Climate change is a multifaceted issue that affects many aspects of our environment and biodiversity. While rising temperatures are commonly associated with climate change, it’s important to remember that other climatic factors, such as rainfall patterns, can have a significant impact on various species.
Giraffes in East African savannahs are adapting remarkably well to rising temperatures brought on by climate change. However, as researchers from the University of Zurich and Pennsylvania State University have demonstrated, they are under threat from increasing rainfall.
Climate change is expected to cause widespread population declines in wildlife around the world. However, little was previously known about the combined effects of climate change and human activity on the survival rates of large African herbivore species, including giraffes. Researchers from the University of Zurich and Pennsylvania State University have completed a decade-long study of a giraffe population in Tanzania’s Tarangire region, the largest to date. The study area covered over a thousand square kilometers and included areas both inside and outside of protected areas. Contrary to popular belief, higher temperatures were found to benefit adult giraffe survival while rainier wet seasons harmed adult and calf survival.
Our findings suggest that giraffes living on the outskirts of protected areas are especially vulnerable during heavy short rains. These conditions are likely to increase disease risks associated with livestock, and muddy terrain hinders anti-poaching patrols, resulting in increased threats to giraffe survival.
Arpat Ozgul
First exploration into the effects of climate variation on giraffe survival
The research team, led by Monica Bond, a postdoctoral research associate in the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, quantified the effects of local anomalies in temperature, rainfall, and vegetation greenness on giraffe survival. They also investigated whether climate had a greater impact on giraffes near the edges of protected reserves, which were also impacted by human activity.
“Studying the effects of climate and human pressures on a long-lived and slow-breeding animal like a giraffe requires monitoring their populations over a lengthy time period and over a large area, enough to capture both climate variation and any immediate or delayed effects on survival,” Bond explained. The researchers collected nearly two decades of data on local rainfall, vegetation greenness, and temperature during Tanzania’s short rains, long rains, and dry season, and then tracked the movements of 2,385 individually identified giraffes of all ages and sexes over the final eight years of the two-decade period.
Surprising effects of temperature on giraffe survival
The researchers predicted that higher temperatures would harm adult giraffes because their large body size would cause them to overheat, but they discovered that higher temperatures improved adult giraffe survival. “The giraffe has several physical features that help it to keep cool, such as a long neck and legs for evaporative heat loss, specialized nasal cavities, an intricate network of arteries that supply blood to the brain, and spot patches that radiate heat,” said Derek Lee, senior author of the study and associate research professor of biology at Pennsylvania State University.
However, Lee also pointed out that “temperatures during our study period may not have exceeded the tolerable thermal range for giraffes, and an extreme heat wave in the future might reveal a threshold above which these massive animals might be harmed.”
Heavy rains may increase parasites while reducing nutritional value of vegetation
The survival of giraffe adults and calves was reduced during wetter seasons, which the researchers attributed to an increase in parasites and disease. A previous study in the Tarangire region found that the intensity of gastrointestinal parasites in giraffes was higher during the rainy season than during the dry season, and heavy flooding has caused severe outbreaks of diseases known to cause mortality in giraffes, such as Rift Valley fever virus and anthrax. The current study also discovered that higher vegetation greenness reduced adult giraffe survival, possibly due to lower nutrient quality in giraffe food.
Human pressure places additional stress on already declining populations
The giraffes’ proximity to the edge of protected reserves exacerbated climate effects, but not all of the time. “Our findings suggest that giraffes living on the outskirts of protected areas are especially vulnerable during heavy short rains. These conditions are likely to increase disease risks associated with livestock, and muddy terrain hinders anti-poaching patrols, resulting in increased threats to giraffe survival,” said Arpat Ozgul, a University of Zurich professor and study author.
The team concluded that projected climate changes in East Africa, such as heavier rainfall during short rains, will likely threaten the existence of giraffes in one of the world’s most important landscapes for large mammals, highlighting the need for effective land-use planning and anti-poaching to improve giraffes’ resilience to the coming changes.
