Frans Lanting/Nat Geo Image Collection

Animal friendships change with the weather in African savanna

Some animals stick with each other through thick and thin, but others are—literally—fair-weather friends, abandoning their buddies from other species when the dry season dries up food resources. A new study of herbivore social interactions in Kenya’s savanna suggests two things bring such grazers back together: rain and roaming wildebeest herds.

Plant-eating animals often benefit from grazing alongside other species. Thomson’s gazelles, for example, are less at risk of being killed by predators such as lions and hyenas when they join with their cousins, Grant’s gazelles. But not every such species-to-species relationship lasts the year.

To find out which species like to hang out together—and how that shifts when the environment changes—researchers studied 12 common herbivores, including ostriches, zebras, buffalos, and four species of antelope. The researchers examined species-on-species interactions for 1 year in Kenya’s Msasai Mara National Reserve.

Msasai Mara has two short rainy seasons, punctuated by one short dry season and one long one. Some animals—like elands and zebras (above)—hang out together through all seasons, and even more in the rainy months. But in the dry seasons, when food resources are scarcer, ostriches and buffalos tend to strike out alone, and Thomson’s and Grant’s gazelles prefer the company of their own species. When the rains come again and food is more plentiful, these animals are more likely to socialize with other species, the researchers reported last week in the Philosophical Transactions of the Royal Society B.

Another factor seems to drive some herbivores together: the annual arrival of more than 2 million wildebeests, which migrate to Maasai Mara during the long dry season from June to October. Elands and buffalos, for example, spend more time with other species when the wildebeests arrive, probably because of competition from the wildebeests. Zebras, Thomson’s gazelles, and topis, on the other hand, prefer the company of wildebeests, probably because their large numbers offer protection from predators.

Understanding the complex dynamics of these “friendships” could help guide conservation efforts, especially as habitat fragmentation and climate change become bigger and bigger problems,the scientists say. They did not say, however, whether their study will land on one of YouTube’s “unlikely animal friendships” channels.