770 
SYSTEMATIC SYNOPSIS. — LONGIPENNES-^ GA VI^. 
315. HYDROCHELI'DON. (Gr. vdcop, hudor, water; x^^*^*^"? chelidon, a swallow.) Black 
Terns. Bill a little shorter than head, longer than middle toe and claw; very delicate, slender, 
acute ; culmen and commissure decidedly declinato-convex, the amount of curvature increasing 
toward the tip; outline of rami and gonys both concave, the former most so; emineutia sym- 
physis prominent and very acute. Wings exceedingly long, pointed, of same color as back, 
without distinct markings on either web. Primaries broad and not very tapering, not acute ; 
tertials very short, rounded, not slender nor flowing, reaching in the folded wing only half-way 
to tip of longest primary. Tail rather short, contained 2^ times in the wing, only moderately 
emarginate (much as in Gelochelidon) , the lateral feathers but little exceeding the next, not 
tapering and acuminate ; all the feathers broad and rounded. Feet slender and short ; tarsi 
much abbreviated, rather less than the middle toe alone. Toes moderately long ; the webs 
rather narrow and very deeply incised (fig. 51). Size small, general form delicate; colors 
mostly black, the wings and tail plumbeous. 
Analysis of Species. 
"Wings and tail above like back lariformis 806 
Wings whitening along border of forearm ; upper tail-coverts white leucoptera 807 
806. H. larifor'mis. (Lat. lariformis, guil-shaped.) Black Tern. Short-tailed Tern. 
Adult, in summer : Head and neck all around and under parts to the vent, jet black ; under 
tail-coverts pure white. On back of neck, and between shoulders, the black lightening into 
leaden-gray, which extends over all the upper parts to the very tips of the tail-feathers. Ter- 
tials like back ; secondaries darker, tending to the color of the primaries, which are grayish- 
black, silvered, with paler margins of inner webs, their shafts white except at tips. Lining of 
wings ashy-white, reaching a little over border on to lesser coverts. Bill and claws black, 
angle of mouth lake red ; feet reddish-brown ; eyes brown. In winter : Very different ; fore- 
head, sides of head, neck all round, and entire under parts, M^hite; under wing-coverts only 
ashy-gray. Upper parts generally as in summer, but paler, many feathers with whitish edges, 
A grayish -black bar along lesser coverts. On the crown, white varied with grayish or ashy, 
darker on nape, with bar through eye. While changing, head and under parts patched with 
white and black. Young : Bill brownish-black, base below flesh-color ; mouth yellow ; feet 
light brown. Forehead grayish-white, deepening on crown and nape to grayish-brown which 
reaches down to the back, obscuring the plumbeous; interscapulars quite brown; on other 
upper parts the brown edges the feathers. Lesser wing-coverts grayish -black. A black cres- 
cent before eye. Under parts pure white, the sides of the breast ashy-brown, the sides of the 
body and lining of the wings ashy. Quills as in the adults, but the shafts of the primaries 
brown. Length about 9.25 ; extent 25.00 ; wing 8.25 ; tail 3.75, forked 1.00 ; bill along cul- 
men 1.10; along gape 1.60; height at base 0.25 ; gonys 0.60. Young smaller, about 8.00; 
bill 1.00 ; tail shorter and less forked. N. Am. at large, interior and coastwise, abundant. 
Breeds in large colonies anywliere, in marshes and reedy sloughs, in June. Eggs on debris of 
dead reeds, often wet and floating, without any nest; 2-3, 1.35 X 0.95 average, pointed, yet 
with considerable bulge of the sides ; ground color brownish-olive, rather pale and clear, 
thickly marked with spots and splashes of every size from dots to masses, but mostly large 
and bold, of light brown and blackish -brown, and the usual neutral-tint shell-markings; ten- 
dency to aggregate at or around the larger end. 
807. H. leuco'ptera. (Gr. XevKos, JeuJcos, white ; nrepov, ])teron, wing.) White-winged Black 
Tern. Adult in summer: Bill black, tinged with red; feet red; claws black. Head and 
neck all around and under parts pure black, shading on back and scapulars into dark slaty 
plumbeous ; wings dark silvery-plumbeous, fading to white along border of forearm, the quills 
silvered-dusky with white shafts and dull white area on inner webs of the primaries ; lining of 
wings sooty blackish, varied with white along the border. Tail and its coverts, above and 
