Sunday, 7 September 2014

Mini-Monkeys: Punk Monkeys of Colombia

Cotton-top tamarin
The Amazon rainforest is the region of dense tropical jungle that is drained by the Amazon River and its tributaries, and it is where the majority of marmosets and tamarins are found. In the northwest, it is bounded by the Andean mountain chain. Beyond this, on the northern side, there are more tropical forests, but these are much smaller than, and separate from, the Amazon proper. Once they would have stretched much of the way down to the Carribbean coast, interrupted only by patches of more open grassland and extensive swamps. Today, however, they form a belt of forested land, mostly in hilly terrain, that gives way to the more inhabited parts of Colombia, dominated at first by subsistence agriculture, and then by cities and areas of more intensive farming around the larger rivers.

The tamarins that live here, in the northern Colombian forests, must be descended from some group that crossed the Andes, presumably through some of the lower, shorter, passes near what is now the Venezuelan border, or else along the coast. There are three species here today, all apparently descended from that same original group, and including one of the first of any tamarin species to be formally described, back in 1758. This is the cotton-top tamarin (Saguinus oedipus), and it's at once one of the best known members of the marmoset family, and one of the most threatened.

Cotton-top tamarins have greyish-brown bodies with white limbs and undersides, and red patches here and there. They have black faces with only very short fur, and are about the same size as other tamarins. Their most notable feature by far, of course, is their dramatic punk-like mane of white hair running from the forehead to the neck, and flowing outward over their shoulders. In honour of which they are called "Liszt monkeys" in Germany, although I don't really see it myself.

Cotton-top tamarins are among the most well-studied of all members of their family. They live in groups of about six to fifteen individuals, with one breeding female, a couple of sexually mature males, typically two infants, and a balance of non-breeding adults and sub-adults. Their daily routine consists of laying about in bed for an hour or so after sunrise, and then foraging in the mid to low forest canopy through the day, with breaks of at least 30 minutes every now and then, and settling down around 4:30 p.m. for a couple of hours of evening socialisation before bed. Which doesn't sound terribly stressful.

The female appears to be mainly monogamous, although with two males to pick from, it's unlikely that she's absolutely faithful. While rival males are more physically aggressive towards one another, unfamiliar breeding females compete for the right to be the sole child bearer, and react to one another with increased sexual scent-marking.

Having said which, the non-breeding females don't seem to be particularly stressed out about their subordinate status, so it presumably isn't something that bothers them until they'd normally have the opportunity to breed anyway. Indeed, it's only after they've been on their own with an unrelated male for an extended period of time that they even become capable of getting pregnant, or show any interest in sex - and being placed in such a situation can even accelerate the end of puberty, if they're young enough.

Pregnancy lasts an average of 183 days, which is slightly longer than in related species, and, as with other members of the marmoset family, almost always results in the birth of non-identical twins. If the infants survive their first week (by no means a guarantee in the wild), the father begins to look after them rather more than their mother does - a situation somewhat different to other species, such as common marmosets, where the care-giving is more communal, involving elder siblings as much as the parents. In fact, fathers spend so much time looking after their children that they lose anything up to 11% of their body weight over the first five weeks following the birth.

There has been quite a bit of study on how hormone levels change in the monkeys after giving birth. For instance, the mother's level of prolactin rises at this time, which is hardly surprising, because it's the hormone responsible for, among other things, milk production. What's rather more interesting is that the father's level of prolactin also increases, and this may have something to do with him suddenly taking an interest in the kids. In fact, this starts before the mother even gives birth, and doesn't change for a long time thereafter, so it's not the presence of the children themselves that's causing this. It seems to rise more in experienced fathers than in those having their first children, perhaps because they're more attuned to their mate's pregnancy.

We also know that cotton-top tamarins are relatively intelligent. They have an unusually complex vocal repertoire, consisting of at least eight different chirps and five different whistles, which can apparently be arranged into simple 'sentences' with specific meanings.They are capable of distinguishing at least some individuals by the calls they make, and infants also have their own distinctive (and simpler) call-types.They have at least a basic concept of numbers, responding much as human babies do to surprising events such as two objects moving behind a screen and then three coming out the other side.

While they don't use tools in the wild, they can, even when young, learn to use simple tools such as pulling food towards themselves by pulling a cloth that the food is sitting on - and, indeed, identifying the important aspects of the task (as opposed to, say, learning the trick with a blue cloth, and not realising it will also work with red ones). They can also work cooperatively to solve problems beyond the abilities of any one individual. Having said which, in one study, they were beaten by vervet monkeys in tests to see how well they understood concepts like orientation and the physical connection between tools.

White-footed tamarin
The sad news, of course, is that the forests in which they live are under significant threat. As early as 1978, it was estimated that three-quarters of their original habitat had already been destroyed, and it's likely far more than that by now. It's estimated that as much as 80% of the population may have been wiped out in the last 20 years or so, leaving about 6,000 left alive at the time of the most recent estimate in 2008... and falling. They are a critically endangered species, one of only two in the marmoset family, and at high risk of going extinct in the wild. Conservation efforts continue, including many in zoos worldwide, but they don't cope as well in captivity as one might hope.

Moving further south, however, we come to even more fragmentary remains of forests, lying between the Magdalena and Cauca Rivers. This is the home of the white-footed tamarin (Saguinus leucopus), a species closely related to the cotton-tops. They are somewhat larger, with grey-brown fur above, and reddish-brown on the underparts, with, as their name suggests, white limbs. They don't have the shock of white hair that their relatives do, although they do have a ruff of long brown fur that runs over the back of their neck.

They have been studied far less than cotton-tops, and the little we know suggests that, on the whole, they're pretty similar. Their native habitat is dense forest, from the lowlands up to 1,500 metres (4,900 feet) in the Andean foothills. There is, however, increasingly little of this left, and one might expect them to be as badly off as their better known cousins. Indeed, they have been considered an endangered species since 2008, and over half of their population has likely been wiped out since 1990. This is certainly not good, but it's not quite as bad as the cotton-tops (which have been on the endangered species list since it was first drawn up in 1982, and have only got worse since).

This appears to be because the white-footed tamarins are hardy and adaptable. They can survive, for instance, even in the suburbs, if there are sufficient fruit trees in people's backyards. In what forests remain, they have the highest population density of any wild tamarins, with different family groups crammed together much more closely than one would expect. That's almost certainly because they no longer have anywhere else to go, rather than an illustration of how they lived in centuries past, but the fact is that they seem to be able to do it without a total breakdown of society.

Don't get me wrong - they're an endangered species with a rapidly vanishing habitat. But, for all their massive population loss in recent years, they're hanging on as tightly as they can. One can only hope that that will be enough.

Geoffroy's tamarin
Travelling to the west, across the northernmost arm of the Andes, we finally find ourselves heading down towards the Pacific Ocean. This western coast of Columbia is far less developed than the northern, Caribbean, coast, and much of the region is covered by either dry forest or swampland. The forests here are less lush than those to the east, but they are considerably more intact, which is a great help to their inhabitants. For this is the home of Geoffroy's tamarin (Saguinus geoffroyi). For that matter, these monkeys also live further north, being found in eastern Panama, with one population on the other side of the Canal. As a result, they are the only members of the marmoset family whose natural habitat extends outside of South America.

You may recall that Geoffroy also has a marmoset named after him, but his tamarin was long considered no more than a subspecies of cotton-top. The two were only separated in 1992, and, in fairness, they do look rather similar. Geoffroy's species is a little larger, with fur that tends to be paler, but the main difference is in the mane. Rather than the great shock of hair that the cotton-tops have, Geoffroy's tamarins have a sort of lank mohawk that runs from the top of the forehead to the base of the neck - still rather punk, but not quite so dramatic.

From what we know of the species' behaviour, that, too, is rather similar to the cotton-top species, to which it is closely related. They eat much the same kinds of food, specialising in small succulent fruit, supplementing them with insects, small vertebrates, and gum. They seem to get a lot of their calcium from the latter, and to eat more of it when the females are breast-feeding their young.

They are, however, considerably more active than their kin. They wake up at the crack of dawn, and remain busy searching for food for most of the rest of the day, retiring around sunset. This, most likely, is not some sort of inherent monkey work ethic, but due to the fact that they live in forests that are less bountiful than those to the east - they have to work that much if they don't want to go hungry.

This is more evident where they live in highlands, areas that would be expected to have less suitable food than the forests down in the plains and valleys. In the lowlands, a group of about six Geoffroy's tamarins will inhabit an area of around 25 hectares (60 acres), and defend it from rivals. Higher up, their home will be about 50% larger, presumably because they have to travel further to find enough to eat, and they're too busy to bother defending the borders, with the result that they share some of it with their neighbours.

The forests they live in are not immune from logging, and Geoffroy's tamarins do not breed well in captivity. Nonetheless, they seem to be present in fairly large numbers over at least a moderate geographic area, and, together with an ability to tolerate relatively poor quality land, this means that they are currently doing far better than either of their relatives. While there are doubtless individual places where they have suffered - due to local logging, say - as a whole, the species is not considered threatened.

Geoffroy's tamarin is the last species of "true" tamarin that I have to describe. But the "true" tamarins aren't the only sort, and to find the rest, we have to travel even further from the Amazon, and in the opposite direction - back to where we started, in the Atlantic Forest.

[Photos by Michael Gäbler, "Petruss", and "Stavenn", from Wikimedia Commons]

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