As part of our cross-journal series for Endangered Species Day, Journal of Applied Ecology Associate Editor, Marc-André Villard considers Coppes et al.’s research around human-induced stress, and what this means for vulnerable populations. The full article, The importance of individual heterogeneity for interpreting faecal glucocorticoid metabolite levels in wildlife studies is available in Journal of Applied Ecology.

Ecologists have long been aware that individual animals vary in their response to the environment. Some have been shown to be consistently bolder than others and, in turn, their personality can influence their behaviour and life-history strategies, from their response to predation risk to their ability to colonize habitat patches, or the allocation of reproductive effort through time. Personality may also influence the stress response of individuals in various situations. Because long term exposure to high levels of stress can have detrimental effects of the growth of individuals, their reproduction, or their immune system, this is an important consideration for applied ecologists and conservation biologists.

Capercaillie_(8751340764)
Capercaillie by By sighmanb

With this information in mind, Coppes et al. revisited previous studies indicating that different species of grouse respond negatively to the proximity of winter recreation infrastructures such as ski trails. They wanted to determine whether there was evidence for individual variation in stress levels and, if so, whether those variations exceeded those attributed to winter recreation activities. They estimated stress hormone levels by extracting corticosteroid metabolites from faeces, thus avoiding the need to capture individuals, which would add another stress component. However, this noninvasive approach comes at a price: faecal samples have to be attributed to the correct individual.

Coppes et al. focused on an endangered population of capercaillie, a large grouse, inhabiting the Black Forest of southwestern Germany. There, capercaillies occupy patches of open forest at high altitudes, where winter sports are often practiced. The authors collected faecal samples within a week of the latest snowfall and distinguished faeces from males and females according to their size. For the first time, they also determined the identity of individuals by extracting and analyzing DNA.

With close to 900 samples from 232 individuals collected from all across the Black Forest, Coppes et al. confirmed that stress levels increased with proximity to skiing, snowshoeing or hiking trails, those effects extending up to 180 m. Several weather variables that were deemed to influence stress levels in previous studies were no longer significant when accounting for individual variation. Another important finding was that individual variation in stress level accounted for the bulk of differences observed in stress levels across samples, which calls for caution in future studies using stress responses to assess animal sensitivity to environmental factors.

This study opens up a number of opportunities for future wildlife research. While the authors confirmed the negative effects of proximity to winter sport infrastructures (and, presumably, level of activity) on capercaillies, they did not account for the potential effects of predation risk. The mere presence of predators has been shown elsewhere to induce a stress response in potential prey but collecting data on all potential predators of capercaillies across the Black Forest was beyond the scope of this research project. Nonetheless, this study lays the groundwork for future research addressing the full complexity of environmental and human-induced stress responses in wild animals through non-invasive sampling. Such investigations will be critical to efficiently protect endangered species or populations from the subtle, detrimental effects of recreation and other, seemingly inoffensive activities, in sensitive areas.

Read the full article, The importance of individual heterogeneity for interpreting faecal glucocorticoid metabolite levels in wildlife studies in Journal of Applied Ecology.

This post is part of the British Ecological Society journals’ series for Endangered Species Day. Read our other endangered species posts: