Fossa

The Mysterious Madagascan ‘Mongoose’

The fossa is Madagascar’s top dog. Not that it’s actually a dog, of course, because Madagascar doesn’t have any wild dogs. Nor does it have any wild cats, bears, badgers, weasels or raccoons. In their absence, the top predator on the island is an elusive, medium-sized brown animal that looks a bit like a cross between an elongated puma and a giant otter. Even though it is Madagascar’s largest living carnivore, this strange, slinky animal is smaller than most people expect, standing only 35 cm at the shoulder, but its lithe, muscular body nonetheless oozes power.

With a unique blend of features reminiscent of cats, civets and mongooses, the fossa has baffled people ever since it was first described in 1833. It was initially identified – wrongly – as a feline due to facial resemblance and semi-retractable claws, but we now know it is a member of a small group of mammals called the Malagasy carnivores (or euplerids), which live only on Madagascar. Some of these animals are called mongooses (despite not being true mongooses at all), while others have more fanciful names: in addition to the fossa, there is the vontsira, the falanouc and the fanaloka.

The fossa is a fantastically agile climber and a superb arboreal hunter. It is helped by a long, balancing tail and reversible ankles that enable it to grasp both sides of a tree trunk with its hind feet – a feature shared by several other Malagasy carnivores, along with some civets, the margay, and the clouded leopard. Over 50% of the fossa’s diet consists of lemurs – it chases them through the canopy at speed or ambushes them at night while they sleep – but it also eats snakes, birds, rodents and lizards.

Despite its relatively small size, the fossa is often feared by the people of Madagascar, who claim that the animal takes fowl, piglets, and even young children who walk alone in the forest. It is also said that a fossa may sneak into homes and steal babies from their cribs, while another myth says the fossa can lick a sleeping person in such a way that they fall into a trance from which they will never wake. Because of this, the fossa suffers from a poor reputation among local people, even though there are no official records of the animal ever having harmed a human. Some of these fears may, in fact, be due to the folk memories of its close relative, the now-extinct giant fossa, which grew to the size of a grey wolf.

On the other hand, humans certainly do pose a threat to the fossa. It is hunted and killed by many native people, either because they fear or dislike it, want to use its body parts in traditional medicine, or wish to eat it (although it should be noted that some dare not eat it because they believe it will transfer its ‘undesirable’ qualities into anyone who consumes its meat). A combination of fady (traditional Malagasy taboos), deforestation, and habitat fragmentation has already reduced the fossa population to an estimated 2,500 wild individuals.

The fossa is a shy, mysterious animal, notoriously difficult to find and study – although it loses some of its inhibitions at mating time. A female in oestrus climbs her favourite trees (she may use the same ones every year) and advertises her availability by making loud, high-pitched, cat-like cries. This attracts males from far and wide. If a suitor arrives who she isn’t impressed with, the female simply moves to the thinner branches at the edge of the canopy, safely out of reach of the heavier male. But if she deems a male suitable, the pair will mate up in the tree. Despite weighing only half as much as the male, the female is the dominant one during courtship and she reinforces her status with aggressive vocalisations; a single call from an annoyed female can make a male beat a hasty retreat back down the tree.

The male, meanwhile, possesses one of the largest penises, relative to body size, in the mammalian world. He can also, apparently, maintain an erection for up to six hours. This, coupled with the spines on his penis, locks the pair together, and they may remain like this for hours, yowling like banshees and biting one another as they noisily struggle to maintain their precarious balance in the branches. During the single week that she is in oestrus, a single female may mate with as many as ten males – and mate with each one ten times – until another female arrives and steals her prized spot.

Not wanting to miss out, the female fossa also has odd genitalia. She has a much-enlarged clitoris called a ‘pseudo-penis’, which is covered in the same vicious-looking spines as the male’s real penis. What makes this anatomical feature even stranger is that when a female reaches four years of age, her clitoris shrinks back to normal size. This transformation does not seem to be accompanied by any change in male hormones or even aggression, as is the case with spotted hyenas, so zoologists aren’t sure why this change takes place. Perhaps having a pseudo-penis for the first few years of their lives reduces the sexual harassment of juvenile females by adult males.

In the next Madagascar Month post, we’ll be looking at a whole family of uniquely Madagascan mammals that often look like animals found elsewhere in the world – the tenrecs.