Differences in fur cortisol levels of three migratory bats

Understanding how organisms respond to their environments is challenging, especially due to the complex processes related to metabolism, energetics, and reproduction. Glucocorticoids (GCs) are metabolic hormones that provide insight into internal process and may trigger a variety of behaviors. To understand how changes to the environment influence wildlife, we must ideally measure levels of GCs in wildlife populations that are relatively undisturbed by anthropogenic change or natural disaster. In free-ranging mammals, cortisol is a primary GC hormone and can be measured in fur. Bats are the only mammalian order to have evolved true flight and, in North America, most species of bats are in the family Vespertilionidae. By measuring cortisol levels during energetically expensive periods of an animal's life history, we can document 'baseline levels' related to different life stages, sexes, and ages. We collected fur from hoary (Lasiurus cinereus), silver-haired (Lasionycteris noctivagans), and little-brown Myotis (Myotis lucifugus) bats from southern Alberta and Saskatchewan. Herein we report their baseline levels of fur cortisol, noting interspecific differences between species. We found that bats known to migrate longer distances had higher levels compared to bats that migrate shorter distances, and then hibernate. Interestingly, we found no differences in levels between the reproductive stages for any species. Finally, both silver-haired and hoary bats show a strong difference in fur cortisol levels between adults and juveniles. We suggest that the elevated levels are likely associated with events for mothers during lactation which are then incorporated into the pups' fur while nursing.