The Dawson news. (Dawson, Ga.) 1889-current, 1919-08-19
AT WHAT ALTITUDE
DO The BIRDS FLY?
AVIATORS HAVE SEEN THEM AT
$4,000 FEET HEIGHT. SOME
NEW OBSERVATIONS.

NEW OBSERVATIONS.
The night of Sept. 2, 1887, while
an American scientist, F. M. Chap
man, was observing the moon
through an astronomical telescope he
suddenly became aware of a number
of birds passing in front of the lens,
silhouetted against the glazing light
of the moons face. For more than
two and half hours-from 8 p. m.
to 1850 p. M, to be precise-an IN
termittent stream of migrants flow
ed southwark across his field of view,
and among these Mr.. Chapman was
able to recognize the outlined forms
of Carolina rails, grackle, snipe and
ducks. These, roughly estimated, were
travelling at elevations varying from
5000 to $4,000 feet.
New Means of knowledge.
Until the advent of airplanes, near
ly a quarter of century later, this
observation formed practically the
sum total of our knowledge of the
height at which birds travelled to and
from their summer quarters. 1t was
realized, of course, that certain spe-
cies-e. g., swallows, wagtails, pipits,
larks, rocks, usually migrated
at a comparatively low height; but
of many birds, and especially of the
larger species, we knew next to moth
ing.
True, we occasionally obtained a
distant view of skein of geese NOV
ing in orderly formation across the
gray background of an autumn sky
but it was always difficult to com
pute their height, and one could on
lv guess at the direction and force
of the upper air currents through
which they were passing.
1t is hoped that in course of time
aviators will be able to throw flood
of light upon this obscure but IN
tensely interesting branch of ornith-
ology. Already number of observa-
lions have been recorded, but these
are generally lacking in detail, and
no very definite conclusion can as
vet be formed. Up to the present
the greatest height at which a bird
has been seen from an airplane Is
$4,000 feet, when Lieut.. ]. S. Risen,
of the 57th Squadron, observed two
large birds" over ST. Omer in August,
1917.
Weather Changes Birds Flight.
Probably the majority of species
seldom travel under normal condl-
tions above 10000 or $4,000 feet;
but of course the height at which
they fly on any given day depends
very largely upon the weather. When
the air is thick or heavily charged
with moisture, if birds are migrating
at all under such conditions, they are
inclined to keep low, and it is only
in clear atmosphere that they rise tc
the higher strata.
Wind is another and very import
ant factor. What appears to be {
contrary wind on the ground will al
most certainly veer to. shoulder
wind at 1000 or 5000 feet; while il
it happens to be blowing from the
east a complete reversal of direction
may occur before $4,000 feet Il
reached.
There is every reason to believe
that the power of a birds flight is re
duced as it ascends to more raretlet
atmosphere, for an appreciate de
crease in density must mean, among
other things, loss of buoyancy, al
insufficient supply of oxygen, and
too thin, unresisting medium for wing
profusion. :,
From the few records available. II
may be assumed that the majority
of high-fying migrants-such as plo'
vers, ducks, geese, cranes, etc.-pre'
fer to travel between 1000 and 81
900 feet, but as already stated, more
data and precise information are re-
ouired before any definite conclu-
sions can be arrived at.