Afrotropical passerines grow wing feathers faster than their European counterparts

Abstract Latitudinal gradients in environmental conditions shape avian life-history strategies by influencing resource allocation among growth, survival, and reproduction. Feather production, which is essential for flight, thermoregulation, and predator avoidance, represents a key component of avian energy allocation. We examined interspecific variation in wing and tail feather growth rates and quality in passerine birds from European temperate and Afrotropical regions using data from 679 adults representing 132 species from 36 families. Our findings reveal distinct latitudinal differences in feather growth: tropical breeding passerines exhibit significantly faster wing feather growth rates than temperate zone breeding species, while tail feather growth is lower in tropical species. Additionally, fault bars were common in the tail feathers of tropical species but almost absent in wing feathers across both regions. This absence was particularly apparent among temperate breeding long-distance migratory species. Overall, feather traits were strongly influenced by breeding rather than moulting latitudes, suggesting that latitude-driven selection on energy allocation and intrinsic physiological mechanisms shape feather investment strategies. Our results thus indicate that investments in feather traits are part of a recently uncovered and widening spectrum of avian evolutionary syndromes convergently evolving among phylogenetically unrelated lineages sharing the same breeding latitudes.