BIRD MIGRATION. . 31 



The truth seems to be thai birds pay little attention to natural phys- 

 ical highways except when large bodies of water force them to deviate 

 from the desired course. Food is the principal factor in detennining 

 migration routes, and in general the course between summer and win- 

 ter homes is as straight as the birds can find and still have an abun- 

 dance of food at each stopping place. 



MIGRATION AND MOLTING. 



It is interesting to note the relation between migration and molting. 

 Most birds care for their young until old enough to look out for them- 

 selves, then molt, and when the new feathers are grown start on their 

 southward journey in their new suits of clothes. But the birds that 

 nest beyond the Arctic Circle have too short a summer to permit such 

 leisurely movements. They begin their migration as soon as possible 

 after the young are out of the nest and molt en route. Indeed, these 

 Arctic breeders are so pressed for time that many of them do their 

 courting during the period of spring migration and arrive at the breed- 

 ing grounds already paired and ready for nest building, while many 

 a robin and bluebird in the middle Mississippi Valley has been in the 

 neighborhood of the nesting site a full month before it carries the first 

 straw of construction. 



Various peculiar changes of plumage are presented by certain species 

 during migration. The young golden plover are white breasted as 

 they fly over the Atlantic Ocean in fall. This has given place to jet 

 black as they cross the Gulf of Mexico in spring. The bobolink (PL I) 

 goes south in fall obscurely marked with buff and olive; he returns 

 next spring the well-known black and white denizen of the marshes. 

 The scarlet tanager (PL IV) performs his fall migration in a suit of 

 uniform greenish yellow known to only a small number of his human 

 friends, who welcome him as an old acquaintance when he returns the 

 next spring in his striking black and scarlet. 



CASUALTIES DURING MIGRATION. 



Migration is a season full of peril for myriads of winged travelers, 

 especially for those that cross large bodies of water. Some of the water 

 birds making long voyages can rest on the waves if overtaken by 

 storms, but for the luckless warbler or sparrow whose feathers become 

 water-soaked an ocean grave is inevitable. Nor are such accidents 

 infrequent. A few years ago on Lake Michigan a storm during spring 

 migration forced to the weaves numerous victims, as evidenced by 

 many subsequently drifting ashore. If such mortality could occur 

 on a lake less than 100 miles wide, how much more likely even a 

 greater disaster attending a flight across the Gulf of Mexico. Such a 

 catastrophe was once witnessed from the deck of a vessel 30 miles off 



