THE IVORY-GULL. 775 



white but those along edge of wing with subterminal brown-black 

 marks ; tail white with narrow (but varying) subterminal brown - 

 black band ; wing-feathers and wing-coverts white with sub- 

 terminal brown-black tips, usually restricted in secondaries, often 

 to a shaft-streak and varying number of coverts and often some 

 secondaries pure white. 



First winter and summer. — Like juvenile but lead-grey usually 

 confined to fore-head and chin and fore-part of lores, crown and 

 throat and rest of under- and upper -parts often without any black 

 spots but sometimes a few here and there and scapulars apparently 

 always spotted as juvenile ; tail and wings as juvenile, but brown- 

 black spots on coverts often becoming lessened by wear. The 

 juvenile body-plumage is moulted in Sept., but not wing- or tail- 

 feathers nor wing-coverts and varying number of body-feathers 

 and especially scapulars are retained. None in spring -moult 

 examined. 



Second winter. — After complete moult apparently becomes as 

 adult. 



Measurements and structure. — <J wing 335-350 mm. (juv. 328- 

 350), tail 135-150, tarsus 38-42, bill from feathers 34-38 (juv. 30-35, 

 (6 measured). $ wing 320-345 (one 360), bill 34-38. Primaries : 

 1st narrow, pointed and about two-thirds primary-coverts, 2nd 

 longest, 3rd as long or 5-10 mm. shorter, 4th 10-25 shorter, 5th 

 25-45 shorter ; outer web of 2nd narrow. Tibia feathered nearly 

 to joint, tarsus and toes rather stout, webs concave, claws strong 

 and somewhat curved, that of middle toe considerably dilated. Bill 

 rather stout and gonys comparatively short. 



Soft parts. — Bill (ad.) base greenish -horn or slate-blue, rest 

 yellowish, tip yellowish-red ; legs and feet black ; iris black-brown ; 

 orbital ring vermilion. 



Characters. — No subspecies. Size and pure white of adult and 

 black legs, black spot-like marks on upper-parts of young dis- 

 tinguish species. 



Field -characters. — Though decidedly smaller than Glaucous, is 

 a fair-sized bird, distinguishable when adult by its pure white 

 plumage, black feet, and yellow and reddish bill from other northern 

 Gulls. Immature birds have a few dark spots on wings and head. 

 Carriage peculiar, tail depressed and head raised ; fierce and 

 aggressive in habits. Cry a very harsh and discordant note ; 

 repeated once or twice in flight. (F.C.R.J.). 



Breeding-habits. — Nests in colonies on rocky boulder strewn 

 shores, sometimes apparently also on cliffs, but apparently always 

 where there is much ice on which seals can lie out, which incidentally 

 renders breeding-haunts inaccessible till late in season. Nest. — 

 Built of algse and mosses, lichens, etc. Eggs. — Normally 2, not 

 unlike eggs of Common Gull, ground-colour stone-colour or greenish 

 to brownish, blotched and spotted with dark brown and ashy-grey. 



