121 



There are actually two forms of this bird that occur along the 

 Pacific coast; controversy exists over whether they are subspecies of a 

 bird that occurs world wide in subtropical and tropical waters ("Common" 

 Shearwater) or whether one (Black- vented Shearwater, P. opisthomelas or 

 P.p. opisthomelas) or the other (Townsend's Shearwater, P. townsendi or 

 P.p. townsendi) 3 or both, are distinct species. Little is known about 

 the marine distribution of the Townsend's Shearwater; probably(?) it does 

 not occur very far north along the Baja California coast. Whenever any 

 specimen of the "Common" Shearwater is found, every attempt should be 

 made to determine whether it is a Townsend's or a Black-vented Shearwater. 

 If a Townsend's then without doubt the specimen should be saved, 

 regardless of locality, and donated to a major museum. 



The two shearwaters can be separated by several characters. In 

 Townsend's, the undertail coverts are white (sometimes some are mottled 

 brown and white), the crown is black (not a good character in an old or 

 worn specimen), the side of the upper breast is only slightly mottled, 

 and it is smaller (see table below). In Black-vented, the undertail 

 coverts are brown, the crown and other upper parts are browner, the 

 upper breast is mottled, and it is larger. The following measurements 

 (in mm) were taken from Murphy (1952): 



Townsend's Black-vented 



Culmen 28-35 34-42 



Wing 220-238 214-251 



Tarsus 42-47 43-56 



GADFLY PETRELS (PROCELLARIIDAE, subfamily PUFFININAE) 



SCALED (MOTTLED) PETREL (Pterodroma inexpectata; choice 11, pg. 28). The 

 stout and heavy bill makes this petrel superficially similar to the 

 fulmarine petrels (Plate 5). No other petrel, or seabird, that would 

 likely be encountered in the area has the distinctive underwing color 

 pattern of this one (see keys). It is a strong possibility that Cook's 

 Petrel (peterodroma coofcii; Plate 5) will be recorded soon in Baja California 

 or southern California waters. Its completely white underwing linings and 

 belly would distinguish it from the Mottled Petrel. 



Mottled Petrels could be found at any time of year* Great numbers 

 are present in summer but for some reason most beach specimens have 

 occurred in winter and spring. They occur in small numbers in the 

 Aleutian and southeast Alaska areas and in even smaller numbers as far 

 south as central California along this coast. Any specimens encountered 

 south of Alaska should be saved. 



