Sunday, 13 July 2014

Mini-Monkeys: Monkeys with Moustaches

Emperor tamarin (bearded subspecies)
Monkeys of the marmoset family, which include tamarins, are known, not just for their small size, but also their luxuriant fur, which often forms extravagant tufts on the head. Arguably, none of these tufts are more distinctive than the drooping moustaches of emperor tamarins (Saguinus imperator).

Emperor tamarins live in the lowland jungles just east of the Andes, in the border regions between western Peru, northern Bolivia, and eastern Brazil. Perhaps because of this remote location, they were discovered remarkably late for an animal so distinctive; they were first described by Brazilian zoologist Émil Goeldi in 1907 (and we'll be coming back to him in a later post). On the plus side, this distance from civilisation has kept them relatively secure, with loggers and the like only recently having reached this far into the jungle.

Compared with some other members of their family, they are not especially colourful. Their bodies are grey, reaching near-black on the face and hands, and they have a reddish tail with a grey tip. What makes them so noticeable, of course, are those long, pure white, moustaches, which are present in both sexes.  Indeed, the more widespread of the two subspecies also has a thin and straggly beard hanging from its chin. The moustache apparently reminded Goeldi of Kaiser Wilhelm II, although to be honest, it's hard to see why (one would have thought that some of the Chinese emperors would have made a better fit).

They live high up in the trees, spending most of their lives in the mid to upper forest canopy, ten to twenty metres (30 to 60 feet) above the ground. Fruit forms the largest part of their diet during the wet season, when it is most abundant. However, while fruit is present year round in the Amazon, there is less of it in the dry season, and during this time of year, as much as half of their diet may consist instead of nectar. For the most part, they seem to find plant food by sight, and perhaps some local knowledge, rather than, for example, by scent.

In addition, as with other tamarins, they eat whatever insects and other small prey they can find, with a particular liking for arboreal katydids and caterpillars. Unlike the saddle-back tamarins, which also forage closer to the ground, emperors hunt by stealth, pouncing on suitable prey once they have seen it, rather than feeling about for it in the foliage with their hands. The two kinds of tamarin often feed in the same area, but, being larger, the emperors have the upper hand, being able to chase the saddle-backs away if need be.

Emperor tamarins live in small family groups of no more than ten individuals, and more typically only about four. Only one pair breeds, although almost all the monkeys in the group help to carry and care for the newborn twins. Each group defends an area of around 30 hectares (75 acres), and are quite determined at keeping other emperor tamarins out of 'their' patch.

Moustached tamarins
One of the closest relatives of the emperor tamarin is, perhaps unsurprisingly, the moustached tamarin (Saguinus mystax). Compared with emperors, their moustaches are really rather feeble, forming a white bush of shortish hair around the mouth that is clearly noticeable, but not especially remarkable. They live further north than the emperors, south of the upper Amazon River in eastern Brazil and western Peru. This is a slightly more accessible region, although still remote enough that the species' population seems both large and stable. On the other hand, it does mean that there has been rather more research on moustached than emperor tamarins, even if the latter are more popular in zoos.

Although they're mostly black or dark grey, apart from the moustaches, one subspecies has red hair on the top of its head. Partly because of this, it is sometimes considered to be a full species in its own right, but the current consensus is that that's rather unlikely. This is because it lives in between the other two subspecies, which are otherwise separated by about 800 km (500 miles) of jungle. If it really is a separate species, it seems hard to see how the other two have managed not to separate as well, given that they can't reach each other to interbreed. It's not impossible, by any means, but it would be unusual.

In many respects, moustached tamarins are similar to their close relatives, the emperor tamarins. For instance, they eat much the same food, focussing on fruit, nectar, and insects. Nectar is mainly a backup for when fruits are in short supply, but the monkeys seem to have a good idea of exactly where to find it in their local area, and can spend up to 20% of their time feeding on it at certain times of the year - munching their way through up to sixteen flowers per minute. They may also play a significant role in seed dispersal, of vines as well as fruiting trees. Among insects, katydids are again among their favourites, especially large visible ones that live high up in the trees.

They have also been reported to eat the occasional tree frog and, even more rarely, lizards.  Oddly, given that they prefer to stay high up in the trees, they sometimes descend to the ground to eat soil, presumably to get at mineral supplements. While they may live close to rivers, they don't, however, need to descend to those to drink, finding enough water pooling in epiphytic plants such as bromeliads, that grow on tree branches.

While emperor tamarins often live in the same area as saddle-back species, and forage toegther, as I mentioned last month, moustached tamarins go as far as to live in mixed-species groups. The two species sleep apart, with the moustached tamarins preferring higher branches and dense vegetation, rather than tree hollows closer to the ground. However, the two resting sites are never far apart, and the two halves of the group find one another in the morning with a series of welcoming calls. When the group travels during the day, it's usually a moustached tamarin that takes the lead, but both species evidently benefit from the cooperation, as evidenced by mixed groups having larger and fitter members than those unable to form such an association.

Saddle-back compatriots aside, moustached tamarins live in groups of about five or six, and sometimes up to ten, individuals, often with slightly more adult males than females. In addition to having different alarm calls for predators on the ground and those in the air, they also have "separation calls" that are apparently unique for each group, allowing group members to find an isolated fellow and identify him as one of their own by sound alone.

The group, of course, serves in part to defend against predators, and moustached tamarins have been observed mobbing a boa constrictor that had attacked one of their own until it gave up on its intended meal and went away. But the group also cooperates to protect food sources from others of their own kind. Moustached tamarins don't seem as territorial as the emperor species, and are only likely to get aggressive when rivals get close to either their feeding trees or their sexual partners. For example, while the monkeys (mainly the females) do leave scent marks dotted about their territory, these seem to be placed at random rather than, say, at the boundaries where they could serve as warnings.

Within the group, there is usually (although not quite always) just a single breeding female. Apart from her children, she is not necessarily closely related to the other members of the group, although the adult males are often related to one another, suggesting deeper ties of kinship and bonding among males than females. The breeding female typically has two sexual partners, but they aren't necessarily equal. Within a group, one adult male performs most of the grooming of others, helping to maintain group cohesion, and he also tends to have sex more frequently than his fellow.

Red-bellied tamarin
Which is not to say that he gets things all his own way, and the monkeys can be reasonably described as polyandrous (that is, one female having two or more male partners). When the breeding female dies, the next oldest will step up her grooming of all of the adult males (barring any that happen to be her own relatives), as well as bullying any younger females into submission. This presumably serves to set up her future relationships, since she becomes sexually fertile shortly thereafter. Paternity tests have shown that the female clearly does have children by both of her partners - sometimes even having non-identical twins by two different fathers.

There is one final species of tamarin with a moustache, the red-bellied tamarin (Saguinus labiatus). Sometimes called the "white-lipped" tamarin, as the latter name suggests, the moustache is much thinner than on the other two species, although its white colour contrasts clearly with the black skin of the face. Just as obvious, perhaps, is the red fur of the chest and belly, which also extends a short way down the underside of the tail.

They live further east than emperor tamarins, and to the south of the moustached species, broadly along the south bank of the Rio Purus and as far as the Brazilian-Bolivian border. They have not been as well studied as moustached tamarins have, but they have not been ignored either, and what we do know suggests that the two are very similar in their habits and biology. For instance, they, too, form mixed-species groups with saddle-back tamarins, that work in broadly the same way as those of their moustached kin. Some groups are also formed with Goeldi's monkeys, a non-tamarin species, although these are more likely to break up during the dry season, when the two species seek out different kinds of food.

It has been suggested that red-bellied tamarins may employ facial expressions more frequently when communicating with one another than do other tamarins. If so, this would likely be because the white lips against the dark face make such expressions more visible than they might with other species. Even if this is true (and the evidence is, perhaps, equivocal), there is no doubt that they use scent marking and sophisticated multi-syllable calls as well, and that they are, for example, able to tell the sex of a monkey from the call alone.

[Photos by Javier Ignacio Acuña Ditzel, "Postdlf", and Nils Axel Braathen, from Wikimedia Commons]

1 comment:

  1. Great blog. Love learning more about tamarins and marmosets. Have you ever written about Schmidt's guenons? They're a lot of fun. Thanks for your work!