Saturday, 9 February 2013
Lemurs 6: The Aye-Aye
As recently as the 1950’s, the Aye-Aye (Daubentonia madagascariensis to give it its scientific label) was believed to be either extinct or nearly so. In fact, it is one of the most widespread and adaptable of Madagacar’s lemurs, but lives at extremely low population densities over most of its range.
The Aye Aye has so many peculiarities it is difficult to know where to start. Most famously, it has an extremely long third finger on its hand, which has been modified into a thin probe for hooking insect larvae out of their burrows in rotting wood. To aid it in its quest for beetle grubs, it has continuously growing incisors like a rodent, which enables it to gnaw through almost anything. This includes solid concrete, as one of the keepers at Jersey once told me – the Aye-Aye was kept in a special room heated by water pipes in the walls, and it must have mistaken the sound of water in the pipes for food. It not only chewed straight through the wall, it also chewed through the pipes, and when the keepers came in the next day the enclosure was flooded – fortunately the Aye-Aye itself was unharmed.
Aye Ayes are so specialised that for a long time it was not clear where they fit in the lemur family tree, but from DNA evidence it seems they are closest to the Indris. This is not very close though – best estimates put the line leading to Aye-Ayes splitting off at the base of the lemur family tree, not long after the ancestral lemurs rafted to Madagascar from mainland Africa 60 million or more years ago. Unfortunately, there are no known fossil sites in Madagascar for most of the island’s post-Cretaceous history, and a rare forest dweller like an Aye-Aye is unlikely to be fossilised anyway, so how they acquired their unique adaptations is a question that may never be solved. It is known however that the south east of the island once held a second, even larger, species called the Giant Aye-Aye D.robusta, which probably died out as a result of human persecution in the last thousand years or so.
For an animal with so many specialisations, Aye-Ayes are remarkably adaptable. A large part of their diet is insect larvae of course, but they also eat nuts, nectar, seeds, and fungi and cankers on trees. They seem to switch to whatever food supply is most easily obtained in season, and are quite capable of living in even quite degraded secondary forest and farmland, as long as trees (in which they make their nests) are available. The forest type is not especially significant – they can live in dry forest, rainforest, and even mangroves so long as sufficient food is available. On occasion, they will even travel across open country – one was once seen in open savannah some kilometres from the nearest forest.
Video of Aye-Aye feeding: http://www.youtube.com/watch?v=k1CqxkpfSHc
Although today they are almost entirely nocturnal, their diet does not require them to be so, and it is not clear why they are not diurnal or cathemeral in their activity – possibly this may be a response to human persecution. They seem to see quite well in daylight, and often leave their nests before sunset, returning after sunrise. Although they nest in trees, and can climb and leap well, Aye-Ayes spend a lot of time on the ground, perhaps foraging for fallen nuts.
One feature of Aye-Ayes that is often overlooked is their intelligence. As a group, lemurs are not famed for high IQ’s – from my own observations I would put them about the level of a bright squirrel – but the brain of an Aye-Aye is much larger than other lemurs and it is much more curious about its surroundings. This probably goes with its adaptability and wide use of habitats, and varied diet. This may cause problems in keeping them however – although Bristol has successfully raised two baby Aye-Ayes in the past both times we had to hand rear them, and it is not clear what effect this may have on their own ability to properly care for young in later life.
Aye-Aye society in the wild has proved hard to study. They keep in touch with each other with a variety of calls, and seem to live mostly solitary lives. A number of males may congregate around a female when she is in season, and presumably there is competition among them, but whether neighbouring adults recognise each other as individuals and so constitute an extended community is not clear. What is known is that different Aye-Ayes, even two males at the same time, will use the same nest on different nights as they move around their home range.
A single young is born and is left in the nest until old enough to follow its mother on feeding trips. Youngsters can be born at any time of year, and females seem to give birth, at least in the wild, every two years or so. Sexual maturity is reached at around four years in females. In captivity at least, they can live up to 24 years, which is fairly typical for lemurs and other primates of similar size.
Video of baby Aye-Aye at San Francisco Zoo: http://www.youtube.com/watch?v=i_yJYyT2YKs
Today, with its large range and adaptability, the Aye-Aye is not classed as in as great peril as many other lemurs, and is classed by the IUCN as Near Threatened. The main threat is human persecution as a creature of ill-omen, and habitat destruction.
(images from wikipedia, Bristol Zoo)