The fossa is active during both the day and the night and is considered cathemeral; activity peaks may occur early in the morning, late in the afternoon, and late in the night.
The animal generally does not reuse sleeping sites, but females with young do return to the same den.
The home ranges of male fossas in Kirindy Forest are up to 26 km² (10 sq mi) large, compared to 13 km² (5.0 sq mi) for females.
These ranges overlap—by about 30 percent according to data from the eastern forests—but females usually have separated ranges.
Home ranges grow during the dry season, perhaps because less food and water is available.
In general, radio-collared fossas travel between 2 and 5 kilometres (1.2 and 3.1 mi) per day, although in one reported case a fossa was observed moving a straight-line distance of 7 km (4.3 mi) in 16 hours.
The animal's population density appears to be low: in Kirindy Forest, where it is thought to be common, its density has been estimated at one animal per 4 km² (1.5 sq mi) in 1998.
Another study in the same forest between 1994 and 1996 using the mark and recapture method indicated a population density of one animal per 3.8 km² (1.5 sq mi) and one adult per 5.6 km² (2.2 sq mi).

Except for mothers with young and occasional observations of pairs of males, animals are usually found alone, so that the species is considered solitary.
A 2009 publication, however, reported a detailed observation of cooperative hunting, wherein three male fossas hunted a 3 kg (6.6 lb) sifaka (Propithecus verreauxi) for 45 minutes, and subsequently shared the prey.
This behavior may be a vestige of cooperative hunting that would have been required to take down larger recently extinct lemurs.

Fossas communicate using sounds, scents, and visual signals.
Vocalizations include purring, a threatening call, and a call of fear, consisting of "repeated loud, coarse inhalations and gasps of breath".
A long, high yelp may function to attract other fossas.
Females mew during mating and males produce a sigh when they have found a female.
Throughout the year, animals produce long-lasting scent marks on rocks, trees, and the ground using glands in the anal region and on the chest.
They also communicate using face and body expression, but the significance of these signals is uncertain.
The animal is aggressive only during mating, and males in particular fight boldly.
After a short fight, the loser flees and is followed by the winner for a short distance.
In captivity, fossas are usually not aggressive and sometimes even allow themselves to be stroked by a zookeeper, but adult males in particular may try to bite.
The fossa is active during both the day and the night and is considered cathemeral; activity peaks may occur early in the morning, late in the afternoon, and late in the night. The animal generally does not reuse sleeping sites, but females with young do return to the same den. The home ranges of male fossas in Kirindy Forest are up to 26 km² (10 sq mi) large, compared to 13 km² (5.0 sq mi) for females. These ranges overlap—by about 30 percent according to data from the eastern forests—but females usually have separated ranges. Home ranges grow during the dry season, perhaps because less food and water is available. In general, radio-collared fossas travel between 2 and 5 kilometres (1.2 and 3.1 mi) per day, although in one reported case a fossa was observed moving a straight-line distance of 7 km (4.3 mi) in 16 hours. The animal's population density appears to be low: in Kirindy Forest, where it is thought to be common, its density has been estimated at one animal per 4 km² (1.5 sq mi) in 1998. Another study in the same forest between 1994 and 1996 using the mark and recapture method indicated a population density of one animal per 3.8 km² (1.5 sq mi) and one adult per 5.6 km² (2.2 sq mi).
Except for mothers with young and occasional observations of pairs of males, animals are usually found alone, so that the species is considered solitary. A 2009 publication, however, reported a detailed observation of cooperative hunting, wherein three male fossas hunted a 3 kg (6.6 lb) sifaka (Propithecus verreauxi) for 45 minutes, and subsequently shared the prey. This behavior may be a vestige of cooperative hunting that would have been required to take down larger recently extinct lemurs.
Fossas communicate using sounds, scents, and visual signals. Vocalizations include purring, a threatening call, and a call of fear, consisting of "repeated loud, coarse inhalations and gasps of breath". A long, high yelp may function to attract other fossas. Females mew during mating and males produce a sigh when they have found a female. Throughout the year, animals produce long-lasting scent marks on rocks, trees, and the ground using glands in the anal region and on the chest. They also communicate using face and body expression, but the significance of these signals is uncertain. The animal is aggressive only during mating, and males in particular fight boldly. After a short fight, the loser flees and is followed by the winner for a short distance. In captivity, fossas are usually not aggressive and sometimes even allow themselves to be stroked by a zookeeper, but adult males in particular may try to bite.
Fossa (animal)