Habitat selection and foraging behaviour of breeding Eurasian Woodcock Scolopax rusticola: a comparison between contrasting landscapes

Abstract

Diet, feeding behaviour and habitat selection of breeding Eurasian Woodcock Scolopax rusticola were studied by radiotracking birds from March to July in two contrasting situations: a 171-ha lowland plantation of Sycamore Acer pseudoplatanus , Beech Fagus sylvaticus and pine Pinus sylvestris / P. nigra in Derbyshire, central England, and an area of c . 900 ha of fragmented, naturally regenerating birch Betula pendula / B. pubescens woodland and hill margin in an upland glen in Angus, northeast Scotland. Earthworms were the most important diet component of adults and chicks in terms of biomass at both sites (50-80%), the rest comprising mainly spiders, harvestmen and beetles. In spring both sexes flew c . 1 km after dusk to feed on fields at night, with up to 94% of nocturnal radiolocations on fields in March, dropping to 18% in July. This behaviour probably reflected seasonal changes in the relative availability of earthworms in fields and woodland. Diurnal home range sizes were similar at both sites and the mean size of 30-day ranges was 62 ± 20 ha (± se), although Woodcock changed locations regularly and areas used for feeding on a daily basis were typically smaller than 1 ha. In the lowland plantation, Sycamore with Dog's Mercury Mercurialis perennis ground cover was highly used relative to availability. In the upland margin study area, the same held for dense sapling-stage birch. These habitats appear to represent a compromise between food availability and protection from avian predators. Recently documented changes in the structure of British woods during the last 30 years, suggestive of reduced management and increased grazing/browsing, are likely to have been detrimental to breeding Woodcock.The Eurasian Woodcock Scolopax rusticola breeds widely throughout Britain, with notable absences only on the highest ground in parts of Scotland, and in southwest England and south Wales (Gibbons et al . 1993). Nevertheless, the species is currently 'amber-listed' as a bird of conservation concern because of an apparent long-term decline in breeding numbers (-76% during 1974-99) and range (-31% during 1968(-31% during /72-1988(-31% during /91, Gregory et al . 2002. The Woodcock is difficult to survey owing to its cryptic plumage, secretive behaviour and crepuscular displays, and hence the reliability of current population and trend estimates is questionable, but the magnitude of the estimated decline is sufficient to justify investigation of factors likely to affect Woodcock numbers.

Densities and population estimates of breeding Eurasian WoodcockScolopax rusticolain Britain in 2003

“…Our overall estimate of breeding Woodcock presence of 35% in 1-km squares with at least 10 ha of woodland suggests that there remains much potential habitat, in the form of large woods, which currently supports no birds. Thirty-day spring diurnal home ranges of both sexes are about 60 ha (Hoodless & Hirons 2007 ) and hence the absence of breeding Woodcock from small woods and an increased frequency of occurrence in 1-km squares containing higher proportions of woodland is to be expected. However, absence from squares with at least 50 ha of woodland presumably reflects unsuitable habitat structure or local population decline.…”

“…However, the distribution indicated by the two surveys is in broad agreement, with the exception that in 2003, despite good coverage, no roding males were detected in Galloway Forest, an area of high abundance during in part, to the maturation of many of the conifer forests in these regions. Conifers tend to be used by breeding Woodcock only up to the thicket stage (Shorten 1974, Hoodless & Hirons 2007, which is reached after about 20 years, and the main expansion of coniferous afforestation in Britain took place during 1950-1990(Forestry Commission 2003. Dependent on future forestry policy, it is possible that in northern and western parts of Britain breeding Woodcock numbers may fluctuate in relation to the cycle of forest restocking over a period of approximately 50 years.…”

“…Woodcock are likely to be sensitive to habitat change because they have specific habitat requirements, particularly during the breeding season (Hoodless & Hirons 2007 ). Young stands of trees with high earthworm availability and dense ground vegetation are highly utilized for feeding and brood-rearing and areas with more open ground vegetation are used for nesting (Hirons & Johnson 1987 ).…”

“…Deciduous woodland is preferred to conifers (Clausager 1972, Hoodless & Hirons 2007 used for nesting up to the thicket stage (Shorten 1974 ), and hence forestry practice is likely to influence habitat availability and quality. Changes in agricultural practice, such as the loss of permanent pastures which constitute optimal feeding areas in winter and early spring (Hoodless & Hirons 2007 ), may be important because British Woodcock exhibit high fidelity to the natal area in winter (Hoodless & Coulson 1994 ). The species is also hunted in winter, although a high proportion of the birds shot will be continental migrants (Hoodless & Coulson 1994 ).…”

“…Young stands of trees with high earthworm availability and dense ground vegetation are highly utilized for feeding and brood-rearing and areas with more open ground vegetation are used for nesting (Hirons & Johnson 1987 ). Deciduous woodland is preferred to conifers (Clausager 1972, Hoodless & Hirons 2007 used for nesting up to the thicket stage (Shorten 1974 ), and hence forestry practice is likely to influence habitat availability and quality. Changes in agricultural practice, such as the loss of permanent pastures which constitute optimal feeding areas in winter and early spring (Hoodless & Hirons 2007 ), may be important because British Woodcock exhibit high fidelity to the natal area in winter (Hoodless & Coulson 1994 ).…”