Juan Fernandez Petrel, Pterodroma externa

The Juan Fernandez Petrel (pterodroma externa) is a species of seabird in the family Procellariidae. It breeds only on one island in Chile, Isla Alejandro Selkirk. The breeding population was estimated at 1,000,000 pairs in 1985 to 1986, and there may be up to 3 to 5 million birds worldwide. It is threatened by predation from introduced species such as cats and rats and, to a lesser extent, habitat loss from introduced herbivores such as goats. The IUCN Red List lists this species as Vulnerable due to its endemic status and threats from introduced predators.

This is a large species of gadfly petrel at 17 inches long with a wingspan of 37 to 38 inches and a mass of 1.1 pounds. The upperparts are dark brownish-grey and there is a black M-shaped marking across the extended wings. The underparts are white, with the underside of the wing edged is black. The face is white, with a black “cap” stretching to below the eyes. The bill is black with a hooked tip and houses the tubular nostrils that are unique to Procellariiformes.

Their breeding habitat is high elevation (above 2,460 ft) ridges, where it digs a 6.6 to 9.8 ft tunnel to raise one chick per year. The females lay a single, white egg in mid-November and both birds in a pair will take turns incubating the egg for about 60 days. The chick hatches in mid-February and is fed by both parents for about 90 to 100 days before fledging in May. The chick stays underground in the burrow until it has reached fledgling mass and is fully feathered. The chicks are fed a diet consisting of mainly fish and squid and are brought up to the nest from sea level by the parents.

During the breeding season, the Juan Fernandez Petrel is found foraging in waters surrounding Isla Alejandro Selkirk and Isla Robinson Crusoe, as well as coastal Chile. The birds can be found in flocks with pink-footed shearwaters and other types of seabirds. During the non-breeding season, these birds forage in the equatorial currents and counter currents, north to the Hawaiian Islands.

Previously, the Juan Fernandez Petrel was classified as a subspecies of the White-necked Petrel (pterodroma cervicalis), which is found in the Tropical Pacific Ocean and the Indian Ocean.

Image Caption: Plate 62 from Godman’s ‘Monograph of the Petrels’. Credit: John Gerrard Keulemans/Wikipedia