Proximity to towns stretches giraffe home ranges

A study found that female giraffes that live close to towns have larger home ranges than those living further afield.

Giraffes have to search a wider area for food and water when people live nearby, according to a recent study.

“Giraffes are huge browsing animals that live in African savanna ecosystems where they must find everything they need to survive and reproduce in landscapes increasingly impacted by human activities,” Derek Lee, a biologist at Pennsylvania State University and the Wild Nature Institute and one of the study’s authors, said in a statement. “People are converting natural savannas to towns and farms, and cutting trees for fuelwood and charcoal industries, all of which potentially degrade giraffe habitat.”

Earlier research has shown that the size of the area that giraffes need to provide them with food and water, find mates and raise their young varies widely across the African continent. Ecologists figure that a complex web of factors, ranging from water availability to the presence of people, probably determines how big those home ranges are. But until now, they hadn’t zeroed in on the roles that each factor plays.

Lee and his colleagues began by taking photographs of giraffes throughout the Tarangire-Manyara region of northern Tanzania. The study area is home to parts of two national parks and a private reserve, as well as roads, farms and human settlements. Between 2011 and 2016, the team tracked the movements of 132 Masai giraffes (Giraffa camelopardalis tippelskirchi), feeding the data into a statistical model designed to show how various environmental factors affected the size of the giraffes’ home ranges. (Some scientists argue that four species of giraffe roam Africa’s savannas and dry woodlands. But the IUCN still considers the giraffe a single species, listed as vulnerable on the group’s Red List, with nine subspecies.)

Surprisingly, the type of vegetation available and the density of giraffes, which significantly affect the size of home ranges for other large herbivores, did not have a substantial impact on the size of a giraffe’s home range. What did play a role, for female giraffes at least, was their proximity to big towns. The closer the giraffes lived to them, the larger their home ranges were likely to be.

“Human disturbance and fragmentation of habitat in and around densely populated areas likely reduced the local forage and water resources available for giraffes, forcing individuals to increase their movements and use of space to obtain these resources,” Mara Knüsel, a graduate student in evolutionary genetics at Switzerland’s University of Zurich and the study’s lead author, said in the statement.

The team published its research in the March 2019 edition of Animal Behavior.

The critical determining factor appeared to be the density of the human population, not solely the presence of humans in an area. The researchers did not find a correlation between giraffe home range size and the presence of Maasai bomas. Fewer people live in these often-temporary settlements than in towns, which might make them more tolerable to giraffes, the authors write. Or it could be that the Maasai’s herding of livestock doesn’t affect giraffes’ ability to find food.

The team also analyzed the sizes of giraffe home ranges for eight populations around Africa in relation to average rainfall. Precipitation levels alone accounted for almost three-quarters of the variation in range size between these groups of giraffes. Lee said that finding was “not surprising.”

“Greater availability and access to critical resources such as food and water leads to smaller home range sizes,” he said.

The authors contend that a deeper understanding of how much space giraffes need is vital, especially as their numbers have slid to fewer than 100,000 in recent years as a result of hunting, human conflict and the loss of their habitat.

“Giraffes are vulnerable to extinction after a 40 percent population decline during the past three decades,” Knüsel said. “Identifying factors affecting space use help wildlife conservationists to make better decisions for at-risk species such as giraffes.”

Banner image of a Masai giraffe in Tarangire National Park in Tanzania by John C. Cannon/Mongabay. 

Citations

Knüsel, M. A., Lee, D. E., König, B., & Bond, M. L. (2019). Correlates of home range sizes of giraffes, Giraffa camelopardalis. Animal Behaviour, 149, 143-151. doi: 10.1016/j.anbehav.2019.01.017

Muller, Z., Bercovitch, F., Brand, R., Brown, D., Brown, M., Bolger, D., Carter, K., … & Wube, T. 2018. Giraffa camelopardalis (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2018: e.T9194A136266699. doi: 10.2305/IUCN.UK.2016-3.RLTS.T9194A136266699.en. Downloaded on 06 March 2019.

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