Giraffes are among the iconic wild animals of the African savannah. But how are they coping with the current changes in the climate? When biologists studied this in East Africa for eight years, something surprising became apparent: Contrary to what was thought, it is not the ever-increasing heat that is affecting the long-necked herbivores. Instead, the increasing heavy rain during the rainy season in particular has a negative effect on the survival of the giraffes.
Large herbivores such as giraffes are key species for savannah ecosystems, while at the same time they are endangered because of their large land requirements and increasing conflicts with human land use. In the meantime, climate change has also become an additional stress factor. But until now, little was known about how climate affects the survival of giraffes and other African herbivores.
How is climate change affecting giraffes?
A research team led by Monica Bond from the University of Zurich has now investigated this question using the example of the giraffe population in the Tarangire region in Tanzania. To do this, the scientists collected almost two decades of data on precipitation, green vegetation and temperature during the small and large rainy season in Tanzania and during the dry season. They also followed the fate of 2,385 giraffes in this region over a period of eight years and examined how local anomalies in temperature, precipitation and vegetation affect the giraffes' probability of survival.
"In order to study the effects of climate and humans on a long-lived and slow-breeding animal like the giraffe, we need to look at their populations over a long period of time and over a large area," explains Bond. The evaluation of the data revealed something surprising: the biologists had actually expected that higher temperatures would harm the adult giraffes because they could overheat due to their body size. But this was not the case. Zar, the animals sought shade more and exercised less during hot spells, but the team found their survival was unaffected by increased temperatures.
No problem with heat, but with wet weather
According to the researchers, this confirms that giraffes are particularly well-adapted to heat: "The giraffe has several physical features that help it keep cool, including a long neck and long legs through which heat is dissipated," explains senior author Derek Lee of Pennsylvania State University. "But it also has specialized nasal cavities, a complex network of arteries that supply blood to the brain, and a spot pattern that radiates heat." These evolutionary adaptations allow the animals to avoid overheating their bodies. However, it is not known whether this still applies when the temperature range that giraffes can tolerate is exceeded during extreme heat waves.
However, the long-term observations showed something else: While they were not affected by heat, heavy rainfall had a clearly negative effect on the survival of the giraffes. If more precipitation fell than normal during the rainy season, more calves died and fewer adult giraffes survived the rainy season. The researchers suspect that this decreases with an increase in parasites and pathogens, as both benefit from a wetter climate. Previous studies have shown that giraffes are more likely to suffer from gastrointestinal parasites and diseases such as Rift Valley fever and anthrax in wet weather and flooding. In addition, the reduced nutrient content of vegetation that sprout faster after the rain could also affect the survival of the giraffes.
Threat from extreme weather and humans
This means that climate change could well have a negative impact on the giraffes of East Africa - just in a very different way than previously thought. Because instead of the heat, it is above all the precipitation, which falls more heavily in the rainy seasons, that impairs their survival. "Extreme weather events are becoming more frequent in East Africa: drought and flooding in the Masai Mara have doubled in the period since 1990 compared to the previous 30 years," report Bond and her team. Add to this the loss of habitat by humans and poaching, and this further threatens the survival of the giraffes. Effective land-use planning and the fight against poaching are therefore needed to improve giraffes' resilience to the coming changes, say the biologists.
Source: University of Zurich; Specialist article: Biodiversity and Conservation, doi: 10.1007/s10531-023-02645-4