Willow Warbler

Phylloscopus trochilus

The willow warbler is a very common and widespread leaf warbler which breeds throughout northern and temperate Europe and the Palearctic, from Ireland east to the Anadyr River basin in eastern Siberia. It is strongly migratory, with almost all of the population wintering in sub-Saharan Africa. Source

Where it is now

In the last 8 weeks this bird was recorded 25,627 times across 61 areas (each area is a 5 degree square).

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Movement and weather

Each season it is first heard regularly where daytime highs are around 13°C (typically 11 to 15°C, from 32 areas). That holds across 35° of latitude, which suggests its timing follows temperature more than the calendar.

Over the weeks it was present in the past year, its centre in Europe ranged from 55°N in April to 64°N in July, about 1,000 km apart.

Arrival dates

The week it was first heard regularly in each region, after at least six weeks away. Dates differ from south to north, so a region has a range.

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Figures are effort corrected and come from automatic sound identification, which makes mistakes. How this is measured and how it compares with human observers.