High Quality Content by WIKIPEDIA articles! The Wilson`s Warbler, Wilsonia pusilla, is a small New World warbler. It is primarily greenish above and yellow below, with rounded wings and a long, slim tail. The male has a black crown patch which is greatly reduced or missing entirely in the female. It breeds across Canada and south through the western United States, and winters from Mexico south through much of Central America. It is a very rare vagrant to western Europe.