Climate Change: Rising Rainfall, not Temperatures, Threaten Giraffe Survival

Newswise — Global climate change is anticipated to trigger extensive reduction in wildlife populations worldwide. However, prior knowledge regarding the combined impact of climate change and human activity on the survival rates of not just giraffes, but any large African herbivore species, was limited. Presently, scientists from the University of Zurich and Pennsylvania State University have completed a ten-year investigation - the most extensive thus far - on a giraffe population located in the Tarangire region of Tanzania. The study encompassed an expanse of over one thousand square kilometers, encompassing both protected and unprotected areas. Contrary to expectations, it was discovered that higher temperatures had a positive influence on the survival of adult giraffes, while wetter rainy seasons had a detrimental effect on the survival of both adults and calves.

First exploration into the effects of climate variation on giraffe survival

Under the guidance of Monica Bond, a postdoctoral research associate in the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, the team of researchers measured the impacts of temperature, rainfall, and vegetation greenness variations within the giraffe population to determine the likelihood of their survival. Additionally, they investigated whether the climate had a more pronounced impact on giraffes that were affected by human activity in the periphery of protected reserves.

"Analyzing the impacts of climate change and human influences on a species with characteristics such as longevity and slow reproductive rate, like the giraffe, necessitates extensive monitoring of their populations over a significant duration and across a wide geographical range. This allows for the comprehensive assessment of climate fluctuations and their immediate or delayed repercussions on survival," commented Bond. The research team collected data spanning nearly twenty years, encompassing local rainfall patterns, vegetation greenness, and temperature fluctuations during Tanzania's short rains, long rains, and dry season. They then tracked the outcomes of 2,385 individually identified giraffes of all ages and genders over the final eight years of this two-decade period.

Surprising effects of temperature on giraffe survival

The team initially hypothesized that higher temperatures would have a detrimental impact on adult giraffes due to their large body size, which could potentially lead to overheating. However, contrary to their expectations, they discovered that higher temperatures actually had a positive effect on the survival of adult giraffes. Derek Lee, associate research professor of biology at Pennsylvania State University and the senior author of the study, highlighted various physiological characteristics of giraffes that contribute to their ability to regulate body temperature. These include a long neck and legs for evaporative heat loss, specialized nasal cavities, an intricate network of arteries that supply blood to the brain, and patches on their skin that help radiate heat.

However, Lee cautioned that the temperatures observed during the study period may not have surpassed the tolerable thermal range for giraffes. He emphasized that in the event of an extreme heatwave in the future, there could be a critical threshold beyond which these large animals might experience harm. This suggests that while higher temperatures had a positive impact on giraffe survival within the studied temperature range, it is important to consider the potential risks associated with extreme heat events that could pose challenges for their well-being.

Heavy rains may increase parasites while reducing nutritional value of vegetation

The researchers identified a decrease in the survival rates of adult giraffes and calves during rainier wet seasons, and they suggested that this could be attributed to a potential rise in parasites and diseases. A prior study conducted in the Tarangire region demonstrated that the intensity of gastrointestinal parasites in giraffes was higher during the rainy seasons compared to the dry season. Furthermore, instances of heavy flooding have led to severe outbreaks of diseases, including Rift Valley fever virus and anthrax, which are known to cause mortality in giraffes. The current study also revealed that higher vegetation greenness was associated with reduced survival of adult giraffes. This could be due to faster leaf growth, which potentially diminishes the nutrient quality of giraffe food.

Human pressure places additional stress on already declining populations

The influence of climate on giraffes was intensified when they resided close to the boundaries of protected reserves, although this effect was not consistent across all seasons. Arpat Ozgul, a professor at the University of Zurich and one of the authors of the study, stated that their findings indicated that giraffes located near the peripheries of protected areas faced the greatest vulnerability during periods of heavy short rains. These specific conditions are likely to elevate the risks of disease transmission associated with livestock. Additionally, the presence of muddy terrain during such seasons hampers anti-poaching patrols, leading to an increased threat to the survival of giraffes in these areas.

Based on their findings, the research team reached the conclusion that anticipated climate changes in East Africa, including increased rainfall during the short rains, are expected to pose a significant threat to the survival of giraffes in one of the world's crucial habitats for large mammals. This underscores the importance of implementing effective land-use planning and anti-poaching measures to enhance the resilience of giraffes in the face of these impending changes. Taking proactive steps in these areas can help mitigate the potential negative impacts of climate change and ensure a better chance for the long-term survival of giraffes in this vital landscape.