There is wide-spread misconception concerning the speed at which
birds normally fly, and even regarding the speed they can attain when
occasion demands, as when closely pursued by an enemy. It is not
unusual to hear accounts of birds flying "a mile a minute." While
undoubtedly some birds can and do attain a speed even greater than
this, such cases are exceptional, and it is safe to say that even
when pressed, few can develop an air speed of 60 miles an hour. They
do, however, have two speeds, one being the normal rate for everyday
purposes and also for migration, and an accelerated speed for escape
or pursuit; this in some cases may be nearly double the normal rate
of movement. Nevertheless, the effort required for the high speeds
could not be long sustained, certainly not for the long-distance
migratory journeys that are regularly made by most birds.
[Illustration: B4749M
Figure 5.--Migration of the cliff swallow; a day migrant that,
instead of flying across the Caribbean Sea as does the blackpoll
warbler (fig. 11), follows around the coast of Central America, where
food is readily obtained.]
The theory that migrating birds attain high speeds received
encouragement from the German ornithologist Gätke, who for many
years, made observations on birds at the island of Heligoland and
published thereon in 1891 (_21_). He postulated that the blue-throat
(_Cyanosylvia suecica_), a species of thrush smaller than the
American hermit thrush, would leave African winter quarters at dusk
and reach Heligoland at dawn, which would mean a sustained speed of
200 miles an hour; and that the American golden plover (_Pluvialis
dominion_) flew from the coast of Labrador to Brazil in 15 hours, or
at the tremendous speed of 250 miles per hour. These conclusions are
now considered unwarranted by most ornithologists.
Sportsmen also often greatly overestimate the speed at which ducks
and geese fly and sometimes attempt to substantiate their estimates
by mathematical calculations, based upon the known velocity of a
charge of shot, the estimated distance, and the estimated "lead" that
was necessary to hit the bird. If all three elements of the equation
were known with certainty, the speed of the bird could be determined
with a fair degree of accuracy. The majority of the ducks that are
reported as killed at 40, 50, or even 60 yards, however, actually
are shot at distances much less than estimated. To sight along a gun
barrel and estimate correctly the distance of a moving object against
the sky is so nearly impossible for the average gunner as to make
such calculations of little value.
During the past few years reliable data on the speed of birds have
accumulated slowly. It has been found that the common flying speed of
ducks and geese is between 40 and 50 miles an hour, and that it is
much less among smaller birds. Herons, hawks, horned larks, ravens,
and shrikes, timed with the speedometer of an automobile, have been
found to fly 22 to 28 miles an hour, while some of the flycatchers
are such slow fliers that they attain only 1 to 17 miles an hour.
Even such fast-flying birds as the mourning dove rarely exceed 35
miles an hour. All these birds can fly faster, but it is to be
remembered that at training camps during the World War, airplanes
having a maximum speed of about 80 miles an hour easily overtook
flocks of ducks that it may be supposed were making every effort
to escape. Aviators have claimed that at 65 miles an hour they can
overtake the fastest ducks, though cases are on record of ducks
passing airplanes that were making 55 miles an hour.
The greatest bird speeds that have been reliably recorded are of
the swifts (fig. 6) and the duck hawk, or peregrine falcon (_Falco
peregrinus_) (fig. 7). An observer in an airplane in Mesopotamia
reported that swifts easily circled his ship when it was traveling at
68 miles an hour. To do this, the birds certainly were flying at a
speed as high as 100 miles an hour. Once a hunting duck hawk, timed
with a stop watch, was calculated to have attained a speed between
165 and 180 miles an hour.
The speed of migration, however, is quite different from that
attained in forced flights for short distances. A sustained flight of
10 hours a day would carry herons, hawks, crows, and smaller birds
from 100 to 250 miles, while ducks and geese might travel as much as
400 to 500 miles in the same period. Measured as air-line distances,
these journeys are impressive and indicate that birds could cover the
ordinary migration route from the northern United States or even from
northern Canada to winter quarters in the West Indies or in Central
America or South America in a relatively short time. It is probable
that individual birds do make flights of the length indicated and
that barn swallows (_Hirundo erythrogaster_) seen in May on Beata
Island, off the southern coast of the Dominican Republic, may have
reached that point after a nonstop flight of 350 miles across the
Caribbean Sea from the coast of Venezuela. Nevertheless, whether they
continue such journeys day after day is doubtful.
[Illustration: B988M
Figure 6.--Chimney swift: a speedy day migrant, the flight, of which
on occasions probably exceeds 100 miles an hour.]
It seems more likely that migrations are performed in a leisurely
manner, and that after a flight of a few hours the birds pause to
feed and rest for 1 or several days, particularly if they find
themselves in congenial surroundings. Some indication of this is
found in the records of banded birds. Considering only the shortest
intervals that have elapsed between banding in the North and recovery
in southern regions, it is found that usually a month or more is
taken to cover an air-line distance of a thousand miles. For example,
a black duck (_Anas rubripes_) banded at Lake Scugog, Ontario, was
killed 12 days later at Vicksburg, Miss. If the bird was taken
shortly after its arrival, the record would indicate an average
daily flight of only 83 miles, a distance that could have been
covered in about 2 hours' flying time. Among the thousands of banding
records obtained in recent years, evidences of such rapid flight are
decidedly scarce, for with few exceptions all thousand-mile flights
have required 2 to 4 weeks or more. The greatest speed thus far
recorded for a banded bird is that of a mallard (_A. platyrhynchos_)
banded on November 23, 1930, in Green Bay, Wis., and shot 5 days
later, 900 miles away, near Georgetown, S. C. This bird doubtless
flew at least 1,000 miles in the 5 days, as its route probably was
not in a direct air-line, but, even so, the average daily distance
was only 200 miles, which could easily have been covered in 5 hours.
It seems certain that migratory journeys are performed at the normal
rate of flight, as this would best conserve the strength of the birds
and eliminate the fatigue that would result from effort required for
great speed. Migrating birds passing lightships and lighthouses,
or crossing the face of the moon, have been observed to fly without
hurry or evidence of straining to attain high speed.
[Illustration: B213M
Figure 7.--Duck hawk, or peregrine falcon (Falco peregrinus): a day
migrant and one of the fastest and most graceful fliers of all North
American birds.]
The speed of migration also is demonstrated by the dates of arrival,
particularly during the spring movement. The Canada goose affords
a typical example of regular, but slow, migration. Its advance
northward at this season is at the same rate as the advance of the
season (fig. 8). In fact, the isotherm of 35° F. appears to be a
governing factor in the speed at which these geese move north, and
over their entire trip the vanguard follows closely the advance of
this isotherm.
Few species perform such regular migrations, many waiting in their
winter homes until spring is well advanced and then moving rapidly
to their breeding-grounds. Sometimes this advance is so rapid that
the later migrants actually catch up with species that for a month or
more may have been pressing slowly but steadily northward.
One of the best examples of rapid migration is found in the
gray-cheeked thrush (_Hylocichla minima aliciae_). This bird winters
in Colombia, Ecuador, Peru, Venezuela, and British Guiana and does
not start its northward journey until many other species are well on
their way. It does not appear in the United States until the last of
April--April 25, near the mouth of the Mississippi, and April 30 in
northern Florida (fig. 9). A month later, or by the last week in May,
the bird is seen in northwestern Alaska, the 4,000-mile trip from
Louisiana having been made at an average speed of about 130 miles a
day.
Another example of rapid migration is furnished by the yellow, or
summer, warbler. Coming from the Tropics, the birds reach New
Orleans about April 5, when the average temperature is 65° F.
Traveling north much faster than does the season, they reach their
breeding grounds in Manitoba the latter part of May, when the average
temperature is only 47°. Encountering progressively colder weather
over their entire route, they cross a strip of country in the 15 days
from May 11 to 25 that spring takes 35 days to cross. This "catching
up" with spring is habitual in species that winter south of the
United States and in most of the northern species that winter in the
Gulf States. To this rule there appear to be only six exceptions--the
Canada goose, the mallard, the pintail (_Dafila acuta_), the crow
(_Corvus brachyrhynchos_), the red-winged blackbird (_Agelaius
phoeniceus_), and the robin.
[Illustration: B4508M
Figure 8.--Migration of the Canada goose. The northward movement
keeps pace with the advance of spring, in this case the advance of
the isotherm of 35° F. agreeing with that of the birds.]
The blue goose (_Chen caerulescens_) (fig. 10) presents a striking
example of a late but very rapid spring migration. Practically
all members of the species winter in the great coastal marshes of
Louisiana, where 50,000 or more may be seen grazing in the "pastures"
or flying overhead in flocks of various sizes. Their breeding
grounds are chiefly on Baffin Island and on Southampton Island in
the northern part of Hudson Bay, in a region where conditions of
severe cold prevail except for a few weeks each year. The birds seem
to realize that even though the season in their winter quarters is
advancing rapidly, their nesting grounds are still covered with a
heavy blanket of ice and snow. Accordingly they remain in the coastal
marshes until the last of March or the first of April, when the local
birds are already busily engaged with the duties of reproduction.
The flight northward is rapid, almost nonstop, so far as the United
States is concerned, for although the birds are sometimes recorded
in large numbers in the Mississippi Valley, including eastern South
Dakota, and in southeastern Manitoba, there are few records anywhere
along the route of such great flocks as are known to winter in
Louisiana. When the birds arrive in the James Bay region of Canada
they apparently enjoy a prolonged period of rest, as they are not
noted in the vicinity of their breeding grounds until the first of
June. During the first 2 weeks of that month they pour into the
tundra country by the thousands, and each pair immediately sets about
the business of rearing a brood.
[Illustration: B4505M
Figure 9.--Isochronal migration lines of the gray-cheeked thrush; an
example of rapid migration. The distance from Louisiana to Alaska is
about 4,000 miles and is covered at an average speed of about 130
miles per day. The last part of the journey is covered at a speed
that is several times what it is in the Mississippi Valley.]
The robin has been mentioned as a slow migrant, and as a species it
takes 78 days to make the 3,000-mile trip from Iowa to Alaska, a
stretch of country that is crossed by advancing spring in 68 days.
In this case, however, it does not mean that individual robins are
necessarily slow, for probably the northward movement of the species
depends upon the continual advance of birds from the rear, the first
individuals arriving in a suitable locality remaining to nest, while
the responsibility of the northward movement of the species is
continued by those still to come.
[Illustration: B4766M
Figure 10.--Blue goose, a late but rapid spring migrant that winters
on the coast of Louisiana and breeds on Baffin and Southampton
Islands and flies between summer and winter areas practically without
stops. Photograph by Paul W. Hoffman.]
Special interest attaches to the great variation in the speed
at which birds travel in different sections of the broad flyway
extending from the Gulf of Mexico to the Arctic Ocean by way of the
Mississippi and Mackenzie Valleys. The blackpoll warbler furnishes an
excellent example (fig. 11). This species winters in north-central
South America and migrates in April across the West Indies to
Florida. From this point some individuals fly northwest to the
Mississippi Valley, north to Manitoba, northwest to the Mackenzie
River, and thence almost due west to western Alaska. In tracing
the long route of these birds it is found that a fairly uniform
average speed of 30 to 35 miles a day is maintained from the Gulf
to Minnesota. Then comes a spurt, for a week later the blackpolls
have reached the central part of the Mackenzie Valley, and by the
following week they are observed in northwestern Alaska. During
the latter part of the journey, therefore, many individuals must
average more than 200 miles a day. They use 30 days in traveling from
Florida to southern Minnesota, a distance of about 1,000 miles, and
scarcely half that time to cover the remaining 2,500 miles to Alaska.
It should be noted that the increased speed is directly associated
with the change in direction, the north-and-south course in the
Mississippi Valley being accomplished slowly, while the northwesterly
course across Canada is made at a much greater speed. Increased
speed across western Canada to Alaska is also shown by many other
species. A study of all species traveling up the Mississippi Valley
indicates an average speed of about 23 miles a day. From southern
Minnesota to southern Manitoba 16 species maintain an average speed
of about 40 miles a day. From that point to Lake Athabaska, 12
species travel at an average speed of 72 miles a day; while 5 others
travel to Great Slave Lake at 116 miles a day; and another 5 species
cover 150 miles a day to reach Alaska. This change is in correlation
with a corresponding variation in the isothermal lines, which turn
northwestward west of the Great Lakes.
[Illustration: B4495M
Figure 11.--Migration of the blackpoll warbler. The solid isochronal
lines show the places at which these birds arrive at the same time.
As the birds move northward these lines become farther apart, showing
that the warblers move faster with the advance of spring. From April
30 to May 10 the average speed is about 30 miles a day, while from
May 25 to May 30 it is increased to more than 200 miles.]
As has been previously indicated, the advance of spring in the
northern interior is much more rapid than in the Mississippi Valley
and on the Gulf coast. In other words, in the North, spring comes
with a rush, and during the height of the migration season in
Saskatchewan the temperature in the southern part of the Mackenzie
Valley just about equals that in the Lake Superior area, which is
700 miles farther south. Such conditions, coupled with the diagonal
course of the birds across this region of fast-moving spring, exert
a great influence on migration and are the chief factors in the
acceleration of speed of travel.
Variations in speed of migration in different parts of the country
are illustrated also by the movements of the cliff swallow (fig.
5), which breeds from Mexico to Alaska and winters in Brazil and
Argentina. It would be expected in spring to appear in the United
States first in Florida and Texas, then in the southern Rocky
Mountain region, and finally on the Pacific coast. As a matter of
fact, however, the earliest spring records come from north-central
California, where the bird usually is common before the first
arrivals are observed in Texas or Florida. The route taken, for many
years a migration problem, was solved when it was found that these
swallows went around the Gulf of Mexico rather than across it. The
isochronal lines on the map show the more rapid advance along the
Pacific coast. By March 20, when the vanguard has not quite reached
the lower Rio Grande in Texas, the species is already north of San
Francisco in California.