86 THE STORY OF THE BIRDS 



typical Gulls is strong and the upper mandible 

 is curved ; in the Terns it is nearly straight and 

 pointed, in the Skuas it terminates in a distinct 

 hook, and furnished with a naked cere at the 

 base, whilst in the Skimmers it is much com- 

 pressed, and the lower mandible is a great deal 

 longer than the upper one (conf. p. 43). In 

 the two first-named groups the metatarsus is 

 moderately long, but in the two latter groups 

 it is proportionately shorter. The claws are 

 weak in all groups except the Skuas, in which 

 they are curved and sharp. The wings are long 

 and pointed, especially so in the Terns and 

 Skimmers birds that may be said almost to 

 live in the air. The tail varies considerably in 

 shape ; nearly square in most of the Gulls, more 

 or less acutely forked in many of the Terns, and 

 the two central feathers projecting beyond the 

 others (acute in some species, curiously twisted 

 in another) in the Skuas. These birds are all 

 aquatic in their habits, and most of them are 

 marine. Many frequent inland localities to 

 breed, others are partial to lakes and rivers. 

 They are more or less gregarious at all seasons, 

 and not a few are migratory. They fly well and 

 buoyantly, having great command over them- 

 selves in the air, swim equally well, but do not 



