Willow Warbler Phylloscopus trochilus habitat in woods with different height structure and management in southern England

Abstract

Capsule: Use of LiDAR data identified suitable Willow Warbler habitat based on mean vegetation height. This habitat model provided maps of distribution and occupation of suitable habitat. Aims: To identify habitat associations in woods with different vegetation structure and management systems during a period of low Willow Warbler populations. Methods: Locations of all Willow Warblers were mapped during the breeding season in three woods of contrasting management; recent low intervention, actively coppiced woodland and high forest with clearfells. Height profile models of each wood were derived from airborne LiDAR. The mean vegetation height at locations with Willow Warblers and a sample from the rest of the wood were used to produce models of optimum habitat and breadth of habitat occupied in each wood. The habitat model was then used to produce maps of suitable habitat. Results: The habitat models did not differ between woods, with highest probability of Willow Warbler occurrence in mean vegetation heights of 3.7 m to 5.3 m. Habitat of heights 6 to 11 m appeared less suitable, being only partly occupied. Habitat maps showed that habitat of suitable height was only occupied when it occurred as large patches; smaller patches (mostly < 0.5 ha) and edges along rides and fields were not used. Conclusion: The use of LiDAR derived measures of vegetation height identified areas of suitable habitat for Willow Warbler. Willow Warblers occupied areas of low mean vegetation height either as early successional or open canopy woodland in all woods. Height-based habitat maps can identify areas of suitable habitat within larger expanses of heterogeneous woodland and are a potentially useful tool in assessing changes in extent of what are often temporary patches of habitat