NPS bat research in Poopenaut Valley

Sarah Stock, wildlife biologist with the Resources Management and Science Division of Yosemite National Park, discusses recent bat monitoring conducted as part of Yosemite's Looking Downstream Project.

There are about 1,240 bat species worldwide, 24 of which are native to California. In Yosemite National Park, 17 bat species are known to occur and five are special status species that have experienced statewide declines. While population declines in California are mostly caused by habitat degradation outside of the park, this serves to highlight the importance of parkland as a refuge for bat species and means that bats may be more sensitive to management activities within the park.

The Poopenaut Valley is a unique area downstream of O’Shaughnessy Dam on the Tuolumne River in Yosemite National Park. With its open wet meadows, riparian vegetation, and seasonal pond, the valley provides important habitat for bats. Bats are essential in maintaining ecosystem health by controlling insect populations through nighttime foraging. Most bat species forage either over water or within the adjacent riparian zone, where plant and insect productivity is higher than in drier upslope areas.

National Park Service (NPS) biologists are incorporating the study of bats into ongoing UTREP and Looking Downstream Project efforts in the Poopenaut Valley. The seasonal pond occupying the north side of the valley supports numerous aquatic and terrestrial species. When the pond fills in winter and spring due to snowmelt and runoff from winter rains, an entire food web develops. As the pond fills and the temperature increases, aquatic vegetation begins to grow, and aquatic and terrestrial insect populations begin to develop, which in turn provide food for garter snakes, Pacific chorus frogs, and bats.

Using advanced acoustic monitoring techniques, park biologists are working to understand how bats use the Poopenaut Valley pond and other habitats in the valley. The monitoring effort uses a system of specialized acoustic detectors to match bat echolocation calls to known recordings. In this work, NPS biologists are looking at how bats use the valley during the year and are measuring the amount of bat foraging that takes place in relation to the amount of water present in the seasonal pond.

Bat detection equipment installed near the
Poopenaut Valley pond.  Photo: Sarah Stock.

Data from a pilot study in 2010 and preliminary surveys through mid-May of 2011 indicate that 12 different bat species occur in Poopenaut Valley, including four California Species of Special Concern (Townsend’s big-eared bat, pallid bat, spotted bat, and western mastiff bat). The other eight bat species detected include hoary bat, silver-haired bat, western pipistrelle, Mexican free-tailed bat, California myotis, Yuma myotis, long-eared myotis, and fringed myotis.

This research will be integrated into other work in the Poopenaut Valley to characterize the food web response (including bats) to varying water levels. Since filling of the pond each year is related to flows released from O’Shaughnessy Dam to the Tuolumne River, this research will aid in developing a better understanding of how water releases affect bat populations and the ecology of the seasonal pond, providing guidance to the NPS and SFPUC in making informed flow management decisions.