Bed Time for Wild Hamsters

Golden hamster

After the mice, the second largest family of mammals is the hamster family, with somewhere in the region of 600 known species. The vast majority of these species are, however, not hamsters, and I refer to it as the "hamster family" only because that is the literal meaning of its scientific name, the Cricetidae. Over half of the cricetids, for instance, are "New World mice" visibly more or less indistinguishable from the "true" mice of the Old World. Most of the remainder are voles, and a mere couple of dozen or so are actually hamsters.

The species most people think of when they think of hamsters is the golden hamster (Mesocricetus auratus), which is the animal commonly seen in pet shops. While a few other species are sometimes also kept as pets, most of the varieties named on the basis of things such as hair colour and length are just domesticated breeds of the golden hamster. They are found in the wild only in one relatively small area on the Turkish-Syrian border, just north of Aleppo. Which, right at the moment, does make it somewhat difficult to study their behaviour in their natural environment.

But then, given that there are so many of them in captivity, and that they aren't exactly obscure animals, you might think that we know pretty much all there is to know about them. Certainly, compared with many other species, they are well-studied creatures. Indeed, they are common laboratory animals, due to the ease of breeding them in large numbers and their apparent comfort in indoor environments. On the other hand, while there are obvious advantages, such as not being eaten by predators, hamsters do not naturally live in cages... so maybe they behave differently when given the free run of the countryside?

Ultrasonic Hamsters

Animals can make a lot of different calls, for a lot of different purposes. There are alarm calls, aggressive warning growls, mating calls, the contact calls between a mother and her young, and so on. Not all of these sounds, however, are audible to us; some are at such a high ultrasonic pitch that we humans simply can't hear them.

The most obvious example is, perhaps, the sonar of bats, but bats are not the only mammals to make ultrasonic calls. We know, for example, of fifty species of rodent that use ultrasonics, and, since such studies are still largely in their infancy, and there are over 2,000 species of rodent to pick from, it's a fair bet that there are far, far more we don't know about yet. Obviously, though, the rodents aren't using these calls for sonar (at least, not that we can tell) so what's the point of it?

It's likely just that there's no particular reason why a rodent should want to make sounds that humans happen to be able to hear. So far as they're concerned, their ultrasonic calls aren't really any different from all of their others, and they're using them for much the same sorts of purpose. For the most part, they have been observed during courtship, suggesting that they're basically mating calls. That's probably not the only thing they're used for, and there's evidence that mice, for example, can encode information for quite complex social interactions in their calls, but it does seem to be a common one.