Evolution of Life History Traits
Causes of differential migration in birds: test of hypotheses in the rough-legged hawk
Seasonal migration occurs in animals of all taxa, but we know surprisingly little about why individuals migrate. For example, many birds have differential migration whereby one sex migrates further than the other, and the causes of sex-specific migration behavior is a topic of debate. Recent advances in remote-tracking technologies have greatly enhanced our ability to collect large amounts of fine-scale data on long-distance avian migration behavior. The Rough-legged Hawk (Buteo lagopus) breeds throughout arctic and subarctic regions of North America and winters throughout the coterminous United States, with no spatial overlap between breeding and wintering areas. Since 2014, we have attached satellite or GPS transmitters to over 190 Rough-legged Hawks to document their migration behavior. We trapped and deployed transmitters on hawks on the wintering grounds, the breeding grounds, and during migration. Many of these transmitters are still generating data, and we continued to deploy additional units with 12 transmitters deployed throughout the United States and Canada during the 2023-24 winter. This dataset will provide a foundation allowing us to test a suite of hypotheses proposed to explain why Rough-legged Hawks exhibit differential migration.
Neil Paprocki
Geographic clutch size variation in squamates: a comparative approach
Emily Martin
For many terrestrial vertebrates, clutch size is positively correlated with latitude, with animals producing more offspring per reproductive attempt at higher latitudes. Three hypotheses have been proposed to explain this global latitudinal gradient, but the highly mobile nature of most endotherms has confounded previous attempts to identify the causal mechanism(s). This project uses 2 approaches to test the alternative hypotheses for this global pattern: 1) test explicit predictions across species based on >1,000 species of extant snakes, and 2) test those same predications within one species (the western rattlesnake). In 2023, we collected clutch size data for more than 60 gravid female rattlesnakes at field sites and museums. This work will continue into 2024, where the project will expand to assess seasonal movement variation in prairie rattlesnakes in response to human disturbance, habitation, and roads. The results will help determine the cause(s) of geographic clutch size variation in these species, which will allow us to 1) quantify the role of intraspecific plasticity in latitudinal clutch size variation 2) identify the mechanisms responsible for intraspecific clutch size variation, and 3) improve our understanding of the risks faced by one of North America's most widespread snakes.
