Willow warblers are small warblers with green upperparts and heads and pale buff bellies. Their flanks, breast, and throat have yellow tinges to them and they have a yellow eyebrow stripe (also known as the supercilium). Willow warblers tend to sing and ruffle their feathers while they are looking for food. They are often mistaken for the chiffchaffs but they can be told apart quite easily by their song. Chiffchaffs have a confident onomatopoeic “chiff-chaff-chiff-chaff” song compared to the willow warbler's melodious descending scale.
Average Length: 11 cm
Average Lifespan: 2 Years
Average Wingspan: 16-22 cm
Willow Warblers eat a range of invertebrates but will also supplement their diet with berries and fruit. If you want to attract them to your garden, create insect-friendly zones and plant berry bushes to provide food.
In April Willow warblers build a distinctive dome-shaped nest with a small opening, placed on the ground hidden amongst dense vegetation. 5 to 7 tiny eggs are laid in this nest, 3 willow warbler eggs weigh the same as a penny! The female incubates these eggs alone for 12-14 days and once they hatch they are fed by both parents for another 13-16 days. They finish breeding in July, which means they normally only produce one brood and spend the rest of the summer preparing for their migration.
Population trends differ across the UK, with declines seen in England and Wales but increases seen in Scotland and Northern Ireland. It is thought that these populations migrate to different areas of Southern Africa which may be driving these differences. As with other migratory birds, climate-driven droughts in their winter grounds could be driving declines. Changing habitat and habitat loss are also driving declines in the UK, especially in southern regions. Changing management techniques and decreases in Oak health (which are an important source of invertebrates) are causing these declines.
Create an insect-friendly garden by allowing areas to grow long and avoiding harsh chemicals.
Be careful when walking during the breeding season and keep dogs on leads to avoid damaging active nests.
Petition local areas to protect suitable scrub and woodland habitats.
Unlike other birds, willow warblers moult their feathers twice every year, once in the summer and again during the winter.
Bellamy, P. E., Hill, R. A., Rothery, P., Hinsley, S. A., Fuller, R. J., & Broughton, R. K. (2009). Willow Warbler Phylloscopus trochilus habitat in woods with different structure and management in southern England. Bird Study, 56(3), 338–348. https://doi.org/10.1080/00063650902806914
BirdLife International (2023) Species factsheet: Phylloscopus trochilus. Downloaded from http://datazone.birdlife.org/species/factsheet/willow-warbler-phylloscopus-trochilus. Accessed: 16/10/2023.
British Trust for Ornithology (2023) Willow warbler, BTO. Available at: https://www.bto.org/understanding-birds/birdfacts/willow-warbler. Accessed: 16/10/2023.
Thingstad, P.G., Hogstad, O., & M Speed, J. D. (2015). The influence of climatic conditions in breeding grounds and migratory flyways on a subalpine Norwegian Willow Warbler (Phylloscopus trochilus) population. Ornis Fennica. 92:23-33.
Remisiewicz, M., & Underhill, L. G. (2020). Climatic variation in Africa and Europe has combined effects on timing of spring migration in a long-distance migrant Willow Warbler Phylloscopus trochilus. PeerJ, 8. https://doi.org/10.7717/peerj.8770
RSPB (2023) Willow warbler, RSPB. Available at: https://www.rspb.org.uk/birds-and-wildlife/willow-warbler. Accessed: 16/10/2023.
Stostad, H. N., & Menéndez, R. (2014). Woodland structure, rather than tree identity, determines the breeding habitat of Willow Warblers Phylloscopus trochilus in the northwest of England. Bird Study, 61(2), 246–254. https://doi.org/10.1080/00063657.2014.901293