People who have siblings are probably well aware of the annoyances that can come from sibling rivalry. For spotted hyenas (Crocuta crocuta ) though, sibling rivalry is a matter of life and death.

Spotted hyena mothers usually have twins. They give birth in a private burrow where the newborns live for the first few weeks of life.

By the time the mother moves her offspring from the natal burrow to the community den however, there's higher than usual chance in mammal populations that one of her infants will be dead (approximately a ten percent chance according to one study). What's more, the survivors often emerge from their nursery covered with wounds.

The Good Son

A look inside the burrow reveals what's going on. After a long gestation cycle, newborn hyenas are remarkably well developed.

Like Red Riding Hood's wolf that they resemble despite being more closely related to cats than canines, they have big, open eyes and full sets of teeth. They won't hunt for many months to come, so what are these adaptations for?

Hyena infants fight each other from the moment they're born, and in one case (in captivity) were observed fighting within the amniotic sac.

What possible advantage could there be in engaging in siblicide? One potential answer might have to do with adult hyena table manners.

Hyenas hunt together, but once they've brought down their prey it's every hyena for itself in a violent feeding frenzy, where the most vicious hyenas steal away the most food. And even when they're not fighting each other, they sometimes have to fight off bigger animals such as lions from stealing their kills.

Siblicide is more likely to occur in hyena communities where food sources are not steady. With food a scarce commodity, brood reduction/siblicide is more likely to occur because they have less access to their mothers.

Sources And Further Reading:

Hofer, Heribert, and Marion L. East. "Siblicide in Serengeti spotted hyenas: a long-term study of maternal input and cub survival." Behavioral Ecology and Sociobiology 62, no. 3 (June 27, 2007): 341-51. Accessed January 18, 2017. doi:10.1007/s00265-007-0421-3

National Geographic Society. "Spotted Hyenas, Spotted Hyena Pictures, Spotted Hyena Facts." National Geographic. Accessed January 18, 2017.