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Bay Delta Region

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Scott Wilson

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Stanislaus River Report


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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept of Fish and Game

Spotted Bat

Euderma maculatum
Category 2 candidate for listing by the U.S. Fish and Wildlife Service as Threatened or Endangered, and a California Department of Fish and Game "Species of Special Concern"

Life History

The spotted bat has extremely large ears, dark body, and a white patch on the rump and each shoulder; abdominal hairs are white-tipped with black bases. A bare patch of skin is found on its throat. The ears, wing and tail membranes are pinkish-red. Total length of the spotted bat is 107 to 115 mm, the ear measures 37 to 47 mm, and the length of the forearm is approximately 48 to 51 mm (Hall 1981).

The spotted bat is considered to be one of North America's rarest mammals (Zeiner et al. 1990). In California it is found mostly in the southeastern Sierran foothills, mountains and desert regions and only occasionally occurs outside this range. This bat may be a yearlong resident with recorded occurrences in Mecca, Red Rock Canyon, Friant, 1971; Yosemite Valley, California; and Reno, Nevada (Hall 1981).

Little is known about spotted bats in California. It is known to inhabit arid deserts, grasslands, and mixed coniferous forests. Horizontal rock crevices provide optimal roost sites (Watkins 1977) although they may occasionally use caves and buildings as well. Spotted bats may migrate from high elevations to lowlands in fall.

This bat is a late flyer compared to most other bats and is not frequently caught until after midnight (Watkins 1977). The spotted bat flies 15 to 45 feet above the ground in large elliptical paths (600 to 900 feet long) while foraging (Wai-Ping 1989). It feeds primarily on moths although there is some evidence of beetles also being eaten. Spotted bats have been observed to land on the ground and capture food items (like the pallid bat) (Watkins 1977). The spotted bat is apparently a solitary animal. It mates in the fall with a single young born before mid-June; lactating females have been found from June to August.

Findings and Conclusions

Due to the rare nature of this animal and minimal information about its range, it has been included as a potentially occurring species. Factors for decline are unknown.

No spotted bats have been recorded in the Stanislaus River area, however the project area is less than 60 miles north of the most northern sighting in Yosemite Valley. This bat could potentially inhabit the upper reaches of the Stanislaus River, roosting in the rocky canyons and feeding in open grassland or agriculture areas.

Any project that affects potential roosting or foraging habitat may have an impact on this species. Further surveys are recommended in order to determine roost sites and foraging areas.