MONOGRAPH OF THE PETRELS. 



This diagnosis appears to be correct when founded on the examples in the 

 Rothschild Collection alone, but in the British Museum there are three specimens 

 which require some consideration. Two were obtained in the Galapagos Islands by 

 Captain Kellett and Lieutenant Wood, during the voyage of the " Pandora," but the 

 exact locality has never been recorded. The third specimen, formerly in our collection, 

 was presented by Admiral A. H. Markham, who obtained it on Charles Island, on 

 the 18th of February (Salvin, P. Z. S., 1883, p. 431). These three specimens are almost 

 similar, differing from the series in the Rothschild Collection in being lighter in colour 

 beneath, with the axillaries either pure white, or only slightly mottled with brown. 

 Salvin referred these birds to P. obscurus, but I believe them to represent a phase of 

 plumage of P. subalaris : they are certainly not P. obscurus. If, therefore, I am correct 

 in referring these forms, one with the axillaries smoky-brown, the other with the 

 axillaries white, to the same species, there seems to be but one explanation, which is, 

 that these differences in plumage are due either to age or season. The evidence tending 

 to support this theory is as follows : — 



February (Tower Island, Wenman Island [nestlings], Bindloe Island, 



Charles Island) : — Under wing-coverts white, clouded with dusky-grey ; axillaries 



white (Markham specimen), or white mottled with dusky towards the tips. 



March (Bindloe Island, Seymour Island) — Under wing-coverts white in one bird, 



rather less clouded with dusky-grey; but in a second specimen the under wing-coverts 



and axillaries are darker sooty-grey, with only a little white near the base. 



July (Culpepper Island, Wenman Island) : — Under wing-coverts nearly pure 



white ; axillaries pure white. Some specimens, however, have a good deal of 



dusky mottling on these parts. 



August (Jervis Island) : — Under wing-coverts and axillaries more dusky, 



but not entirely so. 



November (Albemarle Island, Mus. Brit.) : — Under wing-coverts and 



axillaries dusky throughout. 



I have not been able to examine any specimens obtained between August and 

 November ; in the latter month, the colour of the under wing-coverts and axillaries 

 is darkest, but it will be noticed that, when these are pure white, the birds have been 

 procured in July, when the white on the under-wing reaches its maximum, and from 

 thenceforward a gradual darkening takes place. In February, which is the breeding 

 season, as proved by a downy nestling in the Rothschild Collection, the under wing- 

 coverts and axillaries are again white, though clouded with dusky-grey. 



The two examples procured by Kellett and Wood measure : Wing, 7.1-7.3 inches ; 

 tarsus, 1.3-1.4 ; middle toe and claw, 1.4-1.5 ; culmen, 0.95-1.0. Admiral Markham's 

 bird from Charles Island measures : Wing, 7.55 inches ; tarsus, 1.45 ; middle toe and 

 claw, 1.6 ; culmen, 1.05. This specimen was sent to Washington for comparison with 

 the types, and was pronounced by Dr. Ridgway to be identical with them. 



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