Independent trophic behavior and breeding success of a resident flycatcher and a coexisting migratory congener

Historical biases towards the study of Palearctic and Nearctic bird migration systems has resulted in a dearth of information on the ecology of intratropical migrants, which likely also play important ecological roles within their communities. For instance, there is little information on the foraging ecology and breeding biology of co‐occurring migrants and residents within the intratropical migratory system. Thus, we used two congeneric flycatchers – the resident Plain‐crested Elaenia Elaenia cristata (Aves: Tyrannidae), and the migrant Lesser Elaenia E. chiriquensis (Tyrannidae) – to check whether either of them showed foraging niche plasticity mediating their coexistence and the effects of such syntopy on their breeding behavior and fitness. To do so, we used an ensemble of methods that included the evaluation of food resource phenology, foraging behavior observations, stable isotope ratio analysis in birds’ tissues, and nest monitoring. Our results confirmed that residents have foraging behavior plasticity but reveals its trophic behavior and breeding success is independent of the coexistence with migrants. Since such results depart from the predictions based on the current (and often Northern‐biased) theories of bird migration, we discuss alternative hypotheses explaining our findings, including the influence of physiology on diet and the behavioral responses of nest predators. Once there is a clear knowledge gap about the interspecific interactions between residents and intratropical migrants, our study represents a simple, yet important, step towards understanding the mechanisms underlying this system.