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Bird Study
ISSN: 0006-3657 (Print) 1944-6705 (Online) Journal homepage: http://www.tandfonline.com/loi/tbis20
Preliminary assessment of the release of captive-
bred Gran Canaria Blue Chaffinches Fringilla
teydea polatzeki as a reinforcement population
Alejandro Delgado, Pascual Calabuig, Víctor Suárez, Domingo Trujillo & M.
Mercedez Suárez-Rancel
To cite this article: Alejandro Delgado, Pascual Calabuig, Víctor Suárez, Domingo Trujillo & M.
Mercedez Suárez-Rancel (2016): Preliminary assessment of the release of captive-bred Gran
Canaria Blue Chaffinches Fringilla teydea polatzeki as a reinforcement population, Bird Study,
DOI: 10.1080/00063657.2016.1239694
To link to this article: http://dx.doi.org/10.1080/00063657.2016.1239694
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SHORT REPORT
Preliminary assessment of the release of captive-bred Gran Canaria Blue
Chaffinches Fringilla teydea polatzeki as a reinforcement population
Alejandro Delgado
a
, Pascual Calabuig
a
, Víctor Suárez
a
, Domingo Trujillo
a
and M. Mercedez Suárez-Rancel
b
a
Wildlife Recovery Center ‘Tafira’, Las Palmas de Gran Canaria, Canary Islands, Spain;
b
Departamento de Matemáticas, Estadística e Investigación
Operativa, Facultad de Matemáticas, Universidad de La Laguna, Santa Cruz de Tenerife, Canary Islands, Spain
ABSTRACT
Capsule: The endangered Gran Canaria Blue Chaffinch Fringilla teydea polatzeki has been bred in
captivity with the aim of reinforcing wild populations. We released and monitored 26 males and
15 females between 2010 and 2012. Survival and reproductive success were similar between the
reinforced population and a stable reference population, suggesting that the process could be
useful for the conservation of the species.
ARTICLE HISTORY
Received 3 April 2016
Accepted 15 September 2016
It is widely accepted that breeding animals in captivity
for reintroduction is an important management tool
for recovering endangered species but there have been
frequent calls for increased monitoring of
reintroductions (Maunder 1992, Kleiman et al. 1994,
Hein 1997, Seddon 1999, Fischer & Lindenmayer 2000)
and for critical evaluation of programmes (Sarrazin &
Barbault 1996, Armstrong et al. 2002). For example,
reintroduced captive-bred birds often experience high
post-release mortality and the survival of reintroduced
captive-bred birds is dependent on the release
strategies employed (Bernardo et al. 2011).
The success of a reintroduction is partly dependent on
the translocation procedure and whether a ‘hard’or ‘soft’
release strategy is used (Scott & Carpenter 1987).
Soft release involves a animals being held on-site prior
to a delayed release and can also include the provision
of supplementary food or other resources after
release (Richardson et al. 2013). According to the
International Union for Conservation of Nature (IUCN
2013), animals may be held for some period at the
release site to allow them to become accustomed to
local conditions or enhance social group cohesion;
such procedures are most likely to be useful with
captive-bred animals. The propensity of reintroduced
birds to move during the immediate post-release
period will in part depend on soft release protocols,
specifically the timing and number of release cohorts,
supplementary feeding and the proximity of the soft
release enclosure to freshwater sources. Captive-bred
birds will be unfamiliar with the release site and this
will also influence home-range establishment and site
fidelity (Bernardo et al. 2011).
TheBlueChaffinchFringilla teydea is a specialist
passerine of thick upland Canary Island Pine Pinus
canariensis forest on Tenerife and Gran Canaria (Canary
Islands). One subspecies exists in each of these islands,
although some authors have recently suggested that these
represent two distinct species: the Gran Canaria Blue
Chaffinch Fringilla polatzeki and the Tenerife Blue
Chaffinch F. teydea (Sangster et al. 2015, Lifjeld et al.
2016). The reclassification of Gran Canaria Blue
Chaffinch as a single-island endemic species would make
it Europe’s rarest passerine species. Its population is very
limited because the extent of pine forest on Gran Canaria
is small and highly fragmented, that is why the Red Book
of Birds in Spain termed the Gran Canaria subspecies as
Critically Endangered (Madroño et al. 2004). A
conservation strategy was initially implemented by the
Canary Island Government in 1991, followed by the
approval of a recovery plan in 2005. This plan includes,
among other activities, the formation of at least one other
population by reintroduction (Suárez et al. 2012).
The overall goal of the captive breeding programme
was to decrease the risk of extinction of the Gran
Canaria Blue Chaffinch by establishing a self-sustaining
wild population in other pine forests. This paper
reports a preliminary assessment of the three-year
programme of captive-bred releases and provides
information for future management actions for
conservation and reintroduction of this and other
passerine species.
© 2016 British Trust for Ornithology
CONTACT Alejandro Delgado adelgadogento@gmail.com Wildlife Recovery Center ‘Tafira’, Vivero Forestal, Cabildo de Gran Canaria, 35017, Las Palmas
de Gran Canaria, Canary Islands, Spain Supplemental data for this article can be accessed here: http://dx.doi.org/10.1080/00063657.2016.1239694.
BIRD STUDY, 2016
http://dx.doi.org/10.1080/00063657.2016.1239694
The research was carried out in the only two pine forest
regions on the island of Gran Canaria where the Blue
Chaffinch breeds. The first of these was the pine forest
at the Inagua Nature Reserve (3920 ha, 27°57′N 15°
42′W). The population here is the island’s largest, with
121–339 birds, and has a stable population trend
(Rodríguez & Moreno 2008). Carrascal & Seoane (2008)
estimated the population size at 122 individuals after a
fire devastated part of this pine forest in 2007. Inagua
pine forest is used here as the reference population for
comparison in the analysis. The second pine forest
under study, Cumbre (1800 ha, 27°57′N 15°35′W), is on
the summit of the island. This forest was clear-felled in
the mid-nineteenth century and repopulated in the
1950s and 1960s. There are no historical data on the
presence of the Blue Chaffinch at this location because
when the species was discovered on Gran Canaria in
1905 this area was classified as non-forested land. It is
poorly connected by vegetation cover and separated by
about 4.5 km from the upper pine forest at its most
narrow section (Figure 1). This second Blue Chaffinch
population was discovered by Víctor Suárez in 2008,
when colour-ringed birds from Inagua were observed in
Cumbre pine forest and found to be breeding.
Following the initial discovery, sightings were scarce in
Cumbre forest: two adults were located in 2009 and
three in 2010, two of these managing to successfully
fledge two young. Cumbre forest is located in the centre
of the island, is connected with other pine forests and,
following what seems to be a natural colonization of the
site, it was chosen as a highly suitable area to release
captive-bred birds.
Sixteen Gran Canaria Blue Chaffinches were wild-
caught in Inagua Nature Reserve and are currently
used in the captive breeding programme run since
2005 (see Garcia-del-Rey et al. 2013 for more detail of
the captive breeding stock). A total of 41 Blue
Chaffinches (11 in 2010, 13 in 2011 and 17 in 2012),
26 males and 15 females were reared in captivity, and
released between 15 August and 15 October, 5–18
weeks after hatching to limit the period in captivity.
Birds were liberated through soft release techniques,
remained 14 days in groups of no more than seven in
an acclimatization cage located at the release site. All
the birds wore a combination of colour rings to allow
individual identification at a distance. These facilities
were similar to the pre-release cages at the breeding
centre and birds were held in similar groups in both
aviaries. These installations were watched by day to
monitor bird condition and kept opened up to three
months after liberation, so that individuals could use
feeders that were placed inside. Furthermore, six
artificial feeders were placed in the area surrounding
the release cages. Feeders were suspended from
branches in dense vegetation and held P. canariensis
seeds with a mixture of other seeds. Supplementary
Figure 1. Map of Gran Canaria island showing the sites of the Blue Chaffinch populations at Inagua (circle) and Cumbre (triangle), where
captive-bred birds were released. The extent of pine forest is marked in grey.
2A. DELGADO ET AL.
food was supplied throughout the winter until March.
Additionally, mealworms (larvae of Tenebrio molitor)
were provided during the holding period and for the
first three weeks after liberation.
Translocation success can be determined during two
phases: establishment and longer-term persistence
(Armstrong et al. 1999). We assessed the success of the
translocation programme based on two criteria: (1)
short-term criteria: survival of the captive-bred birds
through the first winter, by comparing the apparent
survival five months after liberation of released and
wild birds in the same periods and (2) long-term
criteria: annual survival of adults, by comparing the
apparent survival after a ten-month period for adults
in the reinforced and reference populations. We also
compared population trends and reproductive success
between the reference and reinforced populations.
Between 16 and 41 fledglings and adults were captured
by mist net and individually colour-ringed at the two sites
each year. Two to three people carried out the fieldwork in
the reference population from March to mid-October
2006–2011. We looked over almost the entire area of
pine forests on foot and by car to find, and individually
identify, marked birds. A large fire in 2007 affected of
the reference population (Carrascal & Seoane 2008),
consequently our database covers periods before and
two years after this fire, when a significant recovery of
the vegetation cover had taken place.
One or two people recorded field data in the
reinforced population between 2008 and 2013 in the
same way as at the reference site. Intensive monitoring
in the small pine area allowed researchers to follow the
entire population. Additionally, nests were locating and
monitoring every 4–5 days in order to determine the
number of chicks that fledged. Given the limited
number of chaffinchs in the Cumbre pine forest, the
whole adult population and all fledglings produced
each year (2010–13) could be ringed and identified in
this new population.
We analysed survival using the live recaptures
Cormack–Jolly–Seber model in MARK 8.1 (White &
Burnham 1999) with two encounter occasions and four
groups: juveniles released into reinforced population,
juveniles of reference population, adults of reinforced
population and adults of reference population
(Supplementary Appendix 1). The data set is not
extensive enough to enable the analysis of time or finer
age classes in the survival analysis. Released individuals
were considered to have survived their first winter if
they were resighted in the two months after 15 March
in the year following hatching (for the winters of 2010–
11, 2011–12 and 2012–13). We compared survival
against similarly collected data from the reference
population but in different winters (2006–07, 2010–11).
Annual survival of adults was assessed between 15 April
and 15 June each year, during 2009–11 in the reference
population and 2011–13 in the reinforced population.
Reproductive success was monitored in the reinforced
population for comparison against similar data collected
by Rodríguez & Moreno (2008) in the reference
population during 1994–2004 (but excluding 2003).
Reproductive success parameters were: nest success
(nests that fledged at least one young), production of a
second clutch (second broods and replacements) and
nest productivity (number of offspring per successful
nest). Statistical analyses were performed using R
program (R Core Team 2014).
In total, 35 of the 41 Gran Canaria Blue Chaffinches
were successfully released into the reinforced
population (7 in 2010, 11 in 2011 and 17 in 2012).
Another six birds were released at another date, hence
are not included in this analysis. Also excluded from the
analysis are six birds killed as a result of attacks by
Eurasian Sparrowhawks Accipiter nisus while feeding in
the release cages (2 in 2010, 4 in 2011). All of them died
due to injuries caused by blows against the walls of the
cage while trying to escape the predator. As these birds
died in the cage, they were excluded from the survival
analysis. Additionally, in one case, we detected wounds
caused by a plastic ring in the tibio–tarsus articulation
after release. This bird was captured and released after
removing the colour markers on that leg.
Of the 35 individuals successfully released, 21 were
detected after winter. In the same period, 46 juveniles
were marked in the reference population, 24 of which
survived the first winter. At the reinforced population
site, 27 adults were observed and 11 of them were
subsequently detected on the following year. At the
reference site, 51 adults were detected and 23 of them
were subsequently relocated the following year.
Winter survival probability was 0.774 (95% confidence
intervals (CI) = 0.653–0.862) for released birds in the
reinforced population and 0.722 (95% CI = 0.612–0.811)
for wild birds in the reference population. Annual
survival of adults was 0.638 (95% CI = 0.484–0.768) in
the reinforced population and 0.671 (95% CI = 0.563–
0.764) in the reference population.
We have reproductive success data on 24 out of the 28
monitored nests produced within the reinforced
population after the first release (10 in 2011, 9 in 2012
and 9 in 2013; excludes nests abandoned before
incubation). At least one chick was fledged from 79% of
the nests and 41% of the breeding females attempted a
second clutch (Table 1). In 46% of the nests, a single
chick fledged and 54% fledged two, giving a productivity
of 1.52 chicks (n= 24, sd = 0.51) per successful nest.
BIRD STUDY 3
There were no significant differences between the
percentage of successful breeders in the reinforced
population and the reference population (χ
2
= 0.31,
df = 1, P= 0.58). Furthermore, the number of fledglings
produced per successful nest did not differ between the
two populations (t= 0.37, df = 29.26, P= 0.71).
All adults displayed breeding behaviour in the
reinforced population and there was an increase in the
number of adults and fledglings following releases.
Despite the lack of increase in adults in 2013, the
number of fledglings increased slightly from 2012
(Figure 2).
According to our assessment criteria, we consider the
release of captive-bred Gran Canaria Blue Chaffinch, as a
reinforcement to the Cumbre population, to be a success.
The birds released had similar survival prospects, during
the first winter, as those of young wild birds in the
reference population. Likewise, adults at Cumbre had
similar annual survival rates as those observed in the
reference area at Inagua pine forest over the same
period. We also found that the reproductive success
measures of both populations did not differ
significantly and there was an increase in the adult
population and offspring production following releases
of captive-bred birds.
Nevertheless, during the time the birds were held in
the acclimatization cage or fed in the enclosure after
release, six Blue Chaffinches died because of injuries
caused by impacts against the mesh of the cage when
trying to escape a predator attack. Occasionally, the
supervising staff observed birds of prey in the area of
the cages and on two occasions they witnessed the
attack on the chaffinches acclimatizing inside. In order
to prevent attacks by predators we recommend
protecting the cage and reducing slightly the holding
period. A reduction in the number of days of the
acclimatization period would logically lower the
chances of a Eurasian Sparrowhawk attack but it also
could put at risk the birds’acclimatization success. As
regards the latter, some authors indicate that a 6–14-
day holding period is enough for captive-bred
passerine translocation (Kuehler et al. 2000, Gálvez
2012, Lagios et al. 2014).
Stacey & Taper (1992) highlight the importance of
immigration to the persistence of small populations.
The movement of Blue Chaffinches from one pine
forest to another occurs, but individuals probably have
to cross a deforested area. Therefore, we emphasize the
need to connect both forests, by creating an ecological
corridor through pine reforestation, in order to
facilitate their movement between populations.
We recommend further monitoring of population size
and reproductive success in the reinforced population, to
create a longer data series which would allow us to
monitor survival rates and generate estimates of
population growth rate. Population viability analysis is an
inexact science (Thomas 1990,Reedet al. 2003, Flather
et al. 2011), but it could be considered a valid and
sufficiently accurate tool for managing endangered
species (Boyce 1992,Brooket al. 2000). Brook &
Kikkawa (1998) conducted a population viability analysis
with parameters estimated from relatively short (5 years)
periods of data collection and produced very different
predictions of extinction risk compared with population
viability analysis based on more comprehensive
ecological data spanning 15–25 years. As a guideline,
population analyses provide information about the
minimum number of birds that this population needs to
remain viable. The information obtained will be
important to design conservation strategies for the species.
Acknowledgements
We are grateful to David Shea for translating the first draft of
this paper and Andy Paterson for helpful comments. Ringing
and translocation permission was obtained from
Table 1. Comparison of survival and reproductive success of Blue
Chaffinch populations at Cumbre (reinforced) and Inagua
(reference), Gran Canaria.
Parameters
Reference
population
Reinforced
population
First-winter survival 0.72 (95% CI 0.61–
0.81)
0.77 (95% CI 0.65–
0.86)
Adult annual survival 0.67 (95% CI 0.56–
0.76)
0.64 (95% CI 0.48–
0.77)
Nests fledging at least one
young
70.80%
a
79.17%
Females produced a second
clutch
33.00%
a
41.18%
Offspring per successful nest
(±sd)
1.47 (± 0.50)
a
1.52 (± 0.51)
a
Data obtained from Rodríguez & Moreno (2008).
Figure 2. Population size and sources of Blue Chaffinches in the
reinforced population at Cumbre. Number of birds released
successfully (columns), adult numbers prior to the year’s
release (circles) and fledglings produced (diamonds) during
each of the years of study.
4A. DELGADO ET AL.
Viceconsejeria de Medio Ambiente of Gobierno de Canarias
(Canary Islands government).
Funding
Funding was provided by Consejeria de Medio Ambiente y
Emergencias from Cabildo Insular de Gran Canaria (Gran
Canaria government).
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BIRD STUDY 5