The Barre daily times. (Barre, Vt.) 1897-1959, 1915-04-12
WHY DO BIRDS MIGRATE?
No Such General Migration of Birds in
South America as in Our Continent.

Although North American birds living
in the colder part of the continent return
South for the winter, there is no similar
movement of birds from the colder to the
warmer parts of South America. accord.
ing to a bulletin (No. 1861 of the U. s
department of agriculture. If the birds
in North America did not 90 South dur
ing the winter, they would perish. Also
ii the birds remained in the South later
than spring, there would be overcrowd-
ing. so they are drawn northward again
by the enormous summer supply of bird
food. In South America, on the contrary.
there are almost no migratory land birds.
because the south temperate ATTITUDES,
on account of their small area, offer no
such inducements to the feathered inhab-
ihants of the limitless forests along the
Amazon.
The new pamphlet, which is entitled,
"Bird Migration" gives much iniorma-
ton regarding the habits of the migra-
tory birds of North America. The fact
that the routes of migration are long
and complex does not mean that these
routes were so in the beginning, says the
bulletin. In the early ages, fight was
probably short, easily accomplished and
comparatively free from danger. Each
lengthening of the course was adopted
permanently only after experience
through many generations had proved its
advantages.
There are some who argue that love
of birthplace is the impulse which causes
spring migration, and these call attention
to the seeming impotence of the earliest
arrivals. Ducks and geese push north
ward With the beginnings of open water
so early, so far, and so fast that many
are caught by late storms and wander
disconsolately over frozen ponds and riy-
ers. preferring to risk starvation rather
than to retreat. The purple martins oft
en- arrive at their nesting boxes so pre-
maturely that the coy home becomes a
tomb il a sleet storm sweeps their winged
food from the air. The bluebird's CHEEKY
MARBLE we welcome as a harblnger of
spring, often only TO find later a lifeless
body in some she'd or outbuilding where
the bird sought shelter rather than re.
turn TO the sunny land so recently left.
As matter of fact. however, only a |
small percentage of birds exhibit these I
pre-seas onal migration propensities. The !
great ma jority remain in the security of
their winter homes until spring is so far
advanced that the journey can be made /
easily and with comparatively slight dan
ger; and they reach the nesting spot
when a food supply is assured and all
the conditions OF weather and vegetation
are favorable for beginning Immediately
the rearing of family.
Breeding Instinct Governs Return.
II may be safely stated that the wealth.
er in the winter home has nothing TO do
with starting birds on the spring migra
tion, except in the case of few, like
some Of the ducks and geese, which press
northward as fast as open water appears.
There is no appreciable change in tenn
perature 10 warn the hundred or more
species of our birds which visit South I
America in winter that IL is time TO mi
CRATE. II must he force from within, a
physiological change warning them Of the
approach Of the breeding season. that i'm.
pels them TO spread their wings for the
long fight. n
The habit Of migration has been
evolved through countless generations.
and during this time the physical struc-
ture and habits OF birds have been under
going a process Of evolution in adapta-
ton 20 the climate Of the summer home.
In spring and early summer climatic con
ditions are decidedly variable. and yet
there must be- some period that has on
the average the best weather for the
birds arrival. in the course Of ages
there have been developed habits Of mi
grafton. under the influence Of which the
bird 20 performs lie migratory move
meuts that on the average Il arrives at
the nesting site ~ the proper time.
Local Weather Conditions Minor Factors
Local weather conditions on the day :
81 arrival a. any stated locality are mi =
nor factors IN determining tire appear :
rBce Of = given speeches az that place
and time. The major factors in the ]
problem are the WEATHER conditions far
10 the southwark. vliere the niglt's Sight I
lleran. and the RELATION which that place .
md time bcar e. tire average position 81 .