Monday, Feb 25, 2013
TULELAKE, California— Lava Beds National Monument staff recently completed a full week of bat hibernacula surveys under a newly developed bat survey plan. The purpose of these annual surveys is to track the health and status of the monument’s winter bat population. Most monument bat species hibernate during the winter to survive the long, cold season when their food source, mainly insects, is unavailable. Caves that are used by bats for hibernation are known as hibernacula, and these sites are chosen by the bats for the stable, cold temperatures that allow them to conserve energy by slowing their metabolism. Because bats remain relatively inactive while hibernating, winter is the ideal time to obtain accurate counts of bat populations. Surveys are only conducted once each winter to minimize disturbances towards the bats. This year’s survey of 48 lava caves yielded a count of 1,219 Townsend’s Big-Eared Bats (Corynorhinus townsendii), 1 Big Brown Bat (Eptesicus fuscus), and 14 bats of the Myotis genus (it is not possible to identify these bats to species level without handling them, which would cause unwanted disturbance).
Due to meticulous planning and a strategic layout of the randomly selected caves chosen from four cave groups, the surveys were highly successful. The superb weather allowed teams to safely hike and ski to cave locations. Surveys are conducted by slowly scanning the cave ceilings and recording the number of individual and clusters of hibernating bats. Counts varied from zero bats to more than one hundred bats per cave, with most caves containing less than 20 bats.
The new, statistically sound, hibernacula survey design will improve the monument’s understanding of its bat population. Records from previous winter bat counts dating back to 1961 provided the baseline needed to create a valid design plan. Collaboration for this design plan began in 2010 with Theodore Weller, a bat biologist out of the National Park Service’s Pacific Southwest Research Station. Over time, the new survey design will produce a trend line for an estimated total winter bat population at Lava Beds. It is important to be able to estimate the population, as it is impossible to survey all 700+ monument caves in a one-week period. Surveys have better accuracy when conducted within a single week, as this reduces the possibility of missing or duplicating the counts if bats become active between caves.
Monitoring winter hibernacula and summer maternity bat activity is vital to understanding the long-term health of this important resource for the Klamath Basin. Bats control pest populations by eating millions of insects over the course of one year. Lava Beds is committed to protecting all bat species within the monument. Visitors are involved in the bat population’s health by participating in the white-nose syndrome (WNS) screening process. WNS is a fatal disease affecting cave roosting bats. Lava Beds reports no sign of WNS during the 2013 survey.