The Homesick Another attempt at an explanation is based 
upon the fact that in the spring migration birds 
are returning home to the place where they were born. May it 
not be then that they are overtaken by a strong desire to revisit 
their birthplace as the changing seasons duplicate the climatic con¬ 
ditions which existed when they formerly dwelt there ? May they 
not be driven by a kind of home-sickness to fly north to the scenes 
of their early life? This is a favorite theory with those who are 
accustomed to endow birds with semi-human attributes upon a 
sentimental rather than upon any anatomical basis. The theory 
suffers somewhat when it is remembered that most birds forsake 
the home they make such strenuous endeavor to revisit, the mo¬ 
ment their nesting duties will allow which would hardly be ex¬ 
pected if they possessed such an overmastering afifection for a par¬ 
ticular locality as the homesick theory implies. 
The Desire to Again, to say that birds have a “desire to dis- 
Disperse Theory perse” in the spring of the year, as Dixon sug¬ 
gests, simply begs the question as to what actually causes the dis¬ 
persal. 
The Nestling Food Alfred Russel Wallace, whose biological 
Theory opinions are certainly entitled to respect, points 
out that the food upon which many nestlings are fed consists of 
soft bodied insects and other materials that become relatively rare 
in the tropics during the dry season. It is so customary to think 
of the tropics as a region continually teeming with all sorts of life 
that testimony to the contrary by one who has spent many years 
there, comes at first as a surprise. It is, however, undoubtedly 
true that food of a quality suitable for nestlings would not be 
present In sufficient quantity if all the migratory species remained 
there to nest. Consequently In this sense, the spring migration 
may primarily depend upon food supply. Omnivorous birds whose 
food supply is to a lesser extent affected by the changing seasons, 
migrate less than those who feed upon a restricted diet. 
The Safe Nesting Another theory has been presented by Pro- 
Site Theory fessor Brooks of Johns Hopkins University, 
namely, that birds go north in the spring In order to find safer 
nesting sites than are available in the over populated tropics. It 
is natural that all animals during the'breeding season should seek 
retirement and a place of security in which to rear their young and 
this seems to be the universal, rule among all those animals which 
In any active way care for their offspring. But is it a fact 
that there are more safe nesting sites in the north than in the 
tropics? Surely in the luxuriant tropical vegetation there are 
more nooks for concealment, acre for acre, than in our open 
