Last night I took myself for another walk. I got onto the Little Sugar Creek greenway path in Freedom Park right as night was overtaking dusk. The light was rapidly disappearing in the trees, but looking up, I could still see the darkening sky. Standing out against that sky were a number of silhouettes zig-zagging all over the place. Yes indeedy! Bats!! Quite a lot of them, in fact.
I’ve seen bats all over the area before, but I haven’t seen them forage in crowds before. The coolest part was that there was clearly more than one species in the same area. Some of the bats were quite small (and I’m leaning towards them being the Eastern Pipistrelle, though bat ID’s in the dark are not the easiest things to do). Some of the bats were more than twice as large and I think it was the Red Bat (based on its size and its reputation for being so common). Now I could be wrong on the ID’s, but I can say quite confidently that in a small patch of sky there were 5 bats of two different species. If you think about how bats forage for insects, a quick problem could pop up in your mind. Bats use echolocation. They scream at very high pitches (frequencies) and their screams are loud!!
So imagine yourself trying to have a conversation with a friend while a large dog is barking right next to you. The sounds get in the way of each other and you have a hard time getting your message across. Well bats seem to be able to avoid that kind of situation.
The authors in this paper studied tropical bats in areas where there might be 10-12 species foraging in the same area. What they found that’s so cool is that the bats use different frequencies of sound. As a result they avoid overlapping with similar species foraging in the same area. This situation represents something that we call acoustic habitat partitioning. Each species has sort of claimed its own little part of the acoustic space which results in all those species being able to forage in the same place without interrupting each other’s echolocation signals. After watching both species of bat zoom around each other while going for all those moths and mosquitos, I’m even more impressed with all their ability to find some food in the middle of all that noise.