Status of Capercaillie Tetrao urogallus in Scotland during winter 2003/04

摘要

Capsule The population estimate was 1980 individuals (95% confidence limits 1284-2758). Aim To produce a new national population estimate with greater precision than the previous survey, but retaining comparability. Methods A total of 643, 2-km-long transects were walked at sites throughout the recently occupied range. The survey intensity was high in a 'primary' stratum of woodland where Capercaillie have been recorded since 2000, and lower in a 'secondary' stratum where Capercaillie have been recorded prior to 2000 only. DISTANCE analysis software was used to calculate densities in the two strata and extrapolate to a total population estimate. Results The population estimate was 1980 individuals (95% confidence limits 1284-2758). Although this value is 84% greater than that from the previous survey in 1998/99 (1073 individuals), it lies within the confidence limits of that estimate (549-2041). A randomization test confirmed that the apparent increase since 1998/99 was not statistically significant. The range of sightings recorded in the survey, and the frequency of Capercaillie sightings in four regions, suggests that the majority of the population is concentrated in Badenoch and Strathspey, with few birds in the south of the range. Conclusion The revision to the survey design since the 1998/99 survey, along with an increase in survey effort, was successful in producing a more precise population estimate than in previous surveys. However, the imprecision in survey estimates still hampers the power to detect changes in the size of the population. A number of alternative sources of Capercaillie data suggest that there may have been a recent increase in the core areas for Capercaillie, most noticeably in Strathspey.