STERNA. 39 



GENUS STERNA LINNJEUS. (Page 24, pi. X., figs. 1-3 ; pi. XI., figs. 1, 2.) 



Species. 

 a 1 . Wing more than 9.00. 



b l . Wing more than 12.00. 



c 1 . Tail much less than half as long as wing, forked for less than one-fifth 

 its total length ; feathers of occiput short, blended ; depth of bill at 

 base equal to nearly one-third the exposed culmen ; inner webs of 

 quills entirely gray, or slaty. (Subgenus Thalasseus KAUP.) 

 Adult in spring : Above pale pearl-gray, becoming white on tail, 

 and more silvery gray on quills ; whole top of head, and nape, 

 uniform glossy black ; rest of plumage pure white ; bill coral- 

 red (drying orange-red) with dusky tinge near tip ; feet black. 

 Adult immediately after pairing season : Similar to spring plu- 

 mage, but black on top of head mixed with white. Winter 

 adult: Similar to summer adult, but black of crown, etc., 

 streaked, instead of speckled or flecked, with grayish white. 

 Young : Above pale grayish, marked with a few roundish and 

 more or less hastate spots of dusky, largest on tertials ; top of 

 head grayish white, the crown flecked with black, this color 

 increasing in extent posteriorly, until nearly uniform on occi- 

 put ; tail-feathers marked with a dusky subterminal spot ; rest 

 of plumage white ; bill dull orange-reddish. Downy young : 

 Above grayish white, the down of the head dusky gray beneath 

 the surface ; back and rump finely and indistinctly mottled 

 with grayish ; throat and fore-neck uniform pale grayish, rest 

 of lower parts white. Length 19.00-22.50, wing 15.00-17.40, 

 tail 5.30-6.75 (forked for about .75-1.60), culmen 2.48-3.10, 

 depth of bill through base .7S-.95, tarsus 1.60-1.90, middle toe 

 1.15-1.40. Nest (usually solitary) a depression in sand near 

 sea-shore. Eggs 2-3, 2.66 X 1-77, ovate or elliptical-ovate, pale 

 grayish buff, varying to olive-buff or dull whitish buff, more or 

 less spotted with brown and stone-gray or lavender-gray. Hob. 

 North America in general, but rare on Pacific coast ; breeding 

 in isolated and widely separated localities throughout its range. 

 (Also occurs in various portions of eastern hemisphere, includ- 

 ing Australia.) 64. S. tschegrava LEPECH. Caspian Tern. 



c 2 . Tail more than half as long as wing, forked for at least half its total 

 length; feathers of occiput lengthened, lanceolate, forming a dis- 

 tinct crest ; depth of bill at base much less than one-third the length 

 of the exposed culmen ; inner webs of quills with inner margin ab- 

 ruptly and broadly white. (Subgenus Actochelidon KAUP.) 

 d 1 . Bill deep orange, or orange-red. 



e 1 . Depth of bill at base more than one-fourth the length of the 

 exposed culmen. Adult in spring : Above pale pearl-gray, 



