OCCURRENCE AND IDENTIFICATION OF THE LEACH'S STORM-PETREL COMPLEX OFF SOUTHERN CALIFORNIA 
Islands: 
ANA ' Anacapa Island 
COR - Islas los Coronados 
SBA - Santa Barbara Island 
SCA - Santa Catalina Island 
SCL - San Clemente Island 
SCR - Santa Cruz Island 
SMI - San Miguel Island 
SNl - San Nicolas Island 
SRO - Santa Rosa Island 
Underwater: 
ARC ' Arguello Canyon 
BEB - Bell Bank 
BUB • Butterfly Bank 
COB - Cortez Bank 
MUB - Mushroom Bank 
NMB - Nine-mile Bank 
ROS - Rodriguez Seamount 
SBC - Santa Barbara Channel 
SJS - San Juan Seamount 
SMB - Sixiy-mile Bank 
TAB - Tanner Bank 
TMB - Thirty-mile Bank 
Figure 2. Map of southern California offshore waters and submarine features. Dotted line indicates the international border. Map by Jon Feenstm. 
pattern of the uppertail coverts 
(often referred to for the sake of 
brevity as the “rump”), on size 
and structure, and more recently 
on breeding season and vocaliza- 
tions (Loomis 1918, Oberholser 
1919, Van Rossem 1942, Austin 
1952, Crossin 1974, Ainley 1980, 
Bourne and Jehl 1982, Ainley 
1983, Power and Ainley 1986). 
The view that has prevailed in re- 
cent years (e.g.. Power and Ainley 
1986 and subsequent literature) 
is that four taxa should be recog- 
nized: nominate leiicorhoa, breed- 
ing in both the North Pacific and 
North Atlantic, and three taxa 
breeding on islands off the Pacific 
coast of Mexico: chapmani, socor- 
roensis, and cheimomnestes. 
For Pacific breeders, from 
Alaska to Baja California, recent 
authors indicate that variation is 
clinal, changing from larger, 
longer-winged breeding popula- 
tions in the north (nominate ku- 
corhoa) to smaller, shorter- 
winged breeding populations in 
the south (subspecies chapmani). 
Three other subspecies have been 
described from southeastern 
Alaska to northern Baja Califor- 
nia (from north to south, beali, 
beldingi, and willetti), but these 
taxa are no longer recognized as 
valid in more recent literature on 
the complex, particularly follow- 
ing Power and Ainley (1986). 
Past authors have argued that these taxa differ 
subtly in size and rump pattern from members 
of the Leach’s group that breed to the north 
and south, but more recent research has not 
found the distinctions to be consistent. Genet- 
ic analysis would probably provide greater in- 
sight into their relationships with other popu- 
lations/taxa to the north and south. 
In addition to the Pacific coastal popula- 
tions, at least two distinct taxa breed on islets 
around Guadalupe Island, about 250 kilome- 
ters offshore of Baja California: soconvensis in 
summer, and the slightly larger cheimomnestes 
in winter. That winter and summer breeding 
populations replaced each other around 
Guadalupe Island was first documented by 
Hubbs (1960) and echoed by Crossin (1974). 
Subsequently, Ainley (1980) described the 
taxon cheimomnestes, noting that “on 
Guadalupe [Island], the two populations of 
0. leucorhoa [i.e., winter-breeding 
cheimomnestes and summer-breeding socor- 
roensis] are morphologically and behaviorally 
distinct” and “so different are their songs that, 
if they met, it is questionable that interbreed- 
ing would occur.” The prevailing taxonomic 
practice of the day was “lumping,” and Ainley 
described cheimomnestes as a subspecies of 
Leach’s Storm-Petrel, also the status he main- 
tained for soconvensis. Interestingly, Ainley 
(1980) drew parallels between the storm-pe- 
trels of Guadalupe Island and the “Soft- 
plumaged Petrel” (Pterodwma mollis sensu 
lato) complex, at that time considered a single 
species. More recent treatments indicate that 
“Soft-plumaged Petrels” comprise three or 
four species (e.g., Robb et al. 2008, Jesus et al. 
2009), but the taxa in the Leach’s Storm-Pe- 
trel complex have languished in obscurity by 
comparison. 
As far as is known, Leach’s Storm-Petrels 
from the North Atlantic and North Pacific have 
very similar vocalizations, whereas vocaliza- 
tions of both of the morphologically distinct 
Guadalupe populations sound different, both 
from each other and from more northerly- 
breeding taxa (Ainley 1980). In light of recent 
re-evaluations of the biogeography, vocaliza- 
tions, and speciation of tubenoses (e.g., as 
summarized for the eastern North Atlantic by 
Robb et al. 2008), we consider that the data 
presented by Ainley suggest that at least three 
species of “Leach’s Storm-Petrel” may be recog- 
nized in the Pacific. Genetic analysis may elu- 
cidate this conclusion. In a forthcoming identi- 
fication guide to North American petrels, alba- 
trosses, and storm-petrels, Howell (in prep.) 
will treat the Guadalupe Island taxa as full 
species, using the English names Townsend’s 
Storm-Petrel for the summer-breeding 0. [Icu- 
corhoa] soconvensis and Ainley’s Storm-Petrel 
for the winter-breeding 0. [Icucor/ioa] 
cheimomnestes. These names recognize the or- 
nithologists who described these taxa, Charles 
H. Townsend and David G. Ainley. 
These potential splits prompt the obvious 
questions: Do Townsend’s and Ainley’s Storm- 
Petrels occur in North American waters? And: 
how might they be identified at sea relative to 
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