50 



Distinctions. Bill with continuous surface and sharp projecting angle on lower man- 

 dible is sufficient to diagnose the family in all plumages. Colours are quite characteristic, 

 though some species during juvenility are evenly (over all) dark, approaching the dark 

 phases of the Jaegers. 



Field Marks. Coloration and flight characteristics are the best field marks. 



Nesting. Gulls generally build on ground, on rocky ledges or flat shores, in either 

 sandy, grassy, or marshy places; rarely, in trees. 



Distribution. Gulls and Terns are distributed over all the world, usually near large 

 bodies of water, but sometimes occurring far inland, for instance in our prairie regions. 



Subfamily Larince. Gulls. 



General Description. With the family description in mind the Gulls can only be 

 confused with the Terns, which follow (see p. 54). 



Distinctions. Can be distinguished from the Jaegers by the bill and coloration char- 

 acters. (See family description on previous page); from the Terns, by their more robust 

 build and mode of flight. Bills especially are heavier and stronger (compare Figures 4 

 and 5, p. 18). As a rule, tails are square without evident fork. Though as much masters 

 of flight as the Tern they have less agility and perform fewer aerial gymnastics. Young 

 Gulls are often quite brownish and dark in coloration, in marked contrast to the adult. 

 Young Terns are usually light in coloration. 



Field Marks. Large birds of heavier flight than the Terns. Square tails and surface 

 feeding habits; not diving from the wing and the horizontal carriage of the bill when flying 

 (see Tern, p. 54) are the best guides by which to separate the Gulls from the closely allied 

 Terns. 



Nesting. On rocky shores or cliffs near the water in various localities, depending 

 upon the species and their distribution. 



Distribution. Almost cosmopolitan in range and few countries without representatives 

 of the subfamily. In Canada about twenty-five species are known to occur, but some are 

 only casual within the bounds of settled areas and are not discussed here. 



Though Gulls are essentially sea birds they are at times found at 

 considerable distances from large bodies of water and flocks often follow 

 the prairie ploughman to search for insects in the newly turned furrows. 

 They feed from the surface of the water, never diving, or glean from the 

 shores, beaches, or fields. 



Economic Status. Gulls eat anything in the way of animal matter, 

 fish, crustaceans, molluscs, insects, offal, and even when opportunity offers 

 young birds and mice. 



The amount of fish they consume is relatively unimportant, as it is 

 usually only very abundant small species occurring in great schools that 

 attract their attention; they are not patient fishers like the Herons. They 

 search low tidal shores for crabs and shell fish, showing considerable ingen- 

 uity in breaking the hard shells and extracting the contents. The food 

 supply from these sources is economically insignificant. The Gulls annually 

 dispose of vast quantities of garbage and offal thrown into harbours and 

 waterways; they frequent agricultural land for insect food and some 

 species have been known to have been instrumental in stopping mouse 

 and other small mammal plagues. The Gulls must be considered, therefore, 

 to be beneficial and consequently should be protected, although they do 

 sometimes destroy eggs and young birds. 



40. Kittiwake Tickler. FR. LA MOUETTE A TROIS DOIGTS. Rissa tridactyla. 

 L, 16. A small or medium sized GuH of the same general coloration as the Herring 

 Gull (see p. 52). 



Distinctions. Rudimentary condition or almost total absence of a hind toe is always 

 diagnostic. 



