Potential effects of livestock water-trough modifications on bats in Northern Arizona

In the southwestern United States, livestock water troughs may be the only water source available to bats during dry seasons or periods of drought. We found that 38% of the 90 livestock water troughs we surveyed in northern Arizona, USA, were modified with either fencing to separate pastures or braces to strengthen the structures. We tested if these modifications could affect bat drinking behavior or increase injury risk by simultaneously videotaping modified and unmodified troughs in a series of crossover experiments performed between 1 March and 26 August 2004. The bats that we observed did not avoid modified troughs but required 3-6 times the number of passes to approach the water surface at both troughs with fences and those with support braces. The number of passes required to drink increased with reduced water surface area, suggesting that modifications of smaller troughs may have a greater effect. Small (e.g., Myotis spp.) and large (e.g., pallid bat (Antrozous pallidus)) bats responded similarly in the experiments. These effects may be energetically expensive for bats, especially during periods of high energy demands, such as pregnancy and lactation. Although we did not document any injuries or mortalities, 16 bats contacted wires at modified troughs with smaller surface area. This suggests that modifications of smaller troughs may pose higher risks of injury. To reduce these risks, we recommend removing modifications on water troughs whenever feasible.