Sunday 29 April 2018

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

Sunday 22 April 2018

The Pig Family: Threatened Pigs of the Philippines

Visayan warty pig (female)
When the animal we now know as the Sulawesi warty pig was first described, back in the 19th century, it was thought that it lived, not only on the island of Sulawesi, but also on a whole chain of islands to the north - the Philippines. But the pigs there didn't look exactly the same as those to the south, so in 1886, German zoologist Alfred Nehring proposed that they be regarded as a distinct subspecies.

And so things remained for a hundred years, until scientists began to look more closely at the animal's genetics. When they did so, they discovered something fairly surprising. Pigs typically have 38 chromosomes (compared with 48 in humans), but it turned out that the warty pigs from the Philippines had only 36 - an entire pair had disappeared, its genetic material shuffled around elsewhere in the genome.

Sunday 15 April 2018

The Curious Necks of Giant Rodents

We tend to think of rodents as small mammals, and the great majority of them are: mice, voles, hamsters, tree squirrels, and so on. Even rats and gophers aren't really all that big. Indeed, when most people think of rodents they probably aren't mentally including the largest ones, such as porcupines and beavers. In fact, the very largest rodent alive today is the capybara, a sort of giant guinea pig that is around 120 cm (4 feet) long and weighs something like 50 kg (110 lbs).

This, you probably won't be surprised to learn, is as nothing compared to some of the fossil species.

Sunday 8 April 2018

No Boys Allowed

Even in mammals that are otherwise social, it is quite common for males and females to live apart for most of the year. The most common pattern involves females living in groups with their children, until the latter approach adulthood, while males either live alone, or in much smaller bands, outside of the mating season. In many hoofed herd animals, however, the males live in herds that aren't much smaller than those of the females - in other words, both sexes live in herds, but the two don't mix until it's time to do the necessary.

Clearly, these are creatures that benefit from the group protection that living in herds provides, and, while there's obviously a limit on how large a herd can be before there isn't enough food to support them all, it's not always so clear why the herds should be single-sex. Why, in short, do so many hoofed herd animals practice sexual segregation?

There are a number of theories, and, as is often the case, they aren't mutually exclusive. Nor is it likely that the reason - or the balance of reasons, if there's more than one - will be the same for every species. It's something we have to examine on a case-by-case basis.

Sunday 1 April 2018

First of the Flightless Penguins

Penguins are unusual birds. They walk fully upright, have short legs that force them to waddle, and have wings adapted into flippers to propel them through the water. Compared with many other bird groups, there aren't all that many of them - there are no more than twenty living species, and possibly less, depending on who you talk to.

Surprisingly, perhaps, we have, however, named many more fossil species than living ones, and our understanding of penguin evolution is rather better than that of most families of flying bird - which tend to have light and fragile bones that don't fossilise well. Unfortunately, as is often the way, it's the earliest and most interesting part of that fossil history that's most obscure, since, being older, these are the fossils least likely to be preserved.

But that doesn't mean we have nothing from that time.