All the World's Deer: The Red Deer Species Complex

Red deer

When the first list of scientific animal names was drawn up in 1758, all six known species of deer were placed in the genus Cervus - which is, of course, simply the Latin word for "deer". Over the following decades, as taxonomy became more refined, all but one of those species were moved to other genera, and when the deer family, Cervidae, was named in 1810, it had roughly the same meaning that the genus had had so many years before. As its name implies, though, Cervus was selected as the type genus of the family - the one that defines the archetypal group against which all others are compared. Although newly described species had been added since, the one species that was so obviously deer-like it had never been moved anywhere else thus became, in a sense, the defining species of its family.

This, the most typical of the typical deer, is the red deer (Cervus elaphus).

As understood for most of the 20th century, the red deer is a remarkably widespread animal, being found in suitable habitats across the entire Northern Hemisphere. But the story of its naming doesn't end in 1810, because it began to become clear in the 1990s that the red deer living in North America weren't really the same species as those living in the Old World. This had, in fact, first been suggested in 1777, by German veterinarian Johann Erxleben, but was later dismissed on the grounds that, unbeknownst to him, the two kinds could breed successfully in captivity. It turns out, however, that they are genetically quite distinct and, indeed, won't interbreed under natural conditions.

Over the last decade or so, it has become increasingly accepted that red deer are, in fact, a "species complex". This is a collection of very similar-looking species that nonetheless retain enough genetic identity to be considered separate. Exactly how many species are in this complex, let alone what we should call them, is currently unresolved. The most common view, however, is that there are three.

The red deer proper is the species found in Europe, with some populations in Turkey and one subspecies, the Barbary stag, that's found along the coast from Morocco to Tunisia. This is the only deer native to Africa in historical times, and it seems to be related to the endangered Corsican subspecies, suggesting that it might have been transplanted to its present home from Italy - although, if so, presumably a very long time ago.

Elk

Over in North America, we have instead, the elk (Cervus canadensis), now pretty much universally regarded as a distinct species. Surprisingly, though, it turns out that elk also live in China, Mongolia, and southern Siberia, so the Pacific is not quite the dividing line that we might suppose it to be. There's a further complication in that the American word 'elk' is often used in Europe to refer to an entirely different animal, so that it's sometimes referred to by the Algonquian name "wapiti" instead.

Sitting geographically between the elk and red deer is the Central Asian deer (Cervus wallichi) which lives mainly in south-western China with a highly endangered and isolated population in Kashmir. This tends to be where the arguments about species boundaries start, with genetic studies producing inconsistent results about which populations in central and eastern Asia belong to which species - in part due to it not always being obvious where the captive animals or collected skins used for the analyses originally came from. As a result, the scientific name I've just given, while the most common as I write this, is by no means the only one used, if the species is even recognised at all.

Given this confusion, it's unsurprising to discover that the three (?) kinds of deer do look very similar. They are, for instance, all unusually large deer, and the stags have particularly impressive antlers. A key similarity is that the antlers of fully-grown animals usually include a bez tine, something that's absent in most other deer. Although this is sometimes defined as the second tine, regardless of position, in the sense I'm using it here, it refers to one that branches off immediately above the first, or brow, tine. The general pattern of the antler is therefore two tines near the forehead (brow and bez), a third one partway up (the trez tine), and then a crown of three or more tines near the tip, where things tend to get complicated if the stag is old or well-fed.

Now that we know that they're different, however, the differences between the species do, perhaps, become more apparent, especially between elk and red deer. Red deer are, for instance, reddish, at least in summer, while elk tend to be a paler, tan-brown, colour, and to have a more prominent mane, especially on the does. Elk are also quite a bit larger on average than red deer, with the stags standing around 150 cm (5 feet) at the shoulder, rather than 120 cm (4 feet). On the other hand, the difference in size between the two sexes is greater in the red deer, where the stags weigh roughly 60% more than the does, compared with around 45% in the elk.

The distinguishing features of the Central Asian deer are less clear, but it tends to more closely resemble the red deer than the elk, despite being genetically closer to the latter, and often doesn't have the bez tine.

Red deer and their kin prefer to live on the open edges of woodland, but they are highly adaptable animals, capable not only of coping with a wide range of different forest types, from coniferous to broadleaf, but also to less wooded habitats. Key examples of the latter are the heathlands of Scotland and the American prairies as well as thorny scrubland in places such as Spain. Diet is correspondingly broad, consisting of a mix of soft leaves and grass, although elk tend to favour the latter. All species, but especially elk, migrate down from higher pastures in the winter to avoid the worst of the snow in places where the terrain is steep enough for this to make a difference. In places such as the Rocky and Altai Mountains, such migration routes can easily stretch for 150 km (95 miles).

The basic social unit is the all-female herd, linked by matrilineal descent, with stags being isolated in smaller, less stable, bachelor herds outside of the rut. In open ground, multiple herds can join together in aggregations of several hundred individuals of both sexes. Even the comparatively rare Central Asian deer have been seen gathering in groups of over 50.

The rut occurs in the autumn, when stags spend all of their time displaying and calling to attract as many females as possible. This takes considerable effort, and while stags reach puberty at the same age as does, around 16 months, it's typically around five years before they're large enough to stand any chance of mating at all. While the mating call of the red deer is a deep-throated roar - and the more often the stag can manage it, the better - that of the elk is an entirely different, and surprisingly high-pitched, 'bugle'. The Central Asian deer is said to use a mixture of both, switching from the low roar to the bugle partway through the call.

The effort of posing, calling, fighting, defending females from rivals, and generally not having any time left over to eat, takes its toll on the stag. They commonly lose 20% of their body weight, and almost all of their fat, over the course of the rut, never mind the effort that has to be expended in growing a new set of antlers once it is over. Although fights are obviously not to the death, and stags will rapidly retreat from a fight they can't win, it has still been estimated that around 6% of them suffer a permanent injury each year.

Calving takes place in the summer, with elk and Central Asian deer apparently having a longer pregnancy than red deer do. The mother leaves the herd to give birth to her single fawn, retreating deeper into the woodlands to do so. For the first two to three months of life, the fawn has a spotted coat, probably as a means of partial camouflage in the dappled sunlight of the forest.

Sika deer

Over the course of the 19th century, many new species of deer were added to the genus Cervus alongside the previously known red deer and elk. Most either turned out not to be new species, or were moved elsewhere in the deer family tree, but today, two are generally considered so close to the red deer that they remain in the same genus.

The first of these to be named was the sika deer (Cervus nippon) which, as its scientific name suggests, was first identified in Japan. It turns out that sika deer do also live in some areas of China and the Russian Far East, but they are very rare there in modern times, with the vast majority of the wild population still living in Japan. In fact, they are arguably too numerous there, with their current overpopulation causing problems due to their habit of stripping the bark from trees. Genetic evidence shows that they first evolved on the mainland, entering Japan during the Ice Ages; the traces of the two original migration routes, one via Korea and the other from the north, can still be seen in the modern populations, although they don't represent distinct subspecies.

Sika deer are smaller than either red deer or elk, standing around 100 cm (3 feet) high at the shoulder. More notably, they are one of only five species of deer to retain the spotted coat of the fawns into adulthood - although this is only in the summer, since the winter coat is a plain, dark, shade. This makes them particularly attractive animals, which probably explains why they have been so widely exported around the world. As just one example, in the 19th century they were introduced to Europe as ornamental animals for parks and private estates. Inevitably, some escaped into the wild, where they can still be found in Britain and in scattered locations across the European mainland. Others now live wild in North America and New Zealand.

They are forest animals and, when they aren't stripping bark, they feed primarily on grasses, including dwarf bamboo. Their habits are similar to those of their larger cousins, but they tend to live in smaller herds. During the rut, males grow manes on their necks similar to those seen in both sexes of elk throughout the year, and they spend a lot of time gouging trees with their antlers as well as howling to advertise their presence. Like most deer, they don't have a true bez tine and, in their case, the crown only consists of a single fork, giving them just four tines in total, including the brow.

Thorold's deer

Thorold's deer (Cervus albirostris) was only described in 1883, taking its name from the collector of the original specimen. The alternative name of "white-lipped deer" is often used instead, from one of its more visually obvious features. Other than that, they are dark-coloured animals about the size of a red deer. The antlers typically have five tines, although the crown may divide into more than three branches in particularly large males.

Thorold's deer inhabits eastern Tibet where it lives in mountainous scrubland over 3,500 metres (11,500 feet) above sea level - remarkably high up for a deer. It primarily feeds on grasses, although rhododendrons are common where they live, and they often eat the leaves of those, too. A key distinguishing feature is that they have unusually wide feet with long dewclaws, both of which are likely adaptations to help them clamber about on steep slopes without losing their balance; they are known for being particularly agile.

They used to live in large herds, sometimes aggregating in their hundreds, as elk do. Even today, when they are less common, groups of a few dozen can be seen, so they seem to be fairly social. Males in rut produce a low-pitched roar similar to that of red deer. In addition to alarm calls and the like, they can, unusually, make snapping sounds with their wrists... although nobody knows why.

For a long time, Thorold's deer was considered to be more closely related to certain species of southern Asia than to the red deer and its kin. For a while, it even had its own genus. That's no longer thought to be the case, but it is to those Asian deer that I will turn next...

[Photos by Rahiane Shomal, "ForestWander", "Altaileopard", and Fang Hong. Cladogram adapted from Pitra et al. 2004 and Gilbert et al. 2006.]