Written by Craig Walker/Photo of hoary bat by Gary Kegel
Monitoring of the emergence of bats from buildings in the headquarters complex at MNWR in was conducted 14-16 June and 8-9 August 2025. Bats were counted as they emerged from buildings at dusk, as well as monitored acoustically.
Buildings monitored were Biology, Museum, Pelican, Visitor Center and Crane’s Nest. In June, some of the same points at some of the buildings were monitored more than once. In August each point was monitored on only one night. Some buildings were monitored at different points on the assumption that there would be different bats coming out of each point.
Call monitoring was also conducted on the nights of 1, 2, 3 and 6 August between 10:00 pm and midnight. The purpose of this monitoring was to compare calls recorded during the emergence at around dusk to calls recorded after the emergence was over and use these to identify species flying in the area around Headquarters to forage and possibly returning to the buildings to night roost or nurse pups.
Total bats counted in June ranged between 484-784. The low was arrived at by taking the lowest number of bats counted at a site monitored more than one night and adding it to the total count at sites monitored only once. The high was arrived at by taking the highest number counted at a site monitored more than once and adding it to the counts at sites monitored only once. Total bats counted in June ranged between 484-784. In August 595 bats were counted.
Calls of the following species were recorded and identified by specialized software: pallid bat, big brown bat, silver-haired bat, Mexican free-tailed bat, little brown bat, western small-footed bat, hoary bat, California bat, long-legged bat, Yuma bat, canyon bat and long-eared bat.
The three most frequently recorded calls in this study were California bat, followed by long-legged bat and western small-footed bat. In June the bat with the highest number of calls recorded was little brown bat, followed closely by California bat. In August, the bat with the highest number of calls recorded was California bat.
Post-emergence monitoring revealed no difference in the species assemblage from monitoring conducted during the emergence. The same species were detected during the emergence as well as after the emergence. However, only 2 species, California bat and little brown bat, were detected all 4 nights of the post-emergence monitoring. These 2 species, along with long-legged bat, had by far the most calls recorded post-emergence. This indicates that it is primarily these 3 species that stay around the headquarters complex and forage after the emergence is over.
