26 THE MIGRATION OF BIRDS 



the Pacific golden plover has an east and west 

 extension of some 1700 miles, but in winter it 

 ranges over an area with an east and west ex- 

 tension of about 10,000 miles. The scarlet tanager, 

 however, has a breeding range extending for some 

 1900 miles across eastern Canada and a winter 

 home in north-western South America of only 

 some 700 miles in extent. 



The winter quarters, or the outermost limits of 

 the individual but not necessarily the specific range, 

 having been reached, the bird spends its time in 

 seeking food, remaining in one place if food is plenti- 

 ful, or wandering, according to necessity or the habit 

 of the species. The assertion that some birds have 

 a second breeding season in their southern home 

 is either unsupported by any direct evidence or 

 is the result of a mistake in identification ; the 

 bird which has been found breeding has in 

 several instances been shown to be a southern 

 form or a related species of the one it was thought 

 to be. 



As the northern spring approaches, the strongest 

 of all animal instincts, on which reproduction and 

 the very existence of the species depend, overcomes 

 all other desires, and the bird grows restless. The 

 hereditary instinct, the origin of which we have 

 endeavoured to show, urges the bird to seek the 

 breeding area which has by degrees become so far 



