Impact assessment research: use and misuse of habituation, sensitisation and tolerance in describing wildlife responses to anthropogenic stimuli

Studies on the effects of anthropogenic activity on wildlife aim to provide a sound scien- tific basis for management. However, misinterpretation of the theoretical basis for these studies can jeopardise this objective and lead to management outcomes that are detrimental to the wildlife they are intended to protect. Misapplication of the terms 'habituation', 'sensitisation' and 'tolerance' in im- pact studies, for example, can lead to fundamental misinterpretations of research findings. Habituation is often used incorrectly to refer to any form of moderation in wildlife response to human disturbance, rather than to describe a progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial. This misinterpretation, when coupled with the widely held assumption that habituation has a positive or neutral outcome for animals, can lead to inappropriate decisions about the threats human interactions pose to wildlife. We review the conceptual framework for the use of habit- uation, sensitisation and tolerance, and provide a set of principles for their appropriate application in studies of behavioural responses to anthropogenic stimuli. We describe how cases of presumed habit- uation or sensitisation may actually represent differences in the tolerance levels of wildlife to anthro- pogenic activity. This distinction is vital because impact studies must address (1) the various mecha- nisms by which differing tolerance levels can occur; and (2) the range of explanations for habituation- and sensitisation-type responses. We show that only one mechanism leads to true behavioural habitu- ation (or sensitisation), while a range of mechanisms can lead to changes in tolerance.