Weather conditions influence breeding initiation of an intra-tropical migrant bird, <i>Sporophila lineola</i> (Lined Seedeater)

Abstract Ecological results from climate change can be observed in various biological systems. Evidence suggests that several bird species have advanced their migration and breeding schedule in response to global warming. While such phenological changes have been extensively studied in species within temperate climates, there has been limited attention to tropical regions. Using climate window analyses, we investigated the influence of climatic conditions on various breeding traits (e.g., date of first laying attempt within a season) in Sporophila lineola (Lined Seedeater), an intra-tropical migratory species. We used long-term climate data associated with breeding data from 9 breeding seasons from the Lined Seedeater Project, which has monitored the breeding population since 2014 in southeastern Brazil. Overall, at the individual level, dates of the first laying attempts correlated with precipitation and temperature. Increased precipitation 22–90 days before the laying date predicted a delay in breeding initiation, while increased maximum temperatures 43–90 days before the laying date predicted an advance in breeding initiation. Interestingly, both time periods encompass the arrival period at the breeding grounds and reinforce that weather conditions before and during the arrival period can influence the onset of breeding initiation of migrant birds. Incorporating patterns of resource phenology and post-migration behavior is paramount for understanding changes to breeding phenology of intra-tropical migrants in the face of an increasingly unpredictable climate.