Thursday, July 2, 2009

Towndsends's Big-Eared Bat

While most people fear the things that go bump in the night, my job actually charges me with studying the critters who make some of those bumps. I really look forward to my night work during the summers. I head out just as the night thrushes are finishing up their last calls and end my night with the sounds of morning birds calling as well. Its an experience that everyone should have at some point in their lives. But I'm getting sidetracked here. The reason I work at night for about a month straight over the summer is because I do a capture-mark-recapture survey method on various bat species in my area. I set up a harp trap system right outside of old caves, abandoned mines, and abandoned barns specifically targeted to certain species like the Townsend's Big-Eared Bat for instance.

The Townsend's Big-Eared Bat (Corynorhinus townsendii), aptly named for its uniquely ample ear-size, is actually a species of special concern so it's really neat to have them as native species in Western Montana and available to study. Several of the subspecies of this particular bat on the east coast are even listed federally as endangered. Townsend's Big-Eared Bat is a medium-sized bat with extremely long, flexible ears and small yet noticeable lumps on each side of the snout. It is brown on the back, and wood-brown on the sides. The underparts are a slightly paler shade of brown. These bats can be identified by the nearly uniform color of their bodies. It's total length is around 10 cm (4 in.), its tail being around 5 cm (2 in.) It's wingspan is about 28cm. It weighs around 7-12 grams. This bat is often distributed near rocky areas where caves or abandoned mine tunnels are available. They may also occasionally inhabit old buildings.

During summer, males and females occupy separate roosting sites. Males live a solitary lifestyle away from females. Females and their pups form maternity colonies which often number from around 12 to 200. During the winter these bats hibernate, often when temperatures are around 32 and 53°F (around 0°C and 11.5°C.) Hibernation occurs in tightly packed clusters, which could possibly help stabilize body temperature against the cold. Males often hibernate in warmer places than females and are more easily aroused and active in winter than females. The bats are often interrupted from their sleep because they tend to wake up frequently and move around in the cave or move from one cave entirely to another. During hibernation, C. townsendii grow incredibly fat, which compensates for the food they do not eat during the winter with a low metabolism.

As far as reproduction goes, Townsend's Big-Eared bats do something quite interesting known as delayed fertilization. The mating season for Townsend's Big eared Bats takes place in late fall. As usual, courtship rituals are done by the male. Until spring, when ovulation and fertilization begin, the female stores the male's sperm in her reproductive tract (hence the term delayed fertilization). Gestation lasts from 50 to 60 days. When the pup is born, it is pink, naked, and helpless. Only one pup is birthed per female, although 90% of females give birth.

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