418 



METAZOAN PHYLA 



the Antarctic, far removed from the northern winter, they return again 

 through the same distance to spend the northern summer at their breed- 

 ing grounds in the Arctic. Like all birds they nest in only one region and 



Fig. 307. — Eggs of the largest bird, an ostrich, Struthio camclus, and the smallest bird, a 

 humming bird, Archilochus colubris Linnaeus, showing the relative size. 



have only one breeding season. As a result of their migrations, Arctic 

 terns cover annually a distance of more than 20,000 miles. Another bird 

 which takes a long journey is the golden plover, which nests in the barren 

 grounds of the northern part of British America and winters in southern 



Fig. 308. — Ahricial young birds. A, a blind, naked, weak and helpless 2U-hour old 

 woodpecker. (Photo, by Ralph S. Palmer, U. S. Nat. Mtis. Bull. 174, Arthur C. Bent.) 

 B, a scantily feathered, blind but stronger 3-day old domestic pigeon. (Photo, by Edson H. 

 Fichter.) 



Brazil and Argentina. Its journey involves a round trip of more than 

 16,000 miles. This trip is taken also by a few other shore birds. 



How birds find their way has never been satisfactorily determined. 

 This faculty seems to rest upon a very accurate sense of location which 

 enables them to fly practically in a straight line from one point to another, 

 even though darkness or fog may hide any features that would guide them. 



