BIRD POPULATIONS IN UPLAND SPRUCE PLANTATIONS IN NORTHERN BRITAIN

The aim of this study was to measure bird numbers and species richness in upland spruce forests in relation to forest habitat variables, as a basis for a computer model to predict how bird populations were like ly to change under different forest management regimes. In each of the two study areas, at Cowal, Argyll and Kielder, Northumberland, 88 stu dy plots were selected randomly from 24 combinations of tree age (0-8, 9-15, 16-25 and over 25 (mainly 25-50) years), plot size (1-2, 2.1-5 and over 5 ha) and elevation (above or below 250 m). Both pure Sitka s pruce Picea sitchensis and mixed conifers were included, as were first and second rotation crops. Point counts, at up to five per plot, were used to estimate bird populations and in larger plots, additional edg e points allowed the comparison of plot centres and edges. Counts were made from 1990 to 1992 in winter (mid-November to mid-March), early s pring (mid-April to mid-May) and late spring (mid-May to mid-June). Ea ch plot was visited once in each period. The counting method gave cons istent results both within and between days at the same counting point s. There was strong and significant variation in bird numbers and spec ies richness with tree age, both being highest in older trees in winte r and in 9-25 year old trees in spring. All of the common species-chaf finch Fringilla coelebs, coal tit Parus ater, crossbill Loxia curviros tra, dunnock Prunella modularis, goldcrest Regulus regulus, meadow pip it Anthus pratensis, robin Erithacus rubecula, redpoll Carduelis flamm ea, siskin Carduelis spinus, song thrush Turdus ericetorum, tree pipit Anthus trivialis, wren Troglodytes troglodytes and willow warbler Phy lloscopus trochilus-showed significant variation in their abundance be tween tree-age categories, with all except the meadow pipit having low est numbers in the youngest trees and their highest in 9-25 year old t rees. There was little detectable effect of plot size, altitude, admix ture of other conifer species or planting generation on either bird nu mbers or species richness. The number of individual birds detected was consistently higher at the edges than in the centres of the same plot s, particularly in the first 10 m from the edge, but the type of habit at outside the plot had little effect on this. Spring numbers of most of the common species that were also resident in winter were significa ntly correlated with their winter numbers, but the correlations were w eak (particularly in 1991/1992) and had little predictive value. The t wo study areas and the 2 years were similar in the way in which bird n umbers and species richness varied with forest characteristics, sugges ting that the conclusions may be of wide relevance. Bird numbers tende d to be higher in 1991 than in 1992, owing mainly to there being more crossbills and siskins in 1991, when there was a very large cone crop.