How stressed are elephants captured from the wild compared to their captive-born workmates, and how does time spent in captivity affect this? How does taming affect stress hormone (cortisol) levels and health, and which factors help to reduce such effects? How do cortisol levels relate to workload, body condition and measures of reproductive ability, and does seasonal variation in cortisol underlay the seasonal patterns in mortality and birth rates of elephants? Can we use information about stress hormone levels and about heterophil / lymphocyte ratios to improve welfare of elephants?
We collect monthly faecal samples of timber elephants with known birth origin and life-history documented in their logbooks, to investigate the factors which cause variation in faecal glucocorticoid metabolites (FGM). We also collect monthly blood samples to determine white blood cell counts. The heterophil / lypmhocyte (H/L) ratio can be used to assess how animals experience stress.
Mean faecal glucocorticoid levels fluctuate across Myanmar‘s three seasons, reaching their lowest in hot season (March–May) and their highest in monsoon season (June–September), while elephants during cold season (October–February) exhibit intermediate levels (Mumby et al. 2015a, Seltmann et al. 2020). Stress is also related to reproductive ageing where calves born in the high stress season (monsoon), where females born in these months exhibit faster reproductive senescence in adulthood and have significantly reduced lifetime reproductive success than their counterparts born at other times of year (Mumby et al. 2015b). Furthermore, we found a positive and consistent link between FGMs and H/L ratios in elephants of our study population, irrespective of their sex, age, and season. Hence, the H/L ratios from blood smears on site can be a potentially cheaper and faster alternative to determining stress than measuring FGM concentrations in the laboratory.
Watch this space for more exciting findings in the near future!