24 Birds of Colorado 
CommonTern. Sterna hirundo. 
A.O.U. Checklist no 70—Colorado Record—Cooke 09, p. 314. 
Description.—Resembling the Arctic Tern in the arrangement of 
the coloration of the tail-feathers, but with a longer tarsus averaging 
longer than the middle toe without claw, and with the dark bands 
on the inner web of the outer primary much more distinct and wide, 
averaging ‘25 to ‘30 instead of 12 to -15; bill red, usually with dusky 
tip, feet vermilion. Dimensions about the same. 
Distribution.—A common species found over the greater part of the 
world north and south ; breeding chiefly in arctic cireumpolar regions. 
One example, taken May 14th, 1908, at New Windsor by Geo. 
Osterhout, was sent to Cooke for identification. This is the only 
Colorado record. 
Arctic Tern. Sterna paradisea. 
A.0.U. Checklist no 71—Colorado Records—H. G. Smith 96, p. 48; 
Cooke 97, p. 51. 
Description.—Closely resembling Forster’s Tern but smaller, though 
with a longer wing and with the outer web of the outer tail-feather 
grey or dark and the inner web white, instead of the reverse ; under- 
parts slightly paler than the mantle but hardly white ; bill red without 
dusky tip, feet vermilion. Length 14—17, varying with length of 
tail; wing 10-0; tail 2°5, to longest feather 6-5 to 8°5; culmen 1-20; 
tarsus ‘65. 
Distribution.—Breeding in the circumpolar regions of the Old and 
New Worlds; in America from Alaska and Labrador south to 
Massachusetts. In winter ranging widely throughout the world’s 
coasts to South Africa and South America, as well as in many parts 
of the United States. 
The Arctic Tern is a rare straggler in Colorado. An example killed 
at Marston’s Lake near Denver in the spring of 1887 was identified 
as this species by Ridgway (H. G. Smith); while a second, an adult 
male, was taken by W. G. Smith at Loveland, July 9th, 1889 (Cooke). 
Genus HYDROCHELIDON. 
Closely allied to Sterna but with a very short tail, less than half 
the wing and very slightly forked ; with feeble legs, the webs Much 
indented so that the toes appear to be only half webbed ; lower-parts 
of the body always black, or very dark grey in the breeding season. 
Four species, only one in North America. 
