Variations in Black Grouse Tetrao tetrix winter survival in a year with prolonged snow cover

Capsule Low Black Grouse survival rate in northern England during a severe winter with prolonged snow was attributed to limited availability and proximity of woodland.

Aims To compare the impact of the severe winter weather on Black Grouse in an open treeless landscape in northern England with more wooded landscapes in Scotland.

Methods We assessed the impact of severe winter conditions in relation to previous milder winters at a sample of leks counted annually in northern England and the Scottish Highlands between 2001 and 2012. In addition, following the severe winter in 2009/10 Black Grouse were surveyed at all leks in 2010 where they were surveyed the previous year. We assessed woodland habitat extent within 1 km of leks and related this to indices of Black Grouse over-winter survival.

Results Black Grouse in northern England were severely affected by the severe winter of 2009/10, declining by 38% in comparison to a 23% increase in the Scottish Highlands. Leks in northern England were at higher altitudes and had less tree cover than those in Scotland.

Conclusion The lack of woodland cover around leks in northern England implies that availability of above snow forage, shelter and cover from predators was too low for Black Grouse to survive during prolonged deep snow. Measures are required to provide emergency food sources in periods of prolonged snow, such as the provision of supplementary food at leks, the cultivation of seed-rich arable crops, and the establishment of pockets of woodland.     

The role of forest maturation in causing the decline of Black Grouse Tetrao tetrix

Black Grouse Tetrao tetrix in Britain have declined through the 20th century, and most birds are now in Scotland. Many causes for this decline have been suggested, notably agricultural intensification, increased grazing levels and moorland afforestation. We examine habitat correlates of Black Grouse distribution and population change from a 700-km² area in the core of the Scottish range, where the numbers of lekking male Black Grouse declined by an estimated 70% to 270 between 1990 and 2002. Habitat data were derived from satellite imagery, in combination with map and field-collected data. Lek occurrence, lek size and changes in lek size were all correlated with forest structure, either positively with the amount of pre-thicket forest cover, or negatively with closed canopy cover. Additional effects of the cover of grass moor and dry heath suggest that Black Grouse are most likely to occur where moorland comprises Heather Calluna vulgaris and grass mosaics. Analysis of the change in Black Grouse abundance within 1.5 km of discrete forest blocks suggests that forest maturation, which has been the dominant habitat change during the course of the study, alone accounts for 58–78% of the decline. Given the close association of Black Grouse and the occurrence of woodland (and particularly conifer plantation) throughout much of their British range, these findings can be used to inform the design of management schemes for the recovery of Black Grouse.     

The role of habitat change in driving Black Grouse Tetrao tetrix population declines across Scotland

Capsule Black Grouse declines across Scotland were greatest on less heterogeneous moorland, at low to intermediate altitudes and, more weakly, around post-thicket woodland.

Aims To examine correlates of change in abundance of Black Grouse across Scotland.

Methods Changes in abundance within 5-km squares between national surveys in 1995/96 and 2005 were modelled in relation to measures of habitat cover and woodland age derived from satellite imagery.

Results Populations across Scotland were most stable where unenclosed moorland comprised rough grassland, intermediate heather cover and at higher altitude. Declines tended to be greatest in squares which had transitioned from pre-thicket to closed-canopy woodland.

Conclusion Moorland will be most beneficial where it is heterogeneous in composition, and the role of woodland maturation in driving regional declines has support, albeit more weakly, at a national scale.     

Designing mosaic landscapes for Black Grouse Tetrao tetrix using multi‐scaled models

With increasing pressures on land for human use, it is important to identify the habitat requirements of key species, not just in terms of a correlation with a given habitat feature, but also the relationship between species presence and its coverage, proximity to other habitat types, and importance at different spatial scales. We used maximum entropy to estimate the optimal proportions of 18 habitat types, plus elevation and habitat richness associated with the presence of leks of Black Grouse Tetrao tetrix within an 800‐km² study area in Perthshire, Scotland. We repeated the analysis at several radii (0.2–3 km) to assess how the importance of different habitats changed with proximity to lek and scale. We then examined habitat features or combinations of features that were associated with large leks or positive lek growth. Models at all radii had satisfactory predictive power. Using response curves from maxent , we constructed ideal habitat mixes for leks at each radius. At the 2‐km radius, suitability was highest with around 20% each of three moorland types and open/mixed forestry, whereas close to leks (0.2 km), higher proportions of grouse moor and lower proportions of closed‐canopy woodland were optimal. The relationship between habitat and lek size or direction of lek growth was complex, indicating that a landscape containing large or productive leks can be the result of more than one combination of habitats. This demonstrates a degree of flexibility in designing landscapes for Black Grouse conservation, so landowners can prioritize combinations of habitats that are the most practical and/or economical, while still serving the requirements of the target species.     

Numbers and breeding success of Capercaillies Tetrao urogallus and Black Grouse T. tetrix at Abernethy Forest,Scotland

Capsule In most years, changes in numbers are associated with variations in breeding success.

Aims To describe the annual variation in numbers and breeding success of Capercaillies Tetrao urogallus and Black Grouse Tetrao tetrix at Abernethy Forest, and their inter‐relationships.

Methods Numbers and breeding success of Capercaillies and Black Grouse were recorded annually at Abernethy Forest (a Scots Pine Pinus sylvestris forest comprising ancient native, or semi‐natural, pinewood and plantations) during 1989–2009. Indices of abundance and densities of Capercaillies were obtained along transects, while counts of males at leks were obtained for both species. Breeding success (number of chicks per female) was obtained using dogs to locate females and chicks.

Results Capercaillie: the index of abundance increased to a peak in winter 1996/97 (2.7 times greater than in 1992/93) and then declined. There was no long‐term trend. In winters 2003/04 and 2004/05, the mean density was 4.2 per km² (95% CLs 3.1–5.7). The total number was 140 (95% CLs 100–220) for 2003/04 and 170 (95% CLs 110–280) for 2004/05, comprising about 8% of the Scottish population. The number of males at leks peaked in 1995 (to 46 males) and again in 2004 (41 males), and there was no long‐term trend. The annual breeding success varied from 0 to 2.93 chicks per female (mean = 0.64). The mean was within the 95% CLs of an independent estimate of the productivity required to maintain numbers. In a free‐running model, annual breeding success and survival rates (which were assumed to improve when mortality owing to fence collisions was removed) largely accounted for the annual variation in the index of abundance, as measured from winter counts along transects during 1990/91 to 2002/03. If mortality associated with collisions with fences had continued, the index would have declined, assuming no immigration.

Black Grouse: The number of male birds at leks increased to a peak in 1997 (to 165 males), before falling back to a smaller number (about 50 males) in the early 2000s. There was a smaller peak in 2007. The annual breeding success varied from 0 to 4.71 chicks per female (mean = 1.76).

Conclusion Numbers of Capercaillies and Black Grouse varied over a 19‐year period at Abernethy Forest, but did not show either upward or downward trends, while the national population of Capercaillies dipped to a low level in 1998/99, and the Black Grouse population continued to decline. In most years, changes in numbers of both species were associated with variation in breeding production. Mortality caused by collisions with fences would have led to a decline in Capercaillie numbers if fences had not been removed.     

The invertebrate diet of Black Grouse Tetrao tetrix chicks: a comparison between northern England and the Scottish Highlands

Capsule: Conservation programmes for Black Grouse Tetrao tetrix need to consider managements that increase invertebrates for chicks.

Aims: To compare invertebrates in chick diet between habitat and region and to relate abundance of preferred invertebrates to Black Grouse breeding success.

Methods: Chick faeces were collected from roosts in the Pennines (northern England) and Perthshire (Scottish Highlands) to identify invertebrates eaten. Larval abundance was determined by sweep netting (Pennines) and related to Black Grouse breeding success.

Results: Invertebrates were recovered out of 98 faecal samples from 63 broods. Ants were more numerous in chick diet in Perthshire, with larvae (both sawflies and moths) more numerous in the Pennines. Sawfly larval abundance was positively correlated with Black Grouse breeding success in the Pennines.

Conclusions: Management for Black Grouse should promote high invertebrate abundance to maintain high breeding success. This may be achieved through creating low-intensity grazed moorland fringes to encourage Bilberry, and associated moth caterpillars, adjacent to areas of higher grazing intensity to retain grasses and rushes that host sawfly larvae.     

Habitat associations of young Black Grouse Tetrao tetrix broods

Capsule: In the Scottish Highlands, Black Grouse Tetrao tetrix females with young broods selected areas rich in wet flushes, grasses and Sphagnum mosses.

Aims: To identify associations between young Black Grouse broods and habitat characteristics.

Methods: We located brood-rearing Black Grouse females in four areas of moorland-forest mosaic in the Scottish Highlands. Each brood was paired with a random reference location 100?m away. We recorded cover of different habitats and fine-scale vegetation and structure within squares of 1 and 0.25?ha, respectively. Associations between brood occurrence and habitat and vegetation variables were examined at the two scales.

Results: Black Grouse broods were positively associated with wet flushes (1?ha), and with Heather Calluna vulgaris, sedges Carex spp., grasses, Sphagnum mosses and taller vegetation with intermediate levels of height variability (0.25?ha).

Conclusions: This study highlights the importance of wet habitats for young Black Grouse chicks. In addition, relatively tall field-layer vegetation comprising Heather, sedges, grasses over a layer of Sphagnum mosses attracted brood-rearing Black Grouse females. Many management practices associated with peatland restoration, including drain-blocking, Sphagnum re-establishment and the avoidance of burning on deep peat soils, are therefore consistent with favourable habitat management for Black Grouse.     

Changes in upland bird abundances show associations with moorland management

Capsule: Changes in abundance of six bird species showed associations with moorland management.

Aims: To assess responses of breeding birds to moorland management over a 14-year period.

Methods: Vegetation and birds were surveyed at 2–3-year intervals and changes examined in relation to sheep and cattle grazing, vegetation burning and cutting.

Results: Seven correlations between change in management and change in bird abundance were detected, and six between change in vegetation and change in bird abundance. On plots where sheep numbers declined, Golden Plover Pluvialis apricaria and Northern Wheatear Oenanthe oenanthe declined. Where a greater area was burned, Golden Plover increased in the initial post-burning period but Red Grouse Lagopus lagopus scotica declined. Eurasian Curlew Numenius arquata and Sky Lark Alauda arvensis increased where a greater area of moorland vegetation was cut. Whinchat Saxicola rubetra declined with increasing cattle numbers on a plot.

Conclusions: Bird populations respond to changes in moorland management, but these changes are not always associated with detectable changes in vegetation. These responses of moorland breeding birds to management could help refine agri-environment options and other conservation interventions on moorland. Responses differed between bird species, ideally requiring site-specific planning where managing for multiple species is a goal.     

The influence of survey frequency on population estimates of moorland breeding birds

Capsule A minimum of four constant‐effort‐search survey visits are required to generate reliable population estimates of breeding birds on moorland that are not subject to biases associated with varying levels of detectability through the season.

Aims To investigate the influence of the number and the combination of survey visits on the population estimates of breeding birds on moorland.

Methods Four constant‐effort‐search surveys (80–100 minutes per km² per visit) of moorland in southwest Scotland were undertaken in each of six years, 2003–2008. Using standard protocols, the numbers of apparent territories that would have been identified for each possible combination of survey visits were determined.glms were used to assess the influence of the frequency of survey visits, and different combination scenarios on the derived population estimates for Red Grouse, European Golden Plover, Common Snipe, Eurasian Curlew, Sky Lark, Winter Wren and Stonechat. Independent assessments of population density were made by transect sampling for Red Grouse and Sky Lark.

Results Robust population estimates were possible from three survey visits for European Golden Plover, Eurasian Curlew and Stonechat. However, there were differences between species in the seasonal variation of their detectability. Four survey visits would underestimate the populations of Red Grouse (probably by 67–91%), Sky Lark (probably by 31–61%) and Winter Wren (by an undetermined proportion). Common Snipe were also likely to be underestimated after four survey visits, but the value of the derived estimate as an index of population density deserves further investigation.

Conclusions If there is a need to carry out a multi‐species survey on moorland, we suggest that a minimum of four survey visits is required to ensure the derivation of reliable population estimates for a suite of the most readily detectable species. Population estimates derived from three or fewer survey visits risk biases through uneven sampling in periods of differing detectability. With evidence for changes in the breeding phenology of birds associated with changing climate or weather patterns, it arguably becomes more important to ensure that surveys sample an adequately broad period of the breeding season.     

A survey and GIS-based estimate of the breeding population of Great Snipe Gallinago media in Central Norway

Capsule By using a GIS-model to identify suitable breeding habitats for Great Snipe in Central Norway, we estimated a total of 276 leks holding approximately 2700 males.

Aim To estimate the size of the Great Snipe population in central parts of the species remaining breeding areas in Western Europe.

Methods GIS-analysis identified an area of 528?km² as suitable habitat for Great Snipe in the total study area (22?000?km²). Complete surveys were made in 8% of these habitats by using a subset of 53 sampling areas.

Results A total of 28 Great Snipe leks were found within the sampling areas. Ten of these were found in previously known lek areas, while 18 leks were found in areas with no previous knowledge of leks. Extrapolating the lek density and the lek size found in the surveyed areas, resulted in a total estimate of 276 Great Snipe leks holding approximately 2700 lekking males. The leks were found on open fens along the forest edge and were mainly situated on base-rich bedrocks. Mean altitude of the leks was 570?m.

Conclusion The total population of Great Snipe in Norway was previously assumed to comprise 5000–15?000 lekking males or ‘pairs'. By extrapolating the densities of leks found in Central Norway to a national scale, we expect the true breeding population of Great Snipe to be approximately 13?500 males. Changes in the elevation of the tree limit and increased overgrowth, as a result of reduced grazing pressure and/or global warming, are possible threats that may reduce the availability of preferred Great Snipe habitats and increase population fragmentation.     

Breeding season habitat associations and population declines of British Hawfinches Coccothraustes coccothraustes

Capsule At both landscape and local scales, breeding persistence in a declining Hawfinch population was greatest where broadleaved woodland cover was high, while at a fine scale, nest sites were associated with openings in the woodland canopy.

Aims To assess which components of habitat are associated with Hawfinch occupancy at landscape (10-km), local (tetrad) and fine (nest) spatial scales, during a period of population decline and range contraction.

Methods Bird Atlas 2008–11 data were used to determine areas of Hawfinch loss and persistence over 20 years. Current habitat was measured and compared to look for correlates that helped explain the differing status at both 10-km and tetrad scales. Fine scale habitat data collected at nest sites were compared with random locations to investigate within-wood nest site selection.

Results At both 10-km and tetrad scales, Hawfinch persistence is more likely where woodland cover is greater. Recent woodland management was less evident in tetrads where the species persisted. At the nest site scale, the only relationship detected was for nests to be close to canopy openings.

Conclusions Maintaining and increasing broadleaved woodland area is likely to benefit Hawfinch. Within woods, maintenance and creation of open areas may enhance nesting opportunities.     

Effects of density on lek-site selection by Black Grouse Tetrao tetrix in the Alps

Capsule: The Black Grouse is a primarily lekking species, but low population density and lack of suitable habitat can lead to the establishment of non-lekking populations.

Aims: To understand if differences in density could be related to differences in the lekking system, if there were differences in lek-site selection, and if there was a direct effect of habitat on the lek size.

Methods: We compared lek sizes between two Black Grouse populations with different male population densities as estimated by distance sampling. We considered land-cover categories, landscape metrics and orographic variables and computed the Ivlev’s Electivity Index to evaluate habitat selection of males in the two study areas. A general linear model was used to assess the relationship between lek size and habitat variables.

Results: We could not demonstrate the direct effect of density on the displaying behaviour but we found strongly different patterns of lek-site selection and different effects of habitat on lek size according to the population density.

Conclusions: We concluded that habitat normally considered as high quality and habitat complexity may play different roles in selection by solitary versus lekking males when different population densities are considered.     

Habitat and diet of young grouse broods: resource partitioning between Capercaillie (Tetrao urogallus) and Black Grouse (Tetrao tetrix) in boreal forests

We compared habitat use and diets of young Capercaillie and Black Grouse broods in a boreal forest in southeast Norway. We used pointing dogs to search for broods (N = 83) in mature “natural” forest types and examined the crop content of 66 chicks 1–9 weeks old. We also measured the abundance of insects in the habitats where broods were found. Although overlapping substantially in both habitat and diets, there were notable differences: Capercaillie broods were more frequently recorded in bilberry-dominated forest types, whereas Black Grouse preferentially used pine bog forest, a more open habitat with little bilberry. Capercaillie chicks ate proportionally more insects, particularly lepidopteran larvae, and insects dominated their diet for a longer period of time (until age 28–29 days) than in Black Grouse (14–15 days). After reaching their peaks, the quantity of insects in the crops declined rapidly especially in Capercaillie, and in one of 2 years this occurred at a time when insects, including larvae, were still abundant in the habitats. Among plant foods, both species ate large amounts of Bilberry (Vaccinium myrtillus) and Bog Whortleberry (V. uliginosum). The main difference between species was a large proportion of both over-wintered and new, not yet ripe, berries of Cranberry (Oxycoccus quadripetalus) in Black Grouse, and a higher proportion of the forb Melampyrum sylvaticum in Capercaillie. The difference in diets reflected their differential use of habitats; the Vaccinium-preferred habitats of Capercaillie were richer in insects, particularly larvae, than the pine bog habitat preferred by Black Grouse. Because insects, especially larvae, comprised a larger proportion of the diet of Capercaillie chicks and chicks of this species need more food to sustain their rapid growth, Capercaillie is likely to be more sensitive to variation in insect food than Black Grouse. Also, by reducing the abundance of bilberry, the main host plant of larvae chick food, clearcutting forestry has negative effects on the brood habitat quality of both species.     

Habitat selection and foraging success of Hen Harriers Circus cyaneus in west Scotland

The foraging behaviour of Hen Harriers breeding in west Scotland was studied in a variety of afforested and moorland habitats. Time budget information from sample areas, stratified by habitat type and controlled for nest distance, was used to investigate habitat selection. Preferences were then related to measures of foraging performance in each habitat. Hen Harriers foraged preferentially over young first rotation coniferous forests, and selected heathland and grassland habitats ahead of closed canopy woodland. Harrier preference for the various habitats was positively correlated with the frequency with which they struck at, and captured, prey. Prey strike success was much lower than that reported for moorland managed for Red Grouse Lagopus lagopus scoticus. The results explain many of the reported changes in local Hen Harrier populations. The extent of young first rotation forestry is currently in decline. It is predicted that this will lead to a reduction in numbers of Hen Harriers breeding in west Scotland, and an increase in the proportion of the British harrier population occupying moorland managed for Red Grouse.     

Large-scale land use change may explain bird species declines in semi-natural areas: the case of Black Grouse population collapse in Lower Saxony, Germany

Farmland birds in Central Europe have been heavily declining in past decades. Among them are many ground-nesting species, adapted to semi-natural but secondary habitats. A vivid example is the Black Grouse (Tetrao tetrix) in the lowlands of north-western Germany, the Netherlands and Denmark, where the species′ populations experienced dramatic declines between the 1950s and 1970s. One explanation for these ubiquitous population declines might be large-scale changes in agricultural land use and land cover. We investigated several agricultural indices at three hierarchic administrative scales in parts of the federal state Lower Saxony, Germany, and related changes in these indicators with the Black Grouse declines. Land cover proportions remained relatively stable whereas indices of agricultural intensification heavily increased from 1952 to 1973. Multiple regression showed that change in farmland area was the best predictor of the trends across scales. Correlates of Black Grouse abundance were moor at the medium scale and pasture cover and fallow land at the smallest scale. Our results support the hypothesis that Black Grouse population dynamics in the lowlands of Central Europe were affected by land use changes. They show that Black Grouse populations in Central Europe were dependent upon extensive farming and may provide additional explanation where underlying factors on the habitat scale cannot fully explain the declines.     

National‐scale analyses of habitat associations of Marsh Tits Poecile palustris and Blue Tits Cyanistes caeruleus: two species with opposing population trends in Britain

Capsule Marsh Tits were strongly associated with both the amount and species diversity of woodland understorey; Blue Tits were associated with large trees and deadwood.

Aims To gather quantitative information on the habitat requirements of Marsh Tits, in comparison with those of Blue Tits, across a large number of sites in England and Wales, and secondly to evaluate the range of habitat conditions likely to encourage the presence, and increase the abundance of, each species.

Methods Counts of birds were made at each of 181 woods across England and Wales, and habitat data were collected from the same locations in each woodland. Marsh Tit and Blue Tit presence and abundance were related to habitat characteristics, interspecific competition and deer impact.

Results Shrub cover and species diversity were important for the presence and abundance of Marsh Tits, across their geographical range in Britain. Blue Tits were associated with large trees and deadwood.

Conclusion Our results support the hypothesis that changes in woodland management, leading to canopy closure and a decline in the understorey available, could have had an impact on Marsh Tits, and may have led to the observed population decline. These same changes were also consistent with population increase in Blue Tits.     

The effect of woodland area on avian community composition in a fragmented southern UK landscape and associated management recommendations

ABSTRACT

Capsule: Smaller woodlands not only support fewer species but also show different avian community composition due to loss of woodland interior and an increase in edge habitat.

Aims: To use observed community composition changes, rather than traditional total species richness-area relationships, to make area-specific management recommendations for optimizing woodland habitat for avian communities in fragmented landscapes.

Methods: 17 woodlands were selected in Oxfordshire, UK, with areas between 0.2 and 120 ha. Three dawn area searches were conducted in each woodland between 1st April and 28th May 2016 to record encounter rates for each species. The impact of internal habitat variation on woodland comparability was assessed using habitat surveys.

Results: Woodlands with area less than 3.6 ha showed a significant positive relationship between total avian species richness and woodland area. Woodlands with area over 3.6 ha were all consistent with a mean (± se) total richness of 25.4?±?0.6 species, however the number of woodland specialists continued to increase with woodland area. Woodland generalists dominated the total encounter rate across the area range, however the fractional contribution of woodland specialists showed a significant positive correlation with woodland area, while the fractional contribution of non-woodland species significantly decreased. Non-woodland species numbers peaked in mid-sized woodlands with enhanced habitat heterogeneity.

Conclusions: Community composition analysis enabled more targeted recommendations than total species richness analysis, specifically: large woodlands (over 25?ha) in southern UK should focus conservation efforts on providing the specific internal habitats required by woodland specialists; medium-sized woodlands (between approximately 4 and 25?ha) should focus on promoting internal habitat variety, which can benefit both woodland species and non-woodland species of conservation concern in the surrounding landscape; small woodlands (under 4?ha) should focus on providing nesting opportunities for non-woodland species and on improving connectivity to maximize habitat for woodland generalists and facilitate movement of woodland specialists.     

Factors influencing patch occupancy and within‐patch habitat use in an apparently stable population of Willow Tits Poecile montanus kleinschmidti in Britain

Capsule Birds selected younger woodland patches with fewer conifers and higher soil moisture content; within these patches, they selected areas with higher vegetation cover at 2–4 m, and less bracken.

Aims For an apparently stable population, to investigate habitat differences between occupied and unoccupied woodland patches and habitat selection within occupied woodlands.

Methods We surveyed woodland patches for breeding Willow Tits in April 2006 in an area with an apparently stable population. Habitat was measured at points spread throughout each woodland patch and at points where Willow Tits were located. We compared habitat between occupied and unoccupied sites. In addition, within occupied sites, we examined habitat differences between Willow Tit locations and the points spread throughout the wood.

Results We surveyed 65 woodland patches, of which 29 were occupied. Willow Tits were more likely to be found in deciduous woodland that was younger and had higher levels of soil moisture. Probability of occupancy fell from 60% for woods aged 20–25 years to only around 15–30% for woods aged over 80 years. Within occupied woods, Willow Tits were more likely to be found in areas with more vegetation cover at the 2–4 m level and in areas with less bracken.

Conclusions Habitat management for Willow Tits should involve provision of young woodland patches with moist soils. Changes to the age structure and/or the soil moisture content of woods may be implicated in the dramatic decline of Willow Tits in Britain.     

Habitat associations of Wood Warblers Phylloscopus sibilatrix breeding in Welsh oakwoods

Capsule Territory locations, density and the change in numbers over 20 years were associated with characteristics of the canopy, understorey structure and field-layer vegetation cover.

Aims To identify habitat characteristics associated with territory locations and density of Wood Warblers Phylloscopus sibilatrix in Welsh oakwoods in 2009–2011, and the change in abundance between 1982–1984 and 2003–2004.

Methods In 2009–2011, habitat characteristics were compared between 106 territories and 226 unoccupied points in 19 woods. Mean wood-scale habitat values were related to density in 27 woodland blocks. The change in Wood Warbler numbers between 1982–1984 and 2003–2004 was related to initial habitat quality in the 1980s and the change in habitat characteristics between the two time periods.

Results The location of territories in 2009–2011 was positively associated with canopy height, and with intermediate values of slope steepness, field-layer vegetation cover, canopy cover, the proportion of Oak Quercus in the tree community and subcanopy cover. Density was positively associated with slope, subcanopy cover at 0.5–2 m height and a landscape dominated by coniferous plantation and moorland; and with intermediate values of the proportion of oaks in the tree community. Wood Warblers declined by 24.4% in the two Welsh regions between 1982–1984 and 2003–2004, and trends were positively associated with the initial cover of Bramble and, in Gwynedd only, canopy cover.

Conclusions Wood Warblers were associated with a number of structural habitat variables, which could be related to the past management of the study woods. Management should be targeted at restoring habitat quality for Wood Warblers through the introduction of a moderate grazing regime.