Master's Theses



Degree Name

Master of Science (MS)


The natural history of a colony of Brazilian free-tailed bats, Tadarida brasiliensis mexicana (Saussure), in an atypical, predominantly male roost in south-central Colorado was investigated in 1982 and 1983. The colony inhabits the Orient Mine which is located at the base of the Sangre de Cristo Mountains in the northern end of the San Luis Valley. The valley is in the Upper Sonoran Life Zone. Iron ore was removed from the mine (elevation, 2800 - 3000 m) between 1881 and 1932. Colonization by free-tailed bats almost certainly occurred no earlier than 1900 and most likely occurred after the mine closed in 1932. The colony roosts in a cavernous underground stope in which ambient temperature varies from 6⁰ to 12⁰ C when bats are present from mid-June through October. At peak numbers, the colony consists of about 100,000 bats. Outflights in both years lasted an average of nearly one hour. Bats emerged earlier relative to sunset in late summer and autumn than in early summer. Timing of outflights was not affected by percent cloud cover. Outflights were dispersed in June and became more concentrated, often with serpentine components, later in the year. Capture samples taken with mist nets indicated that composition of the colony was 98% adult males until mid August, when adult females and young-of-the-year became more common.


Jerry R. Choate

Date of Award

Summer 1984

Document Type

Thesis - campus only access


© 1984 Peggy L. Svoboda


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