96 A MANUAL OF THE BIRDS OF AUSTRALIA. 
Genus HYDROPROGNE. 
Hydroprogne Kaup. Skizz. Entwick.-Gesch, Nat. Syst., p. 91 (pref. April) 1829. Type (by 
subsequent designation, Gray, Gen. Birds, Vol. III., p. 658, Nov. 1846): Sterna caspia Pallas. 
Sylochelidon Brehm, Vogel Deutschl., p. 767, (pref. July) 1831. Type (by monotypy) : 
S. balthica Brehm = S. caspia Pallas. 
Helopus Wagler, Isis, 1832, heft 11, col. 1224, Nov. Type (by monotypy): S. caspia Pallas. 
Pontochelidon Hogg, Edinb. New Philos. Journ., Vol. XLI., p. 69, 1846. Type (by subsequent 
designation, Mathews, Austral Av. Rec., Vol. II., p. 133, 1915): S. caspza Pallas. 
Heroprogne Buller, Suppl. Birds New Zeal., Vol. I., p. 157, 1905. Error only. 
Largest Terns, with long stout bills, long wings, short legs, and short tails. 
The diagnostic features of this genus are the large size and the long stout bills and 
short tail. The metatarsus is much shorter than the culmen, which is longer than 
the head. The tail is forked and only about a third of the wing. 
Coloration as in Sterna. 
69. Hydroprogne caspia.—CASPIAN TERN. 
[Sterna caspia Pallas, Nov. Comm. Acad. Sci. Petrop., Vol. XIV., pt. 1., p. 582, 1770: Caspian 
Sea. Extra-limital.] 
Gould, Vol. VII., pl. 22 (pt. xxm.), March Ist, 1846. Mathews, Vol. IT., pt. 3, pl. 105, Sept. 
20th, 1912. 
Sylochelidon strenuus Gould, Birds Austr., pt. xxu., Vol. VII., pl. 22, March 1st, 1846: Port 
Stephens, New South Wales, error = Tasmania. 
Hydroprogne tschegrava yorki Mathews, Austral Av. Rec., Vol. II., pt. 7, p. 125, Jan. 28th, 
1915: Cape York, Queensland. 
DisTRIBUTION.—Australia generally and Tasmania. 
Adult male in breeding-season.—General colour above pale grey, including the 
back, scapulars, wings, and tail; primary-quills silvery-grey on the outer webs, 
dark brown on the inner edge of the inner webs ; head and nape black, with a short 
white line immediately below the eye; cheeks, chin, throat and neck all round as 
well as the under-surface of body white, like the axillaries and under wing-coverts ; 
bill red ; feet black. Total length 555 mm.; culmen 77, wing 422, tail 164, tarsus 47. 
Adult female—Similar to the adult male. 
Adult in winter —Distinguished from the adult in breeding-plumage by the 
absence of the entire black head, which is represented on the fore-head by black 
feathers with white margins, the black increasing in extent on the nape, ear-coverts, 
and feathers in front of the eye. 
Immature——Pure white below, except for a few minute grey spots on the fore- 
neck ; the feathers of the back with substantial dark brown spots and fringed with 
sandy-buff ; lesser wing-coverts blackish, fringed with white like the bastard-wing 
and primary-coverts ; median and greater coverts ash-grey fringed with white ; 
primary-quills hoary-grey fringed with white on the inner webs, the inner primaries 
tipped and margined with white on both webs; secondaries white with dark slate 
colour on the outer webs; scapulars white at base becoming sandy-buff towards 
the tips, with two longitudinal brown streaks on each side of the shaft which converge 
at the tip. These brown marks do not always follow the same course : sometimes 
they form twin spots, whereas in others they are irregular bars ; rump and upper 
tail-coverts faintly marked with grey, but some of the feathers have darker pear- 
shaped spots ; middle tail-feathers are white, with dark grey running longitudinally 
towards the tips and margined with white, the outer feathers dark brown, tipped 
with white and fringed with the same colour near the base ; feathers of the hind- 
neck white, with an apical spot of black and fringed with sandy-buff ; feathers of the 
head white at the base, centred with black and fringed with buff, the black being 
more pronounced on the nape and sides of crown ; a black spot in front of each eye. 
