New Mexico's Pet Resource WINTER 2005


by Bill Baxter (photo by S. Altenbach)

Unquestionably, the most important piece of New Mexican history found today in the Ortiz Mountains Educational Preserve (OMEP) is the Santo Niño mine shaft, the oldest (1830 or earlier) lode gold mine in the American West. In 2002, in preparation for visitors, the State of New Mexico sealed most of the hazardous mines in the Preserve, but they didn’t fill the Santo Niño because somebody was living there: Townsend’s Big-eared bats.

Three times this year the Santa Fe Botanical Garden (SFBG) has conducted an evening bat census at the Santo Niño. Enumerators sit quietly (or not so quietly) around the cupola on the Santo Niño and try to count bats as they come spiraling up the shaft, one or two at a time, and circle inside the cupola before exiting through the slats to feed for the night. For some reason the tiny fliers seem to like people, as once outside they swoop noiselessly around you, just inches from your face.

During the May-June birthing season we counted thirty to sixty individuals in each census, so we guess the Santo Niño summertime colony is comprised of 75-100 individuals, about double the estimate made by the NM Abandoned Mine Land Bureau in 2002. But the late summer census only showed about a fifth that number. We don’t know why.

What do we know about Townsend’s big-eared bats? They are found from Canada to Mexico, but their numbers are not great and are declining. In New Mexico they are being monitored as a possible endangered species. They depend strongly upon the availability of caves or cave-like roosting habitat (old mines), and about 40% of the larger abandoned mines in New Mexico, like the Santo Niño, show evidence of use by this species.

Summertime colony size may be 10 to 100 individuals or more. Hibernating winter colonies may be 1,000 or larger.

Townsend’s big-eared bats are relatively sedentary. They do not move long distances from hibernacula (permanent habitations) to summer roosts, nor do they move or forage far from their day roosts. They are Lepidopteran specialists with a diet consisting primarily of moths. They live in forested habitat and along vegetated stream corridors, avoiding open grasslands. They do not tolerate human disturbance.

During hibernation if the temperature drops below freezing the bats will move deeper into the tunnel, but arousal from winter hibernation can lead to the expenditure of 10 to 30 days’ supply of fat reserves, which can lead to starvation. It’s beneficial for the bats that December through March the OMEP has no visitors.

If you’d like to know more about what happens after the sun goes down in natural New Mexico (and you don’t mind things that go squeak in the night) be sure to join us for our 2005 OMEP Bat Census.

This article originally appeared in the Autumn 2004 Santa Fe Botanical Garden Newsletter, POB 23343, Santa Fe 87502, (505) 428-1684,

Bill Baxter serves as a docent for Ortiz Mountains Educational Preserve (OMEP) located south of Sant Fe.

The power of dreams . . . is tied to the multiformity of animals: with their disappearance one may soon expect the dreams to dry up as well. - Elias Canetti

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