General information. The willow warbler is a small, brown passerine. It has a brown back and lighter colored belly. This insectivore moves quickly through the foliage, hunting for food. It is a migratory bird that arrives in Vaasa at the end of May. This visit to the north is short and most willow warblers leave the country during August and September.
- Length 12 cm
- Nests on the ground under vegetation cover
- Winters in Africa
- Feeds on insects
Habitat. The willow warbler is the most common and frequently nesting bird in Finland. It thrives in all types of biotopes with deciduous trees. It prefers forests and of the fringes of forests dominated by deciduous trees. The species has adapted to living in an environment inhabited by humans, and therefore is also extremely common in built up areas. Like other species, the nesting density is at its lowest in coniferous plantations.
Distribution in Vaasa. The willow warbler nests almost across the entire area of Vaasa, except for the tree-less islets of the outer archipelago. It was recorded in approximately 290 survey blocks. During the bird census in Vaasa 2002 to 2007, the density of nesting willow warblers varied from 35 to 100 pairs per square kilometer. The National Bird Atlas survey of the 1990’s indicated an average density of 35 pairs/ km2. Based on this information, the nesting population in Vaasa can be estimated to at minimum 10 000 pairs!