The black-capped gnatcatcher (Polioptila nigriceps) is a very small songbird. Adults are blue-grey on the upperparts with white underparts, with a long slender bill and a long black tail with white outer tailbands on the uppertail. The undertail is extensively white, showing black only along a thin vertical center line and at the very tip. Males show a prominent black cap. This species is very similar to the California gnatcatcher and the black-tailed gnatcatcher. These birds are primarily non-migratory, remaining in breeding territories year round.