv e d p a ra m et e rs
# # Pe a rs o n r e si d ua l s
for( i in 1 : n ob s ) {
p ea r s . re s [ i] < - ( s u cc es s [ i ] - p [ i] *n [ i ]) /sqrt(( n [ i ] *p [ i] *
(1 - p [ i ]) ) )
p ea r s . re s2 [ i ] <- p o w ( pe a rs . r e s [i ] , 2)
# # si m ul a te n ew d a ta s et
new[i] ~d b in ( p [ i ] , n [ i ] )
80

new. p e ar s . re s 2 [i ] <- po w (( new [i] - p[i] *n [ i ]) , 2 ) /(n[i] *p[i] *
(1 - p [ i ]) )
}
# # GO F
chi < - s um ( p e ar s . re s 2 [ ] )
chiNew < - s um (n ew . p e ar s . r es 2 [ ] )
# #c - h at
c.hat < - chi/chiNew
}
# # ## Linea r m i x e d e f f e c t models (body c o n dition ) ### #
mode l {
# # P ri o rs ( no n - i nf o rm a ti ve )
beta 0 ~ d n or m (0, 0.001)
beta.treat1 ~ d no rm (0, 0.001)
beta.treat2 ~ d no rm (0, 0.001)
beta.treat3 ~ d no rm (0, 0.001)
beta.block2 ~ d no rm (0, 0.001)
beta.block3 ~ d no rm (0, 0.001)
# # ra n do m e ff e ct o f me s oc o sm
for( m in 1 : nm e so ) {
d el t a . me so [ m ] ~ d no r m (0 , ta u . m es o )
}
##SD of random effect
s ig m a . me so ~ d un if ( 0 , 10 )
t au . m es o < - p ow ( s ig m a . me so , - 2)
# # pr i or f or r es i du a l v ar i an c e
sigm a ~ d u ni f (0 , 1 0)
tau <- 1/( s ig ma *s i gm a )
## likeliho o d
for( i in 1 : n ob s ){
y[i] ~ dn o rm ( m u [ i ], t a u )
mu [ i ] <- beta0 + beta.treat1 *t r ea t 1 [i ] +
beta.treat2 *t re a t2 [ i ] +
beta.treat3 *t re a t3 [ i ] +
81

beta.block2 *b lo c k2 [ i ] +
beta.block3 *b lo c k3 [ i ] +
d el ta . m es o [ m es o Nu m [ i] ]
}
# # de r iv e d p a ra m et e rs
for( i in 1 : n ob s ) {
r es [ i ] < - y [ i ] - m u [i ]
}
}
82

Contrasts estimated in the linear mixed-effects model :
—βtreat 1 corresponds to the comparison of density at 1 tadpole/L without litter against
the same density with litter.
—βtreat 2 corresponds to the comparison of density 0.1 tadpole/L without litter against
the same density with litter.
—βtreat 3 corresponds to the comparison of density 1 tadpole/L against the density 0.1
tadpole/L.
—βblock 2 corresponds to the comparison of block 1 with block 2.
—βblock 3 corresponds to the comparison of block 1 with block 3.
Table A.5.2 – Binomial generalized linear model estimating the probability of metamorph
survival as a function of tadpole density and leaf litter treatments with random effect of
mesocosm identity and a fixed effect of blocks. Results are based on Bayesian estimation
using Markov chain Monte Carlo.
Mean SD 2.5%CI 97.5%CI
β0-0.07 0.37 -0.77 0.73
βtreat1 -0.19 0.27 -0.73 0.36
βtreat2 0.17 0.33 -0.47 0.83
βtreat3 0.14 0.43 -0.71 1.00
βblock2 -0.12 0.52 -1.23 0.86
βblock3 -0.19 0.52 -1.30 0.78
σmeso 0.57 0.32 0.19 1.37
Figure A.5.3 – Predicted mean survival of P. maculata at metamorphosis according to
tadpole density and leaf litter treatments. Error bars denote ±95% Bayesian credible intervals.
83

Table A.5.3 – Parameter estimates of the linear mixed-effects model of Pseudacris maculata
mass at metamorphosis (g) at different tadpole density and leaf litter treatments with ran-
dom effect of mesocosm identity and a fixed effect of blocks. Results are based on Bayesian
estimation using Markov chain Monte Carlo.
Mean SD 2.5%CI 97.5%CI
β00.11 0.01 0.09 0.13
βtreat1 0.01 0.01 -0.01 0.02
βtreat2 0.03 0.01 0.01 0.04
βtreat3 -0.05 0.01 -0.07 -0.03
βblock2 -0.01 0.01 -0.04 0.01
βblock3 -0.01 0.01 -0.04 0.01
σmeso 0.01 0.01 0.01 0.03
σ0.02 0.00 0.02 0.02
Table A.5.4 – Linear mixed-effects model estimating Pseudacris maculata size at metamor-
phosis (mm) as a function of tadpole density and leaf litter treatments with random effect
of mesocosm identity and a fixed effect of blocks. Results are based on Bayesian estimation
using Markov chain Monte Carlo.
Mean SD 2.5%CI 97.5%CI
β09.99 0.24 9.56 10.50
βtreat1 0.17 0.18 -0.19 0.53
βtreat2 0.45 0.21 0.05 0.88
βtreat3 -1.74 0.28 -2.28 -1.16
βblock2 -0.24 0.35 -0.96 0.38
βblock3 -0.38 0.34 -1.13 0.23
σmeso 0.38 0.21 0.11 0.90
σ0.80 0.02 0.75 0.85
84

A.6 Population viability analysis on boreal chorus frog
Context
In conservation biology, demographic transitions and survival rates across life stages must be
known in order to inform management decisions (Benton and Grant,1999;Vonesh and De la
Cruz,2002). VORTEX (Lacy,2000,1993) can be used with less information than the Bayesian
approach, which requires several years of data. The Vortex software became popular in species
conservation after its creation in the 1990s (Pacioni and Mayer,2017). It is commonly used
to estimate the extinction rates of endangered species (Reed,2004). VORTEX is now among
the recognized conservation tools for multiple taxa (VortexAM, Pacioni and Mayer (2017);
Brook et al. (1997)) including amphibian population dynamics Lawrence (2018); Davis et al.
(2019). The approach requires fecundity rates, reproductive success, and the percentage of
available males and females in the population. Mortality rates for each pre-reproductive life
stage must also be specified. Environmental variations in the parameters allow for the inclusion
of variability in births, mortality, and carrying capacity of the population. Once the species
information is stored in a new project, the simulation program models each life-history stage of
the individuals in the population as discrete, sequential events, which are output as calculated
probabilities at the end of the simulations (Lacy,1993,2000). We can build as many scenarios
as desired, and compare them using the estimated parameters. The main purpose of this
appendix is to provide a picture of possible scenarios for the reintroduction of new populations,
and the removal of individuals from source populations within the study area. The results of
this analysis will help optimize and better orient reintroduction efforts. This part of the study
has three objectives :
1. To synthesize empirical data on the reproductive cycle and survival of the different stages
of Pseudacris maculata.
2. To identify the best individual-based demographic model available in VORTEX after ga-
thering known information on the species in order to compare collection and population
reintroduction scenarios.
3. To determine the elements to prioritize in the reintroduction program and offer management
recommendations.
Methods
Literature review
To parameterize our population viability analysis, we conducted a literature review to gather
published information on life traits associated with population dynamics of P. maculata.
We included studies from Canada and the United States to obtain the most comprehensive
information possible (Moher et al.,2015). Following the same logic, it was sometimes necessary
85

to supplement missing information from some life-history traits of P. maculata with data from
two closely related species : the spring peeper (Pseudacris crucifer) and the western chorus
frog (Pseudacris triseriata). The spring peeper is the most common tree frog in Quebec and
is present in our study area. The western chorus frog has long been confused with the boreal
chorus frog and there is still debate on the identity of the species in our study area, including
possible hybridization between the two species (Moriarty-Lemmon et al.,2007).
We searched various scientific databases to find articles for our literature review : Web of
Science, Google Scholar, BioOne, BioRxiv, and Science Direct. The database sites use Boolean
operators to refine the searches. For example, the acronym « TS » (topic search) means that
the words must be related to the overall topic, and be present in the title, abstract, or
keywords. The Boolean operator « AND » allows you to search on all the terms entered, while
« OR » searches on at least one of the terms entered. Finally, the symbol « * »replaces one
or more characters at the beginning or end of a word. No time scale restrictions have been
imposed. Our search equations for Web of Science (WoS) and Google Scholar (GS) were as
follows :
3. Web of Science : TI = « (chorus frog* OR Pseudacris OR Trilling frog*) AND TS=
(survival OR survivorship OR recruitment* OR population size OR demography OR
longevity OR lifespan OR population dynamic OR growth rate OR reproductive success
OR life history) ».
4. Google Scholar : « Survival OR survivorship OR demography OR longevity OR lifespan
OR dynamic OR growth OR reproductive success OR life history AND chorus frog*
OR Pseudacris ».
From the articles obtained, we selected those that dealt with the survival or the reproductive
cycle of the three species Pseudacris, from natural populations or from laboratory experi-
ments. Among the selected references, we extracted the survival estimates of the different life
stages, as well as the particularities of their reproductive cycle. When different estimates of
the same parameter were found in several articles, we presented the range of values in the
table. Google Scholar and Web of Science were the sources that returned the most results. In
Web of Science, our search returned 66 articles, whereas Google Scholar generated 102 articles
with the same keywords. The table A.6.1 presents the results.
The basic model we used included the parameters presented in the table A.6.1. This model
provides an optimistic basis for comparison of an undisturbed natural population, without
harvesting or translocation. The next section describes our choice of parameter values in the
model.
Age and density-dependence
Individuals in the simulated populations are structured by age class (Figure A.6.1).
86

Table A.6.1 –P. maculata life-history traits used as constants in the population viability
analysis. Numbers in parentheses indicate SDs.
Parameter Values reported Reference Species
Reproductive system Polygamous — P. maculata
Birth sex ratio 50 :50 Oplinger 1966 P. crucifer
Initial population size
(N0)
200 adults Whiting 2010;
Lawrence 2018
P. maculata
P. crucifer
Eggs mortality 0.62 Hossack et al. 2017 P. maculata
Maximum hatched eggs
per cluster per year
793 eggs * 0.62 = 492
eggs
Pettus and Angleton
1967;Whitaker 1971;
Dodd 2013
P. triseriata,
P. maculata
Mean hatched eggs 445 eggs * 0.62 = 276
eggs
Varoux 2015;Pettus
and Angleton 1967
P. triseriata,
P. maculata
First breeding age of
males and females
2 years Whiting 2004 P. maculata
Maximum breeding age of
males and females
5 years Muths et al. 2018 P. maculata
Males in breeding pools % Year 2 : 63 ;
Year 2+ : 100 (10)
Smith 1987 P. triseriata
Females in breeding pools
%
Year 2 : 63 ;
Year 2+ : 83 (10)
Smith 1987 P. triseriata
Percent annual mortality
Metamorphs (ages 0–1) density dependent this study P. maculata
Juvenile (age 1–2) 75 (25) Lawrence 2018;
Auffarth et al. 2017
this study
Hyla arborea
Adult females (> 2 years
of age)
65 (5) Smith 1987;Muths
et al. 2018;Whiting
2004
P. triseriata,
P. maculata
Adult males (> 2 years of
age)
72 (5) Smith 1987;Muths
et al. 2018;Whiting
2004
P. triseriata,
P. maculata
Survival of dispersers % 50 — P. maculata
Reintroduction survival % 15 this study P. maculata
We divided the life cycle of P. maculata into three age classes :
5. "0" : Larval stage (from hatched eggs to metamorphosis).
6. "1" : Metamorphic and juvenile stage, the first year of life of the amphibian in the
terrestrial stage.
7. "2" : Adult stage of 2 years and older.
A preliminary study of density dependence in herpetofauna populations indicates that three
species of the genus Pseudacris, including P. nigrita of the same clade as P. maculata (Trilling
87

Figure A.6.1 – Simplified representation of the life cycle of P. maculata by distinguishing
three age classes. The symbol « * »indicates that density dependence is taken into account
in some of our demographic models, Φrepresents the average clutch size of a reproducing
female, and σthe survival probabilities of the animal’s stages. Pmaturation is the probability
that an individual will reach maturity.
frog clade), are regulated via density dependence (Leão et al.,2018). Even more recently,
density dependence was found to be a common phenomenon in the regulation of growth
rate in sub-populations and populations by Cayuela et al. (2020a). However, it is sometimes
complex to know at which life stage this dependence acts on amphibians (Kissel et al.,2020).
Larval survival may be strongly density-dependent in temporary ponds (Burgman et al.,1993;
Caswell,2001)). In order to model the density factor at this stage, we incorporated a function
of the mortality of the 0–1 age classes as :
Mortality =100 ∗1−σtmin
1+d·Tγ(A.1)
modified from Vonesh and De la Cruz (2002). σtmin is the maximum larval survival in the
absence of density dependence. The larval density (m2/larva) is denoted d,Tcorresponds to
the number of larvae, and γrepresents the density-dependence weight. Although this factor
theoretically depends on each amphibian species, Vonesh and De la Cruz (2002) did not find
differences between the four amphibian species they studied (Bufonidae and Ambystomidae
families). We used the γand the density coefficient from Lawrence (2018) for the American
Toad (Table 4, Vonesh and De la Cruz (2002); Beebee et al. (1996)).
Reproduction
88

The maximum age of reproduction corresponds to the longevity of the animal, which implies
that boreal chorus frogs reproduce several times in a lifetime. This remains hypothetical
based on studies by Muths et al. (2016). Smith (1987) observed that only 63% of the male P.
triseriata matured in the first year, and then in the second year 100% reached maturity. This
hypothesis is supported by the work of Pellet et al. (2007) on Hyla arborea. They found that
only 80% of female tree frogs are available for breeding each year. Thus, we assumed that not
all females mature in their first year of life, which amounts to having about 80% of them fit
to breed each year (pers.com. Muths, 2020). We included this information as a conditional
function in VORTEX.
Population size
Whiting (2004) estimated the population size of P. maculata of between 600 and 1100 males
in one of the temporary ponds we monitored in this study (BCV2). However, Whiting (2004)
did not correct his estimates for imperfect detection and only monitored the population for
two consecutive years. Population sizes of this species can vary greatly between years. Indeed
Muths et al. (2018) estimated the dynamics of two populations of P. maculata in Colorado
over 28 years and found that recruitment is positively correlated with season length as well
as the snow-pack. We set an initial population size of 200 individuals (100 females and 100
males), which is consistent with the work of Lawrence (2018) on the Spring Peeper, and
consistent with the average size of the two Chorus Frog populations studied by Muths et al.
(2018).
Scenario projections and sensitivity analysis
Each scenario was iterated 1000 times over a time step of 25 years (365 days per year).
Extinction was defined by only one sex remaining in the population, and the sex ratio was set
to 50 :50, using the Oplinger (1966) study on P. crucifer, due to lack of data on P. maculata.
We used the default values in VORTEX for inbreeding depression (6.29 lethal equivalents),
as well as for post-dispersal survival, as these are unlikely to be major factors influencing the
viability of P. maculata populations.
To quantify the robustness of the models to our parameter choices, we performed sensitivity
analyses (Benton and Grant,1999). Six factors were tested according to a pessimistic scenario
and an optimistic scenario, the latter using the parameter values of the basic model (Table
A.6.2). The goal was to test the influence of some factors involved in the dynamics of the
species (life cycle and reproduction), in order to know their impact on the predictions. With
six factors that could each take one of two values, we had a total of 26= 64 different scenarios,
in addition to the two base scenarios with no harvest or reintroduction.
For the reintroduction scenarios, the initial size of the reintroduced population was 0 (N0). We
intervened with reintroduction or harvest events according to the planned program schedule
89

of three years of once-a-year introductions. Thus, harvests or translocations in the models
occurred from year 4 through year 6. Harvest scenario 1 means that 21 adults will be removed
per population (represented by one breeding pond). Similarly, for reintroduced populations,
the number introduced corresponds to one created pond.
Table A.6.2 – Combinations of scenarios tested by varying six factors of the population
viability model of P. maculata.
Parameter Pessimistic scenario Optimistic scenario
Maximal lifespan 3 years (Whiting,2004) 5 years (Muths et al.,
2018)
% Mature females 43% (1–2 years), 63%
(2+ years)
63% (1–2 years), 83%
(2+ years) (Lykens and
Forester,1987)
% Juvenile mortality (Age
1)
91% (Whiting,2004) 75% (Auffarth et al.,
2017)
Adult harvest at age 2 20 females, 40 males 8 females, 13 males
Reintroduction age 0 100/year 500/year
Survival of reintroduced
ind. (age 0)
14% 44% (Lawrence,2018)
Statistical analysis
We built our models with VORTEX 10.3.6.0 (Chicago Zoological Society, Brookfield, Illinois,
USA ; Lacy,1993). Model output processing was performed using the vortexR 1.1.9 package
in R 4.0.2 (Pacioni and Mayer,2017;R Core Team,2020). To summarize the results, we
present the probability of population persistence, i.e., the accumulation of simulations where
populations survive extinction over the 25-year period, as well as the average population size
at the end of the 25-year period.
Results
Lifespan and juvenile mortality
The results suggest that there is a greater benefit to extended longevity, as numbers after
25 years exceeded 300 individuals, which is not the case at 1-year longevity. In addition, the
probability of persistence of a population was close to 100% when juvenile mortality was 75%,
regardless of longevity. When juvenile mortality reached 91%, natural populations responded
differently, as few populations survived beyond 25 years, regardless of the longevity scenario.
In contrast, the persistence of introduced populations differed between longevity scenarios,
increasing from 11% to 13% for one-and-three-year longevity, respectively. Juvenile survival
was an important contributor to the dynamics of natural and introduced populations. In fact,
population sizes were almost five times higher when juvenile mortality was 75% instead of
91%.
90

Harvest
Removing 60 individuals each year had a significant impact on wild population dynamics.
Fewer than half of those simulated populations survived, regardless of the percentage of
sexually mature females. In contrast, removing 21 individuals per year led to a probability of
extinction of less than 10% in the worst predicted scenario, and to a population size of more
than 200 individuals over time.
Sensitivity analysis
We identified the combinations of factors that provided the best population viability over the
25-year period based on the following criteria :
— Mean positive population growth rate ;
— Proportion of non-extinct populations greater than 80% ;
— Proportion of extinct populations near 0% ;
— Average of at least 200 individuals in a population over the 25 years ;
For natural populations, the combination leading to the best chances of persistence and the
largest population sizes corresponded to the longevity of 5 years, 63% of females sexually
mature at 1 year, juvenile mortality of 15%, and a collection of 8 females and 13 males per
year (Figure A.6.2). Only a quarter of the scenarios among the 64 led to an abundance as large
as at the beginning of the simulations (in addition to having a persistence probability of 0.8
and a positive average growth rate, n = 16). The best conditions for introduced populations
were associated with a longevity of 3 or 5 years, 63% of females sexually mature at 1 year,
juvenile mortality of 75%, a release of 100 or 500 individuals per year, and 14% survival of
introduced individuals.
Recommendations
The reintroduction of a threatened species is complex and must be prepared in collaboration
with the various stakeholders (Muths and Dreitz,2008). Based on the results of the population
viability analysis and our literature review, the recommendations for the boreal chorus frog
population establishment project are (1) to reintroduce at the most advanced larval stage
possible in order to maximize success, (2) to determine juvenile mortality through post-
reintroduction monitoring for at least four years.
91

Figure A.6.2 – Scenarios tested with density-dependence at larval stage (26= 64 combinations) in natural populations. The scenarios
with five-year longevity (blue and pink lines) lead to larger population sizes than three-year longevity (brown and green lines). However,
the parameter that really drives the numbers down after about five years is the high juvenile mortality rate (0.91 instead of 0.75, green
and pink lines).
92

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