Monotypic
Formerly considered subspecies of White-necked Petrel.
Also known as Pacific Petrel
 

Identification

Dorsal view of a Juan Fernandez Petrel. This individual shows a limited amount of white on the uppertail coverts. Photographed at sea near the Juan Fernandez Islands. Copyright of Martin Reid©.

A large long-winged petrel with a dark cap, gray upperparts and white underparts. Larger than 'Cookilaria' types and flight less erratic. Wings often held slightly curved back. Not attracted to ships. Often seen over feeding tuna. In light winds flies with low, wheeling glides on bowed wings interspersed with easy wingbeats. In moderate to strong winds, flies fast with high arcs and little or no flapping.

Upperparts: gray with an obvious dark 'M' mark. In bright light, the upperwing may appear brown. Dark eye patch and dark cap, sharply differentiated from the grey neck. Variable amount of white on the uppertail coverts. Some immatures and worn individuals show an extensive white nape (reminiscent of the closely related White-necked Petrel). In worn plumage the crown and upperparts become darker (sooty-brown) and the cap may begin to look blackish.

Underparts are white with a dark spot at the carpal joint and a narrow dark trailing edge. Potential confusion species such as Dark-rumped Petrel and pale-morph Wedge-tailed Shearwater have broader trailing edge. Primary tips dark.

Separated from very similar White-necked Petrel by less extensive dark leading edge to underwing. Less clear cut division between dark cap and white/pale neck.
Separated from Barau's Petrel and Stejneger's Petrel by underwing pattern and larger size.
Dark-rumped Petrel and Galapagos Petrel have a more extensive dark cap and more extensive black carpal-ulnar bar on the underwing.

Dorsal views of Juan Fernandez Petrel.  Note the different amounts of white on the uppertail coverts. Photographed at sea near the Juan Fernandez Islands. Copyright of Martin Reid©.

Greg Lasley has posted some excellent photos, again from the islands. Mounted wings from the University of Puget Sound collection can be viewed here (dorsal view and ventral view).
 

Where and When

Breeds on the Juan Fernandez Islands off Chile. Approximately 1 million pairs on Isla Alejandro Selkirk. Suffers from predation by introduced mammals. Outside of breeding season, ranges into the north Pacific to 5-20 deg. N. Has been recorded in waters off New Zealand and Australia.
 

Literature