; OcQirrence and identification 
I of the tachli Stomi-^trel 
{(km(Mbma Imorim) complex 
I off southern Califomia 
STEVE N, G. HOWELL • P. 0. BOX 423, BOLINAS, CALIFORNIA 94924 
TODD MCGRATH • 3550 ELM DRIVE, CALABASAS, CALIFORNIA 91302 • (CORRESPONDING AUTHOR: TODDAMCGRATH@YAHOO.COM) 
W. TERRY HUNEFELD • 105 NORTH VULCAN AVENUE, ENCINITAS, CALIFORNIA 92024 • (THUNEFELD@GMAIL.COM) 
JON S. FEENSTRA • 566 SOUTH FAIR OAKS AVENUE, SUITE 108, PASADENA, CALIFORNIA 91105 • (FEENSTRA@ALUMNI.CALTECH.EDU) 
Figure 1 . Presumed Leach's or Chapman's Storm-Petrel (left) and presumed Townsend's Storm-Petrel (right) off Santa Barbara, California, 21 July 2007. This photograph conveys well the rangier build and 
larger size of the paler, browner Leach's/Chapman's versus the smaller size and more compact build of the darker Townsend's. A series of photographs of these individuals supports the consistency of the 
differences shown here. Photograph by Steve W. G. Howell. 
Abstract 
Observers of seabirds over deep water off the 
Pacific coast of California have long noticed 
distinct variation in plumage, structure, and 
size exhibited by members of the Leach’s 
Storm-Petrel (Oceanodroma leiicorhoa) com- 
plex. Herein, variation within the complex is 
reviewed and tentatively linked to recent ob- 
servations of Leach’s Storm-Petrels off south- 
ern California. We discuss provisional identi- 
hcation criteria and possible occurrence pat- 
terns for four taxa within the complex: the 
widespread Leach's Storm-Petrel, found in 
both the North Atlantic and North Pacific 
Oceans (0. 1. leiicorhoa)- Chapman’s Storm- 
Petrel (0. 1. chapmani), breeding in the Coro- 
nado Islands and San Benito Islands of Mexi- 
co; and two taxa breeding on islets off Mexi- 
co’s Guadalupe Island (soccoroensis and 
chcimomnestcs), treated herein as full species. 
with English names Townsend’s Storm-Petrel 
and Ainley’s Storm-Petrel, respectively. 
Background 
Leach’s Storm-Petrel (Oceanodroma leiicorhoa) 
is a rather variable seabird that breeds in both 
the North Pacific and North Atlantic Oceans. 
Over the years, it has been the subject of a 
convoluted taxonomic history, with authors 
placing variable emphasis on the color and 
540 
NORTH AMERICAN BIRDS 
