Sunday, 26 April 2015

The Seals That Swam in Tuscany

Hawaiian monk seals
There are two species of monk seal alive in the world today. One (Monachus monachus) lives in the Mediterranean and adjacent parts of the eastern Atlantic, while the other (M. schauinslandi) lives in Hawaii. You probably don't need to be a world-class expert in geography to at least have some idea that these two places aren't exactly what you'd call close to one another.

Now, monk seals don't have have the same sort of problems when it comes to dispersal as lemurs and the like do. Given time, they can just swim across vast stretches of ocean, feeding on fish as they do so. The apparent puzzle of their wide separation is also reduced by the fact that there used to be a third species, living in the Caribbean, which sadly went extinct in the late 20th century. The Caribbean is about half way between the other two locations, and that helps rather more than you might think at first glance.

Sunday, 19 April 2015

How the Lemurs Reached Madagascar

Pygmy mouse lemur
Madagascar is an island. It's quite a large island, to be sure - at nearly 227,000 square miles, it's the fourth largest island in the world, after Greenland, New Guinea, and Borneo. That's nearly twice the size of the UK, or, if you prefer, almost 90% the size of Texas. Even at that size, however, the fact that it's an island has been highly significant for the sorts of animals that live there.

When it comes to islands, the problem for land-dwelling mammals is how they're supposed to get there in the first place. Sure, it's not a problem for bats, which can cross all but the most ridiculous amounts of sea (although not necessarily on purpose!) But, for everything else, it's something of an issue.

Of course, one possibility is that the ancestors of whatever animals we're talking about "were there already". Britain, for example, has been an island since around 6,000 BC, so whatever animals could wander there from the continent before that were already part of the native fauna. True, many of them have been killed off since, which is why we no longer have wild wolves or bears in the UK... but they were there once. And it clearly explains why the various small mammals found on Britain, from red squirrels to harvest mice, badgers, and hedgehogs, are also native to continental Europe. We haven't been an island for that long.

Sunday, 12 April 2015

A Time to Breed and a Time to Die

Grey slender opossum
Looking after the children can be a stressful and exhausting activity. Other issues aside, offspring need feeding and looking after, which can put a drain on the mother's own energy reserves, never mind the need to feed the extra mouths in the first place. For mammals, one particular energetic stress is the need to provide milk, and this seems to be particularly true for marsupials, who carry their young around, permanently clamped onto teats inside their pouches, for the earliest part of their life.

Given these extra energy requirements, it's unsurprising that most mammals time their births for times when the greatest amount of food is likely to be available in their environment. Certainly there are species that breed pretty much year round, at least in the absence of unexpected drought or the like, but most have at least some kind of 'breeding season', arranged so that the young are born at the best time of the year - often the spring, in temperate climes, but more likely the rainy season near the tropics, where there isn't a winter to avoid. In the case of marsupials, the breeding season and the birthing season are pretty much the same thing, since pregnancy is an extremely brief affair, and it's the time spent in the pouch that's really crucial.

Sunday, 5 April 2015

The Dog Family: African and Asian Wild Dogs

African wild dog
So far, my survey of the dog family has looked at the "wolf-like" dogs, rather than the foxes and their kin. Most of these are either wolves, coyotes, or jackals, but there are two species that stand slightly apart, although modern genetic analysis has shown that they are, indeed, more closely related to wolves than they are to foxes.

The more distinctive, and probably the better known, of the two species (Lycaon pictus) has a wide number of different names. I'm going to call it the African wild dog here, but it is also known as the "African hunting dog", the "painted dog", or by some combination of these terms. (In French, Spanish, and Italian, it's simply the "lycaon", or some spelling variant thereof. The word commemorates a character from Greek mythology, who Zeus turns into a wolf).

Whatever it's called, the African wild dog is a distinctive animal. The large rounded ears and the slender, athletic body are noticeable enough in themselves, but it's the coat pattern that really makes it hard to mistake for anything else. The exact pattern varies tremendously - every animal is unique, and they can readily be distinguished one from another. Once found throughout almost the whole of sub-Saharan Africa, animals from the north tend to be dark with white and yellow patches, while those from further south are generally pale, with a few black patches. It was once thought that these might represent different subspecies, but they seem to blend into one another gradually as you cross the continent, which would rule that out. African wild dogs are adapted for running, and shedding the heat that results from doing so. They also, for less clear reasons, have no dewclaws on their front feet, as all other dogs do.