Adult female giraffes in northern Tanzania
Adult female giraffes who spend time with lots of other females live longer than less sociable animals.
Monica Bond at the University of Zurich, Switzerland, and her colleagues observed 512 female giraffes over 1500 square kilometres in the Tarangire Ecosystem in northern Tanzania. They surveyed the landscape six times a year between 2012 and 2016 and took photographs of any female giraffes they encountered.
The team used a piece of software called WildID to identify giraffes from their spot patterns. Each giraffe is born with a unique pattern of spots and these remain unchanged throughout their life, says Bond.
The researchers built a giraffe social network – based on similar research studying human ones – to map each female giraffe’s relationships with other females, the strength of these relationships and their average group size.
From this, the team found that female giraffes that socialised in groups with at least three other females have a higher likelihood of survival than more solitary individuals. Sociability was also the largest contributor to survival, compared with other environmental factors including proximity to human settlements, food sources and vegetation type.
“Friends matter for their survival,” says Bond. “We think it reduces stress in general for these female giraffes and allows them to live a more relaxed life.”
This isn’t true of male giraffes. Previous research has shown that they are solitary animals that move around looking for females to mate with and don’t form stable, long-lasting relationships with other giraffes.
“Mixing in small groups seems to foster the giving and receiving of information about where is best to feed,” says Daniel Rubenstein at Princeton University. Roaming with other females could also help the giraffes keep an eye out for predators and care for calves.
“With more females in a group, it even reduces male harassment as solitary females are more likely to get harassed by males,” says Bond.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2020.2770
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