Assessing the impact of human disturbance on penguins

Abstract

Nature conservation places great hopes on ecotourism, yet despite increasing pressure on the Earth's last wild areas, there is insufficient knowledge about human disturbance impact, and hence, visitor management must often remain inadequate. Penguins are an important tourism attraction. Lack of overt behavioural responses to human proximity at breeding sites has led to the common public misconception that penguins would be little affected by human visitation. However, even a single one-off disturbance or a series of low-key disturbances can have far-reaching impacts that are often not immediately discernable to the people involved.

I studied behavioural and physiological stress responses of three penguin species that according to anecdotal evidence respond very differently to human proximity. While behaviour could give an indication of the relative severity of a disturbance stimulus, measuring physiological responses was a more objective and powerful tool to quantify stress in all three species studied. As accumulating effects of human disturbance may affect breeding populations, I also monitored a range of reproductive parameters at sites that provided similar breeding habitat and overlapping foraging grounds yet were exposed to different levels of human visitation.

Human disturbance can be interpreted as perceived predation risk. Similar to antipredator responses, reaction to disturbance stimuli can affect individual fitness via energetic and lost opportunity costs of risk avoidance. I demonstrated that human proximity is energetically costly for penguins and more so than most stimuli that naturally occur at their breeding sites. Yet the severity of the same disturbance stimulus is perceived differently between species, populations and even individuals.

Snares penguins, Eudyptes robustus, appear to be little affected by human activity outside their immediate breeding colony. In comparison, Humboldt penguins, Spheniscus humboldti, proved to be very sensitive to human disturbance. They responded to a person visible at more than 150 m distance from their nest and needed up to half an hour to recover from even careful human approach. Nest densities were lower and breeding success was significantly reduced at more frequently visited sites.

In Yellow-eyed penguins, Megadyptes antipodes, I found elevated hormonal and heart rate responses at sites exposed to unregulated visitor access associated with reduced breeding success and lower fledgling weights, which result in reduced first-year survival and recruitment probabilities. Contrary to my expectations, birds that continued to breed despite frequent disturbance had not habituated to human proximity but appeared to be sensitised and responded more strongly to human disturbance. Hence, tourist-exposed penguins were not only disturbed more often, each disturbance event was more costly for the affected birds, eventually leading to poorer breeding performance.

Both initial stress response and habituation potential of Yellow-eyed penguins depended on sex, character and previous experiences with humans, and the observed individual differences in behavioural and physiological stress responses related to fitness parameters. Birds characterised as "frozen" were apparently best able to cope in human-disturbed habitats. Thus, human disturbance may drive contemporary evolutionary change in the composition of breeding populations with as yet unrealised consequences for conservation.

I give a detailed account of the current understanding of human disturbance related effects on penguins and list future research needs. Complex secondary effects of human disturbance and multiple stressor interactions are still little understood and require longterm population studies that enable us to disentangle human disturbance effects from environmental variability. Similarly, we still know very little about what factors drive habituation or sensitisation in wild populations, thus habituation to even apparently minor human disturbance cannot be assumed.

Subtle costs of what we think is minor disturbance can accumulate and may ultimately lead to lower nest numbers, poorer breeding success or reduced fledgling weights in more frequently visited penguin breeding areas. As the growth of nature-based tourism is expected to continue, it is important not only for ecological but also for economic sustainability to minimise any associated negative human impacts. It is clear that generic guidelines for managing human visitation of penguin colonies cannot be applied. Only rigorous research can provide the basis for appropriate site- and species-specific visitor management decisions.

I hope this study can provide a framework for better understanding human disturbance effects on penguins and maybe even on wildlife in general.