A BIRD'S YEAR 



reached by a much shorter land route via Mex- 

 ico and Central America. Truly instinct is a 

 strange and exacting master! The Golden 

 Plover winters in far-away Patagonia but builds 

 its nest within the Arctic Circle, covering twice 

 each year a journey of nearly or quite ten thou- 

 sand miles. Is it not a strange and powerful 

 impulse that prompts birds to cover these enor- 

 mous distances with all the perils and vicissi- 

 tudes incident thereto.^ 



The cause of these movements is still a mys- 

 tery, although scientists have given much atten- 

 tion to the matter. The most reasonable expla- 

 nation seems to be that they had their beginnings 

 ages ago when the ice cap which covered a great 

 portion of the Northern Hemisphere receded and 

 advanced under varying conditions of tempera- 

 ture. It seems that much force is given to this 

 theory by the fact that birds of the southern 

 hemisphere where the ice movements did not 

 occur do not, as a rule, migrate, but are per- 

 manent residents in their various localities. It 

 seems clear that the migratory movement can 

 scarcely result from the food problem alone, or 

 the desire for secure nesting places, for in either 

 case the northern journey would not necessarily 

 help them. 



The relative time of the arrival of the many 

 varieties that make up the vast bird army 

 naturally depends upon one's location. The 

 slow fliers arrive in the latitude of New York 

 City a week or ten days earlier than in central 

 New England and northern New York, and 

 about two weeks earlier than in northern Maine. 



