Resumen en inglés

Delayed plumage maturation (DPM), the retention of subadult plumage beyond the first potential breeding season, is widespread among birds, yet its evolutionary drivers remain poorly understood. We conducted a global comparative analysis across 1,175 passerine species to test whether ecological seasonality and social or sexual signaling predict interspecific variation in DPM. Using phylogenetically informed models and ancestral state reconstructions, we found that DPM has evolved repeatedly but has been more frequently lost than gained, indicating a highly labile evolutionary history. The degree of DPM increased significantly with sexual dichromatism, supporting the hypothesis that delayed acquisition of adult-like plumage functions as a signaling delay that mitigates social aggression and competitive costs during early life stages. Among environmental predictors, DPM was positively associated with latitude and climatic axes reflecting intense warm-season conditions, suggesting that ecological seasonality and thermal stress may favor delayed maturation by constraining breeding windows or amplifying the costs of ornament production. Conversely, vegetation productivity (NDVI) and proxies of social bonding or territoriality showed no detectable effects, possibly due to limited behavioral resolution. Together, these findings indicate that DPM likely arises and is maintained through the joint influence of environmental constraints and social signaling pressures, functioning as a flexible life-history strategy that balances survival and reproductive trade-offs under variable ecological regimes. Our results position DPM as an adaptive, dynamically regulated trait at the interface of sexual selection, development, and environmental seasonality, highlighting the need for integrative behavioral, hormonal, and genomic studies to unravel its underlying mechanisms.