|Golden Lion Tamarin|
|Golden-headed Lion Tamarin|
|Black Lion Tamarin|
|Black-faced Lion Tamarin|
The group dynamics of Lion Tamarins are quite interesting. A single animal is at extremely high risk of predation, so they are extremely dependent on family groups. Typically these are a single pair plus offspring, but cases where there are two adult males (usually brothers) or two adult females (usually a mother and daughter) are also known. Young disperse at around three years, but if an adult female dies one of her daughters may inherits the territory. Both males and females may leave to try and set up their own families, but males are much more successful at immigrating into groups than females are. When males leave, it is common for two to leave together for mutual protection. They may try to evict a male from an existing family, or try to get a dispersing female to join their groups. As they are so rare, there is still much to be studied in their behaviour, and it is not entirely clear what the ‘normal’ structure of their society is in some cases.
One of the oddest features of the biology of the marmosets and tamarins is a result of their tendency to produce multiple births. As with other monkeys, they have a simplex uterus, with gestation taking place in a single central horn (by contrast, dogs have a bicornuate uterus). With multiple foetuses developing in a single uterus, the placentas of the twins or triplets fuse, and cells can pass between them. As a result, baby tamarins are chimaeric, with cells from two separate fertilized eggs forming their bodies. This is true even if the twins are of different genders, and both XX and XY cells can be found in the blood of each twin from a mixed litter. Whether this just affects blood and bone marrow, or possibly other parts of the body, is not yet clear and may in any case vary between species.
In addition to the wild population, there are around 400 Golden Lion Tamarins in zoos around the world. In the UK, standard accommodation is a heated indoor house with the nest boxes, and access to a planted outside screen cage or lake island. This enables the group to forage for insects and other prey as they would in the wild, and improves their general level of activity. In some places they can even be kept at semi-liberty. The habit of callitrichids of always sleeping in the same tree hole means that an established family group will always stay close to home base without additional confinement. In the past Bristol had a group of Geoffroys marmosets running loose in this way, and they bred successfully, but unfortunately as the group size grew they decided they needed more room and one summer evening left the zoo grounds. After that they had to be confined for their own safety. In zoos with more extensive woodland areas they have had more success, and if you visit Jersey you can walk through Tamarin Wood and find them running past you on the fence.
There is one more marmoset to cover before we move on to the next group of South American primates. This is one we do not yet have on show, but are working with in the wild – more on that next week.
Sources: IUCN, Primateinfo.net, wikipedia, Bristol zoo)