380 



GENERAL ZOOLOGY 



both fresh and salt water. Owing to the forked tail and 

 graceful flight, the terns are often called sea swallows. 



Petrels and Allies. The petrels and their allies are strong- 

 winged pelagic birds, many of which externally resemble 

 the gulls and terns. They may be distinguished from other 

 water birds by the nostrils, which are inclosed in tubes lying 



Fig. 198. Photograph of a tern on its nest 



on the dorsal or lateral surface of the upper mandible ; hence 

 their scientific name, Tubina'res (Lat. tubus, "tube" ; naris, 

 "nostril"). The beak is usually strongly and sharply hooked. 

 The food consists of fishes and other small animals which 

 live near the surface of the ocean. The birds often follow 

 ships, like the gulls, to pick up refuse. They occupy various 

 nesting sites along shores. The wandering albatross (Dio- 

 mede'a ex'ulans, Fig. 197) of southern oceans is the best- 

 known species. It is the largest of sea birds, measuring 

 over twelve feet between the tips of the wings. One of the 



