Density of Chiffchaffs Phylloscopus c. collybita and Willow Warblers Phylloscopus trochilus in a south Swedish villa suburb

Abstract

The expansion of the Chiffchaff Phylloscopus c. collybita in southern Sweden during the last decades is well documented. Regionally the densities of the Chiffchaff now even exceed the densities of the ubiquitous Willow Warbler Phylloscopus trochilus. However, there are few quantitative studies on Chiffchaff densities, not least from urban areas. During spring 2013 a survey of singing Chiffchaffs and Willow Warblers, complemented by territory mapping, was conducted in three villa suburb areas (total ea 1.27 km²) and a nearby recreational area in the southwestern parts of the city of Malmö, Sweden. The villa areas held a substantially higher number of Chiffchaffs (16.5 pairs/km²) than Willow Warblers (6.3 pairs/ km²). In one villa sub-area, with little undergrowth and denser housing, there were no Willow Warblers at all, in contrast to the recreational area close to the villa areas, where the Willow Warbler dominated (10.9 pairs/km²). The Chiffchaff had its highest density (18.7 pairs/km²) in the sub-area that had the largest trees. Thus, in the investigated villa suburb, the Chiffchaff clearly outnumbered the Willow Warbler as a breeding bird.