THE GREAT BLACK-BACKED GULL. 763 



are partially moulted Sept. to Dec, but many juvenile feathers are 

 retained and wing- and tail-feathers and wing-coverts are not 

 moulted. First summer. — A partial body-moult similar to that of 

 first autumn takes place Jan.-March. Head and neck become 

 whiter and less streaked, under-parts rather whiter and upper- 

 parts rather more barred with buff but often only a few new body- 

 feathers are acquired. 



Second winter. — Crown and back of neck whiter, less streaked 

 than 1st winter ; mantle, scapulars and wing -coverts darker and 

 more grey-buff and dark barring not so prominent, basal part of 

 feathers more blackish-slate and varying number of mantle-feathers 

 and sometimes a few scapulars uniform black-slate with brownish 

 tinge and often brownish tip ; rump and upper tail-coverts more 

 narrowly barred than in 1st winter ; under-parts less barred 

 brown ; tail-feathers varying but with black usually more broken 

 up by white or whitish wavy bars and marks ; 2nd primary with a 

 penultimate patch (varying in shape and size) of mottled brownish - 

 white, inner primaries rather paler than in 1st winter with narrow 

 dark brown subterminal wavy bar ; secondaries with outer webs 

 more greyish-buff not so white as in 1st winter and more vermicu- 

 lated dark brown ; primary -co verts much as 1st winter but usually 

 darker and tips rather buffer not so white. This plumage is acquired 

 by complete moult as adult but sometimes commencing as early as 

 April. Second summer. — Some body -feathers are moulted Dec- 

 March. Crown and under-parts become rather less streaked and 

 mantle usually more blackish-slate. 



Third winter. — Head as adult but feathers of back of neck 

 with brown tips much as 2nd summer ; mantle, scapulars and back 

 as adult but more or less tinged brown and usually with some 

 feathers as 2nd winter especially on scapulars ; rump and upper 

 tail-coverts white with a few brown marks ; under-parts white, 

 sometimes a few brown marks on under tail-coverts and usually 

 some dusky-brown edgings to under wing-coverts ; tail white with 

 black-brown fine, wavy barring varying greatly in amount indi- 

 vidually ; primaries as adult but tip of 2nd often with penultimate 

 black band, white on 3rd sometimes much restricted and brownish, 

 inner primaries usually browner, not so pure grey as in adult ; 

 secondaries as adult but usually some brownish and more or less 

 vermiculated near tip ; primary-coverts brown, tipped pale brown, 

 outer feathers with black median streaks (varying in width) ; wing- 

 coverts varying, sometimes almost like adult but tinged brown, 

 sometimes mostly dark brown with paler tips. Third summer. — 

 Head, neck, rump and upper tail-coverts pure white or with a few 

 dark streaks. 



Fourth winter and summer. — Probably usually indistinguishable 

 from adult but some show black median streak on outer primary- 

 coverts and some brown tinge on wing-coverts. 



Measurements and structure. — $ wing 485-510 mm. (juv. 475- 

 505), tail 180-200, tarsus 76-84, bill from feathers 61-70 (12 British 



