REPORT OF FEW JERSEY 
STATE MUSEUM. 
:;i 
CAUSES OF BIRD M IGRATIOA. 
There are several causes for bird migration. The most import¬ 
ant are no doubt the seasonal changes of climate and failure of the 
supply of suitable food. Tbe following are the most potent causes 
of tbe spring migration : 
First. The food-supply fails. 
Second. The climatic conditions are unsuited to their needs. 
Third. The approach of the breeding season gives rise to physio¬ 
logical restlessness. 
Fourth. The birds inherit an irresistible impulse to move at this 
time of year. 
The first three causes no doubt are applicable to the fall migra¬ 
tion. 
There are two groups of bird migrations, according to tbe time 
and manner of migration—tbe day migrants and the night mi¬ 
grants. Those that belong to the first or day class include the 
doves, hawks, hummingbirds, chimney swifts, night hawks, horned 
lark, crows, jays, grackles, blackbirds, swallows, cedar birds, tit¬ 
larks, bluebirds, robins and a few others. Also most water birds. 
The night migrants are woodpeckers, cuckoos, flycatchers, tit¬ 
mice and! most of the thrushes; and among the water birds are 
bittern, woodcock, Wilson’s snipe, spotted sandpiper and rails, 
which migrate exclusively by night. The night migrants include 
mostly the timid and shelter-loving birds. 
Day migrants journey usually as scattered individuals or in com¬ 
pact flocks—that is, very little mixture of species. 
Right migrants are different. All the species of night migrants 
that fly in any particular night become more or less mingled to¬ 
gether in an immense column, not compact, but composed of indi¬ 
viduals and small bunches, flying sufficiently near to one another 
to be guided by the chirping of those just ahead. The leaders of 
the flights are probably old birds, which have had the experience 
of previous migrations, and have thoroughly learned the route 
of travel. It is a fact that migrating birds seem to follow 
the same course year after year, so it is possible to closely mark the 
lines of flight. You can, during the flight of night birds, hear a 
