The phenology of molting, breeding and their overlap in central Amazonian birds

The energetically challenging periods of molting and breeding are usually temporally separated in temperate birds, but can occur simultaneously in tropical birds, a condition known as moltbreeding overlap. Here, we document great variation in the timing and duration of molting and breeding, and in the extent of moltbreeding overlap, among 87 species of understory passerines in central Amazonia. We analyzed molt and breeding from 26 871 birds captured over a 30-yr period near Manaus, Brazil. Although most species typically bred during the late dry season (about October through January), many thamnophilids apparently bred year-round, whereas a few other species from a variety of families bred mainly during the wet season (about January through May). Of all breeding birds with an active brood patch, 12.7% were simultaneously molting. Moltbreeding overlap was more frequently observed among suboscines (13.3%), especially thamnophilids (23.0%), than oscines (6.4%). Some families had <5% moltbreeding overlap frequency, including Tyrannidae (4.4%), Tityridae (0.0%), Pipridae (1.5%), Turdidae (0.0%), and Thraupidae (0.0%), indicating that not all tropical species exhibit moltbreeding overlap. Among 31 well-sampled species (n =15 brood patches), variation in moltbreeding overlap frequency was positively correlated with each species average duration of flight feather replacement (range 98301 d). We also measured feather growth rates of individual birds in nine species; in five of these, slower-growing feathers increased with an individual's probability of having moltbreeding overlap. Among furnariids, moltbreeding overlap occurred either at the beginning or end of the molt cycle, suggesting that physiological mechanisms typically separate molting from breeding. Thamnophilids showed a much different pattern; moltbreeding overlap occurred at any stage of feather replacement, apparently not regulated to be independent of breeding. These results reveal substantial life-history variation among Amazonian birds. Future work to resolve the physiological regulation of molting and breeding in tropical birds will greatly contribute to understanding these patterns and their relevance to avian diversity.