Studies evaluating effects of human activity on wildlife typically emphasize short-term behavioral responses from which it is difficult to infer biological significance or formulate plans to mitigate harmful impacts. Based on decades of detailed behavioral records, we evaluated long-term impacts of vessel activity on bottlenose dolphins (Tursiops sp.)

Studies on the effects of anthropogenic activity on wildlife aim to provide a sound scientific 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 impact 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 habituation, 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 habituation or sensitisation may actually represent differences in the tolerance levels of wildlife to anthropogenic activity. This distinction is vital because impact studies must address (1) the various mechanisms by which differing tolerance levels can occur; and (2) the range of explanations for habituationand sensitisation-type responses. We show that only one mechanism leads to true behavioural habituation (or sensitisation), while a range of mechanisms can lead to changes in tolerance.

We documented immediate, behavioural responses of Indo-Pacific bottlenose dolphins (Tursiops sp.) to experimental vessel approaches in regions of high and low vessel traffic in Shark Bay, Western Australia. Experimental vessel approaches elicited significant changes in the behaviour of targeted dolphins when compared with their behaviour before and after approaches. During approaches, focal dolphin groups became more compact, had higher rates of change in membership and had more erratic speeds and directions of travel. Dolphins in the region of low vessel traffic (control site) had stronger and longer-lasting responses than did dolphins in the region of high vessel traffic (impact site). In the absence of additional information, the moderated behavioural responses of impact-site dolphins probably would be interpreted to mean that long-term vessel activity within a region of tourism had no detrimental effect on resident dolphins. However, another study showed that dolphin-watching tourism in Shark Bay has contributed to a long-term decline in dolphin abundance within the impact site (Bejder et al., in press, Conservation Biology). Those findings suggest that we documented moderated responses not because impact-site dolphins had become habituated to vessels but because those individuals that were sensitive to vessel disturbance left the region before our study began. This reinterpretation of our findings led us to question the traditional premise that short-term behavioural responses are sufficient indicators of impacts of anthropogenic disturbance on wildlife.

Infant-carrying, the most costly form of primate parental care other than lactation, was investigated in savannah baboons of Amboseli, Kenya. Measurements of physical growth, counts and length of paces, and simultaneous records of carrying and locomotion were used to evaluate the time, distance, and energetic expenditure of infant-carrying. Finally, we modeled the energetics of independent infant locomotion and considered ontogenetic patterns in the alternative energetic costs of carrying versus independent infant locomotion under assumptions of complete nutritional dependency. The youngest infants were carried by their mothers during all travel and foraging, for a total of 8 10 kin/day. By 8 months of age, both carrying time and distance were almost zero. However, daily carrying distance, unlike carrying time, did not decline in the first few months, because older infants were carried disproportionately during rapid travel and, consequently, for greater travel distances per unit carrying time. Females of low dominance rank carried their infants the most; the highest ranking mothers not only carried their infants least but biased their carrying against sons. Although carrying a growing infant is an increasingly costly behavior, during the period of nutritional dependence energetic costs to the mother are appreciably greater if an infant travels independently instead of being carried by its mother. Yet infants increased locomotor independence at a younger age than predicted by a simple model of maternal energetic efficiency. Trade-offs in energetic economy may enhance a mother's future reproduction at the expense of her present infant, may enhance survival of the present infant by promoting early acquisition of developmentally essential skills, or may suggest the importance of additional factors that influence the mother's and infant's behavior.Offprint requests to : J. Altmann