Quantifying faecal glucocorticoid metabolites in rock hyraxes Procavia capensis (Pallas, 1766) living in an urban green space

Abstract

Although rock hyrax (Procavia capensis) is an abundant species in urban areas of South Africa, limited information exists of their physiological stress response when exposed to anthropogenic disturbances. Previous endocrine studies investigating stress hormone levels related to social factors, utilized hair as hormone matrix. As hormone metabolite concentrations tend to accumulate over time in hair, such an approach presumably offers only insights into longer-term endocrine patterns. Using faeces as a substitute hormone matrix for non-invasive monitoring can be a suitable alternative way to investigate species-specific hormone fluctuation over a short-term period. For this purpose, the study aims to establish an enzyme-immunoassay (EIA) for reliably quantifying faecal glucocorticoid metabolites (fGCM) in hyrax faeces, by performing an adrenocorticotropic hormone stimulation test (ACTH challenge test) on captive individuals housed at the SANBI Mokopane Biodiversity Conservation Centre. After identifying the most appropriate EIA for monitoring fGCM concentrations in the rock hyrax, the technique was used to analyse faecal samples from free ranging individuals at the National Botanical Garden (PBG) of Pretoria. At the NBG, three areas with differing levels of anthropogenic disturbance were chosen. Seasonal differences in fGCM concentrations of different hyrax colonies living in these areas were examined, and the possible relationship between anthropogenic disturbance and fGCM concentrations were investigated. Additionally, during two monitoring periods at the PBG (winter and late spring 2019), species’ habituation to human presence was examined by calculating the flight initiation distance (FID) in meters with a laser range finder, and the use of camera traps estimated anthropogenic presence. Results from the ACTH challenge test demonstrated a variation over 3-fold within 15-30 min post ACTH administration. The maximum rises of fGCM concentrations were found 15-24 hours postinjection. Out of five enzyme-immunoassays (EIA) tested, a 11β-hydroxyaetiocholanolone EIA was the most suitable to monitor alterations in fGCM concentrations in rock hyraxes, with respective fGCM concentrations remaining stable for up to 8 hours post-defecation. Thus, faecal material should be collected within 8 hours post-defecation, to address adrenocortical activity analysis reliably. Animal fGCM concentrations at the PBG were ~10% higher in the section with lowest disturbance compared to those in the section with medium disturbance, and ~20% higher compared to those in the section with the highest disturbance. Moreover, these values were higher in late spring compared to winter across all three study sections. Animal FID and fGCM concentrations were positively correlated. The method developed here for the non-invasive assessment of adrenocortical function in rock hyrax can contribute to understanding whether and at which extent anthropogenic pressure may cause stress in this species.