Oh my, what praytell shall I post this evening? It’s been a long, busy day, so whatever I do can’t take too much effort. Let me see what I have sitting here on my desktop (computer desktop, that is). Hmmmm … how about a recording of … a couple of Eastern Chipmunks giving “aerial predator alarm calls” in response to a Broad-winged Hawk perched in a nearby tree, the hawk giving its penetrating alarm whistle because it could see me sitting there with my headphones on, a few hundred feet away? (FYI, I had set my microphone close to the hawk’s nest just to get his alarm screams; the two chipmunks that started calling off to one side were a complete surprise.)
Will this be exciting enough for everyone, or have I pampered you so much that it won’t impress at all? Well, whatever, here it is:
Eastern Chipmunks giving aerial predator alarm calls in the presence of a Broad-winged Hawk that is also calling. 9am, 27 June 1995, in hardwood forest near Ithaca, New York. Recording © Lang Elliott.
This is quite an instructive recording. The “clucking” of the Eastern Chipmunk is, in fact, given in the presence of aerial predators such as hawks or day-hunting owls. Guess who discovered this? Yep, ME, yours truly. Way back in the mid-1970s, for my masters degree in Animal Behavior and Ecology at the University of Maryland, I studied the social behavior of a population of chipmunks in the Adirondack Mountains of upstate New York. I made lots of interesting discoveries and described many aspects of their social life that nobody else had witnessed, but figuring out that the hollow cluck-calls are given in the presence of aerial predators was perhaps my most important contribution to their natural history.
At first I had no idea what it was about. I’d hear one chipmunk start clucking, then another, then another, as a “clucking bout” seemed to spread through the forest along a path. It wasn’t until autumn and spring, when the leaves were no longer on the trees, that I was able to put it all together. Seventeen times altogether I was lucky enough to see hawks fly by—mostly Broad-winged Hawks, but also Cooper’s Hawks and even a Goshawk—and in every instance clucking gradually erupted along the flight path of the hawk. When chipmunks gave these calls they became alert, and often sat still on a log, rock, or stump. As you might suspect, an alert chipmunk does not make good prey. If a hawk were to swoop at one, the perched chippie would see it coming and dash to safety.
Why do chipmunks give these calls when they see an aerial predator? Well, I’m not totally sure, but it might have something to do with altruism and genetics, with the “relatedness” of neighbors in the forest habitat. Biologists theorize that if neighbors are related, then it’s a good idea to alert your neighbor of danger, as long as it’s not too dangerous to do so. From an evolutionary perspective, this means that the calling chipmunk is helping pass on its genes, by helping neighbors that share genes . . . or something like that. In addition to the relatedness hypothesis, it is also possible that the sound simply tells the hawk that it has been spotted, that it won’t fare well here, and that it might as well move on down the road.
If you’re interested, you can download a hi-resolution PDF of my original study, provided online by Smithsonian Institution:
Elliott, Lang. 1978. Social Behavior and Foraging Ecology of the Eastern Chipmunk (Tamias striatus) in the Adirondack Mountains, Smithsonian Contributions to Zoology, Number 265, Smithsonian Institution Press, Washington, D.C.