Constant or varied survival? Effects of seasonal and unpredictable factors on bird survival in a Neotropical semi-arid region

Bird demography in the semi-arid tropics is poorly understood and potentially distinct from that in the humid tropics. In dry environments, rainfall dynamics lead to temporal concentration of food resources and to animals' responses to these resources, which together influence survival. Using six years of sampling from a dry forest in Brazil, we describe the temporal relationship among rainfall, breeding and feather moult to test how these events interact to influence the survival of the Pearly-vented Tody-Tyrant. The first four years were marked by drought. Birds seldom had brood patches in the final years of drought, whereas moulting was uncommon in the subsequent rainy years. Rainfall, breeding and moults were concentrated in the first half of the year. Apparent survival was low during the final two years of drought, increased in subsequent years and was seasonally higher during periods of rain, breeding and moulting. Our findings indicate that survival is somewhat resistant to climate unpredictability but declines during multiyear drought events. A strategy of phenotypic flexibility seems to have minimized the intense negative effects on survival. We believe that these findings provide insights that contribute to a better understanding of the demography and annual routines of birds in seasonal environments.