Differential Energetic Demands of Chiropteran Maternity Roosts as Determined by Diet
Authors:   , Marquardt Shauna 
Published: February 2023

The cave myotis (Myotis velifer), a predominately cavernicolous species, selects various types of sites for maternity roosts. In Kansas, some females remain in caves during the summer whereas others travel from cave hibernacula to maternity roosts in barns. The driving factors behind the distribution of the M. velifer in Kansas, including the selection of multiple types of roosts, are unknown. Ambient summer temperatures in barns usually are significantly warmer than those in caves. Because pregnant females must maintain an elevated body temperature at low ambient temperatures regardless of energetic cost, selection of roosts with high ambient temperatures, such as barns, likely helps facilitate energy conservation. I tested the hypothesis that the lower energetic costs associated with occupation of warm maternity roosts in barns, as opposed to cool maternity roosts in caves, are reflected in the diet of reproductive females. I predicted that bats in roosts with warmer temperatures will consume different prey than those in cooler roosts. In the summer of 2004 (25 May to 13 July), I studied maternity roosts of M. velifer in the Red Hills region of south-central Kansas, in Barber, Comanche, Kiowa, and Pratt counties. I located 2 caves and 2 barns occupied by reproductive M. velifer females. Weekly samples of guano were collected for qualitative food habits analysis. Roost temperatures were recorded hourly. Descriptive analysis of the food habits of M. velifer females roosting in eaves and barns suggested that the diet of bats in both types of roosts was similar. Four arthropod orders dominated the diet: Coleoptera, Diptera, Hemiptera, and Lepidoptera. Percentage volume and frequency of dietary components were similar for Bergner Barn. Whitney Barn, and Gentry Cave. Percentage volume and frequency of dietary components in Gates Cave showed the most variation, but this likely is because fewer guano samples were collected from this site and used in the description of the diet of bats roosting at this site. Different thermal environments impose varying energetic demands. For reproductive female bats, the demands of reproduction are compounded with those of thermo-regulation. Roost temperatures within the thermal neutral zone cause little additional energetic costs, whereas temperatures below the thermal neutral zone, such as those in caves, induce homeothermic bats to thermoregulate to maintain elevated body temperatures. Because not all females form maternity colonies in caves, barns might provide some sort of benefit relative to cave roosts. Originally, dispersal of females to locations outside of caves might have been driven by the bats following the ideal free distribution to reduce intraspecific competition for food. If fitness were lower in barns, one would expect bats to use more of the caves in the Red Hills, including those outside the foraging range of individuals that already inhabit cave roosts. However, the opposite appears to be true as females have abandoned historical maternity sites in the Red Hills and are continuing to move northward away from caves.