Breeding Biology of the Chilean Elaenia Elaenia chilensis, a Long-Distance Migratory Passerine in South America

Studies examining breeding biology provide information about reproductive parameters, which are useful in formulating life-history theories. Although these studies have notably increased in the Neotropics in recent years, some gaps remain; thus, more research is needed to better understand life-history strategies of New World birds. Furthermore, research into the breeding biology of migratory birds is crucial to advance our understanding of trade-offs between reproduction and migration in Neotropical austral migrant birds. Our aims were to describe in detail the breeding biology of the Chilean Elaenia Elaenia chilensis, a long-distance Neotropical austral migrant, and to discuss current life-history theories for New World passerines. We monitored 113 nests during four consecutive breeding seasons (2014/2015–2017/2018) in the Andean-Patagonian Forest. The breeding season lasted 77 days and the nesting period, from egg laying to fledging, had a mean duration of 29.9 days. Mean clutch size was 2.4 eggs (range: 1–3) and decreased throughout the breeding season. The incubation and nestling stages lasted c. 14 days each. Fledgling number also decreased as the season progressed. The mean ± SE daily nest survival rate was 0.960 ± 0.005, corresponding to an overall nest success of 29.5%. Predation was the main cause of nest loss (61.1%). Reproductive parameters of the Chilean Elaenia coincide with characteristics of high-survival species that invest little in reproduction. Despite being a long-distance migrant, its life-history strategy does not seem to be much faster than that of its tropical resident congeners. This might not support the result reported in the Northern Hemisphere that migratory birds have a faster pace of life than resident birds.