When do tropical birds breed? The case of Colombian species assemblages

Understanding when tropical birds breed is key to life-history theory and to predicting how species will respond to environmental change. While early views emphasized the potential for year-round breeding in the tropics, accumulating evidence suggests that reproductive activity in most tropical birds follows some degree of seasonality, often linked to rainfall and associated food pulses. However, large-scale evaluations across ecological gradients remain scarce. Here, we investigated the breeding seasonality of Colombian resident birds using over 80,000 records compiled from bird banding programs and the Global Biodiversity Information Facility (GBIF). These data included birds in breeding conditions, active nests, nestlings, and adults displaying reproductive behavior. We asked four main questions: (1) Do Colombian birds exhibit seasonal breeding activity? (2) Does the degree of seasonality vary with latitude and elevation? (3) Are there geographic differences in breeding patterns across Colombia’s biogeographic regions? (4) How does breeding activity vary among feeding guilds? We used time-series, circular statistics, and generalized additive models (GAMs) to evaluate breeding patterns at national and regional levels, incorporating geographic variables and trophic guild. We found a clear seasonal pattern in breeding activity, with a main peak in April and low but consistent activity throughout the year, especially in the Andes. Breeding was more synchronized at higher latitudes and more extended near the Equator. Elevation also shaped seasonality: lowland bird assemblages showed broader breeding seasons, while mid- and high-elevation assemblages had narrower seasonal windows, driven by a shift in the breeding peak toward mid-year in highland birds. Regional and trophic guild variation was also marked. Caribbean birds bred sharply in April, Andean birds had prolonged reproductive activity peaking in March and June, and Chocoan birds peaked in March, followed by a decline. Breeding generally coincided with the start of rains and avoided extreme dry or wet months, in line with hygric niche theory. Feeding guilds differed as well: frugivores-nectarivores, omnivores, and invertivores bred mainly early in the year, while granivores peaked mid-year. Together, our findings offer new insights into tropical bird reproduction by showing that breeding activity in Colombia follows clear seasonal patterns shaped by rainfall regimes, elevation, and trophic ecology, contributing to the growing evidence of the complexity of breeding seasonality at tropical and near-equatorial latitudes.