Hudson’s Black-Tyrant is named for Argentina’s premier naturalist, William Henry Hudson, who later in life was also one of the first officers (in the 1890s) of a fledgling organization known as the RSPB in Britain. This is a highly sexually dimorphic flycatcher. Males are black with a white wing stripe in flight, and two hidden white patches on either side of the lower back. The female is brownish, streaked below with a rufous rump and largely dark tail. It is similar to the White-winged Black-Tyrant (Knipolegus aterrimus) but smaller, less strikingly plumaged, and the Hudson’s keeps to more shrubby habitats and is less conspicuous. This species is highly migratory, but the details of its movements remain to be worked out. It appears to breed largely in the Monte and Espinal habitats of Argentina, and migrates north to Bolivia and W Paraguay in the non-breeding season.