Migration of Northern Birds

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EA-Zoology

(William Rowan)

THE MIGRATIONS OF NORTHERN BIRDS

        The spring and fall migration of birds in the northern hemisphere are

schoolboy knowledge. One does not have to be ornithologist to know that

robins, swallows, and many other species are here during the summer months

and absent in winter; their journeying back and forth from place to place

are called migrations. Hans Gadow’s definition of the word (3) is perhaps

the best extant and runs as follows: “Migration is the wandering of living

creatures into another, usually distant, locality in order to breed there:

this implies a return, and the double phenomenon is annual. All other

changes of the abode are either sporadic, epidemic or fluctuating within

lesser limits.”

        Typically, migration routes extend north and south, for many birds must

vacate the Far North during the winter months in order to avoid starvation

and death. Since food of great variety is available the year round in the

more equable climates of lower latitudes, the fall migration is, generally

speaking, southward. Yet there are many exceptions, some of which will be

noted.

        Many of our common northbound migrants of spring do not remain with us

through the summer months at the latitudes of, say, the northern United States

or Canada, but travel through and beyond them to make a transitory reappearance

in the fall on their return journey. Certain species, such as knot

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( Calidris canutus ) and sanderling ( Crocethia alba ) go so far north for the

summer as to breed wholly within the Arctic Circle. Numerous other species,

including the snow goose ( Chen hyperborea ), Canada goose ( Branta canadensis ),

and snow bunting ( Plectrophenax nivalis ), breed both within the without the

Circle. Since the total arctic bird populations of the summer run into mil–

lions of individuals, the inference is that there is no limit to the food

supply at this season, a supposition amply supported by explorers, and afford–

ing an important contrast between the Arctic and Antharctic. The point war–

rants brief consideration.

        The map on page 52 of Rowan’s Riddle of migration (16) conveys at a glance

one of the two outstanding aspects of the case, which is this: whereas the

land masses of the Southern Hemisphere (Australia, Africa, and South America)

extend only to latitudes 40°, 35°, and 55° S., respectively, and are compara–

tively restricted, much larger land masses spread continuously in the Northern

Hemisphere to beyond latitude 80° N. the southern end of Australia, for in–

stance, if that island were inverted and placed in the Northern Hemisphere,

would just reach to New York, w h ile the extreme tip of South America under the

same circumstances would barely stretch to Edmonton, Alberta. Except for ice–

bound Antarctica, and remainder of the Southern Hemisphere (save only for cer–

tain islands) is open ocean.

        The second significant point is one of temperature. While the winter of

of the Antarctic is on the average less severe than that of the Arctic, summer

temperatures are lower and remain consistently below the minimum tolerated by

most plants; from the whole of Antarctica only two flowering species and a

mere handful of mosses and algae are known (4). In contrast, over 760 species

of flowering plants have been recorded from the Arctic, 120 of them, including

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chickweed and dandelion, as far as 600 miles north of the Circle. In addition

there are some 600 nonflowering species (17). At latitude 64° S. the mean

temperature of the warmest summer month (January) is −0.9°C., resulting in an

in e vitably flowerless world. In contrast, latitude 64° N. (about the level of

Trondheim in Norway) is a mass of bloom during its warmest month, July. Insect

life presents an analogous picture of extreme paucity in the Antarctic and un–

limited plenty in the Arctic. The only insects known to be abundant in the

Antarctic are parasites on seals (1), while the only birds of numerical note

are the penguins and various petrels — including the so-called cape pigeon

( Daption capense ) — which depend on the sea, not the land, for their food sup–

ply, and the skuas ( Catharacta skua ), which parasitize the penguins.

        The Arctic thus affords a bounteous summer haven for a surprising variety

of birds and offers certain advantages over conditions at lower latitudes,

length of day possibly being the t g reatest. Most species summering in the Arctic

take full advantage of continuous daylight in rearing their families and feed

them throughout the 24 hours, thus probably abbreviating the nestling period.

In the case of the larger species this may be a factor of importance in en–

abling them to make the best use of the brief period of optimum conditions.

Larger clutches of eggs are also characteristic of numerous northern species.

Many of the arctic-breeding shore birds passing northward through central Al–

berta reach the local height of their migration in the latter half of May,

with the first adults already returning in July, barely two months later.

Even at Edmonton (lat. 54° N.), where only a faint glow is visible in the

northern sky in June, slate-colored juncos ( Junco hyemalis ), Leconte’s spar–

rows ( Passerherbulus lecontei ), and certain other species may be heard sing–

ing at midnight. Many birds which breed in the Arctic are said not to sleep

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at all, or merely to snatch sleep at irregular intervals, mainly between the

hours of 8. P.M. and 2 A.M. (2).

        The Arctic thus offers a limitless breeding ground to those species of

birds of sufficient migratory ability to reach it, that do not require trees

for nesting or woodlands for feeding, and that find the northern summer en–

vironment suitable in other respect. Several questions of interest immediately

pose themselves. When and how did birds first discover the Far North? How

do they annually find their way there and back? What is the timing mechanism

that enables them to pick their traveling dates with the extraordinary pre–

cision that most of them show? Why do so few species winter in the North?

        To consider the last question first, it is quite evident that numerous

species would starve to death if they attempted to remain in the North through

the winter months. Birds which feed on mature insects would stand no chance

whatever of survival, for such food is available for only a few weeks in summer.

Seed-eating birds would not survive because for eight months of the year or

more seeds would be covered by snow. Most aquatic birds could not survive

because of the freezing of the water. Such species as the black guillemot

( Cepphus grylle ) and ivory gull ( Pagophila alba ) do find food in open tide rips,

however, and the Greenland mallard ( Anas platyrhynchos conboschas ) is said to

be resident on Greenland coasts, north to Upernivik on the west and to Angmags–

salik on the east. Certain predatory birds, notably the snowy owl ( Nyctea

scandiaca ) and gyrfalcon ( Falco rusticolus ) would starve but for lemmings, and

these small mammals spend so much of their time under the snow that they are

not readily available. Those beautiful northern grouse, the ptarmigan ( Lagopus ),

manage to live on willow buds and twigs, but even Lagopus is migratory. Of

all far northern birds the ravan ( Corvus corax ) is best equipped for strictly

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nonmigratory existence. It can live on lemmings, if they happen to be abun–

dant; it can steal bait from traps; or it can share a whale or walrus carcass

with the foxes and bears. Since birds are homiothermic animals with a normal

temperature of over 100°F. this level must be maintained, and its maintenance

depends on ready availability of food supply. Where food is unfailingly

available, as in captivity, most species, including even domestic canaries

(13), can tolerate temperatures of −50°F. and doubtless lower. In the Ant–

arctic, the emperor penguin ( Aptenodytes forsteri ) may incubate its eggs at

−78°F. while exposed to gales of 70 miles per hour. Availability of food

thus appears to be a decisive factor. There is also total darkness within

the Arctic Circle to contend with, and excessively long nights and short days

hundreds of miles below the Circle. Even a brief period of starvation at low

temperatures is fatal to birds; to survive they must be able to meet the

severest known conditions of the arctic winter.

        About wintering species in the Arctic much more information is needed

than is at present available. Birds have been seen within the zone of total

winter darkness, but such records are few and scattered. How far north

individuals actually survive the entire winter is open to question; it ap–

pears that the vast majority of species and individuals move varying dis–

tances southward from the extreme north with the coming of winter. Such

movements should probably be considered in the nature of true, if limited,

migrations, although they are difficult to disentangle from purely local

movements, which cannot be strictly classed as migrations since they vary

from year to year according to circumstances. These are well developed in

the Arctic (as also at much lower latitudes under stress of exceptional

weather conditions). Ptarmigan, for instance, may require snow to burrow

into during extreme weather and may collect in suitable areas by moving out

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of others. The willow ptarmigan ( L. lagopus ) shifts annually from its breed–

ing place on the barrens into wooded country along their southern edge, al–

though the rock ptarmigan ( L. mutus ) appears to remain on the tundra. Spruce

partridges ( Canachites canadensis ) concentrate in the best feeding areas.

Sharptails ( Pedioecetes phasianellus ) move southward regularly, though , ac–

cording to McDonald, the winter in fair numbers just south of Great Bear Lake

at latitude 65° N. The snowy owl ( Nyctea scandiaca ) moves south in certain

years in large numbers, presumably when the supply of lemmings and hares is

deficient. On these occasions the owls straggle into the United States and

become abundant in central Alberta, where the species is normally represented

every winter by only occasional individuals.

        Certain northern birds such as the Bohemian waxwing ( Bombycilla garrulus ),

white-winged [ ?] cro ssbill ( Loxia leucoptera ), and evening grosbeak ( Hesperi –

phona vespertina ) are inexplicably nomadic. The first two of these range north

to the limit of trees, and south, sporadically, to the southern United States.

The grossbill has been noted every month of the year and the waxwing all months

but February and March at Yellowknife, according to McDonald. The grosbeak

certainly ranges north to central Alberta but beyond that nothing seems to

be known of it. The waxwing and crossbill may occur at Edmonton in large num–

bers through the entire winter, and the grosbeak from January on. The fact

that this species is practically never seen until January suggests that it may

have more regular habits than its congeners. Both the waxwing and crossbill,

however, undertake extensive wanderings and may be present in thousands one

year and totally absent the next, this applying to both breeding and winter–

ing grounds. The assumption is that they follow the food supply regardless

of points of the compass and so, in some years, may actually go south to

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breed, a reversal of the regular trend of migration.

        The opinion is held by some authors that bird migrations into the Far

North have developed since the cessation of the ice age which began and ter–

minated during the past million years (the Pleistocene period), but modern

birds go back in the fossil record for some millions of years, and it seems

unlikely that the migratory habit should be as recent as this. There are

generally believed to have been four periods of glaciations with intervening

s p ells warmer than our present climate, but even at the maximum development

of the ice sheets which covered most of this continent, there remained an

open north-south flight way both east and west of the Rockies, while much

of Alaska and the arctic coast were never glaciated at all. It thus seems

probable that the habit is older than the ice age rather than newer. One can

logically picture the origin of migrations as the outcome of an early increase

in numbers both as to species and individuals of birds and a constant pushing

outward from the center of evolution ever since the days of Hesperornis ,

Ichthyornis , and other toothed precursors of modern forms, taking us back

perhaps 30,000,000 years. The Far North was then comparatively warm, but

slowly cooling. As conditions became more difficult, individuals that re–

mained at high latitudes over winter paid the penalty of death, while those

retreating southward survived. Thus a seasonal oscillation ultimately evolved,

resulting in the annual migrations with which we are now familiar. The abler

migrants tended to exaggerate the performance, producing such extravagant

flights as those of the knot, which breeds as far north as latitude 81°77′ N.

and winters south to southern Australia and New Zealand; and of the arctic tern

( Sterna paradisaea ) which performs a 22,000-mile round trip annually from the

Arctic to the Antarctic.

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        Not all migrations are as spectacular as this, however, nor are all of

them strictly north and south. The breeding crows ( Corvus brachyrhynchos )

of Alberta habitually travel southeast in the fall when they leave that

province. The Ross’s snow goose ( Chen rossii ) nests in the Queen Maud Gulf

region and travels southwestward to its winter home in California. Many red–

head ducks ( Aythya americana ) which ne x s t in Utah winter in the Finger Lakes

region of New York. The yellow-billed loon ( Gavia adamsii Gavia adamsii ) is said to reach

its breeding grounds on the barrens by turning south in the spring from the

arctic coast. Virtually all the adult American golden plovers ( Pluvialis

dominica ) breeding in continental North America and the Arctic Archipelago

travel southeastward in the fall to Labrador and Newfoundland before heading

for South America over the open Atlantic.

        Some migrations are largely altitudinal. The Attu rock ptarmigan ( Lagopus

mutus evermanni ) descends from the rough, high interior of the island to the

valleys and coasts in winter. The blue or dusky grouse ( Dendragapus obscurus ),

a bird of the Rocky Mountain system, breeds in Alberta in the foothills east

of the Rockies and moves westward across the mountains into the milder valleys

of British Columbia in winter. In the tropics, some migrations are definitely

correlated with wet and dry seasons, their extent and direction apparently

being determined by the availability of fruits or insect food.

        Migration in progress is an impressive spectacle, not merely by virtue of

the vast numbers of birds that may be seen together in passage, but perhaps

more so on the ground of the biological mechanism that underlies the regularity

and infallibility of migration. The problems that remain to be solved in this

connection are among the outstanding questions in biology.

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        Apart from the notable antarctic migrations of penguins, which are

achieved by swimming since the birds are flightless, and which have been

described by various authors, spectacular migratory movements are character–

istic principally of the Northern Hemisphere. In southern Manitoba, for ex–

ample, in the Whitewater Lake district, snow geese and blue geese ( Chen

caerulescens ) have been recorded in aggregations of several millions in the

spring before the final dispersal to the breeding grounds takes place in

what may be a single flight of a thousand to fifteen hundred miles. Such

banking up of individuals at suitable resting grounds en route for the North

possibly occurs with more species than is yet known. It is usual among

shore birds (15) and is found even in some passerines. On April 20, 1945,

for instance, on the shores of Beaverhill Lake in central Alberta, the author

encountered a single flock of snow buntings that covered several acres of

ground; a million birds would probably be a conservative estimate.

        Some vivid accounts of migration in progress have been published, as in

Thomson’s Problems of Bird Migration (18), Low’s report of rock ptarmigan

crossing Chesterfield Inlet (7), Manniche’s discussion of ravens in Greenland

(6), and Rowan’s report on waterfowl in Alberta (14). It is more or less an

accident that large-scale movements should ever be witnessed, frequently as

they must occur, since the necessary combination of time, place, and qualified

observer is inevitably a rare event. With the larger and numerically abundant

species, however, diurnal migratory movements may be conspicuous. Such is the

case with the little brown or lesser sandhill crane ( Grus canadensis canadensis ),

for instance, which passes through Alberta in scores of thousands in mid–

September. Particularly with a high barometer, dozens of clear-cut, V-shaped

flocks may be seen almost anywhere during the day winging their way southwestward,

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often at great altitudes. Because, like geese, they are seldom silent,

they are particularly easy to spot. Under these circumstances the author

has counted as many as 30,000 cranes in a single day. When one considers

that this represents the number seen from one point only, and that there may

be a spread of two weeks in time and a great spread in space, one may imagine

the impressive proportions of the movement as a whole.

        To some authors [ ?] migration appears a hazardous habit, but there seems

no good reason for this assumption under normal conditions. When, however,

an ice storm or analogous weather phenomenon happens to hit migrating hordes

of small birds such as Lapland longspurs ( Calcarius lapponicus ) scores of

thousands may be wiped out (see Roberts, 9). Yet this can also happen to

them when they are not migrating, and such catastrophes have overtaken small

species on their usual wintering grounds on an enormous scale from time to

time (see Witherby and Jourdain, 19).

        Migratory flights at night are familiar to most northerners, for the

nocturnal passage north or south of large flights of geese, shore birds, coots

( Fulica _mericans ), and numerous passerine species are constantly heard and

are well recognized. Many species are then traveling relatively fast, but

the speeds of both flight and migration of birds [ ?] have in the past tended

to be exaggerated. Few birds exceed 60 miles per hour. Many fly no faster

than 20, while the average cruising speed of ducks is in the neighborhood of

40. Altitudes are also lower than generally supposed and various diurnal species

effect large parts of their migrations at heights only a few feet above ground

or water level. Exceptional heights are occasionally attained by long-distance

specialists such as cranes; in crossing mountain ranges, altitudes of 10,000

feet and over are not uncommon. With regular air services now becoming a

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commonplace in the Far North and bush pilots still plying their trade in

remoter areas, more precise observations on bird altitudes and speeds during

migration are gradually accumulating.

        How birds find their way north and south, especially at night, still

remains essentially a mystery. Topographical memory is known to play an

important part with many diurnal species, but that there is more to it than

that is made clear by the performances of many young birds undertaking their

initial migrations. The parents of numerous shore birds, for instance,

desert their young as soon as they are able to feed themselves, and return

south. Weeks later, the juveniles themselves set out, but although they

have no parental guidance, they nevertheless reach the habitual wintering

grounds of their own species. Young crows, released in Alberta in November

under experimental conditions without any adults, and long after all wild

crows have gone south, ha v e adopted the standard flight lines to Oklahoma

without error (12). (Oklahoma and Kansas are the wintering grounds of

probably 90% of Alberta Crows.) Nothing tangible is yet known of the

mechanism on which such achievements depend.

        Finally, there is the question of timing. Most species arrive in the

North as though by the calendar and, among the stronger fliers least affected

by weather conditions, with truly astonishing precision. The experimental

method has been applied up to a point to this aspect of migration (10; 11)

but the answer is still far from clear. Length of day, however, appears to

be one of the important factors, at least with birds of the Northern Hem–

isphere, the increase in the amount of daylight in spring conditioning the

physiological mechanism in such manner as to instigate the onset of the

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northern passage. An internal rhythm, kept in phase by the annual sum total

of the bird’s environmental experiences may, among transequatorial migrants

wintering in the Southern Hemisphere, be responsible for the impulse to move

northward.

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BIBLIOGRAPHY

1. Enderlein, . Erg., D. Sűdpol. Exped . vol.10, no.2, 1909.

2. Fisher, J. Birds as Animals . London, Heinemann (1939?)

3. Gadow, H.F. “Migration (under Zoology),” Encyclopaedia Britannica , 11th

ed., vol.18.

4. Hesse, R., Allee, W.C., and Schmidt, K.P. Ecological Animal Geography .

N. Y., Wiley, 1937.

5. Levick, G.M. Antarctic Penguins . London, Heinemann, 1914.

6. Low, A.P. Cruise Of The Neptune. Report on the Dominion Government Ex–

pedition to Hudson Bay and the Arctic Islands . Ottawa, Govern–

[?]ment Printing Bureau, 1903-1904.

7. Manniche, A.L.V. “The terrestrial mammals and birds of North-East Greenland,”

Medd. Grønland , vol.45, pt. 1, pp.93-200, 1912.

8. Phillips, J.C. A Natural History Of The Ducks . Boston, Houghton Mifflin,

1922-26.

9. Roberts, T.S. The Birds of Minnesota . Minneapolis, University of Minnesota

Press, 1932, vol.2.

10. Rowan, W. “Experiment in bird migration, III. Effects of artificial light,

castration and certain extracts on the autumn movements of the

American crow,” Nat. Acc. Sci., Wash. Proc . 1932, pp.639-54.

11. ----. “Experiments in bird-migration. 1. Manipulation of the reproduc–

tive cycle: Seasonal and histological changes in the Gonads,”

Boston Soc. Nat. Hist. Proc . vol.39, pp.151-208, 1929.

12. ----. “Homing,migration and instinct,” Science , vol.102, pp.210-11, 1945.

13. ----. “Light and seasonal reproduction in animals,” Cambridge Phil. Soc.

Biological Reviews , vol.13, pp.374-402, 1938.

14. ----. “Migration in relation to barometric and temperature changes,”

Northeast Bird-Banding Ass. Bull . vol.5, pp.85-92, 1929.

15. ----. “Notes on Alberta Waders included in the British list,” British

Birds , vol.20, p.41, 1926.

16. ----. The Riddle of Migration . Baltimore, Williams & Wilkins, 1931.

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17. Stefansson, Vilhjalmur The Friendly Arctic . N. Y., Macmillan, 1944.

18. Thomson, A.L. Problems of Bird-Migration . London, Witherby, 1926.

19. Witherby, H.F., and Jourdain, F.C.R. “Report on the effect of severe

weather in 1929 on bird-life,” British Birds , vol.23, 1929.

       

Williams Rowan