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Abstract

In response to a changing climate and the loss of habitat, avian species are displaying changes in body size, migration phenology, and demography. Several species have adhered to Allen’s and Bergmann’s rules by displaying increased wing length and decreased mass, respectively, over time in response to higher temperatures. Climate change has also resulted in earlier spring migration and depending on species, either earlier or later fall migration. Finally, species affected by habitat loss often display male-skewed sex ratios and juvenile skewed age ratios. Our goal was to determine how body size, migration phenology, and demography have changed for grassland birds over 17 years. We used data from birds captured in mist-nets between 2007 and 2024 at a restored grassland, and fit generalized linear models (body size and migration phenology) and linear regressions (age and sex ratios). Contrary to Allen and Bergmann’s rules, three species displayed shorter wings and two showed greater fat-free mass over time; this is likely in response to changes in climate variability, rather than increasing mean temperatures, or it is unrelated to climate change. One species, unexpectedly, exhibited later spring migration, possibly due to longer migration distances or increased severe weather events during migration, and two species exhibited later fall migration, consistent with other literature. One species displayed a male-skewed sex ratio, possibly a result of increased predation at Panola Mountain State Park or an indication of a declining capture rate for that species. One species showed a juvenile-skewed age ratio, likely due to increased fecundity resulting from improved habitat, or mist netting resulted in a biased sample.

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