called the cowbird, acts in the same careless fashion. It lives in
the midst of herds, and owes its specific name to this custom; it
feeds on the parasites on the skin of cattle. This bird constructs
no nest. At the moment of laying the female seeks out an inhabited
dwelling, and when the owner is absent she furtively lays an
egg there. The young intruder breaks his shell after four days’
incubation, that is to say, usually much before the legitimate
children; and the parents, in order to silence the beak of the
stranger who, without shame, claims his share with loud cries,
neglect their own brood which have not yet appeared, and which they
abandon.
The habits of the Molothrus bovariensis, a closely allied Argentine
cowbird, have been carefully studied by Mr. W. H. Hudson, who has
also some interesting remarks as to the vestiges of the nesting
instinct in this interesting parasitical bird, which is constantly
dropping eggs in all sorts of places, even on the ground, most
of them being lost. Mr. Hudson suggests that this bird lost the
nest-making instinct by acquiring the semi-parasitical habit, common
to many South American birds, of breeding in the large covered nests
of the Dendrocolaptidæ, although, owing to increased severity in the
struggle for the possession of such nests, this habit was defeated.
The Rhodius anarus, a fish of European rivers, also ensures a quiet
retreat for his offspring by a method which is not less indiscreet.
At the period of spawning, a male chooses a female companion and
with great vigilance keeps off all those who wish to approach her.
When the laying becomes imminent, the Rhodius, swimming up and
down at the bottom of the stream, at length discovers a Unio. The
bivalve is asleep with his shell ajar, not suspecting the plot which
is being formed against him. It is a question of nothing less than
of transforming him into furnished lodgings. The female fish bears
underneath her tail a prolongation of the oviduct; she introduces it
delicately between the mollusk’s valves and allows an egg to fall
between his branchial folds. In his turn the male approaches, shakes
himself over it, and fertilizes it. Then the couple depart in search
of another Unio, to whom to confide another representative of the
race. The egg, well sheltered against dangers from without, undergoes
development, and one fine day the little fish emerges and frisks away
from his peaceful retreat.
The hermit-crab perhaps knows best how to take advantage of old
clothes. He collects shells of Gasteropods, abandoned flotsam,
the first inhabitant of which has died. The hermit-crab (Pagurus
Bernhardus) is a Decapod Crustacean--that is to say, he resembles a
very small crab. But his inveterate habit during so many generations
of sheltering his abdomen in a shell prevents this part from being
incrusted with lime and becoming hard. The legs and the head remain
in the ordinary condition outside the house, and the animal moves
bearing it everywhere with him; on the least warning he retires into
it entirely. But the crustacean grows. When young he had chosen a
small shell. A mollusk, in growing, makes his house grow with him.
The hermit-crab can not do this, and when his dwelling has become
too narrow he abandons it for one that is more comfortable. At
first inclosed in the remains of a Trochus, he changes into that of
a Purpura; a little later he seeks asylum in a whelk. Besides the
shelter which these shells assure to the crustacean, they serve to
mask his ferocity, and the prey, which approaches confidently what it
takes to be an inoffensive mollusk, becomes his victim.
The great horned owl likewise does not construct a nest, but takes
possession of the dwellings abandoned by others. These birds utilize
for laying their eggs sometimes the nest of a crow or a dove,
sometimes the lair which a squirrel had considered too dilapidated.
The female, without troubling about the bad state of these ruins, or
taking pains to repair them, lays her eggs here and sits on them.
It is time to turn to animals who have more regard for comfort,
and who erect dwellings for themselves or their offspring. These
dwellings may be divided into three groups: (1) Those which are
hollowed in earth or in wood; (2) those which in the simplest
form result from the division of material of any kind; then,
as a complication, of materials bound together; then, as a last
refinement, of delicate materials, such as blades of grass or threads
of wool woven together; such are the nests of certain birds and the
tents of nomads; (3) those which are built of moist earth which
becomes hard on drying; the perfection of this method consists of
piling up hard fragments, pieces of wood or ashlar, the moist earth
being only a mortar which unites the hard parts together. Animals
exercise with varying success these different methods, all of which
man still practices.
We will first occupy ourselves with the dwelling hollowed in the
earth. It is the least complicated form. The number of creatures
who purely and simply bury themselves thus to obtain shelter is
incalculable; I will only mention a few examples, and pass on from
simple combinations to the more perfected industries, of which they
present the first sketch.
Speaking generally, birds are accomplished architects. Certain of
them are, however, content with a rudimentary cavern. There is no
question here of those who retire to clefts in the rock or in trunks
of trees, for in these cases the cavity is only the support of the
true house, and it is in the construction of this that the artist
reveals his talent. I wish to speak of animals which remain in a
burrow without making a nest there. A paroquet of New Zealand called
the kakapo (Strigops habroptilus) thus dwells in natural or hollowed
excavations. It is only found in a restricted portion of the island
and leads a miserable life there, habitually staying in the earth
and pursued by numerous enemies, especially half-wild dogs. It tries
to hold its own, but its wings and beak do not suffice to protect it,
and the race would have completely disappeared if these birds were
not able to resist, owing to the prudence with which they stay within
their dwellings. They profit by a natural retreat, or one constructed
in rocks or beneath roots of trees; they only come out when impelled
by hunger, and return as soon as they can in case of danger.
A large number of animals also hollow out shelters for their eggs,
with the double object of maintaining them at a constant temperature
and of concealing them. Most reptiles act in this manner.
It is not only land animals which adopt this custom of living in the
earth, and there sheltering their offspring. Fish also make retreats
on the bank or at the bottom. To mention only one case, the bullhead
(Cottus gobio) of English rivers, which spawns in the Seine in May,
June, and July, acts in this manner. Beneath a rock in the sand it
prepares a cavity; then seeks females and brings them to lay eggs in
its little lodging. During the four or five weeks before they come
out it watches the eggs, keeping away as far as possible every danger
which threatens them. It only leaves its position when pressed by
hunger, and as soon as the hunt is concluded, returns to the post of
duty.
Other animals when digging have a double object: they wish to shelter
themselves, and at the same time to find the water which they need
for themselves or for the development of their young.
It is well known that frogs and toads generally go in the spring to
lay their eggs in streams and ponds. A batrachian of Brazil and the
hot regions of South America, the Cystignathus ocellatus, no doubt
fearing too many dangers for the spawn if deposited in the open
water, employs the artifice of hollowing, not far from the bank, a
hole the bottom of which is filled by infiltration. It there places
its eggs, and the little ones on their birth can lead an aquatic life
while being guaranteed against its risks.
Many beings live permanently in a burrow; reptiles--snakes or
lizards--are to be placed among these. Among others, the Lacerta
stirpium arranges a narrow and deep hole, well hidden beneath a
thicket, and retires into it for the winter, when cold renders it
incapable of movement and at the mercy of its enemies. Before giving
itself up to its hibernal sleep, it is careful to close hermetically
the opening of the dwelling with a little earth and dried leaves.
When spring returns and the heat awakens the reptile, it comes out
to warm itself and to hunt, but never abandons its dwelling, always
retiring into it in case of alarm and to pass there cold days and
nights.
Darwin has observed and described how a little lacertilian, the
Conlophus subcristatus, conducts its work of mining and digging.
It establishes its burrow in a soft tufa, and directs it almost
horizontally, hollowing it out in such a way that the axis of the
hole makes a very small angle with the soil. This reptile does not
foolishly expend its strength in this troublesome labor. It only
works with one side of its body at a time, allowing the other side
to rest. For instance, the right anterior leg sets to work digging,
while the posterior leg on the same side throws out the earth. When
fatigued, the left legs come into play, allowing the others to repose.
Other animals, without building their cavern with remarkable skill,
show much sagacity in the choice of a site calculated to obtain
certain determined advantages. In Egypt there are dogs which have
become wild. Having shaken off the yoke of man, which in the East
affords them little or no support, they lead an independent life.
During the day they remain quiescent in desert spots or ruins, and at
night they prowl about like jackals, hunting living prey or feeding
on abandoned carcasses. There are hills which have in a manner become
the property of these animals. They have founded villages there, and
allow no one to approach. These hills have an orientation from north
to south, so that one slope is exposed to the sun from morning to
midday and the other from midday to evening. Now, dogs have a great
horror of heat. They fear the torrid heat of the south as much as
in our climate they like to lie warmed by gentle rays; there is no
shadow too deep for their siesta. Therefore, on these Egyptian hills
every dog hollows out a lair on both slopes. In the morning, when he
returns from his nocturnal expeditions, the animal takes refuge in
the second, and remains there until midday, sunk in refreshing sleep.
At that hour the sun begins to reach him, and to escape it he passes
over to the opposite slope; it is a curious sight to see them all,
with pendent heads and sleepy air, advance with trailing steps to
their eastern retreat, settle down in it, and continue their dream
and their digestion till evening, when they again set forth to prowl.
The trap-door spiders of the south of Europe construct burrows which
have been studied with great care and in much detail by Moggridge. He
found that there were four chief types of burrow. The whole burrow
as well as the door are lined with silk, which also forms the hinge.
The great art of the trap-door spider lies in her skilful forming
of the door, which fits tightly, although it opens widely when she
emerges, and which she frequently holds down when an intruder strives
to enter, and in the manner with which the presence of the door is
concealed, so as to harmonize with surrounding objects. Perhaps in
no case is the concealment more complete than when dead leaves are
employed to cover the door. In some cases a single withered olive
leaf is selected, and it serves to cover the entrance; in other cases
several are woven together with bits of wood or roots.
The trap-door spider (Mybale henzii, Girard), which is widely
diffused in California, forms a simple shaft-like burrow, but,
like the European trap-door spider, it is very skilful in forming
an entrance and in concealing its presence. Its habits have lately
been described by D. Cleveland of San Diego. In the adobe land
hillocks are numerous; they are about a foot in height, and some
three or four feet in diameter. These hillocks are selected by the
spiders--apparently because they afford excellent drainage, and can
not be washed away by the winter rains--and their stony summits are
often full of spiders’ nests. These subterranean dwellings are shafts
sunk vertically in the earth, except where some stony obstruction
compels the miner to deflect from a downward course. The shafts are
from five to twelve inches in depth, and from one-half to one and a
half inches in diameter, depending largely upon the age and size of
the spider.
When the spider has decided upon a location, which is always in clay,
adobe or stiff soil, he excavates the shaft by means of the sharp
horns at the end of his mandibles, which are his pick and shovel and
mining tools. The earth is held between the mandibles and carried
to the surface. When the shaft is of the required size, the spider
smoothes and glazes the wall with a fluid which is secreted by
itself. Then the whole shaft is covered with a silken paper lining,
spun from the animal’s spinnerets.
The door at the top of the shaft is made of several alternate layers
of silk and earth, and is supplied with an elastic and ingenious
hinge, and fits closely in a groove around the rim of the tube. This
door simulates the surface on which it lies, and is distinguishable
from it only by a careful scrutiny. The clever spider even glues
earth and bits of small plants on the upper side of his trap-door,
thus making it closely resemble the surrounding surface.
The spider generally stations itself at the bottom of the tube. When,
by tapping on the door, or by other means, a gentle vibration is
caused, the spider runs to the top of his nest, raises the lid, looks
out and reconnoitres. If a small creature is seen, it is seized and
devoured. If the invader is more formidable, the door is quickly
closed, seized and held down by the spider, so that much force is
required to lever it open. Then, with the intruder looking down upon
him, the spider drops to the bottom of his shaft.
It has been found by many experiments that when the door of his nest
is removed, the spider can renew it five times--never more than that.
Within these limitations, the door torn off in the evening was found
replaced by a new one in the morning. Each successive renewal showed,
however, a greater proportion of earth, and a smaller proportion of
silk, until finally the fifth door had barely enough silk to hold the
earth together. The sixth attempt, if made, was a failure, because
the spinnerets had exhausted their supply of the web fluid. When the
poor persecuted spider finds his domicile thus open and defenceless,
he is compelled to leave it, and wait until his stock of web fluid is
renewed.
Skilful diggers prepare burrows with several entrances; some even
arrange several rooms, each for a special object. The otter seeks
its food in the water, and actively hunts fish in ponds and rivers.
But when fishing is over, it likes to keep dry and at the same time
sheltered from terrestrial enemies. Its dwelling must also present an
easy opening into the water. In order to fulfil all the conditions,
its house consists first of a large room hollowed in the bank at a
level sufficiently high to be beyond reach of floods. From the bottom
of this keep a passage starts which sinks and opens about fifty
centimetres beneath the surface of the water. It is through here
that the otter noiselessly glides to find himself in the midst of
his hunting domain without having been seen or been obliged to make
a noisy plunge which would put the game to flight. If this were all,
the hermetically closed dwelling would soon become uninhabitable,
as there would be no provision for renewing the air, so the otter
proceeds to form a second passage from the ceiling of the room to the
ground, thus forming a ventilation tube. In order that this may not
prove a cause of danger, it is always made to open up in the midst of
brushwood or in a tuft of rushes and reeds.
Marmots also are not afraid of the work which will assure them a warm
and safe refuge in the regions they inhabit, where the climate is
rough. In summer they ascend the Alps to a height of 2,500 to 3,000
metres and rapidly hollow a burrow like that for winter time, which I
am about to describe, but smaller and less comfortable. They retire
into it during bad weather or to pass the night. When the snow chases
them away and causes them to descend to a lower zone, they think
about constructing a genuine house in which to shut themselves during
the winter and to sleep. Twelve or fifteen of these little animals
unite their efforts to make first a horizontal passage, which may
reach the length of three or four metres. They enlarge the extremity
of it into a vaulted and circular room more than two metres in
diameter. They make there a good pile of very dry hay on which they
all install themselves, after having carefully protected themselves
against the external cold by closing up the passage with stones and
calking the interstices with grass and moss.
In solitary woods or roads the badger (Meles), who does not like
noise, prepares for himself a peaceful retreat, clean and well
ventilated, composed of a vast chamber situated about a metre and
a half beneath the surface. He spares no pains over it, and makes
it communicate with the external world by seven or eight very long
passages, so that the points where they open are about thirty paces
distant from one another. In this way, if an enemy discovers one of
them and introduces himself into the badger’s home, the badger can
still take flight through one of the other passages. In ordinary
times they serve for the aeration of the central room. The animal
attaches considerable importance to this. He is also very clean in
his habits, and every day may be seen coming out for little walks,
having an object of an opposite nature to the search for food. This
praiseworthy habit is, as we shall see, exploited by the fox in an
unworthy manner.
The fox has many misdeeds on his conscience, but his conduct toward
the badger is peculiarly indelicate. The fox is a skilful digger,
and when he can not avoid it, he can hollow out a house with several
rooms. The dwelling has numerous openings, both as a measure of
prudence and of hygiene, for this arrangement enables the air to be
renewed. He prepares several chambers side by side, one of which he
uses for observation and to take his siesta in; a second as a sort
of larder in which he piles up what he can not devour at once; a
third in which the female brings forth and rears her young. But he
does not hesitate to avoid this labor when possible. If he finds a
rabbit warren he tries first to eat the inhabitants, and then, his
mind cleared from this anxiety, arranges their domicile to his own
taste, and comfortably installs himself in it. In South America,
again, the Argentine fox frequently takes up permanent residence
in a vizcachera, ejecting the rightful owners; he is so quiet and
unassuming in his manners that the vizcachas become indifferent to
his presence, but in spring the female fox will seize on the young
vizcachas to feed her own young, and if she has eight or nine, the
young of the whole village of vizcachas may be exterminated.
The badger’s dwelling appears to the fox particularly enviable.
In order to dislodge the proprietor he adopts the following plan:
Knowing that the latter can tolerate no ordure near his home, he
chooses as a place of retirement one of the passages which lead to
the chamber of the peaceful recluse. He insists repeatedly, until at
last the badger, insulted by this grossness, and suffocated by the
odor, decides to move elsewhere and hollow a fresh palace. The fox is
only waiting for this, and installs himself.
The vizcacha (Lagostomus trichodactylus) is a large rodent inhabiting
a vast extent of country in the pampas of La Plata, Patagonia, etc.
Unlike most other burrowing species, the vizcacha prefers to work
on open level spots. On the great grassy plains it is even able to
make its own conditions, like the beaver, and is in this respect,
and in its highly developed social instinct, among the two or three
mammals which approach man, although only a rodent, and even in this
order, according to Waterhouse, coming very low down by reason of its
marsupial affinities.
The vizcacha lives in small communities of from twenty to thirty
members, in a village of deep-chambered burrows, some twelve or
fifteen in number, with large pit-like entrances closely grouped
together, and as the vizcachera, as this village is called, endures
for an indefinitely long period, the earth which is constantly
brought up forms an irregular mound thirty or forty feet in diameter,
and from fifteen to thirty inches above the level of the road; this
mound serves to protect the dwelling from floods on low ground. A
clearing is made all round the abode and all rubbish thrown on the
mound; the vizcachas thus have a smooth turf on which to disport
themselves, and are freed from the danger of lurking enemies.
The entire village occupies an area of one hundred to two hundred
square feet of ground. The burrows vary greatly in extent; usually in
a vizcachera there are several that, at a distance of from four to
six feet from the entrance, open into large circular chambers. From
these chambers other burrows diverge in all directions, some running
horizontally, others obliquely downward to a maximum depth of six
feet from the surface; some of these galleries communicate with those
of other burrows.
On viewing a vizcachera closely, the first thing that strikes the
observer is the enormous size of the entrances to the central
burrows in the mound; there are usually several smaller outside
burrows. The entrance to some of the principal burrows is sometimes
four to six feet across the mouth, and sometimes it is deep enough
for a tall man to stand in up to the waist.
Certain rodents have carried hollow dwellings to great perfection.
Among these the hamster of Germany (Cricteus frumentarius) is
not the least ingenious. To his dwelling-room he adds three or
four storehouses for amassed provisions. The burrow possesses
two openings: one, which the animal prefers to use, which sinks
vertically into the soil; the other, the passage of exit, with a
gentle and very winding slope. The bottom of the central room is
carpeted with moss and straw, which make it a warm and pleasant home.
A third tunnel starts from this sleeping chamber, soon forking and
leading to the wheat barns. Thus during the winter the hamster has
no pressing need to go out except on fine days for a little fresh
air. He has everything within his reach, and can remain shut up with
nothing to fear from the severity of the season.
It is not only the soil which may serve for retreat; wood serves as
an asylum for numerous animals, who bore it, and find in it both food
and shelter. In this class must be placed a large number of worms,
insects, and crustaceans. One of these last, the Chelura terebrans,
a little amphipod, constitutes a great danger for the works of man.
It attacks piles sunken to support structures, and undermines them to
such a degree that they eventually fall.