Date of Award

Fall 10-25-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Alfred Mead

Second Advisor

David Weese

Third Advisor

Bruce Snyder

Abstract

In response to a changing climate and habitat loss, avian species are displaying changes in body size, migration phenology, and demography. Species have often adhered to Allen’s and Bergmann’s rules, displaying increased wing length and decreased body mass, respectively, over time in response to higher temperatures. Additionally, climate change has 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 1) body size, 2) migration phenology, and 3) demography have changed for grassland birds at a restored grassland located in Panola Mountain State Park (PANO) in Stockbridge, Georgia, USA over 17 years. We expected the avian species at PANO to display 1) increases in wing length and decreases in wing length over time, concordant with Allen and Bergmann’s rules, respectively, 2) advanced spring migration and species-specific changes in fall 23 migration phenology, and 3) non-skewed and unchanged sex and age ratios. We used data from birds captured in mist-nets between 2007 and 2024 at PANO’s year-round banding station to fit generalized linear models for body size and migration phenology, as well as linear regressions for age and sex ratios. Contrary to Allen and Bergmann’s rules, three species displayed shorter wings and two showed greater fat-free body mass over time, likely in response to changes in climate variability, rather than increasing mean temperatures, or it is unrelated to climate change. Unexpectedly, one species 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 PANO 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. The unexpected morphological and phenological changes we observed emphasize the complexities of avian responses to climate change. We suggest the many species that did not display changes in morphology, phenology, or demography are the result of successful habitat restoration of the site mitigating the effects of climate change.

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