The Willow Warbler Phylloscopus trochilus is a very common and widespread leaf warbler which breeds throughout northern and temperate Europe and Asia. It is strongly migratory, with nearly all of the population wintering in sub-Saharan Africa.
It is a bird of open woodlands with trees and ground cover for nesting, including most importantly birch, alder, and willow habitats. The nest is usually built in close contact with the ground, often in low vegetation. he highest population densities are found in Scandinavia (where it is the commonest bird of any), with up to 1,100 pairs per square kilometre, and a total population in Sweden and Finland of 24 million pairs. In England this species has on average decreased in population by 70% within the last 25 years, with the biggest declines in the southeast.
Range Map for Willow Warbler along the African-Eurasian Flyway showing breeding range (red) and non-breeding range (green).