Fossa are terrier-sized, cat-like relatives of mongoose with tails as long as their bodies.
Mention wildlife on Madagascar and the first thing listeners probably picture is the island’s famed lemurs. As many people know, these unique primates are found nowhere else, and are the most endangered group of mammals in the world. 

But few people realize that lemurs’ fate is directly bound up with that of Madagascar’s largest predator, the fossa (Cryptoprocta ferox), which is threatened by some of the same pressures.

Fossa are terrier-sized, cat-like relatives of mongoose with tails as long as their bodies. Like other top predators such as lions and wolves, they play a critical ecological role regulating the populations of their prey.

Like much of Madagascar’s wildlife, fossa are found nowhere else in the world. But scientists know little else about them, including how many fossa there are. They are rare, difficult to see in the wild, and lack unique coat patterns that would make it easy to distinguish individual animals.

Fossa weigh about 20 pounds and can prey on most of Madagascar’s other species. They are capable hunters on land and in the trees, using their tails for balance and killing by biting through their prey’s skulls.
One study found that fossa were largely responsible for two lemur family groups disappearing from forests over a two-year period. Fossa, like other top predators, help keep prey populations at a level that their habitat can support, and rid the population of diseased and weak individuals.

Fossa also exhibit some very interesting behaviors. They are one of nine mammalian species whose sexually immature females go through a period of transient masculinization. During this phase, their clitorises enlarge and grow spines to look like an adult male fossa’s penis. Researchers think this helps sexually immature females avoid the aggressive attentions of males looking for females with which to mate.

In the deciduous forests of western Madagascar, scientists have discovered that male and female fossa will gather together at the same spot year after year to mate. Otherwise, however, fossa were thought to be solitary until 2010, when researchers observed three male fossa working together to kill a lemur. Since then, some male fossa have been seen to team up with another male or two to hunt prey and protect a larger territory than solitary males. 

Tracking fossa with cameras

Automatic cameras, known as camera traps, are a standard tool for collecting information on elusive wildlife in remote areas. The only thing “trapped” is the animal’s digital image.

Images showed what type of habitat fossa used, when they were active, and how they co-existed with other carnivores such as dogs. Variations among individual animals, such as scars, tail width and kinkiness, and the presence and number of ear nicks, made it possible to start picking out certain fossa from the population and “follow” them from one camera to another.

One of our top goals was assessing how many fossa were present in the reserve and how close together they were. Determining density is key for conserving species. Once we knew know how many fossa there were, on average, in a unit of area such as square kilometer, we could estimate how many there were in the entire region and compare between different protected areas.

Over a seven-year period we ran 15 surveys across seven study sites in the reserve. For months on end, we set up cameras, checked them, downloaded data and then moved cameras to survey as much area as possible.

Next came three years of analyzing photos, recording which animals had identifying marks and how far those marked fossa moved during their daily activities. Finally, nearly a decade after the very first survey in Masoala-Makira, we had a population estimate.

We calculated the fossa population in Masoala-Makira at 1,061, give or take around 500 animals. This worked out to about 20 fossa per 100 square kilometers. 
There are estimated to be 8,626 fossa in the entire world.

Rare and charismatic species typically get the most conservation attention, especially through events like National Geographic’s Big Cat Week. In fact, however, there are four times more lions than fossa in the entire world. Maybe it’s time for Fossa Friday.
The Conversation