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Social monogamy has evolved multiple times and is particularly common in birds. However, it is not well understood why some species live in long-lasting monogamous partnerships while others change mates between breeding attempts. Here, we investigate mate fidelity in a sequential polygamous shorebird, the snowy plover (Charadrius nivosus), a species in which both males and females may have several breeding attempts within a breeding season with the same or different mates. Using six years of data from a well-monitored population in Bahía de Ceuta, Mexico, we investigated predictors and fitness implications of mate fidelity both within and between years. We show that in order to maximize reproductive success within a season, individuals divorce after successful nesting and re-mate with the same partner after nest failure. Therefore, divorced plovers, counterintuitively, achieve higher reproductive success than individuals that retain their mate. We also show that different mating decisions between sexes predict different breeding dispersal patterns. Taken together, our findings imply that divorce is an adaptive strategy to improve reproductive success in a stochastic environment. Understanding mate fidelity is important for the evolution of monogamy and polygamy, and these mating behaviours have implications for reproductive success and population productivity.
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Ecology and Evolution. 2019;9:10734–10745.
Received: 5 March 2019 
Revised: 11 June 2019 
Accepted: 17 June 2019
DOI: 10.1002/ece 3.5591
Mate fidelity in a polygamous shorebird, the snowy plover
(Charadrius nivosus)
Naerhulan Halimubieke1| José O. Valdebenito1| Philippa Harding1|
Medardo Cruz‐López2| Martín Alejandro Serrano‐Meneses3| Richard James4|
Krisztina Kupán5| Tamás Székely1,6
1Department of Biology and Biochemistry, Milner Centre for Evolution, University of Bath, Bath, UK
2Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. México, Mexico
3Departamento de Ciencias Químico‐Biológicas, Universidad de las Américas Puebla, San Andrés Cholula, Puebla, Mexico
4Department of Physics and Centre for Net works and Collective Behaviour, University of Bath, Bath, UK
5Max Planck Institute for Ornithology, Behaviour Genetics and Evolutionary Ecology Research Group, Seewiesen, Germany
6Department of Evolutionary Zoology and Human Biolog y, University of Debrecen, Debrecen, Hungary
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2019 The Authors. Ecology an d Evolution published by John Wiley & Sons Ltd.
Krisz tina Kupán and Tamás Sz ékely are co‐auth ors shared sen ior authorsh ip to this work.
Naerhulan Halimubieke, Depar tment of
Biology and Biochemistry, Milner Centre for
Evolution, University of Bath, Bath, UK.
Krisztina Kupán, Max Planck Institute
for Ornithology, Behaviour Genetics and
Evolutionary Ecology Research Group,
Seewiesen, Germany.
Funding information
This project was funded by China
Scholarship Council, CONICYT BECAS
CHILE 72170569, ÉLVONAL KKP‐126949
(the National Research, Development and
Innovation Office of Hungary), CONACY T
(Mexico), through the Convocatoria de
Investigación Científica Básica 2010‐01
(project number 157570).
Social monogamy has evolved multiple times and is particularly common in birds.
However, it is not well understood why some species live in long‐lasting monoga‐
mous partnerships while others change mates between breeding attempts. Here,
we investigate mate fidelity in a sequential polygamous shorebird, the snowy plover
(Charadrius nivosus), a species in which both males and females may have several
breeding attempts within a breeding season with the same or different mates. Using
6 years of data from a well‐monitored population in Bahía de Ceuta, Mexico, we
investigated predictors and fitness implications of mate fidelity both within and be‐
tween years. We show that in order to maximize reproductive success within a sea‐
son, individuals divorce after successful nesting and re‐mate with the same partner
after nest failure. Therefore, divorced plovers, counterintuitively, achieve higher re‐
productive success than individuals that retain their mate. We also show that differ‐
ent mating decisions between sexes predict different breeding dispersal patterns.
Taken together, our findings imply that divorce is an adaptive strategy to improve
reproductive success in a stochastic environment. Understanding mate fidelity is im
portant for the evolution of monogamy and polygamy, and these mating behaviors
have implications for reproductive success and population productivity.
breeding dispersal, Charadrius nivosus, divorce, mate fidelity, nesting success, polygamous
The decision of retaining a mate for several breeding events or di‐
vorcing is a key element of reproductive decisions in several species,
as it can affect reproductive success and subsequent survival of the
parents (Culina, Radersma, & Sheldon, 2014; Neff & Pitcher, 2005;
Székely, Thomas, & Cuthill, 2006; Székely, Weissing, & Komdeur,
2014). Social monogamy, defined as a system where an adult has only
one social partner of the opposite sex at a given time or throughout a
time period, is commonly observed in birds, but also occurs in inver‐
tebrates, fish, amphibians, reptiles, and mammals (Lukas & Clutton‐
Brock, 2013; Møller, 2003). Social monogamy partnerships are
highly variable in terms of duration. Some species show long‐term
mate fidelity or even life‐time mate fidelity until one partner dies
(Black, 2001; Reichard & Boesch, 20 03). Oth er species , however, ex
hibit short‐term mate fidelity, in which an individual terminates the
relationship at the end of one breeding attempt and initiate another
breeding with a new mate while the old partner is still alive (termed,
sequential polygamy). Why do males and females adopt short‐term
mate fidelity, while others pair for life?
Several hypotheses have been put forward emphasizing the im‐
pact of either breeding time‐constraints (or breeding success) on
mate fidelity or divorce in socially monogamous species. On the
one hand, retaining a mate reduces the time and energy costs of
searching for a new mate therefore facilitate a fast re‐mating (“fast‐
track hypothesis,” Adkins‐Regan & Tomaszycki, 2007; Perfito, Zann,
Bentley, & Hau, 2007). Retaining a mate also enhance breeding per
formance thereby improving reproductive success (“mate familarity
hypothesis,” Ens, Choudhury, & Black, 1996; Gabriel, Black, & Foster,
2013; Sánchez‐Macouzet, Rodríguez, & Drummond, 2014). In addi‐
tion, successful breeding may also facilitate retaining the mate for
future breeding (Black, 2001; Flodin & Blomqvist, 2012). On the
other hand, changing a mate may be beneficial in long‐lived species,
individuals divorce their partner to mate with good quality partners
in order to improve breeding success (“incompatibility hypothesis,”
Coulson, 1966; see also Kempenaers, Adriaensen, & Dhondt, 1998).
In species with short life span (or short breeding season), individu‐
als improve reproductive success by mating with multiple mates to
make the most out of limited time (“extra‐pair mating hypothesis,”
Arnqvist & Nilsson, 2000; Birkhead & Møller, 1992).
Mating decisions may be related to breeding dispersal—the lat
ter defined here as the movement of an adult from one breeding
location to another within or between years (Clobert, Danchin,
Dhondt, & Nichols, 2001; Greenwood, 1980). On the one hand,
breeding dispersal may differ between the sexes in response to sex
differences in mating strategies since the more polygamous sex is
expected to disperse farther to find new mating partners (D'Urban
Jackson et al., 2017; Greenwood, 1980; Székely, 2019; Trochet et
al., 2016). On the other hand, mate fidelity can be viewed as a by‐
product of site fidelity in some species (Bried, Pontier, & Jouventin,
2003; Morse & Kress, 1984), whereas changing the nest site would
lead to mate change in some other species (Pietz & Parmelee, 1994;
Thibault, 1994).
A further factor that may influence mate fidelity is re‐mating
opportunity. In species or populations with a biased adult sex ratio,
divorce is commonly initiated by the rare sex since the rare sex has
higher mate availability than the common sex (Liker, Freckleton, &
Székely, 2014; Parra, Beltrán, Zefania, Dos Remedios, & Székely,
2014). For example, experimental studies of species with biased
adult sex ratio showed that by experimentally creating unmated
males and females, re‐mating times were shorter for rare sex than
for common sex (Parra et al., 2014; Székely, Cuthill, & Kis, 1999).
Neverth ele ss, studies of mate fide lit y ten ded to fo cus on monog
amous species across breeding years, yielding different adaptive im
plications of mate fidelity (Bried et al., 2003; Dubois & Cézilly, 2002).
Monogamous systems are generally characterized by high level of
breeding philopatry (Moore & Ali, 1984; Saalfeld & Lanctot, 2015)
and/or bi‐parental care of the young (Eberhart‐Phillips et al., 2018),
features that tend to promote mate fidelity. However, the causes
and fitness implications of mate fidelity in sequential polygamous
species that exhibit variable duration of pair bonds (e.g., within a
breeding year), different levels of philopatry, or breeding dispersal
are still poorly understood.
Here, we investigate potential predictors and fitness implications
of mate fidelity in a sequential polygamous shorebird, the snowy
plover (Charadrius nivosus), a ground‐nest ing, near threatened shore
bird distributed on sparsely vegetated coasts and alkaline lakeshores
across the tempera te and tr opical regio ns of the Amer icas. They typ
ically lay a 3‐egg clutch with both parents providing care during the
incubation stage, chicks are precocial and nidifugous, which only
require uniparental care (usually males) during brood rearing (del
Hoyo, Elliott, Sargatal, Christie, & Juana, 2018). This species is an
ideal model for investigating mate fidelity: they have a flexible mat‐
ing system, and both males and females may have several mates se
quentially in a single breeding season up to four breeding attempts
(Page, Stenzel, Warriner, Warriner, & Paton, 2009). It is typically fe
males that mate with more partners than males do, since females
tend to desert their broods soon after hatching, and leave the males
to look after the young until independence (Carmona‐Isunza et al.,
2017; Warriner, Warriner, Page, & Stenzel, 1986). Female desertion
has been linked to male‐biased adult sex ratio (ASR): 0.53 (propor‐
tion of males in the adult population) was estimated by Stenzel et al.
(2011) based on adult survival, whereas more recent estimate that
took into account hatchling sex ratios, chick survival and adult sur‐
vival estimated a strongly male‐biased ASR (0.638, Eberhart‐Phillips
et al., 2018). Snowy plovers may still retain their mate between
clutches within or between years. Furthermore, a recent paternity
analyses showed low rates (<5%) of extra‐pair paternity in the snowy
plover so that social pairs are a good proxy for genetic relationships
and thus reflect Darwinian fitness (Maher et al., 2017).
Using snowy plovers as a model organism, here we investigate
whether mate fidelity (or divorce) is an adaptive strategy that maxi‐
mizes reproductive success in a species with limited breeding period
(Choudhury, 1995; Plaschke, Bulla, Cruz‐López, Gómez del Ángel,
& Küpper, 2019). We focus on three main aspects of mate fidel‐
ity. First, we investigate patterns of mate fidelity both within and
between years in both males and females. Second, we exp lore if pre
vious nesting success predict mate retention (or divorce) by males
and females both within and between years. Finally, we investigate
mate fidelity in relation to breeding dispersal and re‐mating time: (a)
whether breeding dispersal is related to mate fidelity both within
and between years; (b) whether the re‐mating time may differ be‐
tween divorced and retained mates within years.
2.1 | Study site and field methods
The present study was conducted at Bahía de Ceuta, Sinaloa, Mexico
(23°54′N, 106°57′W). In this population, snowy plovers nest on
extensive saline ponds and saltpans (approximately 150 hectares;
Carmona‐Isunza, Küpper, Serrano‐Meneses, & Székely, 2015). The
breeding season generally occurs from mid‐April to mid‐July, with
30–100 breeding pairs every year. Breeding data were collected
from 2006 to 2011 (n = 625 nests). Data collection in the field fol
lowed the methods of Székely, Kosztolányi, and Küpper (2008).
Briefly, we searched for nests using a mobile hide intensively within
the study site, we recorded the nest location with handheld GPS,
and the egg‐laying date was estimated based on the floatation stage
of each egg in a transparent jar with clean water. Breeding pairs were
captured with a walk‐in funnel trap placed over the nest, and they
were banded with a unique combination of three color rings and an
alpha‐numeric metal ring. Nests were monitored every 2–5 days
until 20 days of incubation and then were checked every day until
hatching to obtain nesting success data. Broods were searched in
tensively daily to determine the date of brood desertion. Re‐sight
ings of previously color banded plovers were also recorded.
2.2 | Data collection
2.2.1| Quantification of mate fidelity
Snowy plovers that were monitored in this study were actively
choosing to retain or to divorce their mates. The mating decision
of each individual was recorded as either mate retention or divorce
in regard to their previous breeding attempt. We evaluated mating
decisions separately for banded males and females in the popula
tion, since the decisions may influence one another and as such
may not be independent. Individuals were included in the analyses
if they satisfied the following conditions: (a) we knew the identity
of their mate(s), (b) they were observed in at least two reproduc‐
tive attempts that were either within or between years, and (c) if
there is a mate change, only those who change their mates while the
previous mate is known to be alive are included. In total, 149 breed
ing events (Table 1A, 75 divorces in females, 26 divorces in males,
and 24 retentions in each sex) fitted the criterion for the within‐year
mate fidelity analysis from 2006 to 2011. For plovers with more than
two nests within a year, only the data from the first two nests were
included in the within‐year mate fidelity analysis due to the small
number of individuals with three or more nests: during the study
TABLE 1 Mate fidelity in snowy plover. (A) Number of males and females divorced or retained a mate within years, n = 149 breeding
events. (B) Number of males and females divorced or retained a mate between breeding years (late–early mate fidelity, n = 102 breeding
events; early–early mate fidelity, n = 116 breeding events; 2006–2011)
(A) Within years
Year 2006 2007 2008 2009 2 010 2011 Tota l
Number of divorces in females 11 21 10 14 12 775
Number of retentions in females 683 2 3 2 24
Number of divorces in males 583 3 4 3 26
Number of retentions in males 683 2 3 2 24
(B) Between years
Year 2006–2007 2007–2008 2008–2009 2009–2010 2010–2011 Total
late–early mate fidelity
Number of divorces in females 12 6 7 12 542
Number of retentions in females 4 1 1 3 2 11
Number of divorces in males 8 8 11 7 4 38
Number of retentions in males 4 1 1 3 2 11
early–early mate fidelity
Number of divorces in females 13 4 4 7 7 35
Number of retentions in females 1 4 2 6 3 16
Number of divorces in males 17 78710 49
Number of retentions in males 1 4 2 6 3 16
Note: See Section 2 for details.
period, there were only seven females and two males in total that
had three breeding attempts.
For individuals with one or multiple nests in each of the two
consecutive years, we evaluate between‐year mate fidelity in
two different ways (see Figure 1). First, when an individual's mate
during late season (see “relative egg‐laying date” below, late sea
son is when the relative egg‐laying date is >0) in year 1, had the
sa m e as the mat e in early se ason (w hen the re lati ve egg‐lay ing dat e
is <0) in year 2, it was classified as mate retention, or otherwise
divorce (hereinafter late–early mate fidelity). In total, 102 breed
ing events (Table 1B, 42 divorces in females, 38 divorces in males
and 11 retentions in each sex) fitted the criteria for the late–early
mate fidelity. Second, if a plover mated to the same individual in
the early seasons of both year 1 and year 2, this was classified
as retention, or divorce otherwise (hereinafter early–early mate
fidelity). In total, 116 breeding events (Table 1B, 35 divorces in
females, 49 divorces in males and 16 retentions in each sex) fitted
the criteria for the early–early mate fidelity. All individuals were
classified into three groups as divorced males, divorced females,
and retained pairs (see Sandercock, Lank, Lanctot, Kempenaers,
& Cooke, 2000).
2.2.2 | Nesting success and reproductive success
Nesting success was quantified based on the fate of the first nest of
each individual that were included in our study. The fate of nest was
recorded as either successful (at least one chick hatched) or failed
(no chicks hatched due to predation, destruction, abandonment,
eggs disappeared <15 days after estimated laying date, eggs did not
hatch, or the nest was flooded). We quantified reproductive success
as the cumulative number of hatchlings each individual produced in
all breeding attempts either within or between years.
2.2.3 | Relative egg‐laying date
The egg‐laying date was used to quantify breeding phenology. We
controlled for breeding phenological differences between years by
converting egg‐laying dates into Julian dates (“lubridate” package in
R, Grolemund & Wickham, 2011), and calculating the relative egg‐
laying date using the z‐transformation (mean = 0, SD = 1).
2.2.4 | Breeding dispersal
Within‐year breeding dispersal was defined as the straight‐line
distance (in meters) between an individual's successive nests
within a year. For between‐year breeding dispersal, we measured
the straight‐line distance between (a) the last nest in year 1 and
the first nest in year 2, and (b) the first nests of two consecutive
2.2.5 | Re‐mating time
Re‐mating time is defined as the number of days that an individual
spent on establishing a new clutch after terminating care of the pre
vious brood. Broods were searched in the breeding area daily. If a
parent was missing during two consecutive sightings or seen paired
to another plover, it was considered to have deserted the brood. We
estimated the date of brood desertion for a parent as the mid‐point
between the time when the individual was last seen with his/her
brood and first seen without the brood. We estimated second nest
FIGURE 1 Schematic illustration of
two estimates of between‐year mate
fidelity in snowy plovers: Early‐late and
early–early mate fidelities
egg‐laying date based on the floating stage of the eggs (see above).
We only estimated the re‐mating times within years.
2.3 | Statistical analyses
2.3.1 | Comparison of male and female mate fidelity
We analyzed mating decision as either mate retention or divorce of
a plover from an individual its previous breeding attempt. We calcu
lated the number of mate retentions and number of divorces in males
and females within the population for both within and between
years. We used the two‐proportion z test (Yau, 2013) to compare
the proportion of divorced females relative to the female population
to the proportion of divorced males relative to the male population
both within and between years.
2.3.2 | The relationship between mate fidelity and
nesting success
We constructed separate models for males and females to investi‐
gate whether mate fidelity is related to nesting success within and
between years. Here, separation of the sexes was necessary since
nesting success is nonindependent variable within a pair; there
fore, individuals of a pair provide the same data points. In the latter
analyses, mate fidelity of an individual was the dependent variable,
and nesting success was used as explanatory variable. To analyse
the females, we used generalized linear mixed models (GLMM) with
binomial error and included Individual ID and Year as random effect
variables to account for the repeated identities of females among
years. For males, we used generalized linear model (GLM) with bi‐
nomial error.
2.3.3 | Reproductive success and mate fidelity
To investigate whether mate fidelity relates to reproductive suc
cess (estimated as the total number of hatchlings from both
clutches), we compared divorced males, divorced females, retained
pairs using Kruskal–Wallis tests followed by post hoc pairwise
comparisons (Dunn test) to test group differences within and be
tween years.
2.3.4 | Breeding dispersal and mate fidelity
Models were built to investigate the relationship between breeding
dispersal and mate fidelity groups within and between years. Log‐
transformed (ln) breeding dispersal was the dependent variable, and
mate fidelity groups (divorced males, divorced females, and retained
pairs) were the explanatory variable. Linear mixed‐effects model
(LMM) via REML was fitted and maintained Individual ID and Year
as random effect variables. Then, the estimated marginal means
(emmeans from package “emmeans” in R) were calculated for each
group, post hoc pairwise comparisons adjusted by Tukey were ap‐
plied to test group differences.
2.3.5 | Re‐mating time and mate fidelity
To investigate whether re‐mating time differs between mate fidel‐
ity groups (divorced males, divorced females, and retained pairs), we
used Kruskal–Wallis tests followed by post hoc pairwise compari‐
sons (Dunn test) to test group differences within and between years.
All statistical analyses were performed using R version 3.5.1 (R Core
Team, 2018).
3.1 | Mate fidelity between sexes
Within breeding years, males showed higher mate fidelity than fe‐
males using 149 breeding events (Table 1A, 75 divorces in females,
26 divorces in males, and 24 retentions in each sex) from 2006
to 2011, two‐proportion z test, p = .002, n = 6 years). The differ
ent numbers of female and male breeding attempts are due to the
fact that more females than males had multiple breeding attempts.
Between breeding years, however, we did not find a difference in
mate fidelity of males versus females (Table 1B, two‐proportion z
test; late–early mate fidelity: p = 1.00, n = 5 years; early–early mate
fidelity: p = .55, n = 5 years).
3.2 | Mate fidelity in relation to nesting success and
reproductive success
Within breeding years, mate fidelity was related to nesting success
since divorce was more likely when the nest hatched successfully,
whereas mate retention was more likely if the nest failed (Table 2,
females: GLMM, p < .001, male: GLM, p < .001; Figure 2). Between
breeding years, however, mate fidelity was not related to nesting
success. The latter result was consistent between the late–early
mate fidelity and early–early mate fidelity (Table 2).
Divorced plovers (both males and females) produced significantly
more hatchlings within breeding years than those retained their
mate. Reproductive success was not different between divorced
males and divorced females (Table 3, Kruskal–Wallis tests, p < .001,
followed by post hoc pairwise Dunn test; divorced females—re
tained pairs: p adjusted < .001, divorced males—retained pairs: p
adjusted = .05, divorced females—divorced males: p adjusted = .07;
Figure 3). Between breeding years, however, reproductive success
was not different between divorced and retained individuals neither
in the late–early nor in the early–early comparisons (Kruskal–Wallis
tests; late–early mate fidelity: χ2 = 0.20, df = 2, p = .90; early–early
mate fidelity: χ2 = 4.21, df = 2, p = .12).
3.3 | Mate fidelity in relation to breeding
dispersal and re‐mating time
Divorced females bred further away than divorced males both within
and between years (Figure 4, Table 4). Divorced males, however, did
not breed further away than retained pairs (Table 4).
TABLE 2 Mate fidelity in relation to nesting success within and between breeding years in snowy plover
Response variable Model used Explanatory variable Estimate SE z value p value
Within years
Mate fidelity Binomial (GLMM) Intercept 0.92 0.42 −2.19 .03
Nesting success 4.38 0.83 5.27 <.001
Mate fidelity Binomial (GLMM) Intercept −1 5.9 2 5.16 −3.09 .002
Nesting success 29.17 7. 59 3.84 <.0 01
Between years: late–early
mate fidelity
Mate fidelity Binomial (GLMM) Intercept 1.39 0.79 1.75 .08
Nesting success −0.06 0.87 −0.07 .95
Mate fidelity Binomial (GLM) Intercept 1.50 0.78 1.92 .05
Nesting success −0.33 0.87 −0.38 .70
Between years: early–early
mate fidelity
Mate fidelity Binomial (GLMM) Intercept 1.47 1.19 1.23 .22
Nesting success 0.75 1.25 0.60 .55
Mate fidelity Binomial (GLM) Intercept 2.30 1.05 2.20 .03
Nesting success −1.3 7 1.10 −1 . 26 .21
Note: Generalized linear mixed models (GLMM) with binomial error family and including “Individual ID” and “Year” as random effect variables to ac‐
count for the repeated identities of female individuals among years. For males, generalized linear model (GLM) with binomial error family was used.
Abbreviation: SE, standard error.
Statistically significant results are presented in bold.
FIGURE 2 Mate fidelity in relation to
nesting success in (a) female and (b) male
snowy plovers within a year (see Table 2
for statistics). Logistic linear regression
lines (blue) with standard error (gray)
Failed Successful
Nesting success
(a) Females
Nesting success
(b) Males
Finally, re‐mating times were not different between divorced
males, divorced females and retained pairs (Kruskal–Wallis test,
χ2 = 2.00, df = 2, p = .37).
Previous analyses of mate fidelity were typically concerned with
either within‐year or between‐year mate fidelity and focus largely
on monogamous systems (sometimes termed mate desertion, mate
abandonment or mate change; Black, 2001; Bried et al., 2003; Flodin
& Blomqvist, 2012). Here, we take an integrative approach and in‐
vestigate mate fidelity both within and between breeding years.
Using a sequential polygamous shorebird, the snowy plover, we
identified factors that predict mate fidelity and its spatial‐temporal
manifestation in a system, in which males and females differ in their
breeding strategies and reproductive efforts.
Our analyses revealed three major results. First, males exhibit
higher within‐year mate fidelity than females. This is consistent with
the previous studies of snowy plover since females tend to desert
the brood whereas males are usually the ones that rear the young
(Carmona‐Isunza et al., 2015; Warriner et al., 1986). We suggest that
male‐biased adult sex ratio entices female parents more than male
parents to desert their brood and breed again (Eberhart‐Phillips et al.,
2017; Stenzel et al., 2011); thereby resulting in different re‐mating
opportunities and mate fidelities between males and females. The
latter results are consistent with experimental and empirical stud
ies that show altered adult sex ratios influences mating decisions
(Karlsson, Eroukhmanoff, & Svensson, 2010; Liker, Freckleton, &
Székely, 2013; Liker et al., 2014; Silva, Vieira, Almada, & Monteiro,
However, between years both male and female snowy plovers
demonstrated low mate fidelity. We note however that our mate
fidelity (and consequently, our divorce decision as well) was based
on local returning rates: if paired birds may breed outside the study
area and/or some of the survived adults may not return to breed
to Ceuta, these survival estimates can be biased. The annual return
rate to Ceuta are 41.5% for males (n = 378 individuals) and 35.4% for
females (n = 339 individuals, 2006–2011). Therefore, further inves
tigation is required to estimate more precisely the return rates using
more comprehensive spatial coverage by visiting additional breeding
sites near Ceuta and/or using GPS tags to monitor the movements of
adults within and between years.
Second, divorce was more likely after a nest hatched than after
it failed since failed breeders typically re‐nested with the same part
ner. Therefore, divorced plovers, counterintuitively, reared more
offspring than faithful individuals. This finding is not consistent with
studies of long‐lived bird species where low breeding success may
trigger divorce (“incompatibility hypothesis,” Black, 2001; Coulson,
1966; Jouventin & Bried, 2001). We propose that by abandoning the
Groups Z p unadjusted p adjusted
Within years
Divorced females—divorced males 1.97 <.0 01 .07
Divorced females—retained pairs 4.08 <.001 <.001
Divorced males—retained pairs 1.92 <.0 01 .05
Statistically significant results are presented in bold.
TABLE 3 Comparison of reproductive
success between mate fidelity groups
(divorced males, divorced females, and
retained pairs) within breeding years
(Kruskal–Wallis tests, p < .001, followed
by post hoc pairwise Dunn test)
FIGURE 3 Reproductive success in
relation to divorce or mate fidelity in
snowy plovers (see Table 3 for statistics).
Medians, upper, and lower quartiles, as
well as extreme values are shown
Divorced females Divorced males Retained pairs
Total number of hatchlings
brood and divorcing, individuals try to maximize their reproductive
success by producing as many clutches over the season as possible.
Divorce may be facilitated by two aspects of natural history: first,
nest and chick mortality in this population tend to be high and sto‐
chastic, and thus, parents may need several trials to produce at least
some fledglings (Cruz‐López, Eberhard‐Phillips, et al., 2017). Second,
the chicks are precocial, and thus, they only require modest care:
brooding and protection, but not feeding (Székely & Cuthill & Kis,
1999). The well‐developed hatchling then gives the opportunity for
one parent to terminate care and start breeding with a new partner
(Houston, Székely, & McNamara, 2013; McNamara, Forslund, & Lang,
1999; Székely, Webb, Houston, & McNamara, 1996). Mate retention
was, however, more likely after nest failure, in which case the paren
tal duties of both parents terminated at the same time; therefore,
the fastest way to breed again was to retain the previous partner
(“fast‐track hypothesis”; Perfito et al., 2007; Zann, 1994; reviewed
by Fowler, 1995; also see Adkins‐Regan & Tomaszycki, 2007).
However, breeding success in previous years may have little
impact on the re‐mating decision of snowy plovers. We presume
that the breeding time constraint facilitates early breeding with
TABLE 4 (A) Breeding dispersal in relation to mate fidelity groups (divorced males, divorced females, and retained pairs) within and
between breeding years. (B) Comparison of breeding dispersal between mate fidelity groups (divorced males, divorced females, and retained
pairs) within and between breeding years
Response variable Model used Explanatory variable Estimate SE t value
Within years
Breeding dispersal LMM Intercept 6.46 0.16 38.85
Divorced males −0.95 0. 26 −3.63
Retained pairs −0.67 0.26 −2 .58
Between years: late–early
Breeding dispersal LMM Intercept 6. 41 0.21 30.25
Divorced males −1 . 01 0.30 −3.37
Retained pairs −0.70 0.39 −1 .77
Between years: early–early
Breeding dispersal LMM Intercept 5.87 0. 29 20.48
Divorced males −0.95 0.38 −2 . 53
Retained pairs −0.73 0.33 −2.23
Groups Estimate SE df t ratio p value
Within years
Divorced females—divorced
0.95 0.26 111 3.60 .001
Divorced females—retained
0.67 0.26 112 2.57 .03
Divorced males—retained pairs −0.28 0.26 68 −1.05 . 55
Between years: late–early
Divorced females—divorced
1.01 0.31 72 3.28 .005
Divorced females—retained
0.70 0. 41 72 1.70 .21
Divorced males—retained pairs −0.32 0.44 85 −0.71 .76
Between years: early–early
Divorced females—divorced
0.95 0.38 70 2 .51 .04
Divorced females—retained
0.73 0.35 56 2.09 .10
Divorced males—retained pairs −0.22 0.44 88 −0.50 .87
Note: The linear mixed‐effects model (LMM) via REML was fitted and maintained “Individual ID” and “Year” as random effect variables.
Abbreviation: SE, standard error.
Statistically significant results are presented in bold.
available mates instead of waiting for the former partner, especially
since early breeding is associated with higher nest survival (Plaschke
et al., 2019; van de Pol, Heg, Bruinzeel, Kuijper, & Verhulst, 2006;
Székely et al., 1999). Since snowy plovers only have about 2 years of
breeding life (average breeding life of males: 2.3 ± 1.6 years; females:
1.9 ± 1.2 years; Colwell, Pearson, Eberhart‐Phillips, & Dinsmore,
2013), they may not discriminate against previous mates even if they
were failed breeders Furthermore, returning to the breeding ground
may be stochastic and this can also produce decoupling between
nesting success and mate fidelity (Bried, Frédéric, & Jouventin,
1999; Gilsenan, Valcu, & Kempenaers, 2017; Handel & Gill, 2000).
Third, we found that females tend to disperse farther than males
after divorce both within and between breeding years. This follows
the general pattern of female‐biased breeding dispersal observed in
most bird species including shorebirds (Clarke, Saether, & Roskaft,
1997; Greenwood & Harvey, 1982; Liu & Zhang, 2008; Sandercock
et al., 2000). However, in polyandrous birds like snowy plovers there
is an additional reason: finding new mate while their previous mate
is taking care of the chicks (D'Urban Jackson et al., 2017). For males,
returning to previous breeding site—that is often thought as a high‐
quality site providing good brood‐rearing opportunities (Sandercock
et al., 200 0)—is a factor that reduces their aptitude moving large dis
tance between nests. Mate fidelity is often related to the degree of
site fidelity (Cézilly, Dubois, & Pagel, 2000; Cézilly & Johnson, 1995),
and while it would be tempting to argue that higher mate fidelity
lead to higher site fidelity in males, or vice versa high divorce rate by
females lead to more extensive breeding dispersal, to conclude the
directionality of causation—and to separate whether the males or
the females drive these relationships—would require experimental
manipulation of mate fidelity, site fidelity, or both.
Together, our results support theoretical arguments that divorce
is an adaptive strategy by which individuals improve their repro
ductive success (Black, 1996; Dubois & Cézilly, 2002; McNamara &
Forslund, 1996). Divorced birds reached higher number of breeding
attempts and higher breeding success than individuals that retained
their mates, at least within years. We suggest that in snowy plovers,
divorce is result from their effort to maximize reproductive out‐
put during a given time period. The birds' urge to re‐mate as many
times as possible within a breeding season and produce the highest
possible number of chicks could be traded off by lowered survival
of their abandoned broods although, given the precociality of the
young, this cost may not be prohibitive (Székely & Williams, 1995).
We suggest that the urge for a fast reproduction in snowy plovers is
an adaptive response to life histories (i.e., short life span) and breed
ing parameters (i.e., short breeding period and breeding success).
Additionally, time constraint in breeding confounded with the bias
FIGURE 4 Breeding dispersal (a) within year, and between year (b, late–early) and (c, early–early) in snowy plover (see Section 2 for
explanations and Table 4 for statistics). Breeding dispersal was estimated in meters and log‐transformed (ln). Medians, upper, and lower
quartiles, as well as extreme values are shown
Breeding dispersal (meters, log−transformed)
Divorced femalesDivorced malesRetained pairsDivorced females Divorced males Retained pairs
Divorced femalesDivorced males Retained pairs
in population demography (i.e., male‐biased adult sex ratio) propels
both sexes adopt different mating strategies, resulting in different
spatial dispersal patterns. Therefore, mate choice and breeding dis
persal are important components of their breeding strategy. We en
courage further investigations of breeding strategy including mate
fidelity between different polygamous shorebird populations and to
understand the generality of our findings across the various natural
populations with the intention of informing conservation decisions.
We thank all fieldwork volunteers and people who have worked and
supported the conservation project of Snowy plovers at Bahía de
Ceuta, especially to Clemens Küpper and Cristina Carmona‐Isunza
for data collection. Thanks to Jennifer McDowall, Luke Eberhart‐
Phillips, Kathryn Maher, Judit Mokos, and Brett Sandercock for their
advice on previous versions of the manuscript.
We have no conflict of interest to declare.
N. H., P. H., and T. S. conceived the project; K. K., M. A. S.‐M., and
M. C.‐L. provided the data; N. H. and K. K. carried out the statisti‐
cal analyses. All authors contributed critically to the drafts and gave
final approval for publication.
Data are available from the Dryad Digital Repository, https ://doi.
All aspects of the fieldwork were authorized by the national authori
ties of Mexico (Secretaría de Medio Ambiente y Recursos Naturales,
SEMARNAT; SGPA/DGVS/01717/10, SGPA/DGVS/01367/11).
Birds were ringed and handled by trained people aiming to cause as
little disturbance to birds as possible.
Naerhulan Halimubieke‐0002‐6928‐5986
José O. Valdebenito‐0002‐6709‐6305
Philippa Harding‐0003‐0763‐3516
Medardo Cruz‐López‐0003‐1737‐9398
Martín Alejandro Serrano‐Meneses https://orcid.
Richard James‐0002‐86477218
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How to cite this article: Halimubieke N, Valdebenito JO,
Harding P, et al. Mate fidelity in a polygamous shorebird, the
snowy plover (Charadrius nivosus). Ecol Evol. 2019;9:10734–
10745. https ://
... For example, arctic bird species have typically short breeding seasons due to the harsh and stochastic environmental conditions, and tend to exhibit high fidelity to a mate, which is likely to improve offspring survival 17,18 . In contrast, mild environments in temperate and tropical regions tend to provide a more prolonged breeding season so that an individual might initiate multiple clutches with the same or different mates 1,19,20 . The influence of environmental conditions on mating decisions has been observed in a variety of taxa including flies, fish, frogs and birds [21][22][23] . ...
... It has also been suggested that divorcing and rapidly changing a mate may be favoured by some species in order to make the most out of a restricted time budget (e.g. short life span or short breeding season) 1,40 . ...
... In a recent study, Halimubieke et al. 1 reported that snowy plovers (Charadrius nivosus), especially females, are more likely to divorce after successful nesting, simultaneously deserting their current brood, and initiate a new breeding attempt with a different mate, whereas, pairs tend to stay together after failed breeding attempts and initiate a second nesting attempt with the same mate. Divorcing individuals reared more offspring than those that retained their mates. ...
Full-text available
When individuals breed more than once, parents are faced with the choice of whether to re-mate with their old partner or divorce and select a new mate. evolutionary theory predicts that, following successful reproduction with a given partner, that partner should be retained for future reproduction. However, recent work in a polygamous bird, has instead indicated that successful parents divorced more often than failed breeders (Halimubieke et al. in Ecol Evol 9:10734-10745, 2019), because one parent can benefit by mating with a new partner and reproducing shortly after divorce. Here we investigate whether successful breeding predicts divorce using data from 14 well-monitored populations of plovers (Charadrius spp.). We show that successful nesting leads to divorce, whereas nest failure leads to retention of the mate for follow-up breeding. plovers that divorced their partners and simultaneously deserted their broods produced more offspring within a season than parents that retained their mate. our work provides a counterpoint to theoretical expectations that divorce is triggered by low reproductive success, and supports adaptive explanations of divorce as a strategy to improve individual reproductive success. in addition, we show that temperature may modulate these costs and benefits, and contribute to dynamic variation in patterns of divorce across plover breeding systems. open
... The decision to remain paired with the same partner or to change partners can be vital to lifetime reproductive output (Bradley et al. 1990;Black 2001;Sánchez-Macouzet et al. 2014). While mate switching has the advantage of improving life-long reproductive success by increasing offspring genetic diversity, pairing with a mate of higher quality/compatibility than the current partner, or increasing the number of breeding attempts during the current season (Choudhury 1995;Spoon et al. 2007;Culina et al. 2015;Halimubieke et al. 2019), mate retention can enhance breeding success via better coordination of parental effort (Black 2001;Griggio and Hoi 2011;Dreiss and Roulin 2014;Sánchez-Macouzet et al. 2014). Mate retention decisions can be affected by the quality of the territory held by the partners and the success of the pair's previous breeding attempts (Desrochers and Magrath 1993;Dubois and Cézilly 2002; but see Handel and Gill 2000). ...
... Beissinger 1987;Olson et al. 2008;Kupán et al. 2021). Uniparental brood desertion is well known in mating systems, in which it is a fixed element of the breeding strategy due to benefits from allocation of parental effort to multiple broods sired with different partners within the same season; the costs of desertion are relatively low if the young are fully precocial and biparental care has little advantage for the offspring over uniparental care (Székely et al. 2006;Pierce et al. 2010;Halimubieke et al. 2019). However, premature brood abandonment by one parent has also been observed in some socially monogamous species in which both mates provide extended and demanding parental care, and deserters may not have enough time or resources to raise another set of offspring (Kelly and Kennedy 1993;Osorno and Székely 2004;Vlug 2007;Ledwoń and Neubauer 2017). ...
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In monogamous birds, pair bond maintenance is often dependent on previous breeding success and each parent’s effort, because partners gain information about one another’s quality and contribution to brood rearing. The asymmetries between mates in parental investment have been theoretically linked to a sexual conflict of interests. Year-to-year pair fidelity decisions in relation to birds’ previous-year information about their mates, including territory quality and relative length of brood care, were explored in red‐necked grebes (Podiceps grisegena), a long-lived species with parent-fed young. Overall, mate retention was a major strategy (81.5% of pair-years). The probability of breakage/maintenance of a pair bond was not affected by previous-year hatching success, fledgling production, or territory quality in terms of food abundance for chicks. Reunited pairs bred earlier in the season than new pairs. In pairs that maintained bonds into the subsequent season, females typically terminated care 1–4 weeks before males. The male fidelity indicates that earlier brood abandonment by females may confer some fitness benefits to males and reflect coordination of reproductive effort at the behavioural level rather than exploitation of one partner by another. Significance statement Pair-living animals deciding whether to keep their old mate for future breeding usually consider their previous reproductive success and the partner’s effort. In some monogamous birds, often one of the parents leaves the brood before its mate, which is usually explained in terms of conflict between the sexes over parental care costs. I studied links between previous year’s parental effort and mate retention in red‐necked grebes, a long-lived waterbird. Grebes showed high pair fidelity irrespective of recent breeding success. In pairs that stayed together, females typically terminated brood care earlier than their mates. The male fidelity indicates that the unequal duration of brood attendance can be interpreted as cooperation and not conflict, especially as departing females did not attempt a second brood, while male-only care after female departure was sufficient to raise the young.
... Deserting and re-mating Snowy Plovers attempt to Reproductive success (a) and breeding time (b) of deserting and locally re-mating (N = 9) and full-term caring (N = 5) Snowy Plover females at Ceuta. maximize their reproductive success by rapid divorce after hatching as divorced females produce a higher number of hatchlings than females that retain their mates (Halimubieke et al. 2019). Yet, we confirmed that desertion does not necessarily translate into producing more fledglings . ...
... However, it also shows that chick survival is generally low. Some of the dispersing females may reach higher reproductive success than locally re-mating females (Halimubieke et al. 2019). However, the breeding time of dispersers must be even higher than that of caring or locally re-mating females as some females disperse to great distances, therefore, breeding dispersal must take up further time (Stenzel et al. 1994). ...
Offspring desertion is often a plastic behavioral strategy that requires precise timing as the termination of parental care may have profound consequences for the fitness of parents and offspring. However, the decision process involved with termination of care is still poorly understood. Snowy Plovers Charadrius nivosus show highly flexible brood care with some females deserting the brood early and re-mate, whereas others provide extended care until the young are independent. Using a dynamic modeling framework, we investigated the effect of multiple factors on the decision-making process of female brood care in Ceuta, Mexico over a 7-year period. Females were more likely to stay with larger broods, while their probability of care was lower at the beginning of the season, when re-mating opportunities are higher than later in the season. Offspring condition at hatching did not influence the length of female care. Chick death and offspring desertion frequently coincided, suggesting that deteriorating offspring condition may trigger female desertion. Females deserted broods with high survival prospects when their absence did not impact negatively chick survival. Conversely, females deserted broods with low survival prospects when chick mortality despite female care reduced the value of the brood and re-mating was still possible. This suggests that female Snowy Plovers are sensitive to the needs and the value of their broods and adjust their parental care strategy accordingly. Taken together, we conclude that offspring desertion is a highly plastic behavior that allows females to maximize their reproductive success in a stochastic environment.
... Our results suggest that the plovers of arid land often select flat areas with little to no vegetation around the normalized difference vegetation index of approximately 0.1. This facilitates the use of the predator detection anti-predation strategies to reduce the risk of predation [57,58]. ...
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Understanding the main ecological factors of the nesting habitat of shorebirds is of great significance in relation to their protection and habitat management. Habitat loss and change due to a lack of water threaten the biodiversity of shorebirds, with impacts likely to be most pronounced in arid lands. We collected the data of 144 nesting sites and 10 ecological factors during the breeding season from April to July each year in 2019 and 2020 in nine river districts in Xinjiang. The MaxEnt model was applied to assess the suitability of nesting habitats for Kentish plovers (Charadrius alexandrinus) in the study area to examine the main factors affecting their nesting habitat. The most suitable nesting habitats are mostly distributed in plain reservoirs in the middle part of the Northern Slope of the Tianshan Mountains, Ebinur Lake and its eastern position in the southwestern Junggar Basin, near Ulungur Lake of the Ulungur river area and the southern Irtysh river area. The distance from water, normalized difference vegetation index, mean temperature of the breeding season, slope, and land use were the main factors affecting the nesting habitat selection of Kentish plovers. It was found that the proportion of suitable nesting habitat protected for the Kentish plovers in the study area was low (851.66 km2), accounting for only 11.02% of the total suitable nesting habitat area. In view of the scarcity and importance of water bodies in arid lands and the lack of protection for Kentish plovers at present, it is suggested to strengthen the conservation and management of the regional shorebirds and their habitats by regulating and optimizing the allocation of water resources.
... El chorlo nevado tiende a tener un cuidado biparental, aunque sesgado hacia los machos y las poblaciones reproductivas están compuestas en su minoría por hembras , Stenzel et al. 2011, Halimubieke et al. 2019, condición que también se presenta en la colonia reproductiva de la laguna de Atotonilco, donde la población registrada tanto para toda la temporada como en los conteos mensuales, los machos conformaron la mayor parte de la población. Se estima que las poblaciones de chorlo nevado en todos sus linajes han estado sufriendo un "cuello de botella", por lo que las poblaciones efectivas de la especie son bajas y la especie es vulnerable (Jackson et al. 2020). ...
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The snowy plover (Charadrius nivosus) is one of the least abundant shorebirds. It is an endangered species whose populations are in steady decline. Mexico is important for the populations of this species, but there is little information on its reproduction and threats. To obtain data on nesting and potential threats, we monitored the snowy plover population at Atotonilco Lagoon during the breeding season (March-July) in 2020. We conducted counts of individuals and nests, clutch size, approximate egg-laying date, and observations on threats present during this period. Males represented 85% (n = 140) of the total population and the month with the highest number of nests was May (n = 15). The average nest size was 2.5 eggs. Water surface area was variable during the sampling months, but it was not statistically proven that the greater the desiccation, the smaller the nest size (p = 0.09). The main threats identified were motorized vehicles and livestock. The Atotonilco Lagoon is a key site for snowy plover reproduction and management actions should be implemented to increase the presence of water and regulate human activities.
... However, an increased divorce rate after a successful breeding attempt does not necessarily demonstrate that divorce is nonadaptive. Divorce after a successful reproduction has been shown to be an adaptive strategy to maximize LRS in multiple plover species (Halimubieke et al., 2019(Halimubieke et al., , 2020 or inbreeding avoidance in long-tailed tits (Aegithalos caudatus) (Hatchwell et al., 2000). We also found that the divorce probability increases when females have a higher breeding success with their previous partner (Appendix S1: Figure S11). ...
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Many animals form long‐term monogamous pair‐bonds, and the disruption of a pair‐bond (through either divorce or widowhood) can have significant consequences for individual vital rates (survival, breeding, and breeding success probabilities) and life‐history outcomes (lifetime reproductive success, life expectancy). Here, we investigated the causes and consequences of pair‐bond disruption in wandering albatross (Diomedea exulans). State‐of‐the‐art statistical and mathematical approaches were developed to estimate divorce and widowhood rates and their impacts on vital rates and life‐history outcomes. In this population, females incur a higher mortality rate due to incidental fishery bycatch, hence the population is male‐skewed. Therefore, we first posited that males show higher widowhood rates negatively correlated with fishing effort, and females have higher divorce rates because they have more mating opportunities. Furthermore, we expected that divorce can be an adaptive strategy, whereby individuals improve breeding success by breeding with a new partner of better quality. Finally, we posited that pair‐bond disruptions can reduce survival and breeding probabilities due to the cost of remating processes, with important consequences for life‐history outcomes. As expected, we show that males have higher widowhood rates than females and females have higher divorce rates in this male‐skewed population. However, no correlation was found between fishing effort and male widowhood. Secondly, contrary to our expectation, we found that divorce is likely non‐adaptive in this population. We propose that divorce in this population is caused by an intruder who outcompetes the original partner in line with the “forced divorce” hypothesis. Furthermore, we found a 16.7% and 18.0% reduction in lifetime reproductive success (LRS) only for divorced and widowed males, respectively, due to missing breeding seasons after a pair‐bond disruption. Finally, we found that divorced individuals are more likely to divorce again, but whether this is related to specific individual characteristics remains an important area of investigation.
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Gamete size variation between the sexes is central to the concept of sex roles, however, to what extent gamete size variation within the sexes relates to sex role variation remains unclear. Comparative and theoretical studies suggest that, when clutch size is invariable, polyandry is linked to a reduction of egg size, while increased female–female competition for mates favors early breeding when females cannot monopolize multiple males. To understand whether and how breeding phenology, egg size, and mating behavior are related at the individual level, we studied the reproductive histories of 424 snowy plover females observed in the wild over a 15-year period. Egg size, but not polyandry, were highly repeatable for individual females. Consistent with theoretical predictions, we found that polyandrous females were the earliest breeders and that early clutches contained smaller eggs than clutches initiated later. Neither egg size nor mating behavior showed clear signs of an age-related deterioration, on the contrary, prior experience acquired either through age or local recruitment enabled females to nest early. Taken together, these results suggest that gamete size variation is not linked to mating behavior at the individual level, and, consequently, the adaptive potential of such variation appears to be limited.
Parental care can enhance offspring survival but may impose significant costs to parents. The costs and benefits of care are key to understanding patterns of parental care, where parents can benefit by having their partner increase investment in care, while reducing their own effort. However, investigating the costs and benefits of parental care in wild populations is challenging. Here we use highly detailed behavioural observations in families of a small shorebird, where one parent frequently deserts its offspring, to explore the potential costs and benefits of desertion in a wild population. We firstly show that females desert their broods more frequently than males. Secondly, we investigate the benefits of this frequent female desertion in terms of additional mating opportunities, and the costs of desertion to females in terms of the growth and survival of deserted offspring. Our results indicate that female desertion is favoured by a combination of remating benefits and a lack of costs to brood growth and survival, as abandoned male parents continue to provide care after desertion. Our results shed light on the costs and benefits underlying natural desertion strategies and suggest that female desertion is a fine-tuned behaviour that responds to seasonally changing benefits of desertion.
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Parents are expected to make fine-tuned decisions by weighing the benefits of providing care to increase offspring survival against that of deserting to pursue future mating opportunities. A higher incentive for the rarer sex in the population indicates an impact of mating opportunities on parental care decisions. However, in a dynamic breeding system, deserting the offspring and searching for a new mate would influence mating opportunities for both sexes. Sex-specific costs and benefits are expected to influence males’ and females’ parenting strategies in different ways. Here, we investigated Chinese penduline tits, Remiz consobrinus, which exhibit flexible parental care strategies: uniparental care by the male or female, biparental care, and biparental desertion occur in the same population. We show that male penduline tits change their parental behavior over the breeding season; they desert clutches produced early in the season but care for the late season clutches. The change in male parenting behavior is consistent with the seasonal decline in mating opportunities. In contrast, parenting by females did not change over the breeding season, nor was it associated with seasonal variation in mate availability. Taken together, mating opportunities have different associations with parental behavior of male and female Chinese penduline tits. We recommend an inclusion of mating opportunities for both sexes simultaneously in order to understand one of the fundamental decisions in parental care evolution—care or desert. Significance statement Divorce is a common feature of both human and nonhuman animal societies. Theoretical studies suggest that one of the drivers of divorce is enhanced mating opportunity, i.e., parents with higher mating opportunities are more likely to abandon their family than those with low mating opportunities. Here, we investigate the dynamics of parental behavior and mating opportunities in a wild population of a small songbird, the Chinese penduline tit Remiz consobrinus. This species exhibits one of the most diverse avian breeding systems wherein both uniparental (male or female) and biparental rearing can be seen in a single population. We show that male penduline tits abandon their offspring in response to enhanced mating opportunities while the female parental behavior remains unaffected. This implies the relationship between mating opportunities and parental care is more complex than currently acknowledged and requires further investigation.
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Shorebirds (part of the order Charadriiformes) have a global distribution and exhibit remarkable variation in ecological and behavioural traits that are pertinent to many core questions in the fields of evolutionary ecology and conservation biology. Shorebirds are also relatively convenient to study in the wild as they are ground nesting and often occupy open habitats that are tractable to monitor. Here we present a database documenting the reproductive ecology of 1,647 individually marked snowy plovers (Charadrius nivosus) monitored between 2006 and 2016 at Bahía de Ceuta (23°54N, 106°57W) – an important breeding site in north-western Mexico. The database encompasses various morphological, behavioural, and fitness-related traits of males and females along with spatial and temporal population dynamics. This open resource will serve as an important data repository for addressing overarching questions in avian ecology and wetland conservation during an era of big data and global collaborative science.
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Divorce occurs when both members of a breeding pair survive to the following year but then pair with other individuals instead of reuniting. Divorce is common in birds, but its frequency can vary widely both between and within species, or even between populations across years. Several explanations for divorce have been described, both adaptive and nonadaptive. Many studies have compared the breeding success of faithful and divorced individuals, but fewer have considered the process of divorce, i.e. the events that lead up to divorce. In this study, we used data from eight breeding seasons to investigate divorce in a population of blue tits, Cyanistes caeruleus, in southern Germany. To compare our results to previous work, we first describe the frequency of divorce and compare the breeding success of divorced and faithful pairs. We then use data from an RFID transponder-based system, where all visits of individuals to any nestbox in the study site are automatically recorded throughout the year, to compare the behaviour of pairs in the interbreeding period. We found that the probability of divorce was not affected by breeding success in Year X. However, divorce was predicted by the difference in arrival time to the study site between the members of Year X pairs. Furthermore, during the interbreeding period, compared to their divorced counterparts, members of faithful pairs had more interactions with one another than with other individuals of the opposite sex. In Year X + 1, faithful females started egg laying earlier, had somewhat larger clutches and produced slightly more fledglings, than females that had divorced. We propose that divorce in blue tits is a by-product of separation of the two pair members after the Year X breeding season, leading to asynchrony in the timing of settlement and pair formation in Year X + 1.
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Shorebirds (sandpipers, plovers and allies) are some of the most charismatic animals that breed on all continents and inhabit diverse habitats, and their ecology, behaviour and evolution have attracted much attention ever since the work of Charles Darwin. Here I summarise the insights from 30 years of research on shorebird biology to illustrate the contributions of these to four research fields: breeding system evolution, sex ratio research, speciation and biodiversity conservation. Two major conclusions can be drawn from these insights. First, as shorebirds live in a variety of habitats and exhibit puzzling adaptations to their environments, studying their ecology, behaviour and life histories provides novel insights into the emergence and maintenance of organismal diversity. Second, to uncover patterns and processes in evolution, it is both important and stimulating to combine different research methods, and detailed single-species studies with multi-species comparative approach. My main thesis is that curiosity-driven research into the natural history of non-conventional model organisms provides novel insights into fundamental processes in ecology, behaviour and evolution. I also argue that scientific funding should follow the Goldilocks principle: not too little, not too much, just the right amount.
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Background Marine and intertidal organisms face the rhythmic environmental changes induced by tides. The large amplitude of spring tides that occur around full and new moon may threaten nests of ground-nesting birds. These birds face a trade-off between ensuring nest safety from tidal flooding and nesting near the waterline to provide their newly hatched offspring with suitable foraging opportunities. The semi-lunar periodicity of spring tides may enable birds to schedule nest initiation adaptively, for example, by initiating nests around tidal peaks when the water line reaches the farthest into the intertidal habitat. We examined the impact of semi-lunar tidal changes on the phenology of nest flooding and nest initiation in Snowy Plovers (Charadrius nivosus) breeding at Bahía de Ceuta, a coastal wetland in Northwest Mexico. Results Using nest initiations and fates of 752 nests monitored over ten years we found that the laying season coincides with the lowest spring tides of the year and only 6% of all nests were flooded by tides. Tidal nest flooding varied substantially over time. First, flooding was the primary cause of nest failures in two of the ten seasons indicating high between-season stochasticity. Second, nests were flooded almost exclusively during the second half of the laying season. Third, nest flooding was associated with the semi-lunar spring tide cycle as nests initiated around spring tide had a lower risk of being flooded than nests initiated at other times. Following the spring tide rhythm, plovers appeared to adapt to this risk of flooding with nest initiation rates highest around spring tides and lowest around neap tides. Conclusions Snowy Plovers appear generally well adapted to the risk of nest flooding by spring tides. Our results are in line with other studies showing that intertidal organisms have evolved adaptive responses to predictable rhythmic tidal changes but these adaptations do not prevent occasional catastrophic losses caused by stochastic events.
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Monogamous birds exhibit considerable interspecific variation in rates of mate fidelity between years, but the reasons for this variation are still poorly understood. In a 4-year study carried out in western Alaska, mate-fidelity rates in Semipalmated Sandpipers (Calidris pusilla; mate fidelity was 47% among pairs where at least one mate returned and 94% among pairs where both mates returned) were substantially higher than in Western Sandpipers (Calidris mauri; 25 and 67%, respectively), despite the similar breeding biology of these sibling species. Divorce was not a response to nesting failure in Western Sandpipers, and mate change had no effect on the reproductive performance of either species. Nor were mate-fidelity rates related to differential rates of breeding dispersal, because the species did not differ in site fidelity. Reunited pairs and males that changed mates showed strong site tenacity, while females that changed mates moved farther. Differences in local survival rates or habitat are also unlikely to explain mate fidelity, since the two species did not differ in local survival rates, φ (Western Sandpipers: $ φ = 0.57 ± 0.05 (mean ± SE), Semipalmated Sandpipers: $ φ = 0.66 ± 0.06), and they bred in the same area, sometimes using the same nest cups. Although we were able to reject the above explanations, it was not possible to determine whether mate retention was lower in Western Sandpipers than in Semipalmated Sandpipers because of interspecific differences in mating tactics, time constraints imposed by migration distance, or a combination of these factors. Western Sandpipers exhibited greater sexual size dimor-phism, but also migrated for shorter distances and tended to nest earlier and more asynchronously than Semipalmated Sandpipers. Finally, we show that conventional methods underestimate divorce rates, and interspecific comparisons may be biased if breeding-dispersal and recapture rates are not considered. 1958 Resumé : Le oiseaux monogames font preuve d'une variation interspécifique considérable de leur fidélité à un parte-naire d'une année à l'autre et les causes de cette variation sont toujours mal comprises. Au cours d'une étude de 4 ans dans l'ouest de l'Alaska, les taux de fidélité au partenaire mesurés chez des Bécasseaux semipalmés (Calidris pusilla; 47 % des couples dont au moins l'un des partenaires est revenu et 94 % dont les deux partenaires sont revenus) se sont avérés plus élevés que ceux mesurés chez l'espèce-soeur, le Bécasseau d'Alaska (Calidris mauri; 25 et 67 %, respectivement), en dépit de la similitude de la biologie de leur reproduction. Le divorce n'est pas une réaction à l'insuccès de la nidification chez le Bécasseau d'Alaska et le changement de partenaire n'a pas d'effets sur la performance de reproduction, ni chez l'une, ni chez l'autre des deux espèces. La fidélité n'est pas non plus reliée à des taux différentiels de dispersion pour la reproduction, puisque les deux espèces manifestent la même fidélité à un site. Les couples reformés et les mâles qui changent de partenaire ont une fidélité tenace au site alors que les femelles qui chan-gent de partenaire s'en éloignent. Des différences dans le taux de survie enregistré localement et l'habitat sont égale-ment des facteurs peu probables de fidélité au partenaire puisque les taux de survie enregistrés localement ne diffèrent pas chez les deux espèces (Bécasseau d'Alaska: $ φ = 0,57 ± 0,05 (moyenne ± erreur type), Bécasseau semipalmé: $ φ = 0,66 ± 0,06) et que celles-ci se reproduisent dans la même région, utilisant parfois des nids posés sur le même support. Nous avons pu réfuter toutes ces explications, mais il n'pas été possible de déterminer si la fidélité au partenaire est plus faible chez le Bécasseau d'Alaska à cause de différences interspécifiques dans les stratégies d'accouplement, à cause de contraintes temporelles imposées par la distance de migration ou à cause de ces facteurs combinés. Le dimor-phisme sexuel est plus important chez le Bécasseau d'Alaska, mais cet oiseau migre aussi sur de plus courtes distances et sa période de nidification est plus hâtive et moins synchronisée que celle du Bécasseau semipalmé. Enfin, nous Can. démontrons que les méthodes classiques sous-estiment la fréquence des divorces et que les comparaisons interspécifi-ques peuvent n'être pas valides si la dispersion de reproduction et les taux de recapture ne sont pas pris en compte. [Traduit par la Rédaction] Sandercock et al.
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The adult sex ratio (ASR) is a fundamental concept in population biology, sexual selection, and social evolution. However, it remains unclear which demographic processes generate ASR variation and how biases in ASR in turn affect social behaviour. Here, we evaluate the demographic mechanisms shaping ASR and their potential consequences for parental cooperation using detailed survival, fecundity, and behavioural data on 6119 individuals from six wild shorebird populations exhibiting flexible parental strategies. We show that these closely related populations express strikingly different ASRs, despite having similar ecologies and life histories, and that ASR variation is largely driven by sex differences in the apparent survival of juveniles. Furthermore, families in populations with biased ASRs were predominantly tended by a single parent, suggesting that parental cooperation breaks down with unbalanced sex ratios. Taken together, our results indicate that sex biases emerging during early life have profound consequences for social behaviour.
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Significance Sex biases are widespread in nature and represent a fundamental component of sexual selection and population biology—but at which point in life history do these biases emerge? We report a detailed individual-based demographic analysis of an intensively studied wild bird population to evaluate origins of sex biases and their consequences on mating strategies and population dynamics. We document a strongly male-biased adult sex ratio, which is consistent with behavioral observations of female-biased polygamy. Notably, sex-biased juvenile rather than adult survival contributed most to the adult sex ratio. Sex biases also strongly influenced population viability, which was significantly overestimated when sex ratio and mating system were ignored. Our study, therefore, has implications for both sexual selection theory and biodiversity conservation.
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Extra-pair paternity is a common reproductive strategy in many bird species. However, it remains unclear why extra-pair paternity occurs and why it varies among species and populations. Plovers (Charadrius spp.) exhibit considerable variation in reproductive behaviour and ecology, making them excellent models to investigate the evolution of social and genetic mating systems. We investigated inter- and intra-specific patterns of extra-pair parentage and evaluated three major hypotheses explaining extra-pair paternity using a comparative approach based on the microsatellite genotypes of 2,049 individuals from 510 plover families sampled from twelve populations that constituted eight species. Extra-pair paternity rates were very low (0 to 4.1% of chicks per population). No evidence was found in support of the sexual conflict or genetic compatibility hypotheses, and there was no seasonal pattern of extra-pair paternity (EPP). The low prevalence of EPP is consistent with a number of alternative hypotheses, including the parental investment hypothesis, which suggests that high contribution to care by males restricts female plovers from engaging in extra-pair copulations. Further studies are needed to critically test the importance of this hypothesis to plover mate choice. This article is protected by copyright. All rights reserved.
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Sexual selection may act as a promotor of speciation since divergent mate choice and competition for mates can rapidly lead to reproductive isolation. Alternatively, sexual selection may also retard speciation since polygamous individuals can access additional mates by increased breeding dispersal. High breeding dispersal should hence increase gene flow and reduce diversification in polygamous species. Here we test how polygamy predicts diversification in shorebirds using genetic differentiation and subspecies richness as proxies for population divergence. Examining microsatellite data from 79 populations in ten plover species (Genus: Charadrius) we found that polygamous species display significantly less genetic structure and weaker isolation-by-distance effects than monogamous species. Consistent with this result, a comparative analysis including 136 shorebird species showed significantly fewer subspecies for polygamous than for monogamous species. By contrast, migratory behaviour neither predicted genetic differentiation nor subspecies richness. Taken together, our results suggest that dispersal associated with polygamy may facilitate gene flow and limit population divergence. Therefore, intense sexual selection, as occurs in polygamous species, may act as a brake rather than an engine of speciation in shorebirds. We discuss alternative explanations for these results and call for further studies to understand the relationships between sexual selection, dispersal and diversification. This article is protected by copyright. All rights reserved.