The home territories of African elephants in Laikipia County, Kenya, have become a mosaic of human settlements and non-protected savannahs. Privately owned land, like the Mpala Cattle Ranch, plays a key role in wildlife conservation by providing a relatively stable and peaceful area for large land mammals to live and forage. Although the elephant population in Laikipia has been increasing, the overall trend of the wildlife population in sub-Saharan Africa has been declining. The negative influence of poaching, acute habitat loss, and population fragmentation has been well documented. However, little is known about the direct impact human disturbance and gradual vegetation changes due to climate change have on elephants’ ranging patterns and adrenal corticosterone stress hormone levels.
To better understand the effects of these disturbances on the African elephants of Laikipia County, a group of Kenyan and American scientists looked at fecal glucocorticoid metabolite (FGM) levels as an important non-invasive biological indicator of environmental stress. During the study, published in PeerJ, researchers collected fecal samples from 156 uniquely identified elephants on the Mpala Ranch for four months spanning parts of the wet and dry seasons. They measured elephant corticosterone by using double antibody enzyme immunoassay kits (K014-H) from Arbor Assays and compared the results to the documented behavior of the individual elephants when research vehicles drove close to them. They also looked at the correlation of the elephant corticosterone FGM levels compared to the Normalized Difference Vegetation Index (NDVI), a standard flora quality measurement technique based on satellite images that indicates food availability for the elephants.
The findings support the scientists’ hypothesis that a positive correlation exists between high reactivity to vehicle presence and high FGM stress hormone concentration in resident and transient elephants on the ranch (p < 0.0001). They also confirmed an expected decrease in FGM levels as the area’s NDVI food quality index increased during the short wet season (p < 0.0001). These correlations help researchers understand and quantify the negative impacts that human presence and climate change have on elephant populations.
Despite the environmental stability and water access that the ranch provided, the scientists were surprised to find that transient elephants had lower overall FGM levels compared to those who lived exclusively within the property. Higher FGM levels in the resident elephants were likely the result of a particularly low NDVI for the Mpala ranch during the studied seasons compared to nearby areas. By being able to forage afield, non-resident elephants could make up for the inadequate food supply at the ranch during periods of low NDVI. This further emphasizes the need for elephants to be able to move freely throughout the landscape to find alternative sources of nutrition.
As global warming creates longer, more extreme dry seasons, scientists anticipate NDVI levels to swing dramatically and negatively impact the food supply. The study found that when elephants increase their foraging range, they can mitigate the worst of these effects and lower their stress levels. However, if housing developments continue encroaching on native territories, elephants will only become more stressed as their interactions with humans increase and traditional forage routes are blocked.