414 A PRACTICAL HANDBOOK OF BRITISH BIRDS. 



flanks adjoining white rump with outer webs and sometimes tips 

 white ; axillaries and under wing-coverts sooty black-brown, 

 median ones slightly paler and sometimes with narrow whitish 

 fringe on outer webs ; tail-feathers black -brown, extreme bases 

 of all except central usually white or whitish (varying), white on 

 outer web of outermost not more than 20 mm. (one 25) from base 

 and usually considerably less ; primaries brown-black, paler on 

 inner webs ; outer secondaries same, inner ones grey-brown with 

 dark tips and often washed ash-grey on outer webs and some 

 (when freshly moulted) with narrow white fringes ; primary- 

 coverts, lesser coverts and innermost greater and median brown- 

 black ; rest of median and greater coverts grey-brown, forming a 

 decided broad pale bar across wing, tips of outer greater brown- 

 black and inner greater and median when fresh with narrow whitish 

 fringes. This plumage is acquired by complete moult Aug.-March. 



Nestling. — Like that of Storm-Petrel. 



Juvenile. Male and Female. — Plumage immediately succeeding 

 2nd nestling down is like adult. Complete moult takes place 

 probably Jan. -March. 



Measurements and structure. — £ wing 150 (one 144) -161 mm., 

 tail : central pair 59-67, outermost 76-90, depth of fork 14r-25, 

 tarsus 23-26, middle toe with claw 22-26, bill from feathers 15-16.5 

 (12 measured). $ wing 149-160 (one 164, one 165). Primaries : 

 1st minute, pointed and concealed by primary-coverts, 3rd longest, 

 4th 1-3 mm. shorter, 2nd and 5th 5-12 shorter, 6th 20-26 shorter. 

 Tail deeply forked, 12 broad feathers, tips slightly rounded. Rest 

 of structure as in Storm-Petrel, but inner secondaries longer and 

 about equal 8th primary. 



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

 black. 



Characters and allied forms. — 0. I. beali and 0. I. kcedingi 

 (western N. America) are smaller. Paler greater and median 

 coverts, deeply forked tail, brownish shafts to upper tail- coverts 

 distinguish species from other British Petrels. 



Field -characters. — Resembles Storm-Petrel in habits and to 

 some extent in appearance, but is larger, greyer, and has distinctly 

 forked tail. Note of sitting birds corresponding with purring of 

 Storm-Petrel is described as " pewr-wit, pewr-wit." 



Breeding-habits. — Breeds in colonies in burrows in peaty ground 

 and among ruins, heaps of stones, and under boulders. Nest. — A 

 handful of dry grass is sometimes found at end of burrow. Egg. — 

 One only : decidedly larger than that of Storm-Petrel ; dull white, 

 elongated in shape, and usually with zone of fine reddish spots at 

 big end. Average of 100 eggs 32.7x23.9. Max.: 36x25.6. 

 Min. : 30x23.5 and 30.4x22.4 mm. Breeding -season. — Rather 

 earlier than Storm-Petrel as a rule ; from early June onward to 

 July. Incubation. — By both sexes. Period about 5 weeks (Hantzsch) . 

 Single brooded. 



