High survival rate of a critically endangered species, the Azores Bullfinch Pyrrhula murina, as a contribution to population recovery

Abstract

This paper reports analyses of a capture-markrecapture (CMR) dataset of 149 Azores Bullfinches ringed on São Miguel island (Azores) between 2005 and 2007, and recaptured-resighted on a monthly basis over a 4-year period (2005)(2006)(2007)(2008) throughout their breeding range. We examined the effect of time, age (adults vs. juveniles), gender (adult males and females), and environmental covariates (temperature, rainfall, NAO index) on survival probabilities. The modelling found a high and constant monthly survival probability (mean ± SE) estimated at 0.96 ± 0.01, similar between both adults and juveniles and independent of environmental conditions and gender. These findings agree with expectations from island-based life-history theory where relatively mild conditions and lack of predators should favour high survival rates to compensate for the low reproductive output. The annual survival rate was estimated at 0.62, which was also consistent with this pattern when compared with survival estimates of mainland bullfinch and passerine species on other subtropical islands obtained in similar CMR studies. Based on a canonical estimator, the size of the studied population (mean ± SE) was estimated at 1608 ± 326 individuals. Given that the population size was only around 120-400 individuals in the early 1990s, we suggest that the high survival probabilities currently applying to this critically endangered species may have substantially contributed to the recent recovery of this population. Future research studies on the species' demography should continue to monitor survival in order to measure the effect of management interventions currently taking place within the range of the Azores Bullfinch, including the restoration of the biodiversity rich laurel forest, but also focusing on nest success, which is important for understanding population dynamics.

Status assessment of the Critically Endangered Azores BullfinchPyrrhula murina

“…Buckland 1985), as it is hard to imagine a search pattern such that all birds on the point are detected but a large proportion are missed just off it, which the absence of a shoulder and the steep slope of the negative exponential both imply. We suggest that the snapshot approach produced the more realistic estimate (despite the much smaller sample size) because it avoids the biases described abovewhich are particularly acute for this speciesand because independent estimates of population size based on capture-mark-recapture yielded similar results (mean 6 SE: 1608 6 326 individuals; Monticelli et al 2010). This study strongly supports the use of the snapshot approach where it is practicable.…”

Survival probability of immature green turtles in two foraging grounds at Culebra, Puerto Rico

“…Mar Ecol Prog Ser 440: [217][218][219][220][221][222][223][224][225][226][227] 2011 survival probability have been widely employed in animal population studies (Lebreton et al 1992, Pradel et al 1997, Bjorndal et al 2003b, Campbell & Lagueux 2005, Monticelli et al 2010) and have become an important means for application in longterm population management (Fujiwara & Caswell 2002).…”

“…One important approach to determine actions for the effective conservation of endangered species is to investigate their population dynamics and demography (Crouse et al 1987, Fujiwara & Caswell 2002, Monticelli et al 2010. Mark−recapture estimates of survival probability have been widely employed in animal population studies (Lebreton et al 1992, Pradel et al 1997, Bjorndal et al 2003b, Campbell & Lagueux 2005, Monticelli et al 2010) and have become an important means for application in longterm population management (Fujiwara & Caswell 2002).…”

The Priolo Atlas: A citizen science-based census initiative for supporting Pyrrhula murina habitat conservation and restoration policies in São Miguel Island (Azores, Portugal)

“…All of the above methods have been tried to monitor the Azores Bullfinch population over the last two decades with different levels of success (Monticelli et al, 2010;Ceia et al, 2011a,b;Bastos et al, 2012). Unfortunately, the Azores Bullfinch population offers important logistic constraints, which hindered the conclusions derived from classic census techniques, namely: (1) the extremely steep terrain (94% of its distribution area has a slope greater than 20%; Gil, 2005) combined with dense vegetation makes most of the distribution area inaccessible or severely restricts observer movement; (2) the small population size renders the use of capture-recapture methods and randomly distributed census across the whole distribution area highly cost-ineffective; (3) different plant/food phenology due to the strong altitudinal window hindered the uniform sampling of the area in space and time; and (4) the species is not evenly distributed but it decreases sharply with altitude and distance to roads, which are probably used differently by birds.…”