THE MADEIRAN FORK -TAILED PETREL. 415 



Food. — Definite records of fish, copepoda (Timora longicornis) and 

 stalk-eyed Crustacea. Saunders also mentions floating greasy 

 matter as well as small mollusca and Crustacea. 

 Distribution. — British Isles. — Resident. Breeds Flannan Isles, 

 St. Kilda group and North Rona (O. Hebrides), and two or three 

 islets off Kerry and Mayo. Elsewhere somewhat irregular visitor 

 (chiefly autumn) to all coasts, and not infrequently driven inland 

 during gales. 



Distribution. — Abroad. — North Pacific and north Atlantic Oceans. 

 Breeds in N. America from Maine northwards, and in north Pacific, 

 in Europe on Westmann Is. near Iceland, stragglers Norway, 

 Heligoland, coasts of Germany, Holland, Belgium, France, Portugal, 

 south to west coast Africa and Brazil, rare west Mediterranean. 

 Subspecies on west coast N. America. 



OCEANODROMA CASTRO 



334. Oceanodroma castro (Harcourt.)— THE MADEIRAN FORK- 

 TAILED PETREL. 



Thalassidroma castro Harcourt, Sketch of Madeira, p. 123 (1851 — ■ 



Desertas near Madeira). 



Oceanodroma castro (Harcourt), Saunders, p. 731. 



Description. — Adult male and female. Winter and summer. — 

 Coloration as in 0. leucorrhoa, but usually rather darker, especially 

 under -parts, greater and median wing-coverts usually darker and 

 not so grey-brown, upper tail-coverts white, lower ones with 

 prominent black tips (in some feathers sometimes spot -like), shafts 

 of upper tail-coverts white, not brown as in 0. leucorrhoa, central 

 pair immediately over tail-feathers white tipped black and not 

 mostly brown as in 0. leucorrhoa, white patch on lower -flanks larger 

 and both webs and shafts of feathers white, lateral under tail-coverts 

 also with varying amount of white, base of tail-feathers with more, 

 or comparatively to length, more white which often extends in 

 outer feathers up shaft in form of streak often 30-40 mm. from 

 base, very seldom less than 20 mm. This plumage is acquired by 

 complete moult Aug.-Feb. Two completing moult in June and 

 July may be birds a year old. Few moulting examples examined. 



Nestling. — Like that of Storm-Petrel. 



Juvenile. Male and female. — Plumage immediately succeeding 

 2nd nestling down is like adult. Sometimes, but certainly not 

 always, young birds have more white than fresh plumaged adults 

 on tips and edges of wing-coverts, inner secondaries and scapulars 

 and have white fringes to the black tips of upper tail -coverts. 

 These differences are not constant and when present soon disappear 

 by abrasion. 



Measurements and structure. — £ wing 150 (one 145)-162 mm., 

 tail : central pair 62-66, outermost 65-78 (one 82), depth of " fork " 

 3-11 (one 14, one 16), tarsus 21-23.5, middle toe with claw 21-26, 



