Home range expansion in response to temperature by evening bats (Nycticeius humeralis) in an urban environment

Abstract

Background: Despite the negative connotation of urban sprawl for bat populations, fragmented green spaces such as parks, cemeteries, and golf courses have the potential to provide necessary resources for bats. For example, water resources in these areas can include natural or semi-natural lakes, ponds, streams, and drainage ditches. Such water resources, however, are frequently ephemeral when subject to prolonged periods of high temperatures. We, therefore, hypothesize that bats will expand or shift their home ranges from these urban green spaces into the surrounding neighborhoods to access alternative resources, such as residential swimming pools. Methods: To explore whether bats expand their ranges from urban green spaces, we conducted a telemetry study in which we radio-tracked resident evening bats (Nycticeius humeralis) in a local park system during their summer activity period from 2017-2019 in Fort Worth, Texas, USA. From radio-tracking surveys, we measured home range size using a k-LoCoH method and the percentage of these home ranges that fell within the park system. We compared these variables using linear and non-linear regressions with temperature. Results: We successfully tracked a total of 30 bats over the 3-year period and found a positive correlation between home range size and temperature. Furthermore, we observed that home ranges increased 6 times in size when temperatures exceeded 30ºC. Conclusions: Our study indicates the importance of urban neighborhoods surrounding green spaces in providing alternative resources, such as water, for bats. If managed appropriately, these urban areas have the potential to act as urban oases for bat populations, which in turn can contribute to their conservation.