Evening star., 1915-04-12
DANGER ATTENDS
BIRDS MIGRATION
Most Travel at Night and
Many Are Killed by High
Structures.
BREEDING TIME CALLS
WARBLERS TO NORTH
Food Supply Regulates Periods of
Coming and Going, Says Agri-
cultural Bulletin.

cultural Bulletin.
The customs of migratory birds in
North America and the dangers which
bcset these birds while going north
each year are told in a bulletin just
issued by the Department of Agricul
ture. entitled Bird Migration
The bulletin comments on the fact
that although large numbers of birds
in North America go south for the win
ter months, there is no similar move
rent of land birds in South America,
due to the fact that the south temper
ate latitudes. on account of their small
area, offer no such Inducements in the
matter of feeding as are offered in the
temperate areas in North America. If
the birds in North America did not 90
south in the winter they would perish
also If the birds remained i'll the south
during the summer there would be
overcrowding. SO they are drawn north
again in the summer by the enormous
summer supply OF bird food.
During migration birds are peculiar
IS liable TO destruction by striking
igh Objects. says the bulletin. The
Washington Monument. at the National
Capital has witnessed the death of
many little migrants: on a single morn
ing in the spring of 19o2 nearly LOO
life1ess bodies were streWn around IT'S
base As long as the torch in the
Statue of Liberty in New York harbor
was kept lighted the sacrifice of bird
life il caused was enormous. even
reaching a maximum of 700 birds in
month.
Routes of Migration.
..T-t. go. .I.r "a. ,n,,taS of ,,iora
tion are long and complex does not
mean that these routes were so in the
beginning In the early ages flight
was probably short, easily accomplish
ed and comparatively free from danger.
Each lengthening of the course was
adopted permanently only after expert
ence 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 impatience of
the earliest arrivals. Ducks and geese
push northward with the beginning of
open water so early, so far and so fast
that many are caught by late storms
and wander disconsolately over frozen
ponds and rivers, preferring to risk
starvation rather than to retreat. The
purple martins often arrive at their
nesting boxes so prematurely that the
al
storm sweeps their winged food from
the air. The bluebird's CHEEKY warble
We welcome as a harbinger of spring,
often only to find later a llfeless BODY
in some shed outbuilding, where the
bird sought shelter rather than return
TO the sunny land SO recently left.
Breeding Instinct Governs Return.
"As a matter Of fact, however. only a
small percentage of birds exhibit these
preseasonaI migration propensities. The
great majority remain in the security
of their winter homes until spring isl
so far advanced that the journey can
be made easily and with comparatively
slight danger. and they reach the nest
ing spot when food supply is assured
and all the conditions of weather and
vegetation are favorable for beginning
Immediately the rearing of family.
TT may be safely stated that the
weather in the winter home has moth
ing TO do with starting birds on the
spring migration. except in the case or
a few, like some of the ducks and geese,
which press northward as fast as open
water appears. There is no appreciable
change in temperature to warn the
hundred or more species of our BIRDS
which visit South America in winter
that il is time to migrate. II must be
a force from within, "A physiological
change warning them of the approach
OF the breeding season, that impels
them to spread their wings for the long
f. ght
.sThe habit of migration has been
evolved through countless generations.
and during this time the physical
structure and ha bits of birds have been
undergoing process of evolution IN
adaptation to the climate OF the sum
Iner home. In spring and early sum
mer climatic conditions are decidedly
IA IA. a nd
period that has on the average the best
weather for the birds arrival.
Major Factors in Migration.
.1n the course OF ages there have
been developed habits Of migration,
under the influence of which the bird
SO performs its migratory movements
that on the average II arrives at the
nesting site at the proper time.
Local weather conditions on the day
OF arrival at any stated locality are
minor factors in determining the ap-
pearance OF given species at that
place and time. The major factors in
the problem are the weather condi-
tions far 10 the southwark, where the
nights fight began, and the relation
which that place and time bear to the
average position of the bird under nor
Ulal weather conditions. Many, if not
most. instances OF arrivals of birds
under adverse weather conditions are
probabl explainable by the supposi-
tion that the flight was begun under
favorable auspices and that later the
weather changed Migration in spring
usually occurs with a rising tempera-
fure, and in autumn with a falling
temperature. In each case the chang
ing temperature seems to be a more
potent factor than the absolute degree
of cold.
THE direction and force Of the winds.
except as they are occasionally inti-
nately connected with sudden and ex-
treme variations in temperature, seem
10 haze only q ali cht intiuence on mi.