Sunday, 17 August 2014
At Home with the Masked Palm Civets
But even when we look at the larger, more charismatic, species there are plenty of holes in our knowledge. This is most likely to be the case where an animal doesn't live in Europe, North America, or Australia, and isn't quite as high in the fame stakes as, say, chimpanzees, elephants, or tigers. Living somewhere it's inherently difficult to get to, like a tropical forest, is also a factor, as is living at sea if you're not valuable to whalers or the like.
Which leaves plenty of opportunity for modern zoologists to do the sort of thing that naturalists used to do in days gone by, and make some pretty basic studies of a particular animal's behaviour while still breaking new ground. Assuming of course, you can go to wherever the animal is and spend a long time there. Which, if it were that easy, would probably have already been done.
The masked palm civet (Paguma larvata) is one such animal. They're not entirely obscure, living in forests from southern China down to Indonesia, and having first been identified as a species back in 1827. They're something like 60 cm (2 feet) long, plus tail, and, in the grand scheme of things, they aren't particularly rare or endangered. Certainly we know a lot about what they look like, where they live, what they eat when they're in captivity, and so on. But actual studies of their wild behaviour, while hardly non-existent, are fairly limited, and typically only of a small number of individuals.
They are, as the name suggests, members of the civet family, or Viverridae, a group of mostly omnivorous and tree-dwelling animals found across the tropics of the Old World, and which are related to (among other things) mongooses. One reason we might be interested in them is because they aren't entirely irrelevant to humans, having been implicated in the spread of SARS, and possibly also of rabies.
So hardly the most obscure mammal ever, then - they are rather better studied than, say, ferret-badgers - but one that could certainly do with some more understanding. But how to do this? They are nocturnal animals, partly because they fear being eaten by tigers or leopards during the day, and partly because it's when the mice that they like to eat come out themselves. As one might imagine, a nocturnal animal that lives in dense forest isn't the easiest thing to just go out and watch.
The most recently published study, conducted over a four year period in the Houhe National Nature Reserve in Hubei, China, used radio tracking to follow the daily activities of the local masked palm civets. It's a humid subtropical region, with a climate not unlike that of the southeastern US, but, at over 1000 m (3,300 feet) elevation, typically somewhat cooler.
In order to do this sort of study, you firstly need to catch your palm civet. In this case, the researchers used trap cages concealed beneath bamboo or other foliage, and baited with tasty fruit or dead chickens (masked palm civets are omnivores, and seem about equally likely to eat either). Once the animal is trapped, it is sedated, measured, collared, and released. These sort of things have to be done under fairly strict rules of animal welfare - at least if you want them published in a reputable journal - but even so, it's a fair bet that it freaks the animal out. So, in practice, you have to wait for at least a further three days before following it, to make sure it's behaving normally again.
That 'following', of course, is where the radio collars come in. There are a number of different types of such things available, but, in this case, it involved wandering about in the forest using hand-held detectors and GPS location markers to figure out where the animals were, without being close enough to disturb them. This has the disadvantage that, while you might know where they are, you don't necessarily know what they're doing, but it's a fair assumption that, if the signal strength keeps changing on a short time-scale, the animal is actively moving about, rather than snoozing. (Plus, of course, they might get the collar off, as two of them did in this study - nature doesn't always like to cooperate).
One of the first things we can tell from this is when the animals are active. As expected, they were nocturnal, and it turns out that they're most active between 11 p.m. and 1 a.m., although they do sometimes wake up in the mid to late morning and travel about then, too.
Another thing we can estimate from this sort of study is the animal's home range - the area through which it wanders about on a daily basis looking for food, or, at the right time of year, members of the opposite sex. In this case, it varied quite dramatically, with individual palm civets living in areas that were anything from 65 to 450 hectares (0.25 to 1.7 square miles) in size, which may reflect local variations in the availability of food. There was some indication that males inhabited larger areas, presumably so that they were likely to meet a greater number of neighbouring females. On the other hand, considering that variation in areas was so large, this could just be a fluke, and it's not something that's been observed in other species of civet.
Aside from one female with young, all the civets did move around quite a lot within their home ranges, typically travelling from 3-6 km (2 to 3.5 miles) each day, albeit in anything but a straight line. The males travelled noticeably further, something that's quite common in mammals, and may be because they were looking for fertile females.
Of more interest, perhaps, is how much the ranges overlap. Many animals are territorial, driving away any rivals that encroach on 'their' turf. The exception is typically between the sexes, with male ranges overlapping those of the local females (especially likely if males travel further than females), but here, even members of the same sex seemed not to mind sharing their land. There can be a number of reasons why this might happen. Civets on the whole are pretty antisocial, preferring to stay on their own when they're not raising the kids, but it is possible that these animal are an exception.
However, it has to be said that it's also possible that the local food supply is sufficiently rich that the civets honestly don't care if somebody else is sharing it. Or, more likely, it shifts about as the seasons change, and they have to be flexible about where they travel, making it hard to defend a single, fixed, territory against all comers. At any rate, why ever it is that they meet up, or come close to another, they apparently do so quite often, and that could be relevant to the whole "spreading SARS" thing. Which is why this is useful information.
One other question they wanted to answer was whether or not masked palm civets hibernate, or at least enter some sort of hibernation-like torpor, during the winter months This had been proposed in some Chinese-language journals in the 1990s, and, since temperatures drop to around zero in the winter in this region, it's not unreasonable - although it might be less likely for the populations in places like Borneo.
But, it turns out that, at least in this part of the world, they don't do anything of the sort. Conceivably, they do so further north, or along the southern foothills of the Himalayas, where they also live, but the evidence may be thinner than we thought.
[Photo by Denise Chan, from Wikimedia Commons]