THE MIGRATION OF NORTH AMERICAN BIRDS Pay 
males has been explained on the theory of territorial possession, under 
which the male selects the area where it elects to breed, each individual 
attempting to protect a definite territory from trespass by other males 
of his own kind, at the same time singing or otherwise announcing his 
presence and inviting the later arriving ‘females to examine the terri- 
tory that he has selected for nesting. The long-billed marsh wren 
(Telmatodytes palustris) is a noteworthy example, and the males of 
this species may enthusiastically build several dummy nests before 
the females arrive. 
In a few species, the males and females apparently arrive at the 
breeding grounds together and proceed at once to nest building. In 
fact among the shore birds, ducks, and geese, courtship and mating 
may take place, in whole or in part, while the birds are in the South 
or on their way north, so that when they arrive at the northern nest- 
ing grounds they are "paired and ready to proceed at once with the 
raising of their families. Mallards and black ducks may be observed 
in pairs as early as January, the female leading and the male following 
when they take flight. Naturally these mated pairs migrate north 
in company, and it was largely to protect such species that duck 
shooting in spring was abolished by Federal law several years ago. 
Many shore birds nest well within the Arctic Circle, and it is the 
opinion of ornithologists that most of these birds share, at least in 
part, the habits of the phalaropes, a family in which the male assumes 
the entire care of the eggs and young. If this be true, it explains why 
in southern latitudes so many of the earliest fall arrivals are females 
that may have deserted the breeding grounds after the eggs were laid. 
Migratory flights are frequently accomplished in close flock forma- 
tion, as with the shore birds, blackbirds, and waxwings, and espe- 
cially some of the sparrows—the snow buntings (Plectrophenax 
niwalis), longspurs, juncos, and tree sparrows (Spizella arborea). 
Other species, however, though they travel in flocks, maintain a very 
loose formation; examples are the turkey vultures (Cathartes aura), 
the hawks, swifts, blue jays, swallows, warblers, and bluebirds. 
Still others, the grebes, great horned owls (Bubo virginianus), winter 
wrens (Nannus hiemalis), shrikes, and belted kingfishers (Megaceryle 
alcyon), for example, ordinarily travel alone, and when several are 
found in close proximity it is an indication that they have been drawn 
together by unusual conditions, such as abundant food. 
WHERE BIRDS MIGRATE 
DISTANCES OF MIGRATION VARY 
Definite evidence shows that both the length and the duration of 
the migratory journey vary greatly. The bobwhite and the western 
quails, the cardinal (Richmondena cardinalis), the Carolina wren 
(Thryothorus ludovicianus), and probably some of the titmice and 
woodpeckers, which are apparently nonmigratory, may round out 
their full period of existence without at any time going more than 
10 miles from the nest where they were hatched. 
SHORT AND UNDETERMINED MIGRATIONS 
Song sparrows, meadow larks (Sturnella), blue jays (Cyanocitta 
cristata), and some other species make such short migrations that 
the movement is difficult to detect, as individuals may be found in 
