The woodcock remains ‘amber-listed’ as a bird of conservation concern within Britain owing to a probable decline in breeding numbers during the last 30 years. In previous Reviews we have reported on survey methods and numbers of males found in our 2003 breeding survey (see Reviews of 2003 and 2004). This highlighted regional differences in woodcock occurrence. However, a clear understanding of what influences woodcock distribution and what constitutes good breeding habitat is important if management is to be implemented to improve the species’ status.
Using our survey of roding males at 907 woods, we investigated which landscapes and types of wood influenced the occurrence and abundance of breeding woodcock. The presence of a roding male cannot be taken as proof of a female nesting, but it is a good indicator of habitat suitability. We split the sample into woods where woodcock were breeding and woods where they were absent. We then compared the countryside around the two groups of woods using Geographical Information System (GIS) data based on satellite images. This was repeated at five scales, within radii of one kilometre, five, 10, 20 and 30 kilometres from the survey point. There were significant habitat differences in every case, which were similar at all five scales. Woodcock were present in more heavily wooded landscapes and were less likely to occur in woods surrounded by land with a high proportion of housing or improved grassland. The biggest differences between woods with and without woodcock occurred at the fivekilometre radius (80 square kilometres) scale (see Figure 1).
|Figure 1. Comparison of mean percentages of habitats within a five-kilometre radius (80 km²) of survey points where roding woodcock were present and where they were absent|
Having established that the amount of woodland in the landscape influenced the likelihood of woodcock being present, we examined this in relation to several additional variables thought likely to be relevant based on the species’ ecology (see Table 1). The likelihood of breeding woodcock being present increased further north and east. Relative to woods where woodcock were absent, woods with breeding woodcock had a greater diversity of types of tree stands (deciduous, coniferous, young trees, coppice, shrubs) and a greater number of individual stands, but a lower overall proportion of young trees. The chance of breeding woodcock being present also increased as the number of gamekeepers within five kilometres increased. Roding male abundance was lower in woods with a high proportion of conifers, but higher in woods with more ground vegetation.
Factors influencing the occurrence of roding male woodcock in woods in Britain
|Amount of woodland (ha/km2)||Positive||***|
|Diversity of tree stands||Positive||*|
|Number of tree stands||Positive||***|
|Proportion of young trees||Negative||**|
|Gamekeeper density (number per km2)||Positive||***|
|Significance: * P<0.05, ** P<0.01, *** P<0.001
A smaller P-value (more asterisks) equates to greater influence.
This takes us a step closer to understanding how woodland and its management can influence breeding woodcock, but it only explains a small proportion (less than 20%) of the variation in our data. We also need to look at other important variables, such as soil type, which is likely to influence food availability for woodcock.