The slim body with gray plumage, the yellow bill and the red tarsi and toes make the Red-legged Cormorant an unmistakable species. The Red-legged Cormorant is smaller and lighter than sympatric species. Atlantic birds are smaller than those on the Pacific coast, and there also are minor plumage differences (Nelson 2005).
In the Atlantic coast, the Red-legged Cormorant often breeds in sympatry with the Magellan Cormorant (also known as Rock Shag; Phalacrocorax magellanicus) and the Imperial Cormorant (Phalacrocorax atriceps). Rock Shags are a little bit heavier than Red-legged Cormorants and their plumage is black, with breast, belly and flanks white. Imperial Cormorants are larger than Red-legged Cormorants, and their plumage is white on the entire underparts, and with upperparts and face.
Adult: Sexes similar. The adult plumage is dark gray. The head, neck, back, wings, and the tail are dark gray with some markings of silvery gray. Ventral surface is somewhat paler. On each side of neck, adults have an elongated white patch, and behind the eye, this species present a scattered patch of white filoplumes.
Juvenile: see Rasmussen (1998) and Nelson (2005).
Iris: green, surrounded by regularly spaced pale blue spots.
Facial skin: orange bare skin around the face.
Bill: yellow with red base.
Tarsi and toes: coral red
Data are from Johnson (1965), Nelson (2005), and Frere et al. (personal observations).
Wing: 24.35 cm
Tail: 9.7 cm
Bill: 5.6 cm
Tarsus: 5.3 cm
Total length: 71-75 cm
Mass: 1.3-1.8 kg