EPOW - Ecology Picture of the Week

Limestone Cave, Humboldt County, northwestern California
and Townsend's Big-eared Bat (Corynorhinus townsendii)

Explanation:  Duck low, all ye who enter here.  This is a seldom-visited limestone cave in a secret corner of the remote Klamath Mountains of northern California.  It is secret because it houses extremely fragile cave formations, but mostly because it is also home to a winter colony of Townsend's Big-eared Bats.

These bats are very sensitive to disturbance, and will readily abandon colony locations.  I made brief visits to several cave sites in this area one winter with several other wildlife biologists to determine if these caves were indeed being used by bats and other wildlife.  We discovered several winter hibernacula (locations for hibernation) of Townsend's Big-eared Bats as well as several overwintering individuals of Long-eared Myotis (Myotis evotis), the first such discoveries for either species in this area.  

Spelunking these unmapped caverns was a fun challenge, entailing belly-crawls through tight tunnels with bats whizzing past your ears, roping down into pitch-dark pits, and chimneying up into ceiling crevices.  Just getting to these locations entailed long hikes through deep snow, being led by a local spelunker whose trust we gained by promising not to reveal the secret locations.  

We spent many hours in these caves.  We captured a few bats for identification, using butterfly nets and leather gloves.   

Much later, I built a computer model to depict habitat use by Townsend's Big-eared Bats (Marcot et al. 2001).  The model shows that these bats have very different habitat requirements for different portions of their life history.  For winter hibernacula, they mostly exclusively use caves or old abandoned mine shafts, but only if the caves provided an optimal temperature range of -2 to 13 degrees C (28- 55 F).  For summer roosts, though, they are less selective and use caves, mines, bridges and buildings, large trees and snags, and sometimes boulder piles.  For maternal roosts, where females give birth, they use mostly caves or mines (with a different optimal temperature range of 20-30 degrees C, or 68-96 F) or large trees or snags.  And they forage for insects on the wing along forest edges, over water, and along cliffs.   

Cave conservation is an important priority for these mysterious bats and many other wildlife species.  

Information:
     Marcot, B. G. 1984. Winter use of some northwestern California caves by western big-eared bats and long-eared myotis. The Murrelet 65:46.
     Marcot, B. G., R. S. Holthausen, M. G. Raphael, M. M. Rowland, and M. J. Wisdom. 2001. Using Bayesian belief networks to evaluate fish and wildlife population viability under land management alternatives from an environmental impact statement. Forest Ecology and Management 153(1-3):29-42.
     Sherwin, R. E., W. L. Gannon, and J. S. Altenbach. 2003. Managing complex systems simply: understanding inherent variation in the use of roosts of Townsend's big-eared bat. Wildlife Society Bulletin 31(1):62-72.