The Dark-sided Flycatcher breeds in northern Asia and winters in southern China and Southeast Asia.
It is a small, dark flycatcher with smudgy gray-brown streaks on the breast and flanks and dark centers on the undertail coverts.
From 17 to 19 September 2025, a Dark-sided Flycatcher was observed around a wetland and buildings in California. Photographs and plumage patterns distinguished it from similar species, establishing the first record for temperate North America.
White-tipped feathers showed it was a first-fall bird. Chest and undertail patterns helped separate it from lookalikes, and its plumage matched the migratory nominate subspecies from northeast Asia. It used about two hectares, fed on berries and caught insects from tall trees, and stayed for three days. Researchers compared 1,032 images of the bird with 6,643 images of other Dark-sided Flycatchers to assess its age, molt, and subspecies.
An extinction-risk assessment has not been added yet.
Recording plumage, molt, and photographs together helps document rare migratory birds.