Tall together: How Giraffes benefit from female friendships

The giraffe's height comes at a price. Picture Dan Linehan

‘No man is an island entire of itself’, wrote John Donne. Cocooners will agree. Lockdown impacts mental health and wellbeing, distress is widespread and sales of antidepressants are up. 

Isolation is not just harmful for people; some other creatures can suffer from it also. According to a paper just published, lack of social contact reduces the life-expectancy of giraffes.

The world’s tallest mammal eats leaves and branches rich in nutrient, beyond the reach of other herbivores. But this ability has a price. To pump blood to a brain so high up, the heart needs to be extra large. Weighing around 60kg, it’s the size of a large dog. The brain, on the other hand, is correspondingly small.

Animals with small brains tend to be less socially sophisticated than those with large ones. Giraffes, however, buck the trend. They live in groups, usually segregated by sex, offering open-ended easy-come-easy-go, ‘fission-fusion’, access to all comers. There is no territory holding.

Recent research, however, shows that ‘stable’ relationships exist between individual giraffes and there are looser associations within groups, often based on kinship. Females, ‘cows’, are more particular than ‘bulls’ when it comes to socialising. Bulls tend to be solitary, seldom forming longer-term associations; they often end their days alone.

Monica Bond of Zurich University tracked 512 female Masai giraffes in a 1,500km2 area of Tanzania over a five year period. Keeping track of individuals didn’t require animals to be fitted with identification tags; each giraffe has a unique arrangement of darker spots on its pelage. The patterns can be computerised, enabling animals to be recognised from photographs taken in the field.

Richard Collins: 'Adult females frequenting large groups were found to live longer than more isolated ones.'

Surveys of the population were carried out six times each year, enabling the researchers to measure the persistence and strength of individual relationships.

The team quantified ‘gregariousness’ (the number of females frequently observed with a particular individual) and ‘betweeness’ (links to other adult females). Non-social factors, such as availability of food and the proximity of human settlements, were factored in.

Adult females frequenting large groups were found to live longer than more isolated ones. Gregariousness, the researchers conclude, ‘appears to be far more important in explaining variation in survival than the other measures of social connectedness, or any of the natural or anthropogenic environmental factors we tested’. ‘Our results suggest that females living closer to towns had lower survival, although this effect was not as strong as gregariousness’. Being socially integrated was even more import than the quality of food available.

The researchers think that, as with humans, access to close friends reduces stress; ‘larger groups can better detect predators or deflect predators from themselves’. Gregariousness may also benefit calves. Females ‘bear a high prevalence of lion claw marks which were likely acquired during calf defence’. Youngsters surrounded by adults in herds are more secure from predators. Also, sexual harassment by aggressive males is less of a problem for females in groups; does the sorority gang together and see off the offender? Giraffes ‘get by with a little help from (their) friends’.

‘And therefore never send to know for whom the bell tolls, It tolls for thee’.

Monica Bond et al. Sociability increases survival of adult female giraffes. Proceedings of the Royal Society B. 2021.