The Bozeman courier. (Bozeman, Mont.) 1919-1954, 1927-03-11
MIGRATION OF
BIRDS STUDIED
Large Specimens Fly by
Day While Small Ones
Journey at Night.

guess at the meaning of the arrival Of
the first robin in the spring or the
southwark fight Of geese across the
late autumn sky, In the opinion Of DR..
Alexander Wetmore, assistant secre-
tary Of the Smithsonian institution and
president Of the American Ornith-
Ologists' union. Behind migration lie
such a multitude Of causes, reaching
back through the ages, that men have
been unable to ascertain the truth.
Constantly a student Of bird life,
Doctor WetmOre has made special
studies In the Salt Lake valley, the
Big Horn basin in Wyoming, the PAM
pas of Argentina, the coasts OF Uru-
quay, the sand dunes Of BuenOs Aires,
and many other vantage points
throughout the western hemisphere.
Doctor Wetmore has written a book
on the migratiOns Of birds, Just pub
lished, in which he sums up his per-
sOnal observations and ~correlates them
with the findings Of ornithOlogists for
the last 200 years, with the result that
a number OF misunderstanding con-
corning bird life are cleared up.
Migration ls Complex.
"The entire act Of migration ia so
utterly complex that no single factor
may be aseribed as the absolute
cause" Doctor Wetmore states, but he
takes as his hypothesis that migration
has arisen from movements induced
by seasonal and climatic changes in
certain species until 1t has become
hereditary instinct, "a part Of the life
cycle Of the individual" and now actu-
ated by physiological conditions.
"The habits Of ages have become so
well fixed that weather conditions now
have little 70 do with the migrations
Of birds except to permit them to
travel or hold them back, az the case
may be. Redstarts w~intering In the
West Indies, or wagtails spending the
cold ason In central Africa, notice
no difference In temperature or climate
conditions between November and
April, yet in the latter month they
regularly move north toward the sum-
mer home.
In such matters as the speed Of
flight Of birds, the time Of migration,
lines of migration, sepse of direction,
and mortality among migrant birds,
! Doctor WetmOre sets down many in
teresting facts. Large birds, such as
looms, cranes, ducks and hawks regu-
larly fly bS day, while the majority
Of small birds, such as warblers, fly
eatchers and sparrows fly by night.
The chief factor here is the necessity
on the part Of the smaller birds to
seek their food by day, and not fear
Of attack in day flight. Fasting for
a day Is no hardship for many Of the
larger birds.
Migrating birds commonly fly at an
altitude no higher than 5000 feet, al
though birds Of strong hight have been
known to reach an altitude of $4,000
feet. Contrary to common belief, flight
becomes increasingly difficult as the
bird rises above 5000 feet. Birds
commonly fly against or across q wind
current, and are upset If they fly with
a strong wind. AS to the speed Of
birds, Doctor WetmOre destroys
number Of illusions. The smaller
perching birds fly at from 20 to 81
miles per hour, while ducks and geese
range from 42 to SO miles. Most birds
are probably capable of doubling theil
normal speed for short distances, bu,
the greatest speed recorded was tina
Of the common swift Of Eurasia, OBJ
served from an airplane to be making
20 miles an hour In normal flight
Sense Of Direction.
The ability Of birds to maintain d
rections unfailingly and to return
year after year to the same spot iron
great distances, as many do, is as
cribed by Doctor WetmOre to a sens
Of direction which is no more expliC
able than a similar sense of direction
In some men and other mammals.
The greatest traveller among tn
birds is the Arctic tern, which make
an 11,OOO-mile journey twice 8 yea
from the Arctic to the Antarctic an
return. Among others that rams
widely are tree sparrows, juncOI
brown creepers, gOlden-crOwned KIM
lets, robins, grackles, .cOwbirds, an
various species Of ducks, which mel
in the northern parts OF the Unite
States or in Canada and winter nes
the Gulf Of Mexico.
One aid In obtaining data on biI
habits has been the banding Of bird
! which was begun scientifically BY
q. MOrtensen In Denmark In 1s0
Banding in the United States Is no
{ under the direction Of the bureau
biological survey Of the Departmel
! Of Agriculture. Adult birds q
trapped without injury and the your
birds are not molested.
Doctor Wetmore concludes tn
while In the last fifty years many .
3 certainties have been cleared away
Z regard to migration, we must look
|. the future to explain definitely q
/ baslc reasons for Il, the cause OF d
, VARYING l@n9fhz 0f the -4ourmav ma,