Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

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.