Giraffes living near people have weaker bonds and social networks, which could impact the “iconic megaherbivore’s” ability to perform social tasks that are important for survival, like forage for food or rearing young, according to new research published in the Journal of Animal Ecology.
Megaherbivores like giraffes are “ecological engineers that play a key role in shaping the vegetation of African savanna ecosystems,” yet their populations, as well as those of elephants and rhinoceroses, have “declined precipitously over most of the continent.” Key threats to these megaherbivores include overhunting for meats and body parts as well as habitat destruction through deforestation and land cultivation.
To determine how proximity to humans may play a role in the social structures of giraffes, researchers from Penn State, the University of Zürich, the Max Planck Institute of Animal Behavior, and the University of Konstanz monitored more than 500 female Masai giraffes over six years in northern Tanzania, an area that has undergone a 3 percent human population growth between 2003 and 2012, adding nearly 800,000 people. Giraffes individually identified by their unique spots were photographed between 2011 and 2016, allowing researchers to create a “social network” of interactions between individual giraffes and how they were impacted by human disturbances.
“In Tanzania, giraffes are generally tolerated by humans because they do not cause conflicts with farmers or livestock,” said Derek Lee, associate research professor of biology at Penn State and principal investigator of the long-term giraffe research project, in a press release. “But even if animals are not hunted and killed by humans, increased interactions with humans could have indirect but profound effects, including on their social structure.”
Females were shown to live in complex, multilevel communities made up of 60 to 90 individuals that prefer to associate with some giraffes while avoiding others. Little mixing between the different groups was observed even when multiple groups were spotted in the same area. Groups observed living near or having been disrupted by people were less likely to associate with their giraffe comrades, suggesting that proximity to people creates greater exclusivity within social groups and weakens relationships.
Changes in the social structure could be a response to changes in their environments that are, in some cases, caused by humans. Giraffes that live near human settlements are more likely to encounter livestock and other people, which can split up the group and make it harder to maintain cohesion. Those living near African livestock enclosures known as bomas showed the weakest relationships, which could be a result of reduced food resources from fuelwood cutting. On the other hand, giraffes with young calves live closer to human settlements, perhaps because it provides protection from predators – a “trade-off” between maintaining important bonds and reducing predation risk to calves.
“Despite the public tolerance and hunting restrictions, Masai giraffe populations have declined 50 percent in recent years,” said Lee. “We believe that disruption to their social system due to interactions with humans — in addition to illegal poaching, habitat loss and fragmentation, and changes in food supply — could be a contributing factor to population declines.”
Conservation efforts need to be adjusted to include changes in interactions within groups, which the researchers note are “critical for survival and reproduction” and “essential for the persistence of social units."