EVALUATION OF CAPERCAILLIE HABITAT

1. A method for measuring the structure of capercaillie (Tetrao urogallus L.) habitat was developed and the relationship between habitat structure and capercaillie numbers assessed. 2. Capercaillie cocks were counted at display sites (leks) in forests ranging from semi-natural pinewoods to plantations of pine and introduced conifers. Leks were on average 2.1 km apart in continuous habitat, implying that cocks held spring territories in the 1 km around the lek, as in Scandinavia. 3. The number of cocks at the lek was correlated with the percentage of forest >45 years old within 1 km of the lek at 16 of 18 lek sites. However, capercaillie were not confined to old forest. 4. A numerical method based on principal components analysis was devised for describing the structure of a forest. The first principal component (PRIN1) grouped attributes tending towards an open semi-natural Scots pine (Pinus sylvestris L.) forest with 'granny' trees. The second (PRIN2), those tending towards an evenly spaced plantation devoid of ground vegetation. A key for scoring stands approximately and quickly was developed and validated. 5. Principal component scores were used to calculate a GRANNY score (based on PRIN1) and a PLANTATION score (PRIN2) for the forest around each lek site. At 16 of 18 sites, densities of cock capercaillie were strongly associated with GRANNY scores and there was a weak negative association with PLANTATION scores. 6. The two forests with more capercaillie cocks than expected from their scores were a pine plantation and a plantation with a high proportion of Sitka spruce (Picea sitchensis (Bong.) Carr.) with many open, wind-blown areas. 7. It should be possible to manage for capercaillie both the semi-natural pine woods, which are their prime habitat, and plantation forests of mixed conifers. However, the ecology of capercaillie in commercial plantations is poorly understood.