About Spheniscus humboldti Meyen, 1834
Humboldt penguins (scientific name Spheniscus humboldti Meyen, 1834) are medium-sized penguins, growing 56–70 cm (22–28 in) long and weighing 2.9 to 6 kg (6.4 to 13.2 lb). They are sexually monomorphic, so sex cannot be identified by differences in plumage; however, males are heavier and larger than females, and can be distinguished by longer bills and wider heads. Among all Spheniscus penguins, which are closely similar in overall size, Humboldt penguins are the heaviest species in the genus: 123 sampled females averaged 4.05 kg (8.9 lb), while 165 sampled males averaged 4.7 kg (10 lb). This species has a black head marked with a white border that runs from behind the eye, around the black ear-coverts and chin, and meets at the throat. They have blackish-grey upperparts and whitish underparts, with a black breast-band that extends down the flanks to the thigh. The base of their bill is fleshy-pink. Juveniles have dark heads and no breast-band. They have spines on their tongue that they use to hold prey. The Humboldt penguin is a top predator endemic to the west coast of South America. Its breeding distribution stretches from southern Chile, along the dry, arid coastal regions of the Atacama Desert near former Bolivia, to subtropical Isla Foca in northern Peru. Its range is restricted to the coast and offshore islands influenced by the Humboldt Current, which supplies a consistent stream of nutrients and food that supports large seabird populations. The most important breeding colony in Chile is located at Isla Chañaral. In July 2002, a Humboldt penguin was caught in a fishing net off the coast of Prince of Wales Island in Alaska. After being released from the net, the penguin was eventually returned to the water by a fisherman. This is the only recorded wild occurrence of this penguin in North America, and it remains unknown whether the individual was a wild penguin or an escaped pet or zoo animal. Introduced feral species and habitat disturbance have harmed Humboldt penguin populations. On the Puñihuil islands, the introduction of feral goats caused detrimental impacts: goats browse the vegetation penguins use to build nests, and their activity can cause dirt burrows to collapse. Connecting the islands to the mainland also allowed new mammal species to move onto the islands. In central Chile, European rabbits and Norway rats graze on nesting vegetation. Norway rats and black rats also prey on penguin eggs, while feral cats and dogs kill chicks, fledglings, and adult Humboldt penguins. Humboldt penguins nest in loose colonies. Most pairs lay two equally sized eggs 4 days apart, and the eggs require 41 days of incubation. Their breeding schedule shifts based on food abundance; they breed immediately after moulting, when food is abundant and solar radiation is lower. They lay eggs from March to December, with peaks in activity in April and August–September, because many individuals lay a second clutch. Half of all females successfully produce two clutches per year, and most of these result in double broods. If a pair loses their eggs during the first breeding season, they will lay a new clutch within 1–4 months. On average, incubation shifts between parents last 2.5 days: one parent takes over incubation to allow the other to leave and forage for food. Males and females contribute equally to provisioning for chicks. Chicks generally hatch 2 days apart. They are semi-altricial and nidicolous, so one parent always guards the chick while the other forages. Chicks are fed only once per day. After chicks reach a certain age, they are left unattended at the nest site, and both parents forage at the same time.
