Over half the world’s population currently lives in cities, and this figure is expected to continue to increase in the future. In this context, the idea of “pristine” nature is no longer very useful for ecologists. In fact, interactions between urban humans and the nature around them may represent our best hope for outreach and education about the importance of biodiversity and conservation.
I’m interested in understanding the dynamics of the ecosystems evolving to co-exist with this urban world. What plants and animal communities share this space, and how are they using it? How can we use that understanding to preserve and protect urban nature? The LeBuhn lab at San Francisco State University explores these questions in the context of bumble bee, other bee, and ant use of natural areas in the city. My master’s thesis was a similar study of urban bats using acoustic monitoring. You can download a copy of my thesis or view a blog I maintained during my research.
I found that bats were present in every San Francisco natural area sampled, and that they were active in the city year-round. As found in other urban bats studies, one species was dominant; the vast majority (84%) of calls recorded were of Brazilian free-tailed bats (Tadarida brasiliensis, the same bats I’m studying for my dissertation). What was unusual was that the species most commonly found in other urban bat studies in North America, Big Brown bats (Eptesicus fuscus) was not detected in this study. I found at least three other species: Yuma myotis (Myotis yumanensis,) Western red bats (Lasiurus blossevillii), and Little Brown bats, Myotis lucifugus.
The factor that best explained patterns of bat activity detected in parks was the amount of “forest edge”, or area next to groups of trees. The Yuma myotis bat is known to prefer habitats near water, and my data showed that those bats were most likely to be found in parks with the lowest distance to water, and the highest percentage of native habitat. I found evidence of all four species foraging in only two of my 22 parks, Pine Lake and the Twin Peaks reservoir. Pine Lake is a small lake in a medium-sized park that has high amounts of recreational use. Interestingly, this park was noted in earlier studies for having lower ant species diversity than other parks, a contrasting response to bat diversity.