Squirrel Chatter

On my recent trip through the Great Basin, I spent a night in a lovely place called Bowers Flat, near the resort town of Duck Creek, Utah.  This grassy meadow surrounded by Ponderosa Pines should actually have been called squirrel meadow, as within a few minutes of arriving, I heard the calls of yellow-bellied marmots, chipmunks, red squirrels and golden-mantled ground squirrels.  As I started to set up camp, I detected the smell of smoke, and looking around, spotted a large plume of smoke rising to the west, with the wind bringing the smoke in my direction.  It wasn’t a lot of smoke, but as dry as the forest was, with a stiff breeze blowing the smoke in my direction, it was enough to make me nervous.  I slept in my clothes that night, ready for a quick evacuation if necessary.

But the breeze calmed down, and by morning it appeared the fire was under control and I couldn’t detect any more smoke.  I woke to the sound of red squirrel territorial calls and started pondering squirrel calls in general.

I like squirrels.  They’re diurnal, quite active and sometimes very vocal.  They also vary not only in size (chipmunk to marmot) but in social living arrangement.  Some, like the red squirrels, are pretty anti-social and maintain strict territories.  At the opposite end of the spectrum are prairie dogs, who live in large colonies that may number in the thousands.  Squirrels can be divided into two main types, tree squirrels and ground squirrels, although some, like chipmunks and rock squirrels, seem to have trouble deciding which group they belong to.  In general, ground squirrels tend to be more social than tree squirrels, and they have been the subject of numerous studies of their alarm calling behavior.  Some studies have found that the complexity of their calls vary with how social they are.

Squirrels usually send out alarms at the sight of a predator, most often a terrestrial predator (coyote, fox, badger) or avian predator (hawk, eagle, raven).  The responses to each type of predator may differ depending on the type of approach (ground or in the air) and it’s speed, and studies have found that ground squirrels transmit this information in their alarm calls.  In other words “coyote approaching slowly” results in nearby squirrels becoming alert and looking for the predator.  “Hawk here right now” means dive into your burrow as quickly as possible.  Some squirrels, like marmots, simplify the message to “danger now” or “be alert”, by adjusting the repetition rates of their calls, while others, like prairie dogs, transmit very detailed messages that distinguish type and size of individual predators.  One study on Gunnison’s prairie dogs found that they not only identified individual people, but distinguished them based on the colors of the shirts they wore.  Spatial information is also conveyed, as the squirrels closest to the danger are usually the ones calling (for example, Sounds of the Pacific Crest Trail).

Here’s an example of the alarm calls of 3 kinds of social ground squirrels: the rock squirrel, a large southwestern squirrel that occasionally forms colonies; the yellow-bellied marmot, a large colonial squirrel; and the Gunnison’s prairie dog, also colonial (all calls in response to my dog and me).

Tree squirrels tend to be less social than ground squirrels, and perhaps for that reason, their alarm calls have been little studied.  But squirrels often live within ear-shot of each other, and the nearest neighbors are usually related.  A recent study on eastern grey squirrels found that they give different calls for aerial and terrestrial predators, and, like ground squirrels, respond appropriately to the calls of other grey squirrels.  If a grey squirrel is out foraging on the ground, and a nearby squirrel issues a “hawk” warning, the squirrel often presses itself to the ground and freezes; however, if the warning is for a house cat, the squirrel runs for the nearest tree and climbs to safety.

Squirrels also flick their tails when alarmed; this visual signal appears to enhance the message in the alarm calls, although tail-flicking has been less studied than alarm calls.

Here’s an example of alarm calls of some less-social squirrels: a golden-mantled squirrel (see top photo and below), which is a ground squirrel but not a very social one; a tassel-eared squirrel, usually solitary but they will share dens in the winter; and a red squirrel, which is very territorial.  Note how much they differ from the social squirrels (all calls in response to my dog and me).

Why squirrels bother to send out alarms was one of the initial questions asked when researchers started studying ground squirrels.  Although the calling squirrel appears to put itself at risk by calling, it turns out that squirrels are pretty careful about when they call.  And the intended recipients are often related to the caller, so the caller may be increasing it’s genetic fitness by letting nearby squirrels know there is danger in the area.

Alarm calls may also serve another purpose.  They alert the predator that it’s been detected.  Predators that know they have been detected often give up the chase (or stalk if they were trying to be sneaky).  If you’ve ever watched a tree squirrel in a tree scolding you, that’s likely what it was doing – letting you know that it’s on to you.  In the meanwhile, nearby squirrels get the message that one of their neighbors has spotted a predator, and they can adjust their behavior accordingly.

You can learn a lot from a squirrel, if you’re willing to listen.

Recording notes: Recorded with Zoom H4n, Sony PCM-M10 and Canon SX20 IS.  Recordings subject to amplifications and noise removal.

References:

Bradbury, J.W. and S.L. Vehrencamp. 2011. Principles of animal communication. 2nd ed. Sinauer Associates.

Digwood, S.M. and D. Rendall. 2009. Predator-associated vocalization in North American red squirrels: to whom are calls addressed and how do they function?  Ethology 115: 1190-1199.

McCrae, T.R. 2012. Predator-specificity of multimodal alarm signals in the eastern gray squirrel (Sciurus carolinenses). Ph.D. dissertation, University of Miami, Miami, FL.

Slobodchikoff, C.N. 2012. Chasing Dr. Doolittle: learning the language of animals. St. Martins Press.