The Galapagos penguin (Spheniscus mendiculus) is the bird that seems most out of place in the equatorial Galapagos Islands. Standing only 35 cm tall, it is the third smallest of the eighteen species in the penguin family and the only species to occur north of the equator and nest entirely within the tropics. Penguins are a group of flightless seabirds characteristic of the Antarctic oceans and islands. It comes as a surprise to find a little penguin swimming amongst the stilt roots of tropical red mangroves.
The closest relatives of the Galapagos penguin are the Humboldt and Magellan penguins of southern South America. The Humboldt penguin occurs primarily in the cold waters of the Humboldt or Peru currents and is only rarely seen off the coast of Ecuador.
The Galapagos penguin is most likely descended from stray individuals of this species that managed to find the cool upwelling of the western islands. It breeds only on the west coast of Isabela and on most of Fernandina's coasts. Some are seen in other parts of the Galapagos archipelago and may breed in sites such as by Pinnacle Rock on Bartolome Island.
Recent estimates put the population of the Galapagos penguins at between two and five thousand individuals and they are common within their breeding range. They are frequently seen sunning or resting on rocks, especially in the early morning and late afternoon, but most often are found swimming, singly or in groups of up to fifty or more, along the shoreline.
The Galapagos penguins adults are black above and white on the under parts, with a stripe around the breast and on the face. The juveniles are greyer, without the white lines, and have a pale patch on the side of the head and chin. They rise before dawn and spend the day swimming, with a few breaks on land. In the mid-afternoon, they start returning to their colonies.
On the surface, Galapagos penguins swim slowly, half submerged, but underwater, they fly through the water using their wings for propulsion and their feet as rudders. They can travel quickly through the water (as much as 40 km/h), especially when they "porpoise" on the surface. They usually do so when pursuing a school of fish. The kinds of fish taken are small, ranging from 10 to 150 mm; some crustaceans are taken as well.
The Galapagos penguin has different feeding strategies dependent on the water temperature. If the water is below about 23°C, they feed in large groups of twenty or more, as fish are abundant when the water is cool and rich. When the water is warmer they tend to feed in smaller groups or singly, as fish are less abundant. This indicates that group fishing is more efficient when fish are abundant.
Galapagos penguins must adapt to two environments, hot land and cool water, while their more southerly relatives need only adapt to cold. In the water, the temperature may range from a cool 16°C to a warm 28°C, while on penguin, has observed a case of a bird watching over its nest in the open sun, becoming overheated to the point where it had to either cool itself or die. It left the nest and took to the water-unfortunately, when it returned to the nest the eggs had heated and died.