The risk of predators affects the behavior of giraffe groups with calves more strongly than that of all-adult groups, a new study shows.
Researchers studied giraffe behavior in a 2,000 square kilometer (about 772 square mile) region of Africa and pinpointed some of the special requirements mother giraffes need to keep their babies safe.
The findings, which appear in Oecologia, may help land managers protect the habitats most important for giraffes.
“Like all herbivores, giraffes need to find quality food to survive, but also need to avoid lions, or at least see them coming,” says lead author Monica Bond, a PhD candidate at the University of Zürich.
“Giraffes in our huge, unfenced study area can choose from among many different places to spend their time—places with different kinds of trees and bushes, places deep inside protected parks, or places closer to farming towns or ranchlands where people live.
“There are lots of options in this landscape, including fewer lions outside the parks versus inside. So, we wondered how do these options influence giraffe grouping behavior?”
Giraffes, predators, and food
The researchers found that groups composed of only adult giraffes focused on food and not predation risk. These adult groups formed the largest groups—up to 66 individuals—in the rainy season when food is plentiful, but formed smaller groups during the dry season when food is harder to find.
In contrast, predation risk was a very important factor influencing groups of giraffes with calves.
“Giraffe calves are vulnerable to being killed by lions and other carnivores, while adults are typically large enough to escape predation,” says senior author Barbara König, a professor at the University of Zürich.
“We were testing hypotheses about mother and calf behavior to see if their strategy was for calves to hide in thick bushes to avoid predators, be in the open to see predators coming, or be in large groups for many eyes and lower individual risk.”
The researchers discovered that in areas with the most lions, groups with calves more often kept to dense bushes rather than open grasslands, and those groups were smaller in size. This observation supports the idea that giraffe mothers and calves have a strategy of hiding in dense bushes, rather than staying in open areas to better see lions or gathering in large groups to dilute the predation risk.
Dense bushlands are therefore important habitat for giraffe calves and land managers should protect them, the researchers say. Some cattle ranchers promote shrub removal to encourage grass for their livestock, but this thinning of brush could be detrimental to giraffes and other animals that share the rangelands.
What about people?
Researches also explored the influence of humans on giraffe grouping behaviors.
“Outside the parks, the human population has been rapidly expanding in recent years,” says coauthor Derek Lee, associate research professor of biology at Penn State.
“Therefore, we felt it was important to understand how human presence affected grouping behavior, as natural giraffe habitat is ever-more dominated by people.”
Interestingly, adult females with calves are more likely to stay closer to traditional pastoralist compounds called bomas, which livestock-keeping, non-farming people make.
“We suspect this is because the pastoralists may disrupt predator behaviors to protect their livestock and this benefits the giraffe calves,” Lee says.
Conversely, groups with calves avoided areas close to the larger towns of farming people, suggesting a difference between traditional bomas versus more densely populated human settlements for giraffe mothers seeking food and safety for themselves and their calves.
“We were happy to find that traditional human settlements by ranchers appear to be compatible with the persistence of giraffe populations,” Bond says.
“But on the other hand, disturbances around towns likely represent a threat and should be limited in areas favored by giraffes. Masai giraffes are the world’s tallest herbivores and are beloved by people around the globe, but they were recently classified as an endangered species by the International Union for Conservation of Nature. The data in this study can help us know what places are most important for these magnificent animals.”
The study was part of the world’s largest giraffe research project and used data from six years of systematic seasonal surveys.
Source: Penn State