Discover the amazing convergent evolution of Madagascar’s wildlife
Nick Garbutt reports on new efforts to unravel the ecology of Madagascar’s aye-aye, the lemur that’s among Earth’s most mysterious mammals.
When I was a child in the mid1970s I avidly collected WWF World Wildlife Collection cards from Shell garages. There were 16 in the set, so it took me a while to get them all, and the species I coveted the most was on Card No. 1: the aye-aye.
I remember few details about the 3D card itself, other than it said that there were fewer than 50 aye-ayes remaining in the remote forests of Madagascar. In 1966 and 1967 the Malagasy government had translocated nine animals ( four males and five females) from capture sites on the mainland to the offshore island of Nosy Mangabe in the north-east, in what was thought to be a last-ditch attempt to save the species. Over the subsequent years these aye-ayes thrived, but on the mainland they were still believed to be restricted to tiny pockets of lowland rainforest in the north-east, and very close to extinction.
That perception continued for another two decades, until in 1990 Durrell Wildlife Conservation Trust (DWCT; then Jersey Wildlife Preservation Trust) organised a rescue mission to collect animals and begin a captivebreeding programme at Durrell Wildlife Park ( formerly Jersey Zoo). The story of the expedition was famously recounted by Gerald Durrell in his last book – The Aye-aye and I: A Rescue Mission in Madagascar.
At the time of the expedition I was working on the neighbouring island of Mauritius with another Durrell project to help the endangered Mauritius kestrel, and we naturally received periodic progress reports from Madagascar. Not surprisingly the task proved to be very challenging. “We were expecting aye-ayes to be elusive, but not nearly impossible to find,” says Lee Durrell, Gerald’s widow and honorary
director of DWCT. “On his first casual night recce one of the senior expedition team saw four or five, gathered for a noisy mating session, but never again were they seen in such numbers. We searched for four weeks, day and night, but with no luck. Finally we were persuaded to host a ceremony in which the local elder, aided by rum and silver, called upon the village ancestors to bless our undertaking. Within a few days six animals had been caught!”
These aye-ayes have done well in captivity and the breeding initiative at DWCT has proved very successful (see box, p85). Indeed two of the original six animals are still alive today, 25 years after their capture.
PECULIAR PRIMATE
Since its discovery and description in 1788, the aye-aye Daubentonia madagascariensis has been the subject of considerable debate and confusion. The animal was first classified as a squirrel-like rodent on the basis of its appearance. The species measures 74–90cm from nose to tail tip, with the tail making up more than half its length, and weighs roughly 2–2.5kg. It was only some 100 years later that it was finally accepted as a primate and lemur.
Indeed genetic analysis indicates that the aye-aye, along with all of the other lemurs, evolved from the same colonising ancestor primate, which rafted onto Madagascar about 55–60 million years ago. There is no question that the aye-aye is the most unusual and distinct offshoot of the lemur evolutionary tree, and it is placed on its own in the family Daubentoniidae. A second species, now extinct, once occurred in the dry regions of southwest Madagascar: the giant aye-aye D. robusta.
The aye-aye combines a peculiar amalgamation of morphological features and behavioural traits that set it apart. As with rodents, the front teeth (incisors) grow continuously throughout its life. Its ears are massive, mobile and leathery, resembling those of a large bat. Its
extraordinary hands have clawed fingers and a skeletal middle digit, and its mammary glands are low on the torso, between the hind legs. Add widely spaced, piercing orange eyes, a coarse, shaggy black coat and a long, bushy tail, and the overall effect is something resembling an electrocuted witch’s cat with gremlin-like features.
SOLVING THE PUZZLE
Aye-ayes are strictly nocturnal, mainly black, prefer to spend a lot of time high in the canopy, occur at low densities and occupy very large home ranges. So it is not surprising that there have been few successful wild studies. Eleanor Sterling from the American Museum of Natural History carried out some of the first ground-breaking investigations in the 1980s, and her studies still underpin much of our knowledge of the species in the wild.
“I spent two years on Nosy Mangabe, following aye-ayes throughout the night,” she says. “During the day they sleep high in the canopy in nests made from interwoven twigs and fresh and dead leaves. Nests may be occupied for several days, but there is high turnover and different individuals often use the same nest on different occasions.”
Aye-ayes have been regarded as solitary, only coming together when breeding, but Sterling’s findings suggest otherwise. “They actually interact quite a lot outside the mating period. Animals come together in ‘tandem foraging’, often occupying adjacent or nearby trees while feeding. When one moves to another tree, they call quietly to one another and the second animal relocates nearby. They scent-mark too, telling others where
THE AYE-AYE RESEMBLES AN ELECTROCUTED CAT WITH GREMLINLIKE FEATURES.
they have been and possibly where to go. There may even be ‘highways’ along branches, routes that animals take and different animals follow on subsequent nights.”
When they become receptive, females scent-mark and are highly vocal, mating with different partners during one oestrus cycle. Each copulation lasts about an hour – a lengthy period for a primate. This is probably the male’s way of guarding against the advances of other suitors, but the ploy often fails, and the female begins calling again immediately to attract an alternative mate. Females begin breeding when three or four years old, and there is a three-year interval between births. Infants remain with their mother for a long period, allowing them to learn the complex foraging techniques needed for survival.
As if its striking appearance wasn’t enough, it is the ayeaye’s feeding habits that really set it apart. It is omnivorous, though insect grubs and ramy nuts Canarium sp. make up 90 per cent of its diet at times. Combining elements of both woodpeckers and squirrels (neither of which are found in Madagascar), it hunts for beetle grubs in rotting wood and uses its bony middle finger (the third digit) to extricate them (see box, p82). In contrast the fourth digit is more robust, so is used for tasks needing more strength such as accessing large fruit, scooping contents and exploring deep recesses.
Indeed most of the aye-aye’s anatomical peculiarities derive from its foraging and feeding adaptations. The roots of its huge, rodent-like teeth extend far back into the jaw,
resulting in the unusually wide spacing between the eyes. The middle finger on each hand is not only excessively thin, but also incredibly flexible and can rotate 360 degrees. Unlike other digits, it articulates through a ball-and-socket joint. The aye-aye also has an unusually large brain relative to the size of its body, a consequence of the complex hand, eye and auditory co-ordination that it requires.
DISTRIBUTION DILEMMA
A quarter of a century after the Durrell ‘rescue mission’, are we any closer to knowing how many aye-ayes still survive in the wild? It’s a tough question. The continuing destruction of Madagascar’s forests is well documented, and this clearly correlates to there being fewer aye-ayes. However, as more research has taken place an unexpected picture has emerged. Not only have aye-ayes now been recorded at numerous sites that stretch the entire length of the eastern rainforest belt, but they have also been found in drier forests in the far north, and in a number of deciduous forest locations on the western side of the island. This makes the aye-aye the most widely distributed primate species in Madagascar, other than Homo sapiens. In light of this broad distribution, the IUCN downgraded the species’ status to Near Threatened in 2008.
However, over the past 25 years Patricia WrightWg and Ed Louis have been at the forefront of lemur research across the island, and their independent studies suggest we may need to think again. On Nosy Mangabe the home ranges for males were upu to 215ha ( females’ are smaller), but in foresttss on the mainland they can be two or three timess larger. And while aye-ayes can live in secondary forrest,r there is far more evidence of their presence in unnddisturbed forests, perhaps because these areas containn more old and dead wood with insect larvae. There is only 6–67 per cent of original forest cover left in Madagascar, so thheseh factors in conjunction with the aye-aye’s taxonomy leaad the two
WHEN THE GUIDE POINTED THE AYE-AYE OUT, MY POUNDING HEART MADE IT HARD TO FOCUS.