Effects of Wildfires on Northern Pacific Rattlesnake (Crotalus oreganus) Growth and Microhabitat Use

Chase, Joseph

Beck, Daniel

Department of Biological Sciences

Central Washington University

Ellensburg, WA USA

Rohrer, John

Range and Wildlife Program Manager

United States Forest Service

Wenatchee, WA USA

Fire is an important force in the Pacific Northwest that shapes ecosystems and influences wildlife, yet little is known of its effects on local predators. Northern Pacific Rattlesnakes (Crotalus oreganus) comprise an excellent model to investigate how fire may influence wildlife because rattlesnakes are important predators that influence prey populations, and are in turn important prey to some raptors, yet are also unable to readily flee from wildfires. We refined a technique to assess growth rates of rattlesnakes by analyzing the widths of their rattle segments over time using digital photography. We compared growth rates and population structure of rattlesnakes inhabiting areas that were affected by recent fires with those inhabiting areas unaffected by recent fires. Rattlesnakes measured in the Methow Valley of northern Washington, affected by the Carlton Complex wildfire of 2015, showed no difference in growth rates, likely a result of snakes having insufficient time to respond to potential changes in their prey populations brought about by fire. Snake populations from dens affected by fire, however, showed a size structure that was significantly skewed toward smaller individuals than those outside the wildfire area. Snakes that were tracked using radio telemetry did not show any avoidance of burned habitat during the tracking period. We anticipate that rattlesnakes in habitats affected by less recent fires, like the Taylor Bridge fire of 2012, may be more likely to show a growth response to wildfire. Our technique for measuring rattle segments can be implemented quickly, reduces handling time, and provides a permanent record, making it a promising method for future studies.