Grown giraffes are not hugging, hugging, and demonstrative animals. Therefore, identity recognition software required five years of data to reveal that female social life is important for survival.
The most gregarious adult female giraffes in the Tarangire ecosystem of northern Tanzania tend to live longer, concludes wildlife biologist Monica Bond of the University of Zurich. Women who normally hung around three other people like this were more likely to survive those who had fewer routine mates, Bond and colleagues reported Feb. 10 in Proceedings of the Royal Society B.
In published science, the idea that giraffes even have social lives doesn’t last much more than a decade, Bond says. (For now, Bond still treats giraffes as one species, Giraffa camelopardalis, until there is more agreement on how many species there are.) Adult males spend most of their time on solitary searches for willing females to mate, but females often hang in groups.
Compared to bats clustered under a bridge or baboons caring for the skin of friends, even the most sociable female giraffes often look as if they are milling feeding on the same bush. These “loose” groups, as Bond describes them, do not curl up or prepare. A group mostly only navigates in the same neighborhood and can then separate and reconfigure with different members in the fission-fusion pattern seen in many animals, such as dolphins. However, a closer look found that females prefer certain neighbors and seem to avoid others.
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Bond found giraffes in the wild in 2007 on his first trip to Africa. "I loved everything," she says, but mostly giraffes that look "as fanciful and weird as a unicorn." To examine their lives, she and her colleagues recorded sightings of nearly 3,000 individuals in the Tarangire region. The spots on each giraffe are unique and remain identifiable throughout life, so photographs of the torsos of the animals make their identification possible (SN: 10/2/18).
Unlike the much-studied Serengeti National Park in Africa, the Tarangire region allows researchers to see animals in a wide range of human impacts. At the low-impact end, giraffes eat acacia trees in a protected park or stroll under baobabs that “sneak up like a giant broccoli,” Bond says. Human influence is becoming more common where the Masai people care for livestock and the heaviest human footprints are in the bustling cities of the region.
Bond and colleagues analyzed how plant types eaten, soil types, proximity to humans, and other factors affected women’s chances of surviving from one season to the next. The most important predictor of survival for 512 adult wild giraffes was the number of other females normally found around them. She doesn’t think it’s just that predators more easily catch solitaires or some resounding groups. In this region, lions don’t hunt in the great prides they can overwhelm adult prey and “a giraffe can kick a lion,” Bond says.
Instead, Bond speculates that gregarious females may suffer less stress. Lions in the area chase giraffe calves, for example. In a larger group, calves can cluster on each other in nurseries that a few females watch over, leaving the other mothers to rest. And when larger female groups settle in at night, Bond sees alert eyes among the sleepy ones who will rest better.
This analysis, however, comes only from the Tarangire region. “It would be great for the methods to be replicated in other ecosystems to see how it holds up,” says Arthur Muneza, the East African coordinator based in Nairobi, Kenya, for the Giraffe Conservation Foundation. A place where giraffes need to travel further to find water or other vital resources, for example, can make a difference in results.