Neotropical migrants exhibit variable body-size changes over time and space


Recent changes in the Earth's climate have been linked to changes in phenology, geographic distributions, and morphology of species, and warming temperatures associated with climate change have been predicted to result in decreases in avian body sizes. We examined changes in wing length and fat-free mass of 34,844 fall migrants from 31 neotropical migratory species captured at Patuxent Wildlife Research Center in Maryland between 1980 and 2012. Body size changes varied across species, but wing length and fat-free mass increased significantly over time in the pooled sample of all species. Magnitudes of change were small and similar to other studies, with mean wing length increasing 0.55% and mean fat-free mass increasing 1.30% across all species. General morphological changes at our site differed from those at a banding station located 235 km away. Across species, changes in wing length were weakly correlated between stations, and changes in fat-free mass were uncorrelated. Populations of some species showed opposite morphological changes, demonstrating that morphological changes can vary regionally. Over short time scales, factors other than climate might drive observed changes in body size of neotropical migrants, and alternative hypotheses for body size changes should be considered.

Publication Title

Northeastern Naturalist