Sunday, 6 August 2017

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?

One of the most basic behavioural parameters we can assign to an animal is what time of day it does its sleeping, and what time it does... whatever else it does. In the grand scheme of things, not least because most of them are either rodents or bats, the typical pattern for mammal species is that they sleep during the day, and are active at night - that is, they are nocturnal. Hamsters are no exception to this rule, and, left to their own devices they are either nocturnal or crepuscular, which is to say, active mostly at dawn and dusk, and sleeping at both the brightest and darkest times of the day.

This, you might think, is hardly the sort of thing that's going to be controversial. Most sources agree that it is broadly true of all the various hamster species, and it's hardly difficult to check. You can easily set up motion sensors to find when your laboratory hamster uses its running wheel, but you can even give hamsters their own artificial burrows to live in, and use the motion sensors to see when they come out. When you do so, the pattern doesn't change; they're nocturnal animals.


It's really only in the last ten years or so that scientists have begun to question just how true this really is. The studies in the artificial burrows ought to be pretty good evidence, since burrows are, after all, how hamsters live in the wild. But what if there is a difference in the really wild environment? For the reasons noted above, studying golden hamsters in the wild is really not the sort of thing you want to be doing right now. There are more important questions for the people of Aleppo than when the local hamsters take a snooze.

Fortunately, the golden hamster is not the only species. Among the many kinds of wild hamster, three are especially close relatives of the golden species, and of the three, the most common is the ciscaucasian hamster (M. raddei). This lives north of the Caucasus Mountains at the southern edge of Russia, just between he Black and Caspian Seas, and, very occasionally, wanders across the border into northern Georgia or Azerbaijan. They are larger than golden hamsters, and have a black patch on the stomach, and they typically live at higher altitudes, but otherwise, the two species are very similar.

Both species are burrowing animals whose natural habitat is open grassland (although Syria is hotter and more arid than southern Russia), although in both cases, they are today, much more common in agricultural land, feeding on the abundant grain crops there. While this can make them a pest animal, and is likely not good news for the local farmers, it does at least mean that we don't need to move out far into the wilderness to find them.

Of course, if we want to determine whether these particular hamsters really do behave differently in the wild, we do need to check that, like golden hamsters, they behave nocturnally under laboratory conditions. So a recent study captured a number of wild hamsters from the fields near a village in Dagestan, and kept them for tend days where they could be monitored with infrared motion detectors. As expected, they proved to be about twice as active during the day, with the peak of their activity typically around 10:30 in the evening. So, just like golden hamsters, they appear to be nocturnal.

Then they took more wild hamsters, and fitted them transponders that would be able to tell when they entered and exited their burrows. If ciscaucasian hamsters are genuinely nocturnal, this should show a similar pattern to that seen in the laboratory. Instead, they behaved in a radically different way, almost always staying in their burrows for the entire night, between about nine in the evening and six in the morning, and with their pea activity outside the burrow being in the mid to late afternoon.

So it turns out that, under natural conditions, the hamsters are actually diurnal. It's true that they aren't necessarily sleeping through the night; we don't exactly what it is that they're doing (or not doing) in their burrows, merely that that's where they are. But they're certainly out and about looking for food during the daylight hours. This sort of thing had been predicted, based on earlier studies on both golden and common hamsters, and on some other burrowing rodents. too. But, aside from a timely lesson on the relevance of labroratory studies, it does raise the question of quite why it should be so.

Clearly, there is something missing in the laboratory that causes many species of rodent to behave entirely differently when kept there. Nocturnality is often thought to be a response to predators, with the animal coming out at times of the day when it can't be seen. Since there are no predators in the lab, the reverse would have to be true here, with the hamsters more concerned about avoiding, say, owls, pine martens, or foxes, than they are about avoiding the likes of day-hunting hawks. But this seems fairly unlikely.

More plausible theories have tended to focus on energetics. In the laboratory, rodents are given as much food and water as they desire, but in the wild, they have to go out and look for it. Even with running wheels, hamsters are likely to be less active when kept in cages then when they not only can run free, but are forced to, if they want to eat. Even in farmland, they may have to travel a distance to find suitable food, particularly since this part of the world is switching towards potato production instead of the grain that the hamsters prefer. And we do know that increased exercise can affect the body clock in hamsters, and that at least some individuals can switch their daily activity patterns based on whether or not they have a running wheel to use.

Temperature is another possibility, since this will not vary so much over the course of a day indoors than it will out. It might be, therefore, that freed from the need to shelter from the night time cold in the depths of their burrows, hamsters are more willing to be active during the hours of darkness than they would be under natural conditions.

The reality is that we don't yet know the answer. Any of the above explanations could be correct, and it's quite possible that multiple different reasons all play their part. But knowing that this holds as true for the ciscaucasian hamster as for the sorts better studied in laboratories may be helpful, as the former is easier to examine in the wild. We could, for example, see whether things change between summer and winter, or when natural extremes of temperature are particularly mild.

In the broader view, however, it shows us that even basic facts about well-studied animals can sometimes be far less clear-cut than we thought.

[Photo by Andreas Hein, from Wikimedia Commons.]

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