The Galápagos is the smallest of the Spheniscus penguins, with males generally larger and slightly heavier than females (table 16.1). The adult has a dark blackish to brown back and a white breast flecked with dark feather spots that are individually distinct. On the side of the head, a narrow white line of feathers extends from behind the eyes, around the ear coverts, and down to join at the throat. Galápagos penguins have a dark throat band and a second dark band on the breast that extends down both sides of the upper white breast and along the flanks to the legs (Williams 1995). Their markings are similar to those of the other Spheniscus penguins but are finer and subtler. Generally, the white feathers on the chin beneath the bill are more pronounced with less mottling in males
than in females (Boersma 1977); the white chin is absent in the other Spheniscus penguins. Flippers are generally dark except for a pale central pattern on the ventral side. The bill is not as deep but nearly the same length as in its congeners, with males having deeper bills than females . The maxilla is black and hooked at the tip, fitting into the groove of the lower mandible. Usually the distal third of the mandible is black, shading from white to yellowish white to pink at the base. The feet of adults are black with some light shading on the web and are less mottled than juvenile feet.

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