Urban wildlife ecology is biased in three main ways: (1) studies have largely been conducted in forested biomes and rarely in grasslands, (2) most studies have focused on birds, and few have examined mammals, and (3) the traditional, community-level approach has not illuminated the population and individual-level processes that are the mechanisms behind community effects.
I conducted the first study of the effects of urbanization on bat populations in the Prairies. My hypothesis was that in a relatively flat, homogeneous Prairie landscape, cities are structurally complex islands, with (1) increased availability of roost sites (human structures and trees), (2) greater availability of insect prey (due to the lack of grazing and agricultural pesticide use), and (3) warmer temperatures due to the urban heat island (thereby reducing thermoregulatory costs and speeding up gestation and postnatal growth).
Ultimately, these features should benefit bats. Specifically, I predicted that urban little brown bats (Myotis lucifugus) (1) are in better body condition, (2) have higher reproductive rates, and (3) are more likely to raise young-of-the-year to independence, than individuals in surrounding non-urban areas. I captured bats in mist nets on 157 nights from 2006-2008 in urban and non-urban riparian sites.
Results/Conclusions
In total, I captured 1615 individuals, and recorded each one’s mass, age and reproductive status. Results do not indicate that urbanization is beneficial to little brown bats. Compared to their non-urban counterparts, (1) urban individuals were not in better body condition, (2) urban populations did not contain proportionally more reproductive individuals, and (3) urban populations did not have higher weaning rates or contain proportionally more volant juveniles.
Overall, it appears that even in the Prairies, among the ecoregions in which the effects of urbanization could be most beneficial, the city of Calgary does not provide a habitat that is especially conducive to little brown bat reproduction and population growth. However, although the little brown bat dominates bat communities throughout my study area, the species is especially dominant in the city. Similarly, community-level research conducted in other biomes indicates that urban bat communities are often dominated by one or a few species. The question is why these bats are attracted to urban areas and whether cities are population sinks for even the most ubiquitous species. Given the longevity of bats, answering the second question will require long-term studies of urban bat population dynamics.
