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: A Test of Three Hypotheses
For many terrestrial vertebrates, clutch size is positively correlated with latitude, with animals producing more offspring per reproductive attempt at higher absolute latitudes. More than seventy years of avian research has produced three hypotheses to explain this pattern, but the migratory nature of birds has confounded attempts to differentiate among them. Our project tests predictions generated from these hypotheses and describing patterns of clutch size variation in a novel taxon. We will accomplish this in an interspecific framework—using a newly-constructed database that contains more than 800 species of extant snakes—and intraspecifically in western rattlesnakes. This approach will give us valuable insight into the processes that shape clutch size evolution across taxa while also permitting us to make inferences about the density-dependent processes, niche partitioning, and trophic interactions that govern within-species plasticity.
Emily Martin