© Copyright: Images: Mervi Wahlroos, M. & W. von Wright: Svenska fåglar (Kansalliskirjasto, The National Library of Finland). Recording: Jan-Erik Bruun. All rights reserved.
- Family: Reed warblers – Acrocephalidae
- Appearance: Resembles Willow Warbler but larger and particularly has a larger head. Tail has even tip, with pale edges to outermost feathers. Legs bluish, beak thick at base. Underparts pale yellow, upper parts greyish green.
- Size: Length 12–13.5 cm, weight 11–15 g.
- Nest: Usually in a deciduous tree at a height of 1–4(–10) metres. Made of skillfully woven grass, spiders’ webs and beard lichen, covered with birch bark scales and lichen, and lined with hair, root fibres and thin grass stalks. Nest bowl deep.
- Breeding: 4–7 eggs laid in May–June, usually incubated exclusively by female for 11–14 days. Fledglings remain in nest for 13–16 days.
- Occurrence: Breeds in lush mixed and deciduous woodland and parkland in Southern Finland. Found in smaller numbers as far north as Oulu. Finnish breeding population estimated at 10,000–15,000 pairs.
- Migration: By night, leaving Finland August–September, returning May–June after wintering in tropical Africa.
- Diet: Invertebrates.
- Calls: Sharp tri-syllabic call “che-che feet”. Song rapid, very varied and melodious, performed during the daytime, usually from a perch high in a tree.
Icterine Warblers resemble the more common Willow Warbler, but are larger and particularly have larger heads. They have greyish green upper parts and pale yellow underparts. The pale edges of their secondary wing feathers form a pale wing panel that stands out on their otherwise dark wings. Their tails have a straight edged tip and white edging on their outermost feathers. Their wings are relatively long, reflected in the length of the protruding tips of their primary wing feathers compared to the length of their tertial feathers.
Younger birds have paler yellow or even whitish underparts with no yellow colouring, making them resemble the rare Olivaceous Warbler (which can be distinguished by its much shorter primary wing feathers). Icterine Warblers have bluish grey legs, dark brown irises, and brown beaks with a broad base (lower mandible yellowish pink). Bright orange colouring may be seen in the gapes of singing Icterine Warblers.