Fossa
The fossa is Madagascar's largest native carnivore and the only predator on the island able to hunt adults of every living lemur species. It looks like a small cougar, with a rounded head, short reddish brown fur and a tail almost as long as its body, but it is not a cat. It belongs to Eupleridae, a family found only on Madagascar whose closest relatives are the mongooses. Its claws are semi retractile and its ankles can turn backward, so it can run down tree trunks headfirst and leap from branch to branch. Lemurs make up more than half of its diet, and it also hunts tenrecs, rodents, lizards and birds, along with chickens near villages. Fossas are cathemeral, which means they can be active by day or by night, and adults live alone in large home ranges. They live in every type of forest on the island, from sea level up to about 2,600 meters (8,500 feet). The IUCN lists the species as Vulnerable, with fewer than 9,000 adults and a decreasing population, mainly because of deforestation, snaring for bushmeat and revenge killings over poultry.
What is a fossa? A cat, a mongoose or neither?
The fossa is a lean, long tailed carnivore that lives only on Madagascar, and it is the largest native predator on the island. Many people search for it as the fossa cat, and at first glance the comparison makes sense: it has a rounded head, short fur, large forward facing eyes and the build of a small cougar. It even has semi retractile claws, something typical of cats but rare in other carnivores. Still, the fossa is not a cat. It belongs to Eupleridae, a family of carnivores found only on Madagascar, and its closest relatives outside the island are the mongooses of Africa and Asia. Scientists believe a single ancestor reached Madagascar from Africa about 20 million years ago and gave rise to the whole family, from small striped species to the fossa itself. With no true cats on the island, the fossa took over the role a cat would fill elsewhere, which is why it looks so familiar. The common name comes from the Malagasy word fosa, and some authors use that spelling in English too. Its scientific name, Cryptoprocta ferox, means something like fierce animal with a hidden anus, because a pouch of skin covers it. Many people first met the fossa as the villain of the animated film Madagascar.
How big is a fossa? Size, weight and the giant fossa
An adult fossa measures 70 to 80 centimeters (28 to 31 inches) from nose to the base of the tail, and the tail adds another 65 to 70 centimeters (26 to 28 inches). From end to end that is around 1.4 to 1.5 meters (4.5 to 5 feet), almost half of it tail. Males weigh 6.2 to 8.6 kilograms (14 to 19 pounds) and females 5.5 to 6.8 kilograms (12 to 15 pounds), so the species is about the size of a large house cat with a much longer body and tail. Fossas from the north and east of Madagascar tend to be smaller than those in the south and west. Reports of animals close to 20 kilograms exist, but researchers consider them doubtful. The fur is short, dense and reddish brown, paler on the belly, and the eyes shine orange when a light hits them at night. The legs are fairly short and muscular, and the soles of the feet are almost bare, which helps with grip on branches. Fossil bones from caves show that Madagascar once had a giant fossa, Cryptoprocta spelea, which may have weighed up to about 20 kilograms (44 pounds) and could hunt the large lemurs that disappeared from the island. It probably went extinct several centuries ago.
Where does the fossa live? Habitat in Madagascar
The fossa is found nowhere else on Earth: it is endemic to Madagascar, and the IUCN lists the island as its only home. Within Madagascar it uses almost every kind of forest, from the humid rainforests of the east to the dry deciduous forests of the west and the spiny forests of the south. It has been recorded from sea level up to about 2,600 meters (8,500 feet), so mountains are no barrier. What it needs is forest. It avoids the open grasslands and farmland that now cover much of the central highlands, and although it can cross degraded areas, it does best where large blocks of forest remain. Each fossa needs a lot of room. In Kirindy Forest, on the west coast, a male's home range can reach 26 square kilometers (10 square miles) and a female's about 13 square kilometers (5 square miles), and the animals often travel 2 to 5 kilometers in a single day. Because of this, only the largest protected areas hold healthy numbers. Studies suggest that just two national parks, Masoala in the northeast and Midongy du Sud in the southeast, are home to 500 or more adults each. As forests shrink and break into pieces, many fossa populations are left small and cut off from one another.
What does a fossa eat? Lemurs and other prey
Lemurs are the main food of the fossa and make up more than half of its diet in many studies. It is the only predator on Madagascar able to kill adults of every living lemur species, including some that weigh almost as much as the fossa itself. In western Madagascar, researchers once watched three male fossas chase a Verreaux's sifaka of about 3 kilograms (6.6 pounds) through the trees for 45 minutes before catching it and sharing the meal. During the breeding season fossas sometimes hunt in pairs: one climbs and chases lemurs from tree to tree while the other waits below to grab any that drop to the ground. The rest of the menu depends on where the fossa lives. It eats tenrecs, rodents, lizards and birds, and studies of its droppings have even found some seeds. The size of its prey changes a lot from one forest to another: in the Andringitra mountains the average catch weighs only about 40 grams, while in the dry forests of the west it is often over 1 kilogram. Near villages, fossas also take chickens and, more rarely, young goats or calves. These raids are the main source of conflict with people and often end with the fossa being killed.
Fossa behavior: climbing, hunting and territory
Fossas are cathemeral, a word that means they are not strictly nocturnal or diurnal. They can hunt at night, at dawn or in full daylight, and they rest in dens, caves, hollow trees or termite mounds between bouts of activity. Adults usually live alone and mark their large ranges with scent from glands on the chest and around the tail, leaving smells that last a long time. Some males, however, team up with another male and hunt together, something rare in a solitary carnivore. The fossa is one of the best climbers among Madagascar's mammals. Its ankles can turn backward, so it can run down a trunk headfirst like a squirrel, and its long tail works as a counterweight when it walks along thin branches or jumps from one tree to the next. Young fossas in zoos have even been seen hanging upside down by their back feet. On the ground it moves with a low, smooth walk and can break into a fast run when chasing prey. It has good hearing, sight and smell, which helps it find lemurs sleeping in the trees. Despite its strength, it is a shy animal that usually avoids people and slips away as soon as it notices them.
Fossa cubs: the mating tree and raising the young
The way fossas mate is unlike any other carnivore. In the wild it happens mostly in September and October. A female climbs a traditional mating tree, often near water, and settles on a wide branch up to about 20 meters (66 feet) above the ground. The same trees are used year after year. Up to eight males may gather below, competing for her, and she chooses which ones to accept. A single mating can last close to three hours, and a female may stay on her tree for up to a week, mating with several males before another female takes her place. The cubs are born in December or January, after a pregnancy of about three months. A litter usually has two to four young, born in a hidden den such as a burrow, a termite mound, a crack in the rocks or a hollow tree. Newborn fossa cubs weigh no more than 100 grams (3.5 ounces), are blind and toothless, and depend completely on their mother, who raises them alone. Their eyes open at about two weeks, they start eating meat at around three months and leave the den at about four and a half months. They become independent after their first year and reach adult size at about two years, although they only start to breed at three or four.
Why the fossa matters to Madagascar's forests
Madagascar has no lions, leopards or wolves, so the fossa fills the place that big cats and other large hunters take on the continents. As the island's top mammal predator and the only one able to kill adult lemurs of every species, it has a strong influence on how lemurs live. Many lemurs choose their sleeping trees with care, move in groups and stay alert for danger, and the fossa is a big part of the reason. Verreaux's sifakas, for example, use different alarm calls for dangers from the air and dangers that climb up from the ground, such as the fossa, and the rest of the group reacts to each one in a different way. By eating tenrecs, rodents, lizards and birds, the fossa also helps keep the numbers of smaller animals in balance. Because each fossa needs a very large area of healthy forest, scientists use it as an umbrella species: protecting enough habitat for a viable fossa population means protecting room for many other animals and plants at the same time. Studies estimate that a small population needs at least 555 square kilometers (214 square miles) of forest and that 500 adults would need around 2,000 square kilometers (770 square miles). Where the fossa disappears, the forest has lost its top predator.
Is the fossa endangered?
The fossa is not classed as Endangered, but it is at risk. The IUCN lists it as Vulnerable, a category it has held since 2008, after a decline of at least 30 percent was estimated between 1987 and 2008. Its latest assessment, from 2015, gives a population of about 2,635 to 8,626 mature individuals and a trend that is still decreasing, and the IUCN notes that the assessment needs updating. The biggest threat is the loss of forest. Madagascar has lost a large share of its original forest to slash and burn farming, logging and fire, and what is left is increasingly broken into small patches that cannot support many fossas. Hunting adds to the pressure. Fossas are killed in revenge for raiding chicken coops, and they are also caught in snares and eaten in some areas: one study in the Makira forest found that people in 8 of 14 villages ate fossa meat. Introduced dogs and cats are another problem, as they compete for prey and can spread diseases. The fossa is protected under Madagascar's laws and listed in Appendix II of CITES, which controls international trade. It lives in many national parks, and long term research at Kirindy Forest and Ranomafana has taught scientists much of what is known about the species.
5 fun facts about the fossa
Here are five fossa fun facts that tend to surprise people: • Young females go through a phase called transient masculinization. At around one to two years of age they develop an enlarged, spiny clitoris that looks like a male's penis, and it shrinks again as they grow up. No other mammal is known to do this, and researchers think it may protect young females from harassment by adult males or aggression from territorial females. • Many people in Madagascar tell apart three kinds of fossa: the large fosa mainty, or black fossa, the pale fosa ondry and the small, reddish fosa mena. Scientists still do not know whether these are just local beliefs, natural variation or something more. • In some regions a fady, or traditional taboo, forbids eating fossas. Near Ranomafana, for example, people believe they feed on ancestors buried in shallow forest graves. • The first fossa born in a zoo arrived in 1974 in Montpellier, France, and most fossas in zoos today descend from a breeding program at the Duisburg Zoo in Germany. In 2018 there were 117 fossas in 47 zoos. • A fossa's eyes glow orange when a flashlight hits them, which is often the first sign of one at night.
