48 HOW BIRDS MIGRATE 
How Birds Migrate—The more we learn of the marvelous semi- 
annual journeys made with such surprising regularity by many birds, 
the greater becomes our interest in the manner by which they are 
performed. It is well enough to point out on the map the routes of 
_nigration followed by Bobolink or Blackpoll, but how do the feathered 
mites traverse the thousands of miles which separate their summer and 
winter homes? : 
It is evidently essential that the bird be prepared for the journey. 
Fall migration usually follows the annual post-breeding molt, and the 
birds, in fresh plumage, proceed slowly, often lingering in favorable 
feeding-grounds, as does the Golden Plover among the crowberries of 
Labrador, or the Bobolink in the rice-fields of our south Atlantic Coast, 
until they are in physical condition to endure the strain of prolonged 
flight. 
In the spring, they have had months’ exemption from family cares, 
with no other duty than to wander where food was most abundant; 
excellent preparation for the return journey to the nesting-ground. 
We know less, however, about birds’ movements at this season than 
when, after breeding, they prepare to leave us. 
Some species begin to flock immediately after the nesting season 
and, as a preliminary to actual migration, develop regular and definitely 
directed movements in their daily returns to and departure from a 
certain roosting- place. Such roosting-places form stations on the 
migratory journey and are focal points for small bodies of birds which, 
later, take flight in one great company. Red-winged Blackbirds, 
Grackles, and the various species of Swallows inaugurate their south- 
ward migrations in this way. 
Less gregarious birds, at the conclusion of their post-breeding molt 
or even before it is completed, simply disappear without our knowing 
when they go. 
The adult birds, either alone or accompanied by birds of the year, 
migrate first. Later, the adults decrease in number and the last flights 
may be composed entirely of young birds. In the fall the sexes appear 
to travel together, but in the spring the males usually precede the 
females. 
Some birds migrate only by day, others only during the night, while 
a smaller number travel both by day and night. In his now classic 
Memoir on “Bird Migration” Brewster (’86) puts the matter clearly 
as follows: ; 
“1, Species which migrate exclusively by night habitually feed in 
or near the shelter of trees, bushes, rank herbage or grass, and when 
not migrating are birds of limited powers of flight and sedentary habits, 
restricting their daily excursions to the immediate vicinity of their 
chosen haunts. As a rule they are of timid, or at least retiring disposi- 
tion, and when alarmed or pursued seek safety in concealment rather 
than by extended flights. 
“2. Species which migrate chiefly or very freely by day, habitually 
