I went out for a run yesterday afternoon. The combination of the cool weather and the late afternoon sun made it a really pleasant day to be outside and gave me the chance to see a lot more activity than I get if I run before sunrise. As I came around one corner, I heard the tell-tale sign of a Gray Squirrel. It was angrily making its whining alarm call. I caught a glimpse of it in the tree doing the tail shake that goes along with this call- part of a multi-modal alarm call. Was I such a threat? I wasn’t even moving towards the squirrel, since it was off to the side in a tree. But then, I saw what was making the squirrel so agitated. Nearby was someone’s cat, sitting low to the ground and just biding its time.
Now, I have to say that I do like cats. I’m more of a dog person, but cats can be quite lovely. In the wild, though (and anywhere outside of your house is ‘wild’) cats can be problematic. I’m not even going to go into detail about that idea right now, but there’s a great deal of data on the cat effect. Check out this article and glance through their citations, too. Cats have effects on wildlife. End of story.
So this squirrel was up in the tree whining about the presence of the cat. What’s the point of this kind of alarm call? Well, in general, there can be multiple functions for an alarm call like the squirrels. Certainly it could be warning other squirrels in the area (relatives or mates) that there’s a predator around. Additionally, and probably more relevantly for this squirrel, it’s a warning to the predator that it has been seen.
Cats generally hunt by stealth. Well, if your prey sees you, it is suddenly much harder to be a successful predator. On top of that, if your prey item announces to the whole neighborhood that you’re around, the challenges become even bigger! So the squirrel’s alarm calling behaviors may actually help to prevent the cat from making a successful kill of any of the other squirrels around the area. But why does the squirrel use both the sound and the tail wag? One benefit of using a sound is that it carries well. Individuals all over can hear it. The broadband (containing many frequencies) alarm call of the squirrel is relatively easy to localize.
Since it is easy to localize, then not only do other squirrels know that there’s a predator around, but they also know where it is. An interesting addition to this call is, apparently, more common in urban squirrels and that is the tail wag. A squirrel who is alarm calling will most often also be waving/flicking its tail around. That additional visual signal is another way to provide the same warning. One group of researchers thinks that the flagging is more common in urban birds because there’s a lot more urban noise that can get in the way of sound transmission. Hearing and localizing an alarm call over the sounds of traffic can be tough. But if you hear just a bit of the warning and then look around and see a big, old tail wagging away in a nearby tree, then you have a second way to get information about that predatory cat.
Partan, S.R., A.G. Fulmer, M.A.M. Gounard and J.E. Redmond. 2010. Multimodal alarm behavior in urban and rural gray squirrels studied by means of observation and a mechanical robot. Current Zoology 56: 313-326.
The squirrels are effectively saying “hello” and waving a hand at the same time. This combined signal is directed at other squirrels and its directed at the cat. That darn cat. Hearing that call as I ran down the street also helps to explain what I saw the cat do as I was getting closer. It got up from its location in a yard and moved to crawl under a car on the side of the road. My guess is that the cat figured it was caught and might as well take the squirrel’s advice to leave it alone.