Climate‐Driven Morphological Variation in Passerine Birds

Aim: Climate change exerts selective pressures on avian morphology; nevertheless family-specific adaptive pathways remain poorly studied. We explore the connections between morphometric traits and climate for 59 bird species of Passeriformes families. Location: South America. Time Period: Current. Major Taxa Studied: Birds. Methods: We quantify climate-morphology relationships in 59 South American passerine species (n = 14,447 individuals; families Furnariidae, Tyrannidae and Thraupidae) using mixed-effects models incorporating PCA-derived seasonality metrics, spatial covariance modelling and temporal random effects with phylogenetic correction. Results: Our findings demonstrate that body mass declined with temperature seasonality but exhibited family specificity. Furnariidae showed negative temperature associations, while Thraupidae responded positively to precipitation seasonality. Tarsus length decreased with precipitation across families, whereas wing length increased with temperature seasonality but declined under precipitation. Bill dimensions demonstrated the strongest climate sensitivity: length increased with temperature but decreased with precipitation seasonality. Random effects showed divergent phenotypic plasticity: Thraupidae displayed high temporal variance in bill length, indicating climate responsiveness, whereas body mass was temporally conserved. Habitat, diet and foraging behaviour showed no importance overall but were significant for Furnariidae essentially for body size, wing length and bill width. We found that forest-dwelling ground foragers exhibited smaller body size, shorter wings and large bills. Main Conclusions: Our results showed that bill dimensions (length/width/depth) change more dramatically across climate gradients than body size traits (mass, tarsus, wing). These family-specific response hierarchies highlight differential vulnerability to climate change in Neotropical passerines.