Behaviour and ecology of the fossa, Cryptoprocta ferox (Carnivora: Viverridae) in a dry deciduous forest, western Madagascar
In the first longterm field study of the fossa, mean adult body mass measured was, in males, 7.4 kg (n=17, s.d.=1.2), and, in females, 6.1 kg (n=11 females, s.d.=0.6). Sexual size dimorphism was most marked in canine width. 376 scats yielded 554 prey items, of which the majority were lemurs (>50%)m, tenrecs and snakes. Incidence of prey in scats correlated positively with abundance. Scat composition varied with season, but not with year nor gender of fossa. Sexual dimorphism could not therefore be explained as niche separation. Home ranges were, for two males, 22.74 km2 and 26.20 km2, and for two females, 12.69 km2 and 7.84 km2. These, and incomplete ranges of six others, overlapped between males but not females, and were larger in the dry season than in the wet season. Censuses and radio-tracking generated consistent population density estimates, averaging 0.17 adults per km2, substantially lower than predicted from body size, and indicating that even Madagascar's largest reserve may not hold a viable population of fossas. The unique mating system resembled a lek: females mated with multiple males on traditional sites. One female occupied a site at a time, for up to one week. The system may benefit species with low population density, by increasing mate choice for females and facilitating mate location for males. It may also reduce sexual harassment of oestrous females. Males fought at the sites, but no size-related advantage in male mating success was observed. A different mating system was predicted from the home range data. The first discovery was made of transient masculinization of a female mammal. Juvenile female fossas (n=8) exhibited an enlarged, spinescent clitoris supported by an os clitoridis, and a pigmented secretion that in adults was confined to males. Masculinization was hypothesized to reduce sexual harassment of young females.