Sunday, 17 October 2021

All the World's Deer: Small Deer of South America

Grey brocket
Deer first entered South America when that continent first connected with its northern counterpart a little over two million years ago. Finding nothing similar already there, they rapidly diversified into several distinct species, taking advantage of a wide range of different habitats. Many of the resulting species were medium to large animals, resembling their northern relatives, such as white-tailed and mule deer. But others instead took on a role closer to the muntjacs of eastern Asia. 

How many species of these small South American deer are truly distinct is a question that is not fully settled yet. In common with the scientific fashions of the time, a great many species were named in the 19th century, only to be merged in the 20th and then split apart again in the 21st (not always along the same lines, of course). As a result, many of the species we recognise today weren't considered such until recently and have not been individually studied to any great extent beyond demonstrating that they exist. On the other hand, the reason that we confused them for so long - and still aren't entirely sure how many they are - is that they are all quite similar. This is especially true of the various kinds of brocket, all of which are currently placed in the genus Mazama.

The most studied of these is probably the grey brocket (Mazama gouazoubira). As currently recognised, this lives in forests south and east of the Amazon, from Brazil through Bolivia, Paraguay, and Uruguay into northern Argentina. The odd-sounding scientific name comes from the words for the animal in two indigenous languages of the region whereas 'brocket' originally meant a young stag whose antlers had not started branching.

The reason that this latter name was picked in English is obvious given the animal's physical appearance. It's about the same size as a muntjac, at around 60 cm (2 feet) tall at the shoulder, making it look like a young deer of a larger species. Moreover, the antlers are, unlike those of larger deer, entirely unbranched even in fully grown bucks - simple spikes with just one point. The coat is a drab greyish-brown, leading to the fact that, just to be confusing, it is sometimes instead called the 'brown brocket'.

Like other small deer, grey brockets are active in both day and night, although they tend to be more nocturnal in places where humans are active. They spend most of their time in open woodlands and forest edges, where they can hide in the undergrowth, but venture out into less forested terrain in search of additional food. While, as one might expect, they avoid agricultural land used for ranching, managed forests seem to be beneficial for them, and actually prefer them over denser, more primeval woodland where less sunlight reaches the ground. They appear to be fairly generalist browsers, eating a mixture of woody plants and herbs with a moderate proportion of fruit in their diet when it's available, but little grass.

Unlike most larger deer, brockets do not live in herds, living largely solitary lives. They are, however, territorial, marking their home range with piles of dung. Both sexes do this and seem happy enough for their home range to overlap with that of a member of the opposite sex (for, one imagines, the obvious reason) but not with same-sex competitors - this is especially true of the bucks. They also have a number of scent glands, which they can use for marking bushes and the like. As is also the case with mile deer, those on the feet are well-developed with specialised hairs for holding on to scented secretions but there are also numerous small glands on the tail. In contrast to muntjacs, the scent glands on the face are small and not well-developed although they clearly do use them.

When kept in captivity, grey brockets are able to breed throughout the year but in the wild, where the food supply may be less stable, they are more likely (but not certain) to time their mating so that the young are born at times of the year when flowers and fruit are most abundant. The fawns are born after a seven-month pregnancy, and keep their spots for up to four months. As with other small deer, fawns spend much of their early life hiding rather than travelling with their mother as she forages for food.

For much of the 20th century, the grey brocket was considered to live over a much wider area than it is today. In 2000, however, genetic analysis showed that the northern subspecies was a full species in its own right. Now called the Amazonian brown brocket (Mazama nemorivaga), this lives across the Amazonian Basin in Brazil and north into Colombia, Venezuela, and the Guyanas. Here it inhabits comparatively dense jungle, avoiding only those areas prone to heavy seasonal flooding, and seems to consume rather more fruit than its southern relative.

Red brocket

The most widespread of the brockets is the red brocket (Mazama americana), which was also the first to be scientifically described, back in 1777. This lives from Paraguay in the south to Venezuela in the north, taking in most of the regions in between that are east of the Andes, save for the easternmost regions of Brazil. Inhabiting relatively dense tropical forest, they live alongside both the Amazonian brown and the grey brocket; they may have some slight differences in habitat preference, but mainly seem to avoid one another by being active at different times of the day, sleeping when the sun is up.

This is the largest of the brockets, standing a good 70 cm (2' 4") at the shoulder and with a distinctive reddish coat. It is, however, also the source of much of the confusion as to the true number of brocket species. Genetic analysis has shown that animals thought to be red brockets, but living in different parts of its range, are clearly distinct and males born from parents taken from different genetic groupings may well be sterile. As a result, it's likely that we currently consider as a single species is, in reality, two or more separate species that can only be reliably distinguished through genetic testing. Where the boundaries between these species lie, what we should call them, and even how many there are is currently unresolved.

To make matters worse, more wide-ranging genetic studies have shown that red brockets are more closely related to white-tailed and mule deer than they are to grey brockets. This means that the genus Mazama, as currently defined, is not valid (since it doesn't have a unique common ancestor) and that at least some brockets will have to be moved to a new one. The grey and Amazonian brown brockets clearly fall into this latter group, but, again, there is as yet no consensus as to what it should be called, and insufficient evidence to decide which other species should join them. Indeed, one recent study placed them even further from the red brocket and its kin than the one I have used in the cladogram, showing a possible close relationship with the pampas deer and marsh deer.

The red brocket, however, certainly won't change genus, since it is the type species that defines what Mazama is. Likely to remain with it are the Central American red brocket (Mazama temama) which lives from southern Mexico to northwestern Colombia, and the small red brocket (Mazama bororo) and pygmy brocket (Mazama nana) both of which live in southeastern Brazil. All three have a similar appearance to the 'true' red brocket, but are much smaller, and were split off from other species in the 1990s.

Little red brocket

The species the two Brazilian animals were split off from, however, was not the red brocket, but the little red brocket (Mazama rufina). This was one of the few that was still regarded as a separate species through the 20th century, partly on account of its small size - it stands only 45 cm (18 inches) high at the shoulder, roughly similar to those Brazilian species. It lives far from them, however, and probably isn't such a close relative after all; it inhabits Andean cloud forests above 1500 metres (4,900 feet) elevation, mainly in Ecuador, but also in neighbouring regions of Colombia and Bolivia.

It's unclear whether the little red brocket is close enough to the red species to remain in the same genus, or whether it needs a third one. But wherever it fits, it will likely be joined by its probable closest relative, the Merida brocket (Mazama bricenii) which was split off from it in 1987, and may yet be merged back again. It lives in similar habitat further north in Colombia and Venezuela.

On the other hand, likely to move to the new genus with the grey brocket is the dwarf brocket (Mazama chunyi), inhabiting the cloud forests of Peru and Bolivia. This is the smallest of all brockets, with a shoulder height of just 38 cm (15 inches) and was first described in 1959. 

Southern pudu

Finally, the Yucatan brown brocket (Odocoileus pandora) lives only in that peninsula, in southern Mexico and northern Belize and Guatemala. It inhabits a broad range of lowland forests, including mangrove swamps. Arguably an even closer relative of white-tailed deer than the red brocket is, the American Society of Mammalogists took the plunge and actually moved it to the genus of that animal a few months ago although it remains to be seen whether or not that will stick.

Small though it is, the dwarf brocket is not the smallest species of deer. This is because the two species of pudu, which also live in the Andes, are even smaller. The northern pudu (Pudu mephistophiles) is marginally the smaller of the two with adults standing as little as 25 cm (10 inches) tall. This is partly achieved by having unusually short legs for a deer, but even so their bodies are small, with short faces and an almost non-existent tail. Their black faces are also distinctive, and presumably responsible for the scientific name. Adults weigh no more than 6 kg (13 lbs), and often less.

Like brockets, their antlers are simple unbranched spikes. In fact, they don't seem to use them much when fighting with other males for access to mates, preferring to kick and bite one another. 

Northern pudu
- the world's smallest deer

The northern pudu lives high in the Andes from Colombia, through Ecuador, to Peru. They are rarely found below about 2000 metres (6,500 feet) in elevation, and live not only in the cloud forests but in the humid 'paramo' meadows above the tree line. The southern pudu (Pudu puda) lives much further south, in southern Chile. While it's also a mountain-dweller, being well outside the warmth of the tropics, it doesn't venture more than 1700 metres (5,600 feet) upslope and can even be found (albeit rarely) on the coastlines of the steep fjords at the foot of the Andes. Except on Chiloe Island, where there may be little alternative, they stick to forests with thick understory.

Both species of pudu are solitary animals, marking their territory in a similar way to brockets. They are browsers, not generally feeding on grass, and the southern species at least seems to eat a high proportion of fruit (apparently, they love blackberries, which are often found in local orchards, but aren't native to the region). Both species are primarily nocturnal. The southern species has its main breeding period in the autumn so that young are born in the spring, although there is some evidence that they may sometimes be able to breed at other times of the year. It's unclear whether this is also true of the northern species, but since it lives along the equator where there is no clear summer or winter, it seems unlikely.

That brings me to the end of the South American deer, and almost to my coverage of the deer family as a whole. But there are still three living species of deer to cover, all of which are, in some way, unusual. It is to those that I will turn next time.

[Photos by "Miguelrangeljr", Bernard DuPont, "T-34-85", Frédéric Bisson, and Eider Joselito Chaves Chaves, from Wikimedia Commons. Cladogram adapted from Heckeberg et al. 2016.]

1 comment:

  1. I assume it was really necessary to use Small Red Brocket and Little Red Brocket for different species?

    I guess that after the next round of splitting we'll also have Tiny Red Brocket, Wee Red Brocket, and Lesser Red Brocket :p