Subspecific taxonomy complex and confused. Some four subspecies recognized.
O. l. leucorhoa - Northern Japan, Kurile Islands, Commander Islands, eastern Aleutians, North Atlantic from Maine to Scandinavia.
O. l. chapmani - San Benito Island, Baja California.
O. l. socorrensis (Socorro Storm-petrel) - Guadalupe Island off Baja, California.
O. l. cheimonestes

Also known as Fork-tailed Storm-petrel(!), Leach's Fork-tailed Storm-petrel or Leach's Petrel.
 

Identification

A medium sized storm-petrel of the north Atlantic and north Pacific. Flies with a distinctive bounding flight reminiscent of Nighthawks or Nightjars. Deep wing beats interspersed with short glides on bowed wings. Rapid changes of direction and speed. Sometimes patters. Not attracted to ships.
 

Where and When

Total world population in excess of 10 million individuals. The vast majority of the Atlantic breeding population breeds in eastern North America (750,000+ pairs) with smaller numbers on Iceland, The Faeroes, Ireland, Scotland and Norway. Disperse to tropical and subtropical waters as far south as South Africa. A few even getting into the Indian Ocean. In the Pacific, breeds in northern Japan (2 million on Hokkaido), Kurile Islands (350,000 birds) Sakhalin, Commanders, Aleutions (more than 1 million), Gulf of Alaska (more than 1.2 million), British Columbia (more than 1.1 million) and south to islands off western Mexico (Los Coronados, San Benito, Guadelupe and Rocas Alijos). Click here to view a range map for the Caribbean and central America. Has reached Australia and New Zealand.
 

Photographs on the web

In hand, showing details of upperwing, rump patch and tail. Taken in Norway. Photo by Frode Falkenberg

Uppersurface in flight. Photo by Monte Taylor, taken off California.

Turning in flight showing forked tail nicely. Photo by Monte Taylor, taken off California.
 
 

Literature

Ainley, DG. (1980) Geographic variation in Leach's Storm-Petrel. Auk 97: 837-853.

Ainley, DG. (1983) Further notes on variation in Leach's Storm-Petrel. Auk 100: 230-233.

Bourne, WRP and Jehl, JR (1982) Variation and nomenclature of Leach's Storm-Petrels. Auk 99: 793-797.

Power, DM., and Ainley, DG. (1986) Seabird geographic variation: similarity among populations of Leach's Petrels. Auk 103: 575-585.