Apparent survival, growth rate and dispersal in a declining European Roller population

Abstract

Studying demographic parameters and how they may influence population growth is critical to the development of meaningful conservation actions for endangered species. The European Roller Coracias garrulus has experienced a drastic decline through its breeding distribution range, but very little is known about its demography (i.e. dispersal and survival). Here, we investigated the apparent survival, population growth and breeding site fidelity in a Roller population in the south of Spain over a period of 8 years. We used capture–recapture histories of 202 ringed adults and 369 fledglings to estimate annual survival, and studied factors affecting site fidelity in 56 adults found breeding over two consecutive years. Adult male and female apparent survival overlapped widely and was similar to that found in other similar migratory species. However, juvenile apparent survival, which was markedly lower than adult survival, was low relative to that found for other birds. Population growth was nearly stable during the study period. Regarding site fidelity, males raising more fledglings one year were more prone to be faithful the following year. In females, however, we did not find any factor influencing either site fidelity decisions or distance between consecutive breeding sites. Concerning settlement decisions, males, but not females, moved to nest-boxes where density of Rollers was lower than that at the nest-box of origin. Altogether, our results suggest that the low productivity and a potential decrease in immigration might be compromising the viability of the population.