Abstract
In Europe, woodland bird populations have been declining since at least the 1970s, and in Britain, around one third of woodland bird species have undergone declines over this period. Habitat change has been highlighted as a possible cause, but for some species clear evidence of this is lacking owing to an incomplete knowledge of the species’ habitat requirements. Here, we analyse national data to explain the variation in abundance of a declining woodland bird, the Eurasian Woodcock. A nationwide, species-specific survey of breeding Woodcock was conducted in 2003 and 2013 at 807 and 823 randomly selected 1-km squares respectively. The counts were compared with a range of landscape-scale habitat variables as well as local habitat measures recorded by surveyors, using generalised linear mixed models. Habitat variables were measured at a variety of spatial scales using ring buffers, although our analyses show that strong collinearity between scales hinders interpretation. At large landscape scales, breeding Woodcock abundance was correlated with total woodland area and the way this interacted with woodland type. Woodcock were more abundant in woods containing a more heterogeneous mix of woodland habitat types and in woods further from urban areas. On a smaller spatial scale, Woodcock were less likely to be found at sites dominated by beech Fagus spp. and more likely to occur in woods containing birch Betula spp. The Woodcock’s association with large, heterogeneous woods and the apparent attractiveness of certain woodland types present the most relevant topics for future research into the role of habitat change in long-term declines.
Highlights
One third of woodland bird species breeding in Britain have experienced population declines over the past 40 years (Hewson et al 2007; DEFRA 2015)
While there have been attempts to link declines to woodland habitat change occurring over the course of the last century (Amar et al 2006; Hewson and Noble 2009), clear evidence of a direct effect remains scarce for most species
These types of woodland habitat are among those most threatened by changes to woodland management occurring during the last century (Fuller and Warren 1993; Hopkins and Kirby 2007), but isolating the effect of habitat change is hindered since most studies have focused on a narrow range of study sites, and because many of these species are long-distant migrants, making it difficult to separate the effects of breeding habitat from the unmeasured factors affecting overwinter survival and migration (Goodenough 2014; Mallord et al 2016)
Summary
One third of woodland bird species breeding in Britain have experienced population declines over the past 40 years (Hewson et al 2007; DEFRA 2015). In Angus, Woodcock tended to use sapling-stage birch Betula spp. and birch thickets more frequently than older birch or coniferous woodland (Hoodless and Hirons 2007) Such studies offer an insight into the species’ selectivity, but their findings vary depending upon the local characteristics of the chosen study area and cannot consider the full range of potential Woodcock habitats. A large-scale, multisite assessment of a species’ abundance in relation to relevant habitat data provides a means of studying basic habitat associations which may be the first step towards identifying causes of decline We provide this by combining broad measures of woodland area, type and surrounding habitat at multiple spatial scales, with the results of two national, species-specific surveys of breeding Woodcock in Britain. By identifying the habitat characteristics with which Woodcock are most commonly associated, and how this changes with time, this study provides a firmer basis for future research into the causes of recent population declines
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