The capercaillie is one of our most magnificent yet elusive species, found only in Scotland in the UK within their preferred pine woodland habitat. Substantial declines have been recorded since the mid-1970s, so a national survey provides updated estimates of the overall population, helping to guide further conservation action for this Red listed species. Today's guest blog by Siân Denney, RSPB Wildlife Advisor explains.

Monitoring importance

Scotland’s capercaillie population is vulnerable and at risk from multiple threats. This includes fragmentation and lack of suitable habitat, collision with deer fencing, human disturbance, predation, and wetter summers, the latter three affecting chick survival and inevitably becoming more frequent with climate change. These pressures continue to put the capercaillie at risk and are why efforts are being made to conserve the species directly.

Monitoring the population of capercaillie can determine how this species is faring and be used to implement measures to help remaining birds. A national survey is completed every six years, with this being the sixth survey carried out by the RSPB in partnership with NatureScot, and the first survey with Cairngorms National Park Authority, Cairngorms Capercaillie Project, Forestry and Land Scotland, and Scottish Forestry.

Male capercaillie displaying at RSPB Abernethy (c) Dave Braddock (rspb-images.com)

Survey methods

The survey team follows the same method used in previous surveys whereby 2km long transects are walked through a random sample of woods throughout the species’ range, counting any capercaillie that are seen.  The minimum number of transects are walked in order to calculate an accurate estimate whilst minimising disturbance. The survey takes place in the winter when the impacts of disturbance are lower compared to the sensitive breeding season, but also since this is when capercaillie feed within the pines and are flushed more readily, so can be observed by the team. Other signs can also be used to identify capercaillie presence, such as their droppings, and feathers.

Surveys are not conducted, as far as possible, on particularly cold days when the need to conserve energy is essential for the birds and surveyors liaise with landowners to minimise disturbance, for example by planning surveys around other activities happening in or near the transects. 

Whilst these transects identify birds within the survey area, there are many that go undetected – the further away from the transect line, the more likely some birds are missed. The number of birds living within areas not surveyed are therefore estimated using the method of distance sampling. This uses data based on the distances of detected birds from the transect line to estimate capercaillie density which is extrapolated to produce the total population size.

The surveys are currently underway, having started in November 2021 and run until March 2022, covering Strathspey, Deeside, Moray, Nairnshire, Easter Ross and Perthshire. Six professional fieldworkers are carrying out the surveys and aim to collectively cover a total of c750 transects. Scientific analysis of the data will be completed, with results ready for release in August 2022.

Prime capercaillie habitat in this Caledonian pine forest (c) Ben Andrew (rspb-images.com)

With results from previous years showing capercaillie populations fluctuating between 1000 and 2000 birds, various measures have been implemented to help. The Cairngorms Capercaillie Project for example, undertake habitat management to create new and improved native woodland, helping to expand and link suitable habitat. Fences that are identified as high risk to capercaillie are made more obvious or removed entirely. The project undertakes predator control in areas where the birds breed and is working with residents and visitors in the Cairngorms National Park to reduce disturbance and habitat fragmentation in capercaillie areas.

The concentrated efforts to conserve the capercaillie in Scotland have likely helped prevent the risk of extinction. However, the population remains at risk, and so the outcome of this survey will be vital for informing how mitigations can continue to support existing birds and try to safeguard their future here.

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