Living close people disturbs giraffe social networks, research finds.
Giraffes near humans having weaker bonds and fewer interactions with others, according to the new study.
The research team monitored more than 500 giraffes over six years and used social network analysis. A paper describing their results appears in the Journal of Animal Ecology.
“In Tanzania, giraffes are generally tolerated by humans because they do not cause conflicts with farmers or livestock,” says Derek Lee, associate research professor of biology at Penn State and principal investigator of the long-term giraffe research project. “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.
“For example, proximity to humans could disturb an animal’s ability to perform tasks that are important for survival, such as feeding together or rearing young. In this study, we have found the first robust evidence that humans modify the social structure of this iconic megaherbivore.”
Over a period of six years, the researchers collected photographic data on 540 adult female Masai giraffes inhabiting a large, unfenced area in Tanzania with varying levels of human disturbances. The researchers were able to identify individual giraffes by their unique and unchanging spot patterns.
“Detecting signals of natural versus human-caused influences on social relationships among wild animals is challenging,” says Monica Bond, research associate at the University of Zurich and first author of the study. “It requires large-scale studies of individually identified animals across numerous social groups living under different environmental conditions. Our study was one of the first to do this and, to our knowledge, is one of the largest-scale social networks ever studied in a wild mammal.”
Giraffe social networks
The research team first characterized the social relationships of giraffes, and then explored the impact of humans. They found that female giraffes live in a complex multilevel society, with individuals preferring to associate with some females while avoiding others. These preferences result in discrete social communities of 60 to 90 females with little mixing among the communities, even when they share the same general area.
The team also found that relationships within these social communities are disrupted by human presence. Giraffes living closer to traditional compounds of indigenous Masai people are less likely to associate with the same individuals as frequently, suggesting they form weaker relationships with all the members of the community, and, when they do form strong relationships, it is with fewer females, suggesting greater exclusivity in their social associations.
“Despite the public tolerance and hunting restrictions, Masai giraffe populations have declined 50% in recent years,” says 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.”
Giraffes living near traditional human settlements are more likely to encounter livestock and humans, potentially causing groups of giraffes to split up. These conditions could make it harder to maintain group cohesion and could thus impact their ability to perform social behaviors.
Mothers and calves
However, according to the team’s previous research, groups of female giraffes with calves actually tend to congregate closer to the traditional human settlements, possibly because they provide better protection from lions and hyenas.
“It seems that female giraffes face a trade-off between maintaining important social bonds and reducing predation risk to their calves near these traditional settlements,” says Bond. “Now that we know that human presence can affect giraffe social structure, we need to adjust our conservation efforts to ensure that this species can survive—living near traditional pastoralists could benefit giraffes as long as their social relationships are not disturbed.”
This study highlights the importance of using a social network approach to reveal otherwise hidden potential causes of population declines.
“Only by characterizing the complex interactions of individuals with their social, biological, and physical environment can we begin to understand and mitigate the impact of humans on wildlife populations,” says Lee.
Additional coauthors are from the University of Zurich, the Max Planck Institute of Animal Behavior, and the University of Konstanz. Support for the work came from the University of Zurich, Penn State, the Sacramento Zoo, the Columbus Zoo and Aquarium, the Tulsa Zoo, the Tierpark Berlin and Zoo Berlin, Parrotia, Temperatio, Promotor, Claraz, and Save the Giraffes.
Additional support came from the Max Planck Society, the German Research Foundation (DFG), and the European Research Council.
Source: Penn State