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THE MIGRATION OF NORTH AMERICAN BIRDS 
VERTICAL MIGRATION 
In the effort to find winter quarters furnishing satisfactory living 
conditions, many North American birds fly hundreds of miles across 
land and sea. Others, however, are able to attain their objective 
merely by moving down the sides of a mountain. In such cases a 
few hundred feet of altitude corresponds to hundreds of miles of 
latitude. Movements of this kind, known as “‘vertical migrations”’, 
are found wherever there are large mountain ranges. In the Rocky 
Mountain region they are particularly notable, as chickadees, rosy 
finches (Leucosticte), juncos, pine grosbeaks (Pinicola), and some 
other species that nest in the Alpine Zone move down to the lower 
levels to spend the winter. It has been noted that such species as 
Williamson’s sapsucker (Sphyrapicus thyroideus), and the western 
wood pewee (Myiochanes richardsoni), which nest in the higher moun- 
tains, move down to the lower regions in August following the breeding 
season. At this time there is a distinct tendency also among the 
young of mountain-breeding birds to work down to the lower levels 
as soon as the nesting season is over. The sudden increases among 
birds in the edges of the foothills are particularly noticeable when 
cold spells with snow or frost occur at the higher altitudes. 
Some species that normally breed in the Hudsonian or Arctic 
Zones find suitable breeding areas on the higher levels of the moun- 
tains, as for example the pipit, or titlark (Anthus spinoletta rubescens), 
which breeds on the tundras of Alaska and northern Canada and 
also south as far as Colorado on the summits of many peaks in the 
Rocky Mountains. On the other hand a few species, as the Clark’s 
crow, or nutcracker (Nucifraga columbiana), nest at relatively low 
altitudes in the mountains and as the summer advances move higher 
up, thus performing a vertical migration that in a sense is comparable 
with the post-breeding movements of herons on the Atlantic coast. 
These illustrations show that the length of a migration route may 
depend upon factors other than latitude. 
VAGRANT MIGRATION 
The most striking feature of the migrations of some of the herons 
is a northward movement after the nesting season. The young of 
some species commonly wander late in summer and in fall, sometimes 
traveling several hundred miles north of the district in which they 
were hatched. The little blue heron (Florida caerulea caerulea) 
breeds commonly north to South Carolina, and by the last of July 
the young birds begin to appear along the Potomac, Patuxent, and 
Susquehanna Rivers, tributary to Chesapeake Bay. Although 
almost all are immature individuals, as shown by their white plumage, 
an occasional adult may be noted. With them come snowy herons 
(Egretta thula thula) and egrets (Casmerodius albus egretta), and on 
occasion all three species will travel in the East as far north as New 
England, and in the Mississippi Valley to southeastern Kansas and 
Illinois. In September most of them disappear, probably returning 
south by the same route. 
The black-crowned night heron (Nycticorax nycticorax hoactli) has 
similar wandering habits, and young birds banded in a large colony 
at Barnstable, Mass., have been recaptured the same season north to 
Maine and Quebec and west to New York. This habit seems to be 
