The bromance of the fossas

Excepting lions and hyenas, most hypercarnivores — critters whose diets are more than 70 percent meat — are solitary creatures. And if you check Wikipedia, fossas from Madagascar are no different. But these large mongooses, which look like a cross between a cat and a dachshund, aren’t quite that simple, finds a study published in Behavioral Ecology and Sociobiology. Some male fossas spend life with a brother or friend.

Mia Lana Lührs and Peter M. Kappeler of Georg-August-University in Göttingen, Germany, GPS-tagged nine male and four female fossas in the Kirindy Forest in southwestern Madagascar and mapped out the ranges of the animals over a period of several weeks. The females’ ranges didn’t overlap much with neighboring unrelated females. Males, however, had ranges that extensively overlapped not only with those of females — not surprising, because they want to mate with the girls — but also of other males. And three pairs of males had shared home ranges. Some males, but not all, in those pairs were related.

The researchers only had GPS data for a month, but they observed the three pairs of males hanging out together for several years. One pair didn’t break up until one of the males died. The other two dyads stayed together until the end of the study. “We assume male associations in fossas to be of a long-term or even permanent nature,” the researchers write.

Why might males be pairing up? It’s not for defending their territory, the researchers say, because male fossas aren’t particularly territorial. Females have to be because they have babies to feed, but the males don’t have to worry about that. Their bigger concern is mating with the females.

By pairing up, male fossas can cooperate in their hunts, which might allow them to eat more and grow bigger than solitary fossas. Bigger fossas are more successful with the ladies, and this might explain why males from fossa pairs also “enjoy greater mating success than solitary males during peak female fertility,” the researchers say.

As for why only some males pair up, Lührs and Kappeler speculate that this might be something that happens during the transition from adolescence to adulthood. Finding a compatible companion may be pretty easy for two brothers, but for a male without a littermate to pair up with, it could depend on whether he finds another fossa he can tolerate enough to turn into an ally. If not, the researchers say, he’ll find himself on the path to being a loner.