By Jesse R. Barber, Frank Turina, and Kurt M. Fristrup

U.S. Fish and Wildlife Service/Tim Bowman

Ruddy turnstones forage by probing and flipping over stones along rocky shores in search of insects and other invertebrate prey. Animals that depend on specialized habitats may become tolerant of disturbance owing to lack of readily available, alternative habitats. In contrast to habituation, tolerance may carry ecological costs.

ANIMALS ARE SAID TO BE HABITUATED when their response to a novel stimulus diminishes over time. Habituation can be viewed as adaptive when the stimulus is irrelevant to the animals. Animals that exhibit tolerance of noise are often cited as evidence that noise impacts to wildlife are transient and of neutral ecological consequence. Both theory and observations refute the equation of noise tolerance with absence of impact.

At the Monkey Mia resort in Australia, a population of bottlenose dolphins (Tursiops spp.) has been exposed to tourism for more than 40 years. Experimental studies of dolphin reactions to boats documented much stronger responses by dolphins outside of tourist areas than inside tourist areas (Bejder et al. 2006). Two decades of surveys at these sites documented a decrease in the dolphin population inside tourist areas coinciding with an increase outside these areas. Dolphins have long generation intervals, so these studies implicate displacement of sensitive individuals, not habituation.

An apparent increase in noise tolerance may actually indicate more severe constraints on animal behavior (Gill et al. 2001). Declining foraging success and body condition can cause animals to diminish their responses to disturbance stimuli because they cannot afford decreased feeding rates (Stillman and Goss-Custard 2002). Recent work with turnstones (Arenaria interpres, see photo) has shown that birds whose food resources were experimentally supplemented flushed earlier and flew farther when approached (Beale and Monaghan 2004).

If animals demonstrate behavioral or distributional changes to acoustical disturbance, management action can be taken. However, in the absence of clear impacts, we suggest managers strive to ensure that (1) sensitive individuals have not already been displaced; (2) decreased body condition, critical habitat needs, social forces, lack of habitat experience, and/or expensive investment in territory formation are not preventing animals from reacting to the disturbance (Bejder et al. 2009); and (3) alternative explanations are not available. For example, in Grand Teton National Park, mother moose (Alces alces) have been giving birth closer to the road over the last 10 years. In the absence of data indicating that this shift protects moose calves from recolonizing, road-averse grizzly bears (Ursus arctos), this behavioral pattern may have been interpreted as evidence for habituation to the roadway (Berger 2007).

Managers should minimize wildlife exposure to noise and avoid habituation to noise wherever possible. However, in situations where acoustical disturbances to wildlife cannot be avoided, park managers should consider structuring human activities to foster habituation. A predictable timetable enhances opportunities for learning. Animals can distinguish between routine and anomalous occurrences of human noise; they might productively utilize habitats that they would otherwise avoid, or perform critical activities during times of reduced human presence. Scheduling can provide more control over interactions between visitors and wildlife, and offer more reliable opportunities to view wildlife under less perturbed conditions. Given increasing evidence of animals avoiding traffic on roads (e.g., Gagnon et al. 2005; Waller and Servheen 2005; Kerth and Melber 2009), scheduling of visitor access to protected lands will likely increase habitat connectivity, reduce wildlife collisions (thus increasing visitor safety), and increase overall habitat quality in the last of our wild places.

References

Beale, C. M., and P. Monaghan. 2004. Behavioural responses to human disturbance: A matter of choice? Animal Behaviour 68:1065–1069.

Bejder, L., A. Samuels, H. Whitehead, and N. Gales. 2006. Interpreting short-term behavioral responses to disturbance within a longitudinal perspective. Animal Behaviour 72:1149–1158.

Bejder, L., A. Samuels, H. Whitehead, H. Finn, and S. Allen. 2009. Impact assessment research: Use and misuse of habituation, sensitisation and tolerance in describing wildlife responses to anthropogenic stimuli. Marine Ecology Progress Series 395:177–185.

Berger, J. 2007. Fear, human shields and the redistribution of prey and predators in protected areas. Biology Letters 3:620–623.

Gagnon, J. W., T. C. Theimer, N. L. Dodd, S. Boe, and R. E. Schweinsburg. 2005. Traffic volume alters elk distribution and highway crossings in Arizona. Journal of Wildlife Management 71:2318–2323.

Gill, J. A., K. Norris, and W. J. Sutherland. 2001. Why behavioral responses may not reflect the population consequences of human disturbance. Biological Conservation 97:265–268.

Kerth, G., and M. Melber. 2009. Species-specific barrier effects of a motorway on the habitat use of two threatened forest-living species. Biological Conservation 142:270–279.

Stillman, R. A., and J. D. Goss-Custard. 2002. Seasonal changes in the response of oystercatchers Haematopus ostralegus to human disturbance. Journal of Avian Biology 33:358–365.

Waller, J. S., and C. Servheen. 2005. Effects of transportation infrastructure on grizzly bears in northwestern Montana. Journal of Wildlife Management 69:985–1000.

About the authors

Jesse R. Barber is a postdoctoral research fellow in the Department of Fish, Wildlife, and Conservation Biology at Colorado State University, Fort Collins, Colorado. He can be reached at 970-491-0672 and by e-mail. Frank Turina is an outdoor recreation planner with the NPS Natural Sounds Program, part of the Natural Resource Program Center, also in Fort Collins. Kurt M. Fristrup is an acoustic scientist with the NPS Natural Sounds Program.