Habitat disturbance effects on the physiological stress response in resident Kenyan white-bearded wildebeest (Connochaetes taurinus)

•Resident wildebeest have experienced widespread declines over the past few decades.•Fecal glucocorticoid metabolites were extracted to assess physiological stress.•Standing biomass and habitat disturbance contributed to elevated stress levels.•ΔNDVI, representing new growth, led to decreased levels of fecal glucocorticoids.•Analyses highlight how landscape factors affect quantified levels of physiological stress. Regarded as a keystone species, white-bearded wildebeest (Connochaetes taurinus) are found across the grassland savannahs of eastern Africa. Over the past 40years, however, many local populations have become threatened with extinction. This is the first study connecting fecal glucocorticoid metabolites (i.e., stress hormones) in wildebeest with landscape variables of natural and anthropogenic disturbance. Using a validated technique, fecal samples (n=168) were collected from wildebeest over a 3-month study period and across three different study areas in Kenya with varying degrees of disturbance. The stress of sampled populations was similar between study areas, with a seasonal decline in stress hormones found between dry and wet season data collection periods. We used an information-theoretic approach to rank models of fecal glucocorticoid metabolites. Our highest ranking model included an interaction between locally collected plant biomass and disturbance, the number of calves in a group, and ΔNDVI (change in Normalized Difference Vegetation Index). A strong positive effect related to biomass and disturbance suggested that tall/standing biomass and high levels of disturbance contribute to elevated levels of stress in wildebeest. A strong negative effect related to ΔNDVI was also observed, suggestive that new growth lowers average stress levels. Our research suggests that increased levels of habitat disturbance may have an adverse effect on wildebeest populations across the region when habitat conditions deteriorate. Wildebeest likely avoid areas of high anthropogenic disturbance which may indirectly lead to lowered fitness.