14 Birds of Colorado 



Habits. — The Parasitic Jaeger, or as it is often called, 

 Richardson's Skua, is remarkable for presenting, irre- 

 spective of age or sex, two very distinct phases of plumage 

 — a light and a dark. Birds of both phases pair wdth one 

 another indiscriminately, where they meet, and the 

 young are sometimes intermediate. This bird is parasitic 

 in its mode of life ; it seldom catches fishes for itself, 

 but is constantly chasing smaller Gulls and Terns, and 

 compelling them to disgorge their prey. So active 

 is the Skua that it usually manages to catch the fish 

 as it drops from the bill of the Gull, before it reaches 

 the surface of the water. 



It is a purely marme form, but seldom seen inland, 

 though it nests in the far north, on moorlands and 

 swamps, using a slight depression in the ground scantUy 

 lined with grasses. The eggs, usually two in number, 

 are olive-brov.Ti, marked heavily with chocolate. 



Family LARID^. 

 Bill without cere, middle tail-feathers never elongated. 



Genus RISSA. 



In most respects resembling Lams, but the hind toe rudimentary 

 or absent, very rarely with a claw ; tail square ; tarsus short, less than 

 the middle toe without claw ; toes fully webbed. 



Two species only of circumpolar range. 



Kittiwake. Rissa tridactyla. 



A.O.U. Checklist no 40 — Colorado Records — Ridgway 79, p. 232 ; 

 Cooke 97, p. 50 ; Henderson 09, p. 225. 



Description. — Adult — Head, neck, tail and under-parts pure white, 

 back and wings pearl-grey ; outer web of the first primarj' and the 

 last three inches of the tip of both first and second primaries black ; 

 the third to fifth black subterminally with an increasing white tip ; 

 hind toe very small — a minute knob without claw ; bill yellowish, feet 

 black. Length 17; wing 12 ; tail 4-5 ; cuknen 1-40; tarsus 1-3. 



