Climate change could ‘raise stress levels’ of endangered mountain gorillas
Global warming could cause stress to endangered Virunga mountain gorillas, potentially raising the risk of health problems and early death, a new study suggests.
Using fecal samples taken in the wild, researchers found that Virunga gorillas show elevated stress levels in months with higher-than-average temperatures and rainfall.
This suggests that Virunga gorillas “might be more sensitive to warming trends than previous research has suggested”, the authors write in their research paper.
The findings provide “robust” evidence of how climate change could heighten the animals’ stress levels, a primatologist tells Carbon Brief. “We don’t know yet what the long-term impact of this physiological response will be, but it could be a harbinger of reduced survival or fertility.”
Mountain gorillas (Gorilla beringei beringei) are an endangered subspecies living in fragmented forests across the Great Lakes region of Africa.
The total population of around 1,000 individuals is split between two regions. The term “Virunga mountain gorilla” refers to the group that live across the Virunga massif, a chain of volcanoes covered by dense cloud forest. The region spans Rwanda, Uganda and the Democratic Republic of Congo.
Virunga gorillas face severe ongoing threats from hunting, habitat destruction and the impacts of nearby human conflicts. However, major conservation efforts have seen population numbers rise from around 250 in the 1980s to 604 in 2016.
The new study, published in the journal Ecology and Evolution.
Over two years, researchers routinely collected fecal samples from 115 Virunga gorillas. This allowed them to continuously monitor the animals’ stress hormone(glucocorticoid) levels.
The scientists then compared these results to local records of monthly temperature and rainfall data. They also considered a range of social factors that can influence stress levels, including gorilla group size and proximity to rival groups.
The findings show that baseline stress levels of Virunga gorillas were raised in months with higher-than-average maximum and minimum temperatures, as well as in months with higher rainfall.
The researchers did not study the reasons why gorillas might have experienced more stress in warmer or wetter conditions.
However, the researchers note that “on hot and sunny days, mountain gorillas often seek shade in vegetation”, leading to “reduced time spent feeding”.
When rain is heavy, “mountain gorillas sit still in a huddle, but if rain persists, they will resume feeding and compensate for lost feeding time”, the authors say. This could raise stress as “gorillas work harder to maintain a stable body temperature” to counteract the rain’s cooling impact.
The findings suggest that Virunga gorillas “may have a harder time coping with warmer temperatures and more extreme rainfall”.
Local temperatures in the gorillas’ habitat could increase by up to 3.6C by 2090, relative to 1990 levels, under a moderately high greenhouse gas emissions scenario (SRES A2).
In addition, rainfall is expected to become “less evenly distributed”, with “more extreme swings between the wet and dry seasons”, the authors say.