The Dusky Warbler, Phylloscopus fuscatus, is a leaf warbler

Leaf warbler

Leaf-warblers are small insectivorous birds belonging mainly to the genus Phylloscopus. They were formerly included in the Old World warbler family but are now considered to belong to the Phylloscopidae, a family created in 2006. The genus is closely related to Seicercus and some species have been...

 which breeds in east Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. This warbler is strongly migratory

Bird migration

Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...

 and winters in southeast Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. It has a foothold in North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 in Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, and has also occurred in California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

This is an abundant bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 of taiga

Taiga

Taiga , also known as the boreal forest, is a biome characterized by coniferous forests.Taiga is the world's largest terrestrial biome. In North America it covers most of inland Canada and Alaska as well as parts of the extreme northern continental United States and is known as the Northwoods...

 bogs and wet meadows. The nest is built low in a bush, and 5-6 egg

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

s are laid. Like most Old World warbler

Old World warbler

The "Old World Warblers" is the name used to describe a large group of birds formerly grouped together in the bird family Sylviidae. The family held over 400 species in over 70 genera, and were the source of much taxonomic confusion. Two families were split out initially, the cisticolas into...

s, this small passerine

Passerine

A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...

 is insectivorous.

This small warbler is prone to vagrancy as far as western Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 in October, despite a 3000 km distance from its breeding grounds. It has wintered in Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

.

This is a warbler similar in size and shape to a Chiffchaff

Chiffchaff

The Common Chiffchaff, or simply the Chiffchaff, is a common and widespread leaf-warbler which breeds in open woodlands throughout northern and temperate Europe and Asia....

. The adult has an unstreaked brown back and buff underparts. There is a prominent whitish supercilium, and the bill is fine and pointed. The sexes are identical, as with most warblers, but young birds are more olive-tinged above. Like most warblers, it is insectivorous, but will take other small food items including berries.

The song is a monotonous whistle, and the call is a harsh check. The call is often the first clue that this typically skulking species is present, away from the breeding grounds.