Physiological responses in free-ranging Asian elephant populations living across human-production landscapes

Monitoring the physiology of elephants living in human-production landscapes has become increasingly important for understanding how they cope with various challenges that affect their overall fitness. We assessed physiological stress by measuring faecal glucocorticoid metabolite (fGCM) levels and metabolic states using faecal triiodothyronine (fT3) across three free-ranging Asian elephant populations (one in Central India and two in Northeastern India) whose home ranges encompass varying extents of disturbance in human-production landscapes. We present landscape disturbance metrics to characterize variations in fragmentation and anthropogenic pressures across the study landscapes and use faecal carbon and nitrogen (C/N) ratio as a proxy for dietary quality, with higher C/N values indicating poorer-quality diets. Elephants living in more fragmented habitats in Central India had higher fGCM and lower fT3 levels compared to the Northeastern populations, as well as when compared (only fGCM levels) with a previously-studied Southern Indian elephant population. A positive relationship was observed between faecal C/N ratio and fGCM levels across the populations, except for the Central population. These findings suggest that elephants in highly fragmented landscapes and experiencing significant anthropogenic disturbances have (i) higher adrenal activity to cope with and (ii) reduced metabolic rates to conserve energy in emerging challenging contexts. While elephants may adapt to living in human-modified landscapes to some extent, they may experience high stress levels beyond a threshold of disturbance which can be physiologically costly. This warrants systematic assessments to evaluate how these biological costs impact their fitness, and a re-evaluation of conflict management practices.