Review: How do you know an animal is stressed?

Brenna M.G. Gormally, L. Michael Romero

            Scientists across disciplines including medicine, psychology, and even wildlife conservation are interested in understanding what it means to be ‘stressed’. As humans, we typically associate stress with negative feelings, usually of anxiety. This characterization, however, is an over-simplification of the phenomenon of ‘stress’ in the scientific world. While long-term stress can lead to harmful side effects including immunosuppression, the short-term response (or acute stress) is beneficial and necessary for animals to respond to unpredictable events in their environment. For example, when a zebra needs to quickly escape an attack by a lion, it is the physiological and behavioral stress response that is responsible.

            Because of the complex nature of the short- v. long-term stress response, it is often challenging for scientists to effectively measure and identify stress in humans and in wildlife. Dozens of techniques have been created to assess stress in wild animals, however they each capture different components of physiology and behavior. Additionally, each technique is specific for a certain timescale; for example, some techniques may be more appropriate when assessing longer stressors, while some may also be sensitive to shorter stressors.

This variation in techniques motivated us to synthesize 37 common stress techniques, focusing on how each changes in response to stressors of different lengths. Unsurprisingly, we found that techniques ranged in their stressor sensitivity from seconds to years. Additionally, we report on what types of scientific questions each technique can answer. For example, some are more appropriate when asking questions about how animals have adapted to different environments, while others are better for questions about responses to short-term disruptions, like predation or weather. We hope that this review provides researchers with a starting point to understanding how they might measure stress in their systems, as well as an appreciation for the complex nature of stress physiology.

Read the paper in full here.

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