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–mark–recapture (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 (2005–2008) 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.