Human impacts on capercaille in Scotland

Submitted by editor on 6 May 2014.

How much do we humans effect the populations of wild animals in the woods? An important issue when it comes to endangered species! Robert Moss and his co-workes have studied human influences on populations of capercaillie in Scotland. Learn more in their paper "Walking iImpacts of human disturbance on capercaillie Tetrao urogallus distribution and demography in Scottish woodland" which is published in Wildlife Biology no 1 2014. Below is the author's summary of the study:

The successful reintroduction of capercaillie to Scotland during the 19th century benefited from trees being replanted in the deforested landscape, obsessive predator killing by game preservers and a benign climate. Their big decline in the last quarter of the 20th century went along with poorer reproduction and climate change. This century, global warming has been on hold ( and the birds’ numbers have remained at 1000–2000.  Despite heroic conservation efforts (e.g., however, over most of their Scottish range they have become increasingly sparse, such that about 75% of the population is now in the Spey valley – an area increasingly disturbed by tourism, recreation and housing developments since the establishment of the Cairngorms National Park in 2003. To manage this conflict, we need to understand what does and does not disturb the birds, and what aspects of disturbance impact their population dynamics.

Two of the authors on a much-disturbed footpath in capercaillie habita

With no concrete interest from the responsible authorities, we began this work ourselves in late 2006. When naturalists encounter animal signs such as capercaillie droppings, we habitually read meaning into them, based on our own experiences plus traditional lore. For this study, we aimed to translate such observations into quantitative generalisations about the birds’ distribution in relation to sources of disturbance. We also wanted to know whether disturbance affected the birds’ reproductive rate. Hence, our main approaches were 1) to map the distribution of capercaillie droppings in relation to tracks, a surrogate for human and canine disturbance and 2) to compare capercaillie reproduction in more- vs less-disturbed areas.

Dogs in capercaillie habitat – ground vegetation

The pleasure of stepping through picturesque Spey valley pinewoods in search of capercaillie droppings (photo 3 – Capercaillie droppings, in unusual quantity) was heightened by occasional sightings of the great birds themselves; this tempered only slightly by the need to walk, at all seasons, in lines as straight as thickets, open water and rough ground would allow. Reproductive rate was measured (as chicks reared per hen) in late summer during standard ‘brood counts’ made with the help of trained dogs.

Capercaillie droppings, in unusual quantity

The distribution of droppings in relation to tracks and habitat was modelled by adapting standard statistical techniques, which gave us lots of fun. Capercaillie avoided ground (or, more accurately, voided less frequently on ground) near busy tracks, and especially near forest entrances. The frequency of droppings was highest on forest bogs, which were wet underfoot and so avoided by people and tracks. On the most disturbed ground, the remaining birds included fewer hens than cocks but, to our surprise, each hen reared at least as many chicks as those in less-disturbed areas. Although disturbance did not seem to depress the hens’ reproductive rate, it did deny birds ground and so could impact the survival of this fragile metapopulation.

During the study period, we issued progress reports demonstrating that disturbance keeps capercaillie away from otherwise suitable habitat. Now the responsible authorities began to pay attention. Being able to quote a paper in a respected scientific journal (WB) should help them to justify science-led actions aimed at reducing disturbance to the birds – actions such as closing tracks, rewetting drained bogs and establishing refuges from recreationists.