Hair, Fur, Bristles, and Spines

Trinomys

Hair is one of the key defining features of mammals. Apart from cetaceans, such as dolphins, no mammals are entirely hairless, although, for example, hippos and some babirusa species come very close. The original purpose of hair was almost certainly to maintain body heat, something that matters to warm-blooded animals in a way that it doesn't to, say, reptiles. Since then, however, hair has adapted to fulfil many other functions as well.

To begin with, there is colouration, a function that hair needs to take over once it obscures the skin. The most obvious way that hair colour can help an animal is camouflage. While this is instinctively true, there have been statistical studies that demonstrate certain hair colours are, indeed, more common in animals living in certain environments. For instance, multi-species analyses of lagomorphs and cloven-footed mammals have shown that animals with grey fur are more likely to live in rocky environments. The same studies, as well as similar ones on carnivores, show that pale fur is associated with open environments, especially deserts, while dark fur is most common in those animals living in jungles, dense forests, or heavily vegetated swamps. And, surely to the surprise of almost nobody, white fur is associated with the Arctic, or with the winter coats of those living where it snows.

Skunks of the World: Spotted Skunks

Eastern spotted skunk

At least outside of the Americas, the most familiar species of skunk is the striped sort and, as I mentioned last time, even scientifically speaking, this is the animal that defines the skunk family. It's perhaps surprising then, to note that, despite it also being very widespread and highly visible, it wasn't the first species of skunk to be named.

That honour goes to the spotted skunk, which appeared in the earliest recognised list of scientific animal names in 1758. This isn't to say that nobody knew at the time what a striped skunk was, merely that the naturalists of the day had yet to identify them as something distinct from the spotted sort, and it was the latter that happened to be described first - the striped skunk followed less than twenty years later, in 1776. Before they were given their own genus, both species were originally placed in Viverra, which comes from the Latin word for "ferret" but seems to have been used for any small, slender mammalian carnivore that didn't fit elsewhere (not including, ironically, the ferrets). 

Out of the Caves

At least if you live in the northern, temperate, parts of the world, when you think of where to find bats, your first thought is likely to be "caves". A great number of bat species do, indeed, spend the day in caves, and this makes sense: if you're a nocturnal animal that doesn't need light to 'see', then caves are both reasonably safe places and ones with a constant, sheltered environment. Why bother trying to sleep in the wind and the rain, or even the bright sunshine, when you don't have to?

But, of course, by no means all bats are cave-dwellers. Amongst the various families of bat, the leaf-nosed bats (Phyllostomidae) of the American tropics are the most varied in terms of diet, and also in terms of their roosting habits and other behaviour. Sure, the majority of phyllostomid species do eat insects and live in caves, as most other bats do. But the group also includes some bats that feed on surprisingly large prey (such as birds) as well as the blood-drinking vampire bats.

It also includes a large number of species that are vegetarian, feeding on fruit such as figs, or subsisting almost entirely on the sugar-rich nectar that they drink from year-round tropical flowers. Many of these fruit-eating species do not live in caves at all, but simply roost in trees - as do the much larger fruit bats of the Old World

Bats Can Be Colourful, Too

Spotted bat, Euderma maculata

It's stating the obvious to say that mammals have a range of different colours and coat patterns. The purpose of all these different markings can be varied: they may help to identify members of particular species to their kin, they may be used for sexual attraction, they can act as camouflage, and so on. Nor is there any particular reason to suppose that a given pattern has to serve only a single function. There are a great many colourful mammals, but bats are generally not among them.

The bats are the second largest order of mammals, after the rodents, including a total of nineteen different families - most of them with really obscure names - and well over a thousand different species. Yet, despite this great diversity, most bats are pretty much the same colour all over - usually a variation on the theme of "it's brown". But not all of them; many bats are surprisingly colourful, and you might wonder what the point of that is if they only come out at night, and spend the rest of the day sleeping in pitch black caves. The question really is not so much why are most bats so bland, but why aren't they all that way?

Except, of course, that not all bats do live in caves, and that may well have something to do with it. For the second largest order of mammals, bats have not been as well studied as most other groups. Most of the studies that have been conducted have tended to focus on the undeniably cool fact that bats navigate using sonar. Yet they are a very interesting, and one might even say peculiar, group of mammals. It may be, for example, that just looking at the colours of bats can tell us something about the reasons for coat patterns in mammals in general. A recently published survey by Sharlene Santana of UCLA, and colleagues, examined published descriptions of over nine hundred species of bat, cross-checking the patterns of their fur with their lifestyle. Was there... well, a pattern to the patterns?