Evaluating methods to quantify anthropogenic stressors on wild animals

Humans have a variety of direct and indirect impacts on wildlife and a number of methods have been proposed to identify and quantify anthropogenic stressors that negatively impact wildlife. The ideal method would ultimately help predict the presence, absence, or population viability of animals living with a particular stressor. We critically review seven methods that have been used, or are potentially useful, to identify anthropogenic stressors on animals. We rank them from fitness indicators to disturbance indicators: breeding success, mate choice, fluctuating asymmetry, flight initiation distance, immunocompetence, glucocorticoids, and cardiac response. We describe each method's ease of use, precision in quantifying the stressor, accuracy in predicting the presence, absence, or population viability of a species experiencing a given stressor, and the repeatability of the results across populations and species. From this analysis, we conclude that there is no single optimal method to quantify anthropogenic stressors; method selection will depend on precise goals and fiscal constraints.