A behavioral and physiological study of a silverback gorilla (Gorilla gorilla gorilla) bachelor group

In this study, the stress responses of two captive adult male gorillas (Gorilla gorilla gorilla) to social pairing and exposure to acute stressors were analyzed. Both behavioral observations and endocrine measurements were employed for a more inclusive examination of stress response. Observations were conducted over a span of two years and were subsequently divided into four periods for analysis. Samples of plasma, urine, and feces were collected over three years for cortisol level comparisons before and after acute stressors. Fecal samples taken over successive months were used for an analysis of seasonal effects.

The results demonstrated that although the two males were non-affiliative and periodically aggressive towards one another, this social pairing did not result in a chronic elevation of fecal cortisol levels. While urinary and fecal cortisol levels failed to show a mean increase in cortisol levels four days after acute stressors such as immobilizations, introductions, and fights, peaks in cortisol levels were observed. The gradual rise in fecal cortisol at the onset of winter, in addition to alterations in behavior and physical health during this time, suggest that the gorillas were affected by seasonal changes in their captive environment.

Data results generated from this study are used to discuss the feasibility of gorilla bachelor groups as housing alternatives for solitary males in addition to other issues related to captive animal welfare.