A survey of breeding Wood WarblersPhylloscopus sibilatrixin Britain, 1984–1985.

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Abstract
Wood Warblers were counted by tetrad within 10 km squares chosen from those occupied in The Atlas of Breeding Birds of Britain and Ireland. About 80% of the planned coverage was achieved. The male population was estimated to be 17,200 with a 95% confidence range of +/-1370. Range changes are mapped; they show no consistent pattern. As a by-product of an unrelated study, single visit counts were shown to be similar to actual numbers of males because some birds may be counted more than once. Song output was fairly constant for the period of the survey because males sing while their mates incubate. Data showing regional variations of density are mapped and tabulated by 10 km squares and by estimated area of broadleaf woodland. Wood area was a poor predictor of Wood Warbler abundance. Habitat associations in 6 separate studies were not totally consistent. Oakwoods with high canopy cover and limited herbaceous vegetation were perferred to more varied stands with more open canopies and stronger shrub and herbaceous cover. Features such as soils, climate, competition or predator numbers probably have an effect on Wood Warbler over and above measured habitat factors.