Crowding increases salivary cortisol but not self-directed behavior in captive baboons

Area of Science:

• Primatology
• Animal Behavior
• Physiology

Background:

• Social animals experience stress when confined to reduced spaces, increasing agonistic interactions and impacting health.
• Physiological defensive coping mechanisms are activated during crowding, potentially affecting overall well-being.

Purpose of the Study:

• To investigate the physiological stress responses in baboons due to increased social density.
• To analyze the relationship between crowding, salivary cortisol levels, and anxiety-related behaviors.

Main Methods:

• Salivary cortisol levels and anxiety-related behaviors were monitored in nineteen baboons during two crowding episodes.
• Cortisol levels were compared between periods of varying social density and enclosure access.
• Behavioral data was analyzed to assess stress indicators.

Main Results:

• Crowding led to significantly elevated salivary cortisol levels compared to non-crowded periods.
• Cortisol levels returned to baseline after crowding episodes, irrespective of duration or climate.
• Self-directed behaviors did not reliably increase during crowding, suggesting limited utility as stress indicators.

Conclusions:

• Elevated cortisol indicates metabolic costs associated with maintaining homeostasis under social stress from reduced space.
• Social threat uncertainty or potential negative interactions trigger physiological stress responses detectable via salivary cortisol.
• Self-directed behaviors may not be adequate indicators of social stress or hypothalamic-pituitary-adrenal axis activation in colony-housed primates.