migrations. When winter approaches in the south-east of Siberia, more
particularly in the high Gobi steppe, all the non-hibernating mammals
are compelled, by the peculiar circumstances of these highlands, to
seek refuge in lower-lying regions. The winter in these high grounds
of Central Asia is not more severe than in districts lying further to
the north or north-east, but it is usually almost snowless, and such
pools of water as have been formed by the extremely slight fall of rain
or snow, are covered with a thick sheet of ice. As soon as this sheet
becomes so strong that the animals inhabiting the Gobi are unable to
break it, they are obliged to change their quarters, and they travel
not only to southern but to northern lands, whose only advantage is
that they are covered with snow, for this affords ready refreshment to
the parched tongues of the wanderers, and offers less resistance to
their weak feet than the hard, unbreakable, and less easily melted ice.
This is the explanation of the fact that the antelope, of which great
numbers are found in the Gobi, forsakes a land which, save for the
lack of snow and therefore of available water, is exactly the same as
that which it chooses for its winter quarters. Not hunger, but thirst,
drives it from its home. At the beginning of winter, the antelopes, at
all times gregarious, assemble in herds of many thousands, spreading
over all the low grounds around their native plateau; they often travel
at the rate of fifty or sixty miles in a single night, and extend
their wanderings many hundreds of miles beyond the boundaries of their
proper habitat. The observer who follows them can detect their tracks
everywhere, and in such numbers that it seems as though vast herds of
sheep, far exceeding in number any ordinary flock, had just passed by.
[Illustration: Fig. 37.--Wild Horses crossing a River during a Storm.]
Before the Chinese antelope begins its migration, restlessness seizes
the kulan or dziggetai, probably the ancestor of our horse, and
certainly the most beautiful and the proudest of all wild horses. The
foals of the summer are by autumn strong enough to be able to endure
a long journey with quick marches, and to bid defiance to all the
accidents and dangers of a wandering life. The young stallions attain
their full strength at the end of their fourth year, and towards the
end of September they leave the parent-herd and press forward. Finally,
the impulse to mate begins to animate the older stallions and mares,
and with it comes unrest and the desire to wander. Thus the fleet,
enterprising animals begin their annual migration long before winter
has set in, before even its approach has become at all apparent; and on
this account their migrations at first lack steadiness and regularity,
and have something of the character of journeys in search of
adventure. With the intention of shaking off the burdensome yoke of the
leader and absolute lord of the herd, and of becoming independent and
in their turn equally despotic, the young stallions forsake the herd,
and thenceforward traverse the sandy steppes singly. All the younger
mares who are mature, and even many of the older ones, seem to be
animated by the same feeling as the young stallions, and they attempt
to escape from the rule of their tyrant and join his young rival, to
fall immediately under his dominion. But not without a struggle does
the new candidate for leadership gain his troop of mares; the old
leader does not readily relinquish his rights. For hours together the
stallion stands on the top of a hill or on the shoulder of a ridge,
keenly scanning the country around. His eye wanders over the desert,
his dilated nostrils are turned towards the wind, his ears are directed
forwards on the alert. Eager for battle, he rushes at full gallop
towards every herd which approaches, every adversary who shows himself;
and a furious struggle takes place for the possession of the mares,
who always attach themselves to the victor. Such combats and strife
set the herd in motion, detach it from the place where the summer has
been spent, and lead on to migrations which become gradually regular,
prolonged, persistent, and almost uninterrupted. In the course of
these, if not before the end of the combats just described, the kulan
troops assemble in ever-growing numbers, until at length herds of more
than a thousand head set out together for fields which give promise of
pasturage. They do not break up while in their winter quarters, and
they are thus compelled to be continually on the move in order to find
sufficient nourishment. The combined tread of the army, as they gallop
on in their usual furious fashion, rings dully out, and more than once,
in Russia, the sound has called the Cossacks of the military cordon to
arms. No wolf ventures to attack such a herd, for the courageous wild
horses know so well how to use their hoofs against him that he soon
gives up any attempt; it is only the sick and exhausted horses which
become his prey, as he follows the wandering herd. Even man can do them
no great damage, for their caution and shyness render them difficult
of approach. But winter, especially if much snow falls, brings them
much suffering. The pasture, at all times scanty, is exhausted the more
quickly the more numerous the herd which feeds on it. Then the animals
devour indiscriminately all the vegetable substances they can find.
For months together they have to maintain life on leafless shoots.
Their bodies cease to be fat and plump, till at length they are like
wandering skeletons. The mother, herself starving, is no longer able to
nourish her foal, for the milk-yielding udder dries up in times of such
need. Many a one whose tender youth is unable to endure the hard fare
dies of starvation. Even the old horses suffer from the poverty and
treachery of the winter. Snow-storms blowing over their feeding-ground
for days at a time depress their usually cheerful courage, and increase
the boldness of the wolves, which, even if they do not fall upon the
already exhausted horses, persecute and annoy to the utmost those who
are not yet worn out. But as soon as circumstances begin to improve,
the wiry, weather-hardened, enduring creatures recover their high
spirits, and, when the snow begins to melt, they set out on the return
journey, reaching their summer home in about a month’s time. There they
break up into single herds, recuperate among the luxuriantly sprouting,
fragrant pasture, and, in a surprisingly short time, become fat and
plump again. Soon the want and misery of the winter are forgotten.
Great as are the distances often traversed by all the mammals already
mentioned, they can scarcely be compared with those covered by seals
and whales. The water favours all the movements of animals adapted to
aquatic life, and offers everywhere the same general conditions of
life and the same amenities. Thus it renders the migrations of its
inhabitants easier, less toilsome and hazardous than those of any other
wanderers. Nevertheless it is somewhat surprising to learn that many
sea-mammals, and particularly the whales, are among the most nomadic
of all creatures; in fact that many, if not most of them, pass their
whole life in travelling. Strictly speaking, no whale has a permanent
place of sojourn for the whole year, but passes singly, in pairs,
with its young, or in more or less numerous companies--the so-called
schools--from one part of the ocean to another, visiting certain
favourite haunts in regular order, and choosing different haunts in
summer and in winter. The seas inhabited by the same species of whale
in winter and in summer often lie farther apart than people seem to
suppose, for some whales travel, twice a year, more than a quarter of
the earth’s circumference; they are to be found in summer among the
ice-floes of the Arctic Ocean, and in winter on the other side of the
Equator. The female whales, who are in the highest degree sociable,
and attached to their young with the tenderest, most devoted love,
assemble together in surprising numbers, and under the guidance of a
few males, traverse the ocean by definite routes and at definite times,
some keeping to the open sea, others making their way along the coasts.
Storms may force them to change their route, or delay in the appearance
of the animals on which they feed, whose occurrence and disappearance
is obviously the chief cause of their migration, may to some extent
influence their course and the time of their visiting certain spots;
but, as a general rule, their migrations are so systematic that on
northern and southern coasts people look for the arrival of the whale
on a particular day, and place watches so that they may be able to
begin the long-desired chase without loss of time. Whales, which are
recognized by the dwellers on the coast by some mark, such as mutilated
fins, and which have been several times pursued in vain, have been
known to appear several years in succession at the same time and at
the same place; and the chase after these most valuable and therefore
increasingly persecuted animals takes place with the same regularity as
do hare-hunts on land, though at any other time of the year it would
be vain to look for them. “After Twelfth Day,” says old Pontoppidan,
“the Norwegians watch from all the hills for the whale, whose arrival
is announced by the herring.” First appears the killer, then, three
or four days, or at the most a fortnight later, the rorqual, though,
apparently, one comes from Davis Straits and the other from Greenland.
On the south coasts of the Faroë Islands, and especially in the
Qualbenfjord, from three to six bottle-nose whales still appear
every year about Michaelmas, as they did a hundred and ninety years
ago. In a Scottish bay there appeared twenty years in succession a
rorqual, which was generally known by the name of “Hollie Pyke”, and
was pursued every year and finally captured. On the coast of Iceland
single whales choose the same bays for a temporary sojourn every year
in the same months, and even weeks, so that the inhabitants have got
to know them individually, and have given them special names. Certain
well-known mother-whales visit the same bays every year to bring forth
their young, and they themselves are spared, but they have to purchase
their own lives, dearly enough, at the cost of that of their young
ones, which are regularly taken captive. It is very unusual for the
migrating whales to keep neither to time nor to route; in general,
their journeys are as regular as if they were arranged according to the
position of the stars, and as if they took place along laid-out paths
bounded on both sides. No other mammal migrates more regularly; indeed,
their wanderings may be compared with the migrations of birds.
The seals, like the whales, migrate every year, on the whole with
great regularity, though not to such a distance. Those species which
inhabit inland seas cannot, of course, leave these, but they traverse
them every year in regular order, or at certain times ascend the rivers
flowing into them; all the ocean species, on the other hand, set out
every autumn and spring, by definite routes, to certain regions or
localities. All the seals in the far north, as well as those in the
seas about the South Pole, are forced to migrate by the extension of
the ice in winter, and may travel with it towards temperate zones,
returning towards the poles again as the ice melts. But they, like all
other members of their order, are impelled to travel for another not
less weighty reason; they require the mainland, or at least large,
spreading, fixed masses of ice, on which to bring forth and nurture
their young, until these are able to follow them into the water, there
to shift for themselves. Thus every year thousands and hundreds of
thousands of seals appear on certain islands and ice-banks, covering
some of these birth-places of their race in such crowds that every
available spot must be utilized in order to secure space for all to
bring forth their young. They pass weeks, even months, on land or on
the ice without hunting, descending into the sea, or taking food; they
suckle their young, then mate, and by degrees break up their great
assemblage, distributing themselves over the wide ocean to resume their
former manner of life, or setting out with their young, who still
require training, on more or less extensive foraging expeditions.[59]
[Illustration: Fig. 38.--Flying Foxes.]
As is well known, there are many mammals which have the habit of
hibernating, which pass the severe part of the year well protected in
deep and carefully closed burrows, and are thus spared the necessity of
leaving their haunts. Even among these, however, at least among those
living in the temperate zones, there are some which migrate during
their waking time, namely, the bats. Defective as the wing of a bat
must appear when compared with that of a bird, it is nevertheless of
such assistance in flight, that it makes journeys possible which seem
out of all proportion to the size of the animal. Another fact makes
travelling easier to the restless bat; it is not tied down by its
offspring to any particular spot, for the young one attaches itself
directly after birth to the breast of the mother, and is borne by her
through the air till it is capable of independent life. The bat is
thus one of the best-adapted of migratory mammals, and, under some
circumstances, it makes full use of its advantages. As a general rule,
the wanderings of the different species of bat are to be regarded
simply as excursions made with a view to taking advantage of any
district which is, for the time being, particularly rich in food; but
they do sometimes become really long journeys, which lead some species
to far distant lands, and they are then not without the regularity
characteristic of all true migrations. The largest bats, the flying
foxes, fly long distances every evening in search of the fruits on
which they chiefly subsist; they do not hesitate to cross an arm of the
sea fifty or sixty miles in breadth, and they must even have traversed
the distance between Southern Asia and the East of Africa, as certain
species occur in both these regions. The bats proper accomplish at
least as much. Following the reappearance of the insects, which occurs
at different times in regions of different altitude, they ascend from
the plains to the mountain heights, and descend in autumn to the low
grounds again; they pursue the numerous flies which congregate about
the wandering cattle-herds of Central Africa, and they migrate also
from the south towards the north and return southwards again, or in
reverse order. The boreal bat appears at the beginning of the bright
nights in the north of Scandinavia and Russia, and leaves these
districts, which may be considered its head-quarters, towards the end
of summer, to spend the winter among the mountains of Central Germany
and the Alps. The pond-bat is regularly seen on the plains of North
Germany during summer, but only exceptionally at that period among the
mountains of Central Germany, in whose caverns it spends the winter.
That other species of bat occurring in Germany change their place of
abode in a similar manner can scarcely be doubted.
In the cases cited, which have been selected from a mass of available
material, I have given examples of those migrations of mammals which
we may call voluntary, because of their regularity; but in so doing I
have by no means completed my task. Hunger and thirst, the poverty and
temporary inhospitableness of a particular region, sometimes press so
severely on certain mammals that they endeavour, as if despairing, to
save themselves by flight. Abundant nourishment and good weather favour
the increase of all animals, and affect that of a few plant-eating
mammals to such an extraordinary degree, that, even under propitious
conditions, their habitat must be extended. But if one or more rich
years--in some cases a few favourable months--be followed by a sudden
reverse, the famine soon passes all bounds, and robs the creatures not
only of the possibility of subsistence, but also of all hope, or at
least of all presence of mind.
It is under circumstances such as these that the field-voles of our
own country, and the Siberian voles, assemble in enormous multitudes,
leave their native haunts and migrate to other districts, turning
back for no obstacles, avoiding the water as little as the forbidding
mountains or the gloomy forest, fighting to the last against hunger
and misery, but perishing hopelessly from diseases and epidemics which
rage among them like plagues, reducing armies of millions to a few
hundreds. Thus, too, the squirrels of Siberia, which, in ordinary
years, undertake, at the most, only short excursions, assemble in vast
armies, hurry in troops or companies from tree to tree, in compact
masses from forest to forest, swim across rivers and streams, throng
into towns and villages, lose their lives by thousands; but suffer no
obstacle or hindrance--not even the most obvious dangers--to delay
them or divert them from their path. The soles of their feet become
worn and cracked, their nails ground down, the hairs of their usually
smooth fur rough and matted. Through the forest lynxes and sables, in
the open fields gluttons, foxes and wolves, eagles, falcons, owls and
ravens follow them closely; pestilence claims more victims from their
ranks than the teeth and claws of beast of prey or the guns and cudgels
of men, yet they press on and on, apparently without hope of return.
A Siberian sportsman of my acquaintance gave me a verbal account of
the appearance of such an army of squirrels, in August 1869, in the
town of Tapilsk, among the Ural Mountains. It was only one wing of a
migrating army, of which the main body travelled through the forest
about five miles farther north. Sometimes in single file, sometimes
in companies of varying strength, but in unbroken succession, the
animals pressed on, crowding as densely through the town as through the
neighbouring forest; used the streets, as well as the hedges, and the
roofs of buildings as paths; filled every court-yard, thronged through
windows and doors into the houses, and created quite an uproar among
the inhabitants--much more among the dogs, which killed thousands of
them, evincing an unbridled bloodthirstiness till then unsuspected. The
squirrels, however, did not seem to concern themselves in the least
about the innumerable victims falling in their midst; in fact, they
took no notice of anything, and allowed nothing to divert them from
their route. The procession lasted for three whole days, from early
morning till late in the evening, and only after nightfall each day was
there a break in the continuity of the stream. All travelled in exactly
the same direction, from south to north, and those that came last took
the same paths as their predecessors. The rushing Tchussoveia proved no
obstacle, for all that reached the bank of that rapid mountain-river
plunged without hesitation into its whirling and seething waters, and
swam, deeply sunk and with their tails laid across their backs, to
the opposite bank. My informant, who had been watching the procession
with growing attention and sympathy, rowed out into the midst of the
throng. The tired swimmers, to whom he stretched out an oar, climbed up
by it into the boat, where, apparently exhausted, they sat quietly and
confidingly, until it came alongside a larger vessel, when they climbed
into that, and remained on it for some time as indifferent as before.
As soon as the boat touched the bank they sprang ashore, and proceeded
on their journey as unconcernedly as if it had suffered no interruption.
It must be similar circumstances which compel the lemmings to the
migrations which have been known for centuries. For many successive
years the heights in the tundras of Scandinavia, North Russia, and
the North of Siberia afford them comfortable quarters and abundant
nourishment; for the broad ridges of the fjelds and the extensive
plains between them, the highlands and the low grounds, offer room and
maintenance for millions of them. But not every year do they enjoy the
accustomed abundance for the whole summer. If a winter in which much
snow falls, and which is therefore favourable to them, as they live
safely below the snow, be followed by an early, warm, and agreeable
spring, their extraordinary fertility and power of increase seem to
have almost no bounds, and the tundra literally teems with lemmings. A
fine warm summer increases their numbers past computing, but it also
accelerates the life-course of all the plants on which they feed, and
before it is over these are partly withered, partly devoured by the
greedy teeth of the insatiable rodents. Scarcity of food begins to
be felt, and their comfortable life comes to an end in panic. Their
fearless, bold demeanour gives place to a general uneasiness, and
soon a mad anxiety for the future takes possession of them. Then they
assemble together and begin to migrate. The same impulse animates many
simultaneously, and from them it spreads to others; the swarms become
armies; they arrange themselves in ranks, and a living stream flows
like running water from the heights to the low grounds. All hurry
onwards in a definite direction, but this often changes according to
locality and circumstances. Gradually long trains are formed in which
lemming follows lemming so closely that the head of one seems to rest
on the back of the one in front of it; and the continuous tread of the
light, little creatures hollows out paths deep enough to be visible
from a long distance in the mossy carpet of the tundra. The longer the
march lasts, the greater becomes the haste of the wandering lemmings.
Eagerly they fall upon the plants on and about their path and devour
whatever is edible; but their numbers impoverish even a fresh district
within a few hours, and though a few in front may pick up a little
food, nothing is left for those behind; the hunger increases every
minute, and the speed of the march quickens in proportion; every
obstacle seems surmountable, every danger trifling, and thousands rush
on to death. If men come in their way they run between their legs;
they face ravens and other powerful birds of prey defiantly; they gnaw
through hay-stacks, climb over mountains and rocks, swim across rivers,
and even across broad lakes, arms of the sea, and fjords. A hostile
company, like that behind the migrating squirrels, follows in their
wake: wolves and foxes, gluttons, martens and weasels, the ravenous
dogs of the Lapps and Samoyedes, eagles, buzzards, and snowy owls,
ravens and hooded crows fatten on the innumerable victims which they
seize without trouble from the moving army; gulls and fishes feast
on those which cross the water. Diseases and epidemics, too, are not
awanting, and probably destroy more than all their enemies together.
Thousands of carcasses lie rotting on the wayside, thousands are
carried away by the waves; whether indeed any are left, and whether
these return later to their native Alpine heights, or whether all,
without exception, perish in the course of their journey, no one can
say with certainty; but so much I know, that I have traversed great
tracts of the tundra of Lapland where the paths and other traces of
a great migrating army were to be seen almost everywhere, while not
a single lemming could be discovered. Such tracts, I have been told,
remain thus for several successive years, and only after long periods
become gradually repeopled with the busy little rodents.[60]