Vigilance Goes Up Near Tourists. Foraging Doesn't Change.

Across the active non-lethal studies in the dataset, animals showed a positive overall effect on vigilance—they were watching humans more carefully. Foraging, though, was not significantly affected. Crucially, the spread of responses was narrower than in the lethal category, meaning that across diverse taxa and geographies, the reaction to hikers, divers, and wildlife watchers was relatively consistent: animals noticed, but did not fundamentally alter how they fed.

Several species showed no measurable behavioural change at all in response to active non-lethal human presence. Blackbirds, thinhorn sheep, whale sharks, semipalmated plovers, and western sandpipers all continued foraging and maintained vigilance at baseline levels despite regular human activity in their habitat. In each case, prior exposure appears to have been sufficient to habituate the animals to the stimulus. Yellow-bellied marmots in heavily visited forests grew progressively less reactive to approaching humans over time, reducing flight distances across repeated encounters. Killer whales, Hector's dolphins, and African savannah species have shown similar patterns in separate work, with tourist-habituated populations treating regular human presence as background noise rather than threat.

Developmental stage complicated the picture in thinhorn sheep. Adult animals increased vigilance in response to non-lethal disturbance; juveniles did not, and only juveniles showed flexibility in foraging behaviour under the same conditions. Hooded cranes varied vigilance but not foraging across age classes. Neither finding undermines the habituation argument, but both point to the risk of treating a species as a single behavioural unit when age structure, prior experience, and internal state all modulate individual responses.

For wildlife tourism managers, the practical implication is not that human presence in protected areas is without consequence. The vigilance increase is real. But animals that continue feeding at normal rates while slightly more alert are in a fundamentally different position to animals that suppress foraging entirely—and that distinction matters when assessing whether visitor access is costing wildlife more than it should.

The Animals That Treat Roads as Shelter

Perhaps the most counterintuitive finding concerns passive human presence. Across road and settlement studies, average vigilance was actually lower near human infrastructure than in undisturbed habitat. Roads typically remove dense cover that ambush predators rely on, paradoxically making open, road-adjacent areas safer for certain prey species. Prairie dogs, white-footed mice, and lemurs in multi-use Malagasy landscapes all showed elevated foraging and reduced vigilance near roads, apparently recognising that their natural predators were less likely to approach there—an effect the researchers describe as the human shield hypothesis.

That benefit is contingent on species identity, predator community, and road type. Elk near roads and human settlements consistently reduced foraging and increased vigilance across multiple studies, the opposite of the prairie dog pattern. Pronghorn showed mixed results depending entirely on study design, with one research team using road distance as a continuous variable and another using categorical comparisons between disturbed and undisturbed sites. Roads also function as ecological traps: roe deer and wild boar that shift habitat use to avoid hunting pressure end up spending more time in terrain that increases their exposure to vehicle collisions. The behavioural adaptation to one type of human threat can amplify vulnerability to another.

Variability in passive interaction responses was consistently wider than in either of the other two categories—large in magnitude and unpredictable in direction. Chipmunks and Gaspésie caribou showed limited responses to road presence for reasons that remain unclear. Some of that unpredictability likely reflects genuine ecological heterogeneity; some is probably methodological, with different study designs producing incomparable baselines. Passive human presence remains the least well-understood of the three interaction types, and the category where simple generalisations are most likely to mislead management decisions.

Repeated Exposure, Diminishing Fear

Where wildlife tourism has operated consistently and non-lethally over years or decades, animals show systematically weaker responses to human presence than populations with less exposure history. A history of lethal encounters, even if hunting has since been banned, appears in some species to sustain elevated wariness for extended periods. Elk populations with documented hunting histories showed stronger anti-predator responses to non-lethal humans than populations without that history, though the relationship was not consistent enough across species to generalise. The researchers note that the duration since the cessation of hunting, the intensity of past persecution, and the nature of current human activity all appear to interact in shaping present-day responses—a combination that makes prediction difficult without site-specific data.

The question the existing literature cannot yet answer is the one managers arguably need most: at what point does behavioural disruption, even the relatively mild disruption associated with tourism and hiking, accumulate into measurable fitness costs? Whether the vigilance increase observed near tourists translates into any demographic consequence—reduced reproductive success, slower juvenile growth, or altered territory use—requires longer-term data than most of the studies surveyed here were designed to produce. That link between behaviour and population-level outcome is where the next generation of wildlife disturbance research will need to go.