THE STORM-PETREL. 411 



2nd down, very similar to first but slightly darker and of 

 slightly closer structure but of same length succeeds 1st down by 

 almost continuous growth so that 1st down clings to tips of 2nd, 

 which thus appears to be longer. 2nd down is short and sparse on 

 chin, lores and round eyes, but these parts are not quite so bare 

 as in first stage. 2nd down is succeeded by feathers also by con- 

 tinuous growth, so that at first feathers have two generations of 

 down clinging to their tips, down appears longer as nestling grows 

 owing to successive stages. 



J uvenile. Male and female* — Plumage immediately succeeding 

 2nd nestling down is like adult and not to be distinguished with 

 certainty when a little worn ; feathers of upper -parts when quite 

 fresh have very faint greyish edgings, black tip of some upper 

 tail-coverts is narrowly fringed white, width of greyish-white tips 

 and edges to innermost secondaries and greater coverts though 

 usually greater in young birds varies in individuals in fresh plumage, 

 and all these slight differences are affected by abrasion. Those 

 birds completing moult in May, June and July are probably birds 

 a year old. 



Measurements and structure. — £ wing 116-123 mm., tail 52-55, 

 tarsus 20-24, middle toe with claw 18-22.5, bill from feathers 10-12 

 (12 British measured). $ wing 114-125. Primaries : 1st minute, 

 pointed and concealed by primary-coverts, 3rd longest, 4th usually 

 as long, sometimes 2-4 mm. shorter, 2nd and 5th 5-10 shorter, 6th 

 14-20 shorter ; primaries not emarginated. Outer secondaries 

 shorter than 11th, and inner ones about as long as 10th primaries, 

 tips somewhat incurved with outer webs sloped off and inner webs 

 broad. Tail slightly round, 12 broad feathers, tips slightly emar- 

 ginated. Three toes long, slender, and webbed, hind toe minute, 

 claws small, concave and rather sharp. Bill slender, tip com- 

 pressed, decurved and fairly sharp. Proximal third of upper 

 mandible with ridge elevated, ending abruptly at opening of 

 parallel tubular nostrils (amount of elevation varies individually). 



Soft parts. — Bill, legs and feet black ; iris deepest sepia, nearly 

 black. 



Characters. — No subspecies. Small size and square tail distin- 

 guish this from other white -rumped black British Petrels. 



Field -characters. — Essentially maritime and during most of 

 year pelagic, Petrels and Shearwaters come ashore only in breeding- 

 season, and never occur inland except as storm-driven waifs. In 

 size and, despite dark under-parts, in appearance Storm-Petrels 

 suggest long-winged, square-tailed House -Martins, but flight, bat- 

 like and fluttering, is very different, and is often assisted by paddling 



* As two distinct generations of down immediately precede the first 

 feathered plumage and as there appears to be no moult in the first autumn 

 and winter, it is possible that the 2nd down takes the place of the juvenile 

 plumage, and that this plumage is really equivalent in generation to a first 

 winter plumage in other birds. — H.F.W. 



