Not everyone is shrinking: increases in body mass and wing length in a Sand Martin ( <i>Riparia riparia</i> ) population in northwestern Italy over two decades

In recent decades, vertebrates, particularly birds, have exhibited notable morphological changes in response to climate change. In birds, these temporal trends usually entail a decrease in body mass and an increase in wing length, sometimes interpreted as a compensatory strategy to maintain migration. This study investigated temporal trends over more than 20 years (2002–23) in wing length and body mass and their relation to environmental conditions, in a Sand Martin Riparia riparia population breeding in northwestern Italy. Our findings revealed a significant increase in both traits within the studied population. Although environmental conditions correlated with Sand Martin morphology, they showed no temporal trend. These morphological trends contrast with those exhibited by most long‐distance migrants. We suggest that this difference may arise from varying climatic or environmental conditions during early ontogenetic stages, alongside a reduction in pressures selecting for small size associated with the relatively more stable climatic conditions in the wintering region.