Wednesday, May 30, 2018

Townsend's big-eared bats at Kentucky stamp mill

General bat anatomy displayed on a board in the Kentucky Mine Historic Park: the distinct Townsend's big-eared bat has horseshoe-shaped lumps on the nostrils and long ears joining at the base
The stamp mill at the Kentucky Mine Historic Park in Sierra City, California, hosts a maternity colony of Townsend's big-eared bats (Corynorhinus townsendii)—a cave-dwelling species that occasionally roosts in man-made structures. The bats of the Kentucky colony have acclimated to local conditions tolerating a certain level of disturbance such as human spectators and short exposure to stamping noise, happening for short times while demonstrating the function ore-crushing stamps to visitors.

Townsend's big-eared bats are named for their extremely long and flexible ears. But there is more in the long common name. The species name—also the shorter scientific name—commemorates the American naturalist and collector John Kirk Townsend (1809-1851), who, in the first half of the 19th century, explored the wildlife between the Rockies and the Pacific Ocean [1]. Various subspecies are found throughout western North America between British Columbia and Mexico.

Corners and crevices of the stamp mill at the historic Kentucky Mine serve as roosting sites for Townsend's big-eared bats
Corynorhinus townsendii is protected under the California Endangered Species Act [2]. Threats include habitat destruction and potential introduction of the white-nose syndrom. Although once created by humans for a noisy business, the Kentucky stamp mill is a a safe refuge for this endangered bat species. A tour guide at the mine park informed me that the “Kentucky stamp mill bats” do not migrate. Townsend's big-eared bats prey on moths but may include some other insects in their diet: They (and also other bats) offer natural pest control by eating insects that may otherwise attack crops or forest land.

Female Townsend's big-eared bats rear their young in maternity colonies. A handout provided at the Kentucky Mine Museum in the Bigelow House describes their mating and breeding cycle:

Mating begins in the fall and continues through the winter. Townsend's big-eared bats have delayed fertilization, storing sperm until ovulation occurs in the spring. In March or April the females begin to form maternity colonies, where theyr rear their young. During the maternity season, males remain solitary or form small bachelor groups. The length of gestation varies depending on the climate, but generally lasts between 56 to 100 days. Females give birth to a single young, called a pup. The babies develop rapidly: they are able to fly by three weeks, nearly grown by four weeks and weaned by six weeks. Females return to the same roost where they were raised to give birth to their own young. Males and females spend the winter together to hibernate.

References and suggested reading

[1] Bo Beolens, Michael Watkins and Michael Grayson: The Eponym Dictionary of Mammals. The Johns Hopkins University Press, Baltimore, Maryland, 2009; page 416.

[2] Noah Greenwald: Townsend's Big-eared Bat Protected Under California Endangered Species Act. Center for Biological Diversity, June 27, 2013. Link:

[3] Gary M. Feller and Elizabeth D. Pierson: Habitat Use and Foraging Behavior of Townsend's Big-Eared Bat (Corynorhinus Townsendii) in Coastal California. Journal of Mammology, February 2002, 83 (1), 167-177. Link:  

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