The largest number of bats appears to be the Mexican Free-Tailed Bat (Tadarida brasiliensis)…family: Molossidae.
Montana Mine underground shaft is one of the most species diverse roosts in southern Arizona.
~Brian Corbett, BCI
These medium-sized bats have a wingspan about 12 inches and weigh 10-12 grams. They have short grayish fur with long and slender wings, round ears and wrinkled upper lips. These bats are migratory, spending summers in N. Mexico and the US and wintering in Mexico and very south US. They breed in late February and early March. One or two young/female are born in mid-June to early July. Young develop rapidly and begin flying in 4-5 weeks. When emerging at sunset they are predated upon by raptors, owl and snakes. (they sometimes fall to the ground at Ruby).
The Mexican free-tail bats emerge from a roost around sunset to forage and drink. They are fast and efficient fliers and usually hunt within a 50 mi. radius, but could forage up to 150 miles. These feed primarily on moths but numerous other insects as well. Nursing females require large quantities of insects that are high in fat, such as egg-laden moths. The Mexican free-tail bats are adept aerial hunters who eat their prey in flight and often forage in groups.
Mexican free-tail bats roost in tight clusters in caves, mines, tunnels, crevices in bridges, buildings, attics and hollow trees. Many roosts are used in spring and fall during migration. At Ruby we have the bats mainly April until late August. Their arrival and departure varies with drought and insect availability seemingly. Ruby probably has a maternal colony. Most of the very large maternity colonies are in Texas and Mexico although the Ruby colony has been estimated by biologists at 70,000 to 200,000. It fluctuates year to year.
Threats to Mexican free-tailed bats include pesticides and destruction or disturbance to roost sites. Suitable sites for large maternity colonies are extremely limited.
Bats found in the underground shafts of Montana Mine:
- Tadarida brasiliensis – Mexican free-tailed bat
- Eptesicus fuscus – Big brown bat
- Corynorhinus townsendii – Townsend’s bit-eared bat
- Choeronycteris Mexicana – Mexican long-tongue bat
- Myotis thysanodes – Fringed myotis
- Myotis velifer – Cave myotis
- Myotis californicus – California myotis
- Myotis ciliolabrum – Small-footed myotis