. A practical handbook of British birds . coverts, also fre-quently a few juvenile body - feathersunmoulted. The juvenile body-feathersand central pair of tail-feathers aremoulted Aug-Dec. but not rest of tailnor wing-feathers nor wing-co verts. First _.„ ... , _, . & . ° 1 Bill of the White-winged Black summer.—A complete moult commences Tern (Chudonias leuoopterus.)Jan. and bird usually becomes exactly like adult winter but occasionally considerable amount of plumage asadult summer is acquired. Measurements and structure.—$ wing 200-218 mm., tail : outerfeather 67-75, central 58-67, dep
. A practical handbook of British birds . coverts, also fre-quently a few juvenile body - feathersunmoulted. The juvenile body-feathersand central pair of tail-feathers aremoulted Aug-Dec. but not rest of tailnor wing-feathers nor wing-co verts. First _.„ ... , _, . & . ° 1 Bill of the White-winged Black summer.—A complete moult commences Tern (Chudonias leuoopterus.)Jan. and bird usually becomes exactly like adult winter but occasionally considerable amount of plumage asadult summer is acquired. Measurements and structure.—$ wing 200-218 mm., tail : outerfeather 67-75, central 58-67, depth of fork 5-11, tarsus 19-22,bill from feathers 23-24 (12 measured). $ wing 192-210. Primaries :1st pointed, narrow, and about two-thirds primary-coverts, 2ndlongest, 3rd 5-12 mm. shorter, 4th 18-26 shorter, 5th 34-42shorter. Other structure as C. niger but tail less deeply forkedand tips of outer feathers rounder, bill shorter and rather lessslender, and webs between toes more deeply incised even thanin C. 694 A PRACTICAL HANDBOOK OF BRITISH BIRDS. Soft parts.—Bill (ad.) black tinged crimson, (juv. and 1st winter)black-brown tinged orange at gape ; legs and feet (ad.) brightvermilion, (juv. and 1st winter) red to red-brown ; iris darkbrown. Characters.—No subspecies. In summer white lesser wing-coverts and black under-wing, and in winter and juvenile absenceof dark brown patches on sides of breast, pale rump and short billdistinguish it from other Marsh-Terns. Breeding-habits.—Nests in colonies in shallow water, marshes,etc., sometimes together with Black Tern. Nest.—Mass of floatingweed or vegetable matter. Eggs.—Usually 3, sometimes only 2,closely resemble those of Black Tern, ground being ochreous orbrown and with bold blotches of black and ashy-grey shellmarks,but are smaller. Average of 50 eggs, X Max.: X Min. : mm. Breeding-season.—Latterpart May and early June. Incubation.—Probably by both s
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