Distinguishing your own species from other species is useful: for one thing, it prevents a lot of potentially embarrassing mating attempts.
“Um. You mean we don’t belong to, er... that is to say... you’re not my species? I am so sorry...”
But how fine a distinction can a species draw? Does it stop at, “You’re not my species,” or can it extend to, “You’re species B, not C or D”? And would species be able to distinguish other species outside of reproduction?
Schuchmann and Siemers tackled these questions by studying the echolocation calls of several related bat species that live in Europe.
Bats use echolocation for, well, location. They are not used in situations where animals are interacting with each other: they are used purely for the bat to get from point A to B without running into trees, and to find food. Even so, the sound that each bat species makes tend to be a little different in pitch. Might one bat species go, “That call is a bit to high to be Rhinolophus euryale, might be Rhinolophus ferrumequinum.”
These, I thought, were very interesting questions. But it wasn’t clear to me how they were going to test it.
The experimental set-up they use reminded me of one that is often used to test the cognitive abilities of babies. Bats, like babies, are easily bored. If you keep presenting the same thing over and over, they stop looking at it. When they detect a change, they react and look towards the new and much more interesting stimulus.
They recorded the echolocation calls of four bat species, and played them back to two (one of them, Rhinolophus euryale, pictured). They kept playing the same call from their own species over and over until the bat stopped responding, then swapped it for a new call.
Bats were very good at detecting when the call switched from their own species to a different species. That isn’t surprising, as it just tells you they can recognize their own species’ calls.
More to the point, when they first habituated the bat to a species different than themselves, and switched the call to yet a third species... the bats were still very good at detecting that difference. So the bats are not reacting with, “Meh. All those other species’ calls all sound alike. Not my species, have a nice day.”
It’s not clear what components of the call the bats are recognizing, although pitch is probably the major one. You could probably do some fun experiments seeing how much you could vary the calls and still have the bats responding. The authors also wonder if these different species might be able to benefit by eavesdropping on other species’s calls. If so, there might be some species that are more worth listening to at some times than others.
P.S. – Dart to the authors for using so many two letter abbreviations for species (Re) instead of writing out species names properly (Rhinolophus euryale)!
Schuchmann M & Siemers B. 2010. Behavioral evidence for community‐wide species discrimination from echolocation calls in bats The American Naturalist 176(1): 72-82. DOI: 10.1086/652993
Photo by by jasja dekker on Flickr. Used under a Creative Commons license.