Sunday, 25 July 2021

A Good Winter's Sleep

Mammals have an advantage over reptiles in that they don't need the weather to be warm in order to stay active. This makes it easier for them to live in parts of the world that have cold winters, but even then, the scarcity of food at such times of the year means that they often need some additional survival strategy. Some, of course, simply migrate somewhere warmer during the winter - which typically means moving downhill from summer grounds on mountainsides, the long-distance migration of birds being less of an option. Others, such as polar bears, are just good at surviving cold weather anyway, and may not need to do anything significantly different in winter.

But, leaving those possibilities aside, three basic options for surviving the winter present themselves. They could do something behavioural, such as storing food during the summer and coming back to their hidden caches later in the year when food is short. Or they could change physically, such as by building up fat over the summer or having an extra-thick winter coat that falls out in the spring. (And these are not, of course, mutually exclusive).

Sunday, 18 July 2021

Coming Down the Mountain

One of the features of behaviour that I've mentioned a few times while covering deer species this year is that, typically, the males and females spend much of their lives apart, only meeting up during the rutting season. While, clearly, many group-living mammals don't do this, deer are hardly unique, with many other species (and not just mammalian ones) having a similar lifestyle. Females gather together in herds, or whatever the group name is for the animal in question, where they can gather together to protect and nurture their young. Males of such species often live in bachelor herds, which are typically smaller.

Sometimes this is due to a simple imbalance in numbers. In species where males monopolise multiple females, a typical herd, while predominantly composed of females, will also have a single dominant male, forcing any subordinate males to live elsewhere. But this is not the case in deer, because, while stags do indeed mate with as many does as they can get away with, they don't live with them outside the rut. Nor are they alone, since other herd animals, such as goats and antelope, often do the same.

Sunday, 11 July 2021

All the World's Deer: White-tailed and Mule Deer

White-tailed deer
When I started this series on deer species, I asked some non-experts how many different kinds of deer they were aware of, to see which ones were best known. I got roughly (but not entirely) what I expected, with red deer and fallow deer topping the list. But that's a reflection of where I live; I suspect that, had I been asking Americans, few could have failed to mention the white-tailed deer.

The white-tailed deer (Odocoileus virginianus) is the most widespread and common species of deer in the Americas, and well-known to anyone familiar with the American wilds. They live throughout the whole of the contiguous US, except for the arid south-west, across southern Canada and almost the whole of Mexico. They are also found right across Central America, and into Colombia and Venezuela beyond, reaching the Guyanas and far northern Brazil in the east and as far as Peru in the south.

Sunday, 4 July 2021

Miocene (Pt 27): Rise of the Apes

From a human perspective, one of the most significant evolutionary developments of the Miocene epoch was the appearance of the first apes. Exactly when the group first arose isn't entirely clear, but it's either very early in the Miocene or very late in the preceding, Oligocene epoch. Part of the reason for the lack of clarity is, as so often, dispute as to where exactly the dividing line is between apes and monkeys when we go this far back in time. But there also seems to be some evidence that the earliest apes evolved in African jungle habitats, which weren't the best for forming fossils.

An example of this early confusion comes from Dendropithecus, from the Early Miocene of Kenya. Comparatively small, at only around 60 cm (2 feet) in length, and with arms that seem to be adapted to swinging from trees, when it was first named as a distinct genus in 1977, it was thought to be an ancestor of modern gibbons. Despite having a somewhat similar lifestyle and diet, this no longer thought to be likely, and one recent analysis places it as belonging to a very early branch in the ape family tree - just early enough that one could legitimately argue as to whether it really counts as an 'ape' or just a very close relative.

Sunday, 27 June 2021

How Giant Rhinos Crossed Tibet

It sometimes appears that just about every sort of animal was larger in prehistoric times. That this cannot be a universal rule is shown by the fact that the largest animal ever to have lived is the blue whale, which is still around today (albeit as an endangered species). Still, it is true that many prehistoric animals were larger than those alive today, and dinosaur researchers do seem to be engaged in a constant battle to find the "biggest land animal ever" - although this is likely a reflection of what sort of palaeontology stories get into the regular news media.

The largest land animal ever to have lived was surely a dinosaur, most likely a member of the aptly named titanosaur group. But what about the largest land mammal? It's hard to know for sure, partly because "largest" is a vague term that could be interpreted in different ways - do we mean weight or linear dimensions? But it's also just difficult to know when all you have to go on is the skeleton, and that's probably incomplete. 

Sunday, 20 June 2021

Girl Power in the Monkey World

There are many advantages to an animal of living in a group, such as it being easier to watch out for predators or even drive them away. One of the downsides, however, is that you also have to compete with others of your own kind for access to resources. Clearly, constant infighting is not a good thing and would lead to a rapid breakup of the social group in question. One way that this can be reduced is through the practice of social dominance.

The first formal model of this concept in animal behaviour was described by Norwegian zoologist Thorleif Schjelderup-Ebbe in the 1920s. Having grown up on a farm, he had observed the behaviour of chickens, and, in his PhD dissertation in 1921, he described what is popularly known as the "pecking order". What happens is that, rather than fighting constantly, chickens establish a hierarchy where each animal knows where it stands. If two chickens face off against one another, the lower-ranking, or submissive, bird almost always backs down, allowing the higher-ranking, dominant bird to win without a proper fight. 

Sunday, 13 June 2021

All the World's Deer: Deer from the Ganges and Beyond

At least before the rise of intensive agriculture, India, with its lush vegetation, was prime habitat for deer. The constraints of geography - the Himalayas to the north and deserts to the west - keep it separate from Europe and central/northern Asia at least, but it's a very large place, able to support a number of local species. When it comes to deer, there are no less than seven species native to the country, although four of those are only found in the north. Across the great bulk of the country, two medium to large species are common: the sambar and the chital. But there used to be three.

That third one was the barasingha (Rucervus duvaucelii). Fortunately, while I say 'used to be', I don't mean that it's extinct, as its closest relative, Schomburgk's deer is. Just that it's no longer common and widespread. It's primarily a grazing species, feeding in long grasslands and on forest edges and there used to be many of these on the Indian subcontinent. As recently as the 19th century, barasingha were found across almost the whole of central and northern India (aside, of course, from the Rajasthan desert) as well as in neighbouring parts of Pakistan, Bangladesh, and Nepal. They were especially common along the great floodplains of the Ganges and Indus Rivers.