Higher fecal glucocorticoid and triiodothyronine metabolite concentrations are associated with agricultural use in male African savanna elephants

Human-wildlife conflict is increasing in frequency and distribution with the accelerating conversion of natural lands to agriculture. These agricultural areas provide valuable resources for wildlife, but also pose risks of conflict with humans. While optimal foraging theory predicts that animals adopt a strategy that maximizes benefits relative to costs, the rewards of foraging on crops come with unclear physiological costs. We investigated how agricultural use by African elephants correlated with ecological conditions as measured by the Normalized Difference Vegetation Index (NDVI) (a measure of vegetation greenness). We also investigated how fecal glucocorticoid metabolite (fGCM) and fecal thyroid metabolite (fTM) concentrations correlated with body condition scores (BCS) and time spent within agricultural areas over different time windows while controlling for ecological conditions as measured by NDVI. Individuals with lower BCSs had higher fGCM concentrations than those with higher scores. Time spent in cultivated areas was negatively correlated with NDVI values. While both fGCM and fTM concentrations were positively correlated with time spent in agricultural areas, those correlations occurred at different time scales. The strongest correlation with fGCM was related to the time spent over the previous 3 days, while for fTM, it was for time spent over the previous 10 days, potentially reflecting differences in physiological response mechanisms related to these two hormones. The association between elephants’ dietary choices and habitat use, influenced by their physiological and metabolic states, provides a proximate explanation for human-elephant conflict.