National Dartford Warbler and Woodlark Surveys 2006

Background

A national survey for both species is planned for 2006, which will involve a collaboration with the BTO, RSPB, Forestry Commission, Natural England and JNCC. Since the mid 1990s, the populations of Woodlark and Dartford Warbler, have increased in size and range. Both species have a vulnerable conservation status in the UK and their current national status is uncertain. The organization of the survey will be jointly undertaken by BTO and RSPB, with BTO taking the lead on the analysis of the Woodlark data and RSPB leading on the Dartford Warbler Survey data.

Woodlark

Previous population estimates registered a six-fold increase between 1986 and 1997, moving the species from a precarious 250 pairs to 1,550 pairs. Since then, further increases have occurred where suitable habitat has become available, especially within forest plantations and more recently on arable farmland. Interestingly, however, population declines are also suspected in some areas, that may not simply reflect changes in the availability of suitable breeding habitat. Instead factors outside the breeding season may be implicated.

Dartford Warbler

Their sedentary nature belies their ability to disperse into suitable habitats when conditions become favourable. A population of around 1,800 pairs was recorded in 1994. Since then a recent series of milder winters has encouraged a further range expansion into coastal areas of East Anglia, South Wales, Exmoor, Dartmoor and Cornwall, presumably from core sites in southern England? This species was probably at its peak in the 19th Century when it reached parts of Oxfordshire, Hertfordshire and even Shropshire, as well as Kent (Holloway 1996). In this context, there is still plenty of ground to be reclaimed, although sadly, many areas of previously suitable habitat have been lost permanently. Nevertheless, while some of the recent range expansion is well accounted for, our picture of the more dispersed breeding population is sketchy and a more accurate assessment of their national status and distribution is timely.

Survey Methods

Both species will be surveyed using similar methods. The recording unit will be a 1-km square. Survey forms for each species, containing maps, will be prepared for all 1-km squares, which are known to have been occupied by breeding Dartford Warbler and Woodlark since the previous national surveys in 1994 and 1997, respectively. In addition, all SPA's, which have been designated for either species, will be fully covered as part of this survey. A number of contract fieldworkers will be used to assist volunteers in coverage of these extensive sites.

In order to determine expansion into new areas a number of sample 1-km squares have been selected. For Dartford Warbler these contain varying amounts of both suitable habitat, up to 10 km away from known breeding sites and for Woodlark a combination of suitable habitat and underlying soil types, have been selected up to 10 km from known breeding sites. As the populations of both species are expanding it is important to consider marginal habitats which may now be occupied as traditional habitats have become fully occupied.

For each species two visits will be required during the survey period (see below), to record and map individuals at breeding sites (see Survey Methods), particularly males. In addition, some basic habitat recording is required to assess habitat within the 1-km squares and in each breeding territory (see Survey Methods). Where both species occur, it is possible to combine the last Woodlark visit with the first Dartford Warbler survey visit, to make a total of three visits.

Records of other species encountered are also sought, particularly: Whinchat, Tree Pipit, Stonechat, Redstart, Grasshopper Warbler and Hobby.

Survey Periods:

Woodlark: 15th February to 31st May 2006 & Dartford Warbler: 1st April to 30th June 2006.

Results

Currently in preparation, which will be available late 2007.