Capercaillie counts

• Breeding densities declined by 16% per annum in the 1990s, but are now stable in Strathspey and Moray/Ross-shire.
• Declines continued in the East and South and were linked with poorer breeding success.
• Breeding success was determined by the percentage of hens with broods, which has not changed over time and averages only 30%.
• More work is needed to identify causes of breeding failure.

We have counted capercaillie and their broods using pointing dogs each summer since 1991 in a range of native and commercial Scottish forests. We have usually based annual estimates of breeding success across all the sample sites on 100 or more hens. Before 2001, we usually sampled 10-14 forests each year, but since 2001 we have sampled at least 20 forests as part of an EU LIFE-Nature funded project. Here we describe national and regional trends in breeding success and density over that period.

Breeding success varied significantly between years (see Figure 1) and averaged 0.78 (se=0.09) chicks reared per hen. During the LIFE project period 2001-06, breeding success did not vary between different forest types or between different regions. Adult densities declined at a rate of 16% per year between 1991 and 1997, but shortly thereafter densities have been stable (see Figure 2). The recent halting of the national decline and more recent local increases have been associated with the work of the Capercaillie Biodiversity Action Plan Steering Group, which initiated significant conservation efforts between 2000 and 2006. These were designed to improve productivity and to increase both adult and juvenile survival. Such was the urgency that significant amounts of public money was spent by the Scottish Executive to remove and mark fences in core capercaillie areas to reduce fence collisions. These efforts were complemented by further fence marking and removal, habitat enhancement and predator (fox and crow) removal as part of the LIFE project.

These measures appear to be working. Breeding success showed a slight, but nonsignificant, improvement during the five years of the LIFE project, with an average of 0.9 chicks per hen per year and in four out of the five years enough chicks were produced to maintain or increase the population. This compared well with an average of 0.6 chicks per hen, the break even point in terms of achieving a stable population, attained in the preceding five-year period. Should these sample sites be representative of the capercaillie breeding range, improvements in numbers appear to be linked not just with a modest improvement in breeding success, but also with a likely increase in the survival of full-grown birds (juveniles and adults). The latter may be associated with extensive predator control or with the removal or marking of hundreds of kilometres of fences, which previously killed an unsustainably high proportion of birds. However, there have been no studies of capercaillie survival rates in Scotland for 10 years, so any important changes in survival attributable to mitigation measures remain undetected.

Figure 1. Capercaillie breeding success, 1991-2006, sampled from 10-20 forests per year in the Scottish Highlands

The estimated level of productivity (0.6 chicks per hen) required to maintain a stable population

Breeding success in 2006 was best since 1992, with an average of 1.4 chicks per hen. This is timely as it comes in the final year of the LIFE project and suggests that the extensive work carried out by forest managers for capercaillie is beginning to produce results, particularly when the weather is good, as was the case in summer 2006. Although there are consistent signs of improvement in the fortunes of capercaillie, there are no grounds for complacency and further management is needed. Despite adult densities remaining stable in Strathspey and Moray, there were continued declines on the eastern edges of the range in Deeside/Donside and to the south in Perthshire and Argyll. Where capercaillie were declining, breeding success was only 0.54 (se=0.07) chicks per hen compared with 0.90 (se=0.10) where numbers are stable. Worryingly, our long-term counts have shown that 70% of hen capercaillie failed to rear a brood and that it is variations in the proportion of hens with broods that are directly related to overall breeding success.

Figure 2. Changes in mean density of hen capercaillie in Scottish forests

In spite of management to increase blaeberry and reduce predation, capercaillie breeding success remains generally low in Scotland and our knowledge of their breeding requirements remains imprecise. We still need research on chick habitat requirements, the relative effect of potential predator species and the stage at which chief breeding losses (clutch or chick) occur. The latter in particular is a fundamental knowledge gap, as corrective management to reduce clutch losses through predation are likely to be quite different to those required to improve foraging habitats for chicks or prebreeding nutrition for hens. We are currently discussing proposals to help fill these gaps in our knowledge and thereby help to ensure that this promising resurgence in numbers of capercaillie is not only maintained, but also enhanced into the future.