THE MIGRATION OF BIRDS
There is something fascinating about the word migration. It sends our
minds back to the dim stories of tribal movements carved on the rocks
by men who wrought in the dawn of history. We wonder at the compelling
force that drove our ancestors through the forests of northern Germany,
or caused the Aztecs to cross the Mexican deserts. It calls to
something in our blood, for even the most stolid must at times hearken
to the Pied Piper and with Kipling feel that "On the other side the
world we're overdue."
Man is not alone the possessor of the migrating passion. Menhaden, in
vast schools, sweep along our Atlantic Coast in their season. From
unknown regions of the ocean herring and salmon return to {62} the
streams of their nativity when the spirit of migration sweeps over the
shoals into the abysmal depths. There are butterflies that in
companies rise from mud puddles beside the road and go dancing away to
the South in autumn. The caribou, in long streams, come southward over
the barrens of Labrador when the word is passed, and even squirrels,
over extended regions, have been known to migrate en masse for hundreds
of miles. There is, however, no phase of the life of birds which is
quite so distinctive. The extent and duration of their migrations are
among the most wonderful phenomena of the natural world.
Ornithologists have gathered much information regarding their coming
and going, but knowledge on many of the points involved is incomplete.
It is only of recent years that the nest of the Solitary Sandpiper has
been found, and yet this is a very common bird in the eastern United
States in certain seasons. Where is the scientist who can yet tell us
in what country the common Chimney Swift {63} passes the winter, or
over what stretches of sea and land the Arctic Tern passes when
journeying between its summer home in the Arctic seas and its winter
abode in the Antarctic wastes? The main fact, however, that the great
majority of birds of the Northern Hemisphere go south in autumn and
return in spring, is well known.
_Moulting._--By the time the young are able to care for themselves the
plumage of the hard-working parents is worn and frayed and a new suit
of feathers becomes necessary. They do not acquire this all at once.
The feathers drop out gradually from the various feather tracts over
the body, and their places are at once taken by a new growth. While
this is going on the birds are less in evidence than at other times.
They keep out of sight and few song notes are heard. Perhaps there is
some irritation and unpleasantness connected with moulting which causes
a dejection of spirit.
With swimming water birds the wing quills disappear nearly all at once
and the birds are unable {64} for a short time to fly; but being at
home in the water, where they secure their food, they are not left in
the helpless, even desperate, condition in which a land bird would find
itself if unable to fly. In a few cases birds begin to migrate before
this moulting takes place, but with the great majority the moult is
complete before they leave their summer homes.
_Why Birds Migrate._--Why birds migrate we can only conjecture.
Without doubt the growing scarcity of food in autumn is the controlling
factor with many of them; and this would seem to be an excellent reason
for leaving the region of their summer sojourn. Cold weather alone
would not drive all of them southward, else why do many small birds
pass the winter in northern latitudes where severe climatic conditions
prevail? Should we assume the failing food supply to be the sole cause
of migration, we would find ourselves at fault when we came to consider
that birds leave the tropic regions in spring, when food is still
exceedingly abundant, and journey northward thousands of miles to their
former summer haunts.
[Illustration: Young robins quarreling at their bath. Photographed in
the yard of Mrs. Granville Pike, North Yakima, Washington]
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There is a theory held by many naturalists that the migrating instinct
dates back to the glacial period. According to this theory North
America was inhabited originally by non-migrating birds. Then the
great Arctic ice-cap began to move southward and the birds were forced
to flee before it or starve. Now and then during the subsequent period
the ice receded and the birds returned, only to be driven again before
the next onrush of the Ice King. Thus during these centuries of
alternate advance and retreat of the continental glacier, the birds
acquired a habit, which later became an instinct, of retreating
southward upon the approach of cold weather and coming back again when
the ice and snow showed indications of passing away.
_The Gathering Flocks._--To the bird student there is keen delight in
watching for the first spring arrivals and noting their departure with
the dying year. It is usually in August that we first observe an
unwonted restlessness on the part of our birds which tells us that they
have begun to hear the call of the {66} South. The Blackbirds assemble
in flocks and drift aimlessly about the fields. Every evening for
weeks they will collect a chattering multitude in the trees of some
lawn, or in those skirting a village street, and there at times cause
great annoyance to their human neighbours.
Across the Hudson River from New York, in the Hackensack marshes,
behind the Palisades, clouds of Swallows collect in the late summer
evenings, and for many days one may see them from the car windows as
they glide through the upper air or swarm to roost among the rushes.
These Swallows and the Blackbirds are getting together before starting
on their fall migration.
In Greensboro, North Carolina, there is a small grove of trees
clustered about the courthouse which is a very busy place during the
nights of summer. Here, before the first of July, Purple Martins begin
to collect of an evening. In companies of hundreds and thousands, they
whirl about over the tops of the houses, alight in the trees, and then
almost {67} immediately dash upward and away again. Not till dark do
they finally settle to roost. Until late at night a great chorus of
voices may be heard among the branches. The multitude increases daily
for six or eight weeks, additions, in the form of new family groups,
constantly augmenting their numbers. Some time in September the
migration call reaches the Martins, and, yielding to its spell, they at
once depart toward their winter home in tropical South America.
_The Usual Movement._--Many of our smaller birds, such as Warblers and
Vireos, do not possess a strong flocking instinct, but, nevertheless,
they may be seen associated in numbers during the season of the
northern and southern movements. Such birds migrate chiefly at night
and have been observed through telescopes at high altitudes. Such
observations are made by pointing the telescope at the disk of the full
moon on clear nights. On cloudy or foggy nights the birds fly lower,
as may be known by the clearer sounds of their calls as they pass over;
at times one may even hear the flutter of their wings. There is a {68}
good reason for their travelling at this time, as they need the
daylight for gathering food.
There appear to be certain popular pathways of migration along which
many, though by no means all, of the aerial voyageurs wing their way.
As to the distribution of these avian highways, we know at least that
the coastlines of the continents are favourite routes. Longfellow, in
the valley of the Charles, lived beneath one of these arteries of
migration, and on still autumn nights often listened to the voices of
the migrating hosts, "falling dreamily through the sky."
A small number of the species migrate by day; among these are the
Hawks, Swallows, Ducks, and Geese. The last two groups also travel by
night. The rate at which they proceed on their journey is not as great
as was formerly supposed. From twenty to thirty miles an hour is the
speed generally taken, and perhaps fifty miles an hour is the greatest
rapidity attained. Flights are usually not long sustained, a hundred
and fifty miles a day being above the {69} average. Individuals will
at times pause and remain for a few days in a favourable locality
before proceeding farther. When large bodies of water are encountered
longer flights are of course necessary, for land birds cannot rest on
the water as their feathers would soon become water-soaked and drowning
would result. Multitudes of small birds, including even the little
Ruby-throated Hummingbird, annually cross the Gulf of Mexico at a
single flight. This necessitates a continuous journey of from five
hundred to seven hundred miles. Some North American birds migrate
southward only a few hundred miles to pass the winter, while many
others go from Canada and the United States to Mexico, Central and
South America.
The ponds and sloughs of all that vast country lying between the Great
Lakes and Hudson Bay on the east and the mountains of the Far West,
constitute the principal nursery of North American waterfowl, whence,
in autumn, come the flocks of Ducks and Geese that in winter darken the
Southern {70} sounds and lakes. One stream moves down the Pacific
Coast, another follows the Mississippi Valley to the marshes of
Louisiana and Texas, while a third passes diagonally across the country
in a southeasterly direction until it reaches the Maryland and Virginia
coastline. Thence the birds disperse along the coastal country from
Maine to Florida.
[Illustration: Migration Routes of Some North American Birds]
_The Travelling Shore Birds._--Turnstones, Sanderlings, Curlews, and
other denizens of the beaches and salt marshes migrate in great numbers
along our Atlantic Coast. Some of them winter in the United States,
and others pass on to the West Indies and southward. The extent of the
annual journeys undertaken by some of these birds is indeed marvellous.
Admiral Peary has told me that he found shore birds on the most
northern land, where it slopes down into the Arctic Sea, less than five
hundred miles from the North Pole; and these same birds pass the winter
seven thousand miles south of their summer home. One of these
wonderful migrants is the Golden Plover. In autumn the birds leave
{72} eastern North America at Nova Scotia, striking out boldly across
the Atlantic Ocean, and they may not again sight land until they reach
the West Indies or the northern coast of South America. Travelling, as
they do, in a straight line, they ordinarily pass eastward of the
Bermuda Islands. Upon reaching South America, after a flight of two
thousand four hundred miles across the sea, they move on down to
Argentina and northern Patagonia. In spring they return by an entirely
different route. Passing up through western South America, and
crossing the Gulf of Mexico, these marvellous travellers follow up the
Mississippi Valley to their breeding grounds on the shores of the
Arctic Ocean. Their main lines of spring and fall migration are
separated by as much as two thousand miles. During the course of the
year the Golden Plover takes a flight of sixteen thousand miles.
_The World's Migrating Champion._--The bird which makes the longest
flight, according to the late Wells W. Cooke, America's greatest
authority on bird migration, is the Arctic Tern. Professor Cooke, to
{73} whom we owe so much of our knowledge of the subject, says of this
bird:
"It deserves its title of 'arctic' for it nests as far North as land
has been discovered; that is, as far North as the bird can find
anything stable on which to construct its nest. Indeed, so arctic are
the conditions under which it breeds that the first nest found by man
in this region, only seven and one-half degrees from the pole,
contained a downy chick surrounded by a wall of newly fallen snow that
had been scooped out of the nest by the parent. When the young are
full grown the entire family leaves the Arctic, and several months
later they are found skirting the edge of the Antarctic continent.
"What their track is over that eleven thousand miles of intervening
space no one knows. A few scattered individuals have been noted along
the United States coast south to Long Island, but the great flocks of
thousands and thousands of these Terns which range from pole to pole
have never been noted by ornithologists competent to indicate their
{74} preferred route and their time schedule. The Arctic Terns arrive
in the Far North about June fifteenth and leave about August
twenty-fifth, thus staying fourteen weeks at the nesting site. They
probably spend a few weeks longer in the winter than in the summer
home, and this would leave them scarcely twenty weeks for the round
trip of twenty-two thousand miles. Not less than one hundred and fifty
miles in a straight line must be their daily task, and this is
undoubtedly multiplied several times by their zigzag twistings and
turnings in pursuit of food.
"The Arctic Tern has more hours of daylight and sunlight than any other
animal on the globe. At the most northern nesting site the midnight
sun has already appeared before the birds' arrival, and it never sets
during their entire stay at the breeding grounds. During two months of
their sojourn in the Antarctic the birds do not see a sunset, and for
the rest of the time the sun dips only a little way below the horizon
and broad daylight is continuous. The birds, therefore, have
twenty-four hours of daylight for at least {75} eight months in the
year, and during the other four months have considerably more daylight
than darkness."
_Perils of Migration._--The periods of migration are fraught with
numerous perils for the travelling hosts. Attracted and blinded by the
torches of lighthouses, multitudes of birds are annually killed by
striking against lighthouse towers in thick, foggy weather. The keeper
of the Cape Hatteras light once showed me a chipped place in the lens
which he said had been made by the bill of a great white Gannet which
one thick night crashed through the outer protecting glass of the
lighthouse lamp. As many as seven hundred birds in one month have
killed themselves by flying against the Bartholdi Statue of Liberty in
New York Harbour. As its torch is no longer lighted the death-rate
here has been greatly reduced, although some birds are still killed by
flying against the statue. Many were formerly killed by striking the
Washington Monument, the record for one night being one hundred and
fifty dead birds.
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Locomotive engineers have stated that in foggy weather birds often hurl
themselves against the headlight and frequently their bodies are later
picked up from the engine platform beneath. Birds seem rarely to lose
their sense of direction, and they pursue their way for hundreds of
miles across the trackless ocean. Terns, Gulls, and Murres are known
to go many miles in quest of food for their young and return through
dense fogs with unerring directness to their nests.
[Illustration: Lighthouses Cause the Death of Many Birds]
During the spring it is not uncommon for strange waterfowl to be found
helpless in the streets or fields of a region in which they are
ordinarily unknown. These birds have become exhausted during the storm
of the night before, or have been injured by striking telephone or
telegraph wires, an accident which often happens. Once I picked up a
Loon after a stormy night. Apparently it had recovered its strength
after a few hours' rest, but, as this bird can rise on the wing only
from a body of water, over the surface of which it can paddle and flap
for many rods, and as {78} there was no pond or lake in all the
neighbouring country, the Loon's fate was evident from the first.
Birds are often swept to sea by storm winds from off shore. Vainly
they beat against the gale or fly on quivering wings before its blast,
until the hungry waves swallow their weary bodies. One morning in
northern Lake Michigan I found a Connecticut Warbler lying dead on the
deck beneath my stateroom window after a stormy night of wind and rain.
Overtaken many miles from shore, this little waif had been able to
reach the steamer on the deck of which it had fallen exhausted and
died. What of its companions of the night before?
On May 3, 1915, I was on a ship two hundred miles off Brunswick,
Georgia. That day the following birds came aboard, all in an exhausted
condition: Brown Creeper, Spotted Sandpiper, Green Heron, and
Yellow-billed Cuckoo. We also encountered three flocks of Bobolinks,
which for some distance flew beside the ship. They appeared to be
lost, for they all left us finally, flying straight ahead of the ship,
{79} which was bound South, yet birds were supposed to be going North
at this season. I wonder if in their bewilderment they mistook the
ship for some immense bird pointing the way to land and safety!
[Illustration: Tired Migrating Birds Often Alight on Ships]
_Keeping Migration Records._--More than thirty {80} years ago the
United States Government put into operation a plan for collecting and
tabulating information concerning the dates on which migratory birds
reach various points in their journeys. More than two thousand
different observers located in various parts of the country have
contributed to these records, many of the observers reporting annually
through a long series of years. As a result of this carefully gathered
material, with the addition of many data collected from other sources,
there is now on file in Washington an immense volume of valuable
information, much of which, in condensed printed form, is obtainable by
the public. This work was in charge of Professor Wells W. Cooke,
Biologist, in the Biological Survey of the United States Department of
Agriculture until his lamented death in the spring of 1916. Who will
take charge of it hereafter is not yet determined; but students may
obtain from the director of the Survey migration schedule blanks upon
application, and bulletins describing the emigration habits of various
North American birds. {81} Watching for the annual appearance of the
first individual of each species is most fascinating occupation.
[Illustration: Feeding station for birds on the grounds of R. G.
Decker, Rhinebeck, New York. The glass sides prevent the seeds from
being blown off the tray a foot or more below the roof.]
Note.--Government bulletins on the migration of various North American
birds may be obtained free, or at slight cost, by addressing H. W.
Henshaw, Chief Biological Survey, Department of Agriculture,
Washington, D. C.
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