Managing Visitors to Prevent Disruption of Emergence of Bats

Public interest in viewing emergences of bats has increased in recent years, and possible disruption by visitors of emergence time of colonies has become a concern for wildlife biologists. Consequently, the objectives of this study were to assess the influence of visitors on time of emergence and flight behavior of a colony of Mexican free-tailed bats (Tadarida brasiliensis mexicana). In summer 1992, we studied dynamics of the bat colony at the Old Tunnel Wildlife Management Area near Fredericksburg, Kendall County, Texas. Data were not recorded until the start of a continuous flight of bats emerged from the tunnel. We compared times of emergence of the colony with sunset and flight behavior relative to the presence or absence of visitors. A regression comparing the number of visitors and time of emergence with sunset indicated a 3% variation in time of emergence was attributed to number of visitors. On average, bats emerged 5.3 minutes after sunset on nights with visitors in the viewing area compared with 6.3 minutes after sunset on nights with no visitors. However, in late summer as the population of bats increased, flight behavior of the emerging colony was affected by the presence of visitors, causing congestion and reduced flight space. For the wildlife manager, the potential disturbance of the colony of bats by visitors must be weighed against the positive benefit of public education about these ecologically beneficial mammals.

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