48 BIRD GiLl-LERY. 



[Case 26.] species are exhibited, one of the most noteworthy being the Pacific Gull 

 {Gabianus pacificus) (417), with its remarkably stout bill; while Tschudi's 

 (430), Hemprich's (431), and Heerman's (429) Gulls are specially inter- 

 esting forms on account of their peculiar dusky coloration. The hooded 

 Gulls comprise such species as our Black-headed Gull (L. ridibundus) 

 (432), the commonest British species, and the Bonaparte's (L. Philadel- 

 phia) (434), Mediterranean Black-headed (L. melanocephalus) (435), 

 Great Hooded {L. ichthyaetus) (436), and Little Gull (L. minutus) (437), 

 all accidental visitors to Britain. In these birds the black hood is only 

 assumed during the breeding-season, at other times the head is white or 

 nearly so. Sabine's Gull {Xema sabinei) (438) and the very rare Ross' 

 Rosy Gull (Rhodostethia rosea) (439) are aberrant forms ; in the former 

 the tail is forked, in the latter cuneate or wedge-shaped. Both belong to 

 the Arctic Seas and are only stragglers to our coasts. 



[Case 26.] The Terns or Sea-Swallows may be recognised by their nearly straight, 

 pointed and comparatively slender bill, forked tail, and more slender 

 build. Specially interesting forms are the White Tern (^Gygis Candida) 

 (440) and the Noddy (Jnous stolidus) (443), with its curious nest of 

 mud and seaweed, etc. placed on the bough of a tree. This bird has twice 

 been recorded from our shores. In the British Islands five species of Tern 

 [Sterna) , y'\z. : the Comvaoxi (^S. fluviatilis) (462), Arctic {S. macrura) 

 (463), Little {S. minuta) (448), Sandwich [S. cantiaca) (466) [PI. VII.], 

 and Roseate {S. dougalli) (464), are regular summer visitors and 

 remain to breed, the last being very much the rarest. Besides these, 

 seven other species of Tern have been recorded as accidental visitors, 

 viz. : the Sooty {S. fuliginosa) (446), Bridled {S. ancRstheta) (447), 

 Caspian {Hydroprogne caspia) (466), Gull-billed (Gelochelidon anglica) 

 (467), White-winged (Hy drochelidon leucoptera) (468), Whiskered 

 (H. hybrida) (469), and Black (H. nigra) (460). All these are repre- 

 sented in the Case, and the last-named may be considered a regular 

 visitor and formerly bred in England. 



The most remarkable members of the family are the Scissor-billed 

 Terns, of which an example will be found in Rliynchops flavirostris (462). 

 They have been given their trivial name on account of the peculiar 

 form of the bill, which is quite unique among birds. Both upper and 

 lower mandibles are compressed to a knife -like thinness, and the lower 

 is produced beyond the upper for a considerable distance. This peculiar 

 modification appears to be for the purpose of catching fishes from 

 •among the surface- swimming shoals. The lower jaw being used as a 

 sort of plough, catches up the prey as the bird flies along over the 

 surface. Five species are known, of which one is Asiatic, one African, 

 and three are American. 



