Community ecology of migratory bats in a northern sky island

Abstract

Animal migrations are often motivated by the opportunity to exploit seasonal abundances of resources, a phenomenon particularly pronounced for species migrating to higher latitudes where seasonality is more extreme. Bats are the only mammalian order to have evolved flight, and three North American migratory bats are the long-distance migrating hoary (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans), and the regionally migrating little-brown Myotis bats (Myotis lucifugus). I describe a highly seasonal community of migratory bats in a northern “sky island” within the Cypress Hills of southern Saskatchewan, Canada, focusing on abundance trends, foraging behavior, niche ecology, and ecophysiology. By collecting data spanning 20 years, my first chapter describes that while long-distance migrating bats are experiencing population declines, the Cypress Hills currently has locally increasing abundances of hoary and silver-haired bats, likely driven by increased roosting habitat. Further in my second chapter, I found that three species of bat separate their ecological niches, allowing for current co-existence, but that silver-haired bats may experience competition with either the hoary or little-brown myotis. My final chapter describes the inter- and intra-specific differences of fur cortisol, a regulatory hormone often associated with stress. Notably, silver-haired bats exhibit elevated fur cortisol levels, but only in juveniles, suggesting it was transferred through their mothers milk while pups grew fur. Thus, female silver-haired bats likely have interactions within their environment causing increased cortisol circulation. Collectively based on my results, I postulate that long-distance migratory bats are disproportionally attracted to the Cypress Hills, and the local population of silver-haired bats may be experiencing increased inter- and intra- competition, resulting in heightened cortisol levels. Although each of the three bat species are seasonally abundant within the Cypress Hills, they are all currently experiencing population declines across their ranges. The environmental conditions hoary, silver-haired, and little-brown myotis bats face consist of highly seasonal resources in a relatively small area of land, while also experiencing habitat loss and increased risk during their annual migrations. My work highlights the importance of both long-term studies and datasets, and lays the foundation to continue to study the summer ecology of at risk species.