Saturday, 7 January 2012

New World Primates 1: Goeldi's marmoset

Mother carrying baby - December 2011
I am going to start 2012 with a series on the eight species of New World Monkeys we have here at Bristol. Between them the species Bristol holds covers all five families of the Platyrrhine monkeys, the scientific term for the monkeys of Central and South America. Their ancestors are believed to have crossed the Atlantic from Africa around 40 million years ago, and they have either developed or retained several adaptations that distinguish them from the monkeys and apes of the Old World. They do not have as good colour vision as Old World monkeys for example, with only two colour sensitive cone types in the retina in males, and either two or three cone types in females. In addition, their physiology is different, and they require much higher blood levels of Vitamin D than Old World monkeys do. Before this last requirement was realised, it was hard to maintain Platyrrhine monkeys in good health at high latitudes, even with exposure to sunlight, as they were very prone to Vitamin D deficiency diseases.

The first of our monkeys I am going to cover is surely one of the cutest, the Goeldi’s marmoset Callimico goeldii. In December our pair had another baby, bringing the family group to six. Goeldi’s are rather untypical marmosets, and appear to have adapted to a habitat and lifestyle somewhat different to the other marmosets and tamarins of South America. They exist at low densities throughout their range, and often associate with other species as they range around their territories. They prefer a densely vegetated understorey, usually staying under 5m from the ground, and streamside vegetation, regenerating secondary forest (including abandoned farmland) and bamboo seem to be preferred. The range extends from northern Bolivia into southern Columbia, east of the Andes.

Feeding on a Morpho butterfly
Most marmosets feed heavily on insects, especially grasshoppers, katydids and phasmids, and Goeldi’s are no exception. However, they differ in not feeding much on saps and gums, instead feeding heavily on various fungi, especially in the dry season. Other important dietary items are fruits and small vertebrates such as frogs and small lizards, with birds’ eggs when available.

Marmosets are highly social creatures, and Goeldi’s fit the general pattern – a single breeding pair plus offspring of various ages. The group size is smaller then their relatives, with usually 6-10 animals in a group. There is some variation, as both polyandrous and polygynous groups have been observed. The territory size can be as much as 1.5km2, several times the size of that of other marmoset species.

Most marmoset species have twins sometimes even triplets at each birth, and when resources are available can have two litters each year. Goeldi’s are much less prolific, with only a single youngster at a time and in the wild at least often only a single baby each year. This probably reflects the lower energy and mineral resources in their diet, and also the energy expenditure in getting around much larger territories. They may also experience less predation than the more visible marmosets, who often feed at higher levels in more exposed positions.

An animal the size of a Goeldi’s marmoset has numerous enemies of course. Mammalian predators are probably not the main enemy, but birds of prey and snakes are probably much more serious threats. I am not aware of any studies on the issue, but Goeldi’s have at least 40 recorded calls, and it is probable that some alarm calls are specific to the type of predator being observed. Many species that have such alarm calls, from Vervet monkeys in Africa to prairie dogs in North America and even some pheasant species in Asia have such predator-specific calls. Given that they associate with other marmoset and tamarins it would not be surprising if they can also understand the alarm calls of their companion species as well.

The main threats to Goeldi’s today are probably those related to development and deforestation. They will have trouble crossing roads, and this can cause fragmentation of their territories and the isolation of non-viable groups in small patches of forest. On the other hand, their ability to utilize secondary regrown forest can count in their favour.

The various species of marmoset and tamarin make good exhibit animals, being sociable and diurnal, and around 500 Goeldi’ marmosets are listed on ISIS. The typical exhibit in the UK will comprise heated indoor quarters with access to either a screen cage or sometimes an island. Access to planted enclosures is highly beneficial where possible, as it provides opportunities for natural behaviour and especially foraging for insects. The captive diet is a variety of fruits and vegetables, combined with a proprietary prepared biscuit and added insects in the form of mealworms, locusts, and crickets.

Next week: Lions tamarins – beauties from the Brazil!

(images from Bristol Zoo website, wikipedia)

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