The Galapagos penguin (Spheniscus mendiculus) is the most northerly of all penguins, occurring on the Galapagos Islands, on the equator. It is the smallest of the South American penguins, with an average length of less than 50 centimetres. This diminutive penguin has a black head and upperparts, with a narrow white line extending from the throat around the head to the corner of the eye. The underparts are white, with two black bands extending across the breast. The upper part of the bill and the tip of the lower part of the bill are black, but the rest of the bill and a bare patch around the eye and bill are pinkish yellow. The female Galapagos penguin is generally smaller than the male. Juveniles have a completely dark head, and lack the dark breast bands seen in adults. The Galapagos penguin has a longer and more slender bill than other penguins. The Galapagos penguin has the smallest population size of any penguin. Male and female Galapagos penguins form pair bonds for life. Standing with its flippers extended, panting and seeking shade are behavioural adaptations the Galapagos penguin uses to keep cool.