Appearance
In summer reddish brown (male) or brownish (female) with white wings. Winter plumage almost totally white, though males have a red wattle over their eyes.
Size
Length 35–43 cm, wingspan 55–66 cm, weight 500–800 g.
Nest
In a shallow depression on the ground, usually in a dry spot by a tree stump or hummock or beneath a small tree or bush on the edge of a marshy area.
Breeding
7–14 eggs laid (most commonly 9–11) May–June, incubated by female for 20–27 days. Fledglings learn to fly within 5–15 days.
Distribution
Has declined lately, and almost vanished from Southern Finland. Breeds in marshy areas and on wooded fell-sides, especially favouring birch woodland. Finnish population presently estimated at 65,000–150,000 pairs.
Migration
Sedentary in most parts of range, though in upland regions of Lapland birds move from higher birch stands down into valleys for the winter. May also roam irregularly for tens (and perhaps even hundreds) of kilometres.
Diet
Varies seasonally and for birds of different ages. Mainly herbaceous plants and the buds, shoots and leaves of shrubs and broadleaved trees. In autumn also feeds on various berries, in winter more exclusively on willow and birch buds. Fledglings initially feed on insects (including mosquitoes), before adopting a more herbivorous diet about the same time as they develop the ability to fly.
Calls
A loud, cackling call reminiscent of laughter, also heard during courtship displays.
Endangerment
Vulnerable, protected. Like other grouse they may still be hunted in season. In northernmost Finnish Lapland they can also be trapped using traditional snares, as can Ptarmigans. European red list status Vulnerable, globally Least concern.

Willow grouse are medium-sized grouse. Their white wings distinguish them from all other grouse except the Ptarmigan. Males have four varying seasonal plumages, and females have three. In summer their plumage is mainly reddish brown (male) or brownish (female) with white wings. In winter both sexes have almost entirely white plumage, except for their black outer tail feathers. The similar Ptarmigan is greyer in colouring in the summer. Male Willow Grouse in winter plumage have red wattles over their eyes, but they lack the distinctive black mask-like facial stripe present on male Ptarmigans.

The legs of Willow Grouse are covered with feathers, except for their grey-coloured claws. Their beaks are black and their irises are dark brown. On cold nights they may dig burrows in the snow for shelter.

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Laji