xvi BIRDS OF AMERICA 



Herons preface their regular journey south with a little pleasure trip to the unexplored 

 north. In fall most of the migrant land birds breeding in New England move south- 

 west in a line approximately parallel with the Allegheny Mountains, but we can not 

 argue from this fact that the route is selected so that mountains will serve as a guide, 

 because at this very time thousands of birds reared in Indiana, Illinois, and to the north- 

 westward are crossing these mountains at right angles to visit South Carolina and Georgia. 

 This is shown specifically in the case of the Palm Warblers. They winter in the Gulf States 

 from Louisiana eastward and throughout the greater Antilles to Porto Rico; they nest in 

 Canada from the Mackenzie Valley to Newfoundland. To migrate according to the " lay 

 of the land," the Louisiana Palm Warblers should follow up the broad open highway of 

 the Mississippi River to its source and go thence to their breeding grounds, while the Warblers 

 of the Antilles should use the Allegheny Mountains as a guide. As a matter of fact, the 

 Louisiana birds nest in Labrador and those from the Antilles cut diagonally across the United 

 States to summer in central Canada. These two routes of Palm Warblers cross each other 

 in Georgia at approximately right angles. It is possible to trace the routes of the Palm 

 Warblers because those nesting to the east of Hudson Bay differ enough in color from those 

 nesting farther west to be readily distinguished even in their winter dress. It must always 

 be remembered, however, that from a common ancestry these two groups of Palm Warblers 

 came to differ in appearance because they gradually evolved differences in breeding grounds 

 and in migration routes and not that they chose different routes because they were sub- 

 specifically different. 



The truth seems to be that birds pay little attention to natural physical highways except 

 when large bodies of water force them to deviate from the desired course. Food is the 

 principal factor in determining migration routes, and in general the course between summer 

 and winter homes is as straight as the birds can find and still have an abundance of food 

 at each stopping place. 



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

 for their young until old enough to look out for themselves, 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 breeding 

 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. 



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 waves 

 numerous victims, as evidenced by many subsequently drifting ashore. If such mortality 

 could occur on a lake less than loo 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 the mouth of the Mississippi River. Large numbers of 

 migrating birds, mostly Warblers, had accomplished nine-tenths of their long flight and 

 were nearing land, when caught by a " norther," with which most of them were unable 

 to contend, and falling into the Gulf they were drowned by hundreds. 



During migration birds are peculiarly liable to destruction by striking high objects. 

 The Washington Monument, at the National Capital, has witnessed the death of many 

 little migrants; on a single morning in the spring of 1902 nearly 150 lifeless bodies were 

 strewn around its base. 



