CHAPTER VIII_The platypus

THE NESTING-BURROW

The earliest statement concerning the burrowing habits of

_Ornithorhynchus_ that I have been able to find is contained in

Jamison’s brief sentence (1818, p. 585):--“The female is oviparous,

and lives in burrows in the ground, so that it is seldom seen either

on shore or in the water.” This would imply that the colonists were

familiar with the burrowing habits of the animal, and it seems strange

that no account of the nesting-burrow was published prior to that of

Maule in 1832.

Hill (1822, p. 623) certainly gives a garbled account, of which we

have made mention before:--“On returning, however, we were gratified

in finding that a female _Ornithorhynchus_ had been brought in alive,

having been found on its nest in a lagoon near Campbell’s River, by

Mr. Rawley, who says that he was obliged to tear the nest to pieces

before he could get the animal out, the nest being formed of reeds and

rushes, with a long tube or entrance into it, out of which the bill of

the animal only was visible.” On the following page Hill gives us a

second piece of information, obtained from his aboriginal informant,

Cookoogong:--“... the female sits a considerable time on her eggs in

a nest which is always found among the reeds on the surface of the

water.” It seems probable that Hill misunderstood both his informants.

Rawley’s description is quite incomprehensible as it stands; that of

Cookoogong has no foundation at all in fact.

In the anonymous article in the _Antologia di Firenze_, quoted in the

_Annales des Sciences Naturelles_ for 1827, we find on pp. 193-4:--

“_Ornithorhynchus_ inhabits the marshes of New Holland. It makes

among the tufts of reeds bordering the water a nest composed of down

and interlaced roots, in which it deposits two white eggs smaller

than those of ordinary fowls: it broods on them for a long time,

hatches them like a bird, and only abandons them when threatened by a

formidable enemy. It seems that during the whole time it eats neither

seed nor herb, but contents itself with mud, taken close at hand,

which serves to nourish it; at least, that is the only substance

found in its stomach.”

With the exception of the reference to the mud, this account seems to

be a mixture of that given by Rawley and Cookoogong, with a dash of

Lesson, and seasoned to taste by the anonymous author’s imagination. It

is possible, however, that the writer had access to some account which

has escaped observation, and even that he had had personal experience.

The first actual description of a platypus’ nesting-burrow is that

given by Lieutenant the Hon. Lauderdale Maule of the 39th Regiment

(P.Z.S., 1832, pp. 145-6):--

“By the care of a soldier of the 39th Regiment who was stationed at a

post on the Fish River, a mountain stream abounding with _Platypi_,

several nests of this shy and extraordinary animal were discovered.

“The _Platypus_ burrows in the banks of rivers, choosing generally a

spot where the water is deep and sluggish, and the bank precipitous

and covered with reeds or overhung by trees. Considerably beneath

the level of the stream’s surface is the main entrance to a narrow

passage which leads directly into the bank, bearing away from the

river (at a right angle to it) and gradually rising above its highest

watermark. At a distance of some few yards from the river’s edge this

passage branches into two others, which, describing each a circular

course to the right and left, unite again in the nest itself, which

is a roomy excavation, lined with leaves and moss, and situated

seldom more than twelve yards from the water, or less than two feet

beneath the surface of the earth. Several of their nests were, with

considerable labour and difficulty, discovered.”

Dr. George Bennett (1835, p. 248) published the first figure of a

burrow--a woodcut, of which the details were not very true to the facts

as we now know them. He also described the burrow, believing himself

to be the first European who had opened one. As he does not give the

precise date, one cannot speak with certainty; but it is most probable

that Maule was before him, as it is hardly likely that Bennett, had he

made such important observations during, or prior to, 1831, would have

withheld them from publication. Bennett’s description in _Gatherings

of a Naturalist_ (1860), is substantially the same as in the paper of

1835. Describing the first burrow discovered, he writes, commencing on

page 114:--

“The entrance or vestibule of the burrow was large, particularly when

compared with the width of the passage continued from it, measuring

1 foot 3 inches in depth and 1 foot 1 inch in breadth. Instead of

laying the burrow entirely open from the entrance to the termination,

which would have been a laborious undertaking, holes were opened at

certain distances in the direction of its course, according to the

method adopted by the natives. Daraga assisted us by digging with a

sharp-pointed stick; and he was able to effect his object with much

greater rapidity by it than we with our spades. The burrow became

narrower as it receded from the entrance, its diameter being about

the usual breadth of the animal. We traced it for the distance of 10

feet 4 inches; and having just delved down upon it again, so as to

perceive it still continuing its course up the bank, the beak and

head of a Water-Mole were seen protruding for an instant from the

upper part, as if it had been disturbed from its repose and had come

down to see what we were about. It only remained for an instant; for

as soon as it beheld us,--imagining, no doubt, that we could not be

making such a noise there for any benevolent purpose,--it immediately

turned up to take refuge in that part of the burrow which yet

remained unexplored. In turning round, however, it was seized by the

hind leg and dragged out. The animal appeared very much alarmed and

astonished when it was hauled out of its subterranean dwelling--that

is, if so paradoxical a creature could look surprised at anything....

“It was a great curiosity to the European residents in the vicinity,

who, though often seeing them dead, had never before had an

opportunity of observing one alive. Although they were supposed to be

burrowing animals, yet I believe this was the first burrow explored,

and the first living _Ornithorhynchus_ captured by a European....

“I found by measurement that the distance of the entrance of this

burrow from the water’s edge was 5 feet; it was on a moderately steep

bank, abounding with long wiry grass and shrubs, among which, and

concealed by them, was the opening of the subterranean dwelling. From

the judgment which I have been enabled to form from the examination

of this, as well as of several other burrows, I do not imagine

that the natives have ever seen, or that anyone could see (except

in a state of confinement), the mother in the act of suckling her

offspring; for in the tedious process of digging the old animal is

disturbed, and either endeavours to escape, or succeeds in escaping

long before the termination of the burrow is attained. I did not

observe any heaps of earth in the vicinity of the holes I examined;

nor can I form any opinion how, in the process of excavation, the

animal disposes of the loose mould. May we not suppose that the

animal carries away the earth collected during the excavation, in

order that the heap, which would otherwise be formed, may not point

out the situation of its retreat? The burrow we explored ran up the

bank in a serpentine course, approaching nearer to the surface of the

earth towards its termination, at which part the nest is situated.

“No nest had yet been made in the termination of this burrow; for

that appears to be formed about the time of bringing forth the young,

and consists merely of dried grass, weeds, etc., strewed over the

floor of this part of the habitation. The whole extent of the burrow,

from the entrance to the termination, I found by measurement to be

20 feet. The burrows of the _Ornithorhynchi_ are situated above the

usual river height, but do not appear to be out of the reach of the

extensive floods of the river which frequently take place during the

winter season.”

On p. 126 of the same work there is another reference to the burrow:--

“I had previously remarked, that the situations where burrows of

these animals were known to exist, had been selected by their

instinct where the ponds of the river contained water even during

the dry summer season, and when other parts of the river were nearly

dry, or formed at best a mere trickling rivulet. Of course, where

the water remained the river-weeds flourished, and the flowers now

produced by them probably attracted insects, which would furnish

these animals with food, in addition to the minute shell-fish which

might also be found among the plants. Can they, I asked myself,

confine themselves to their holes during the period of gestation? To

ascertain this, two burrows were dug up, about the entrance of which

tracks had been seen: one was only half completed, the animal having

very probably been killed before the habitation had been finished;

the second was empty, the owner having probably met with the same

fate. The long grass and shrubs were very luxuriant and dense at

this, the summer season of the year, rendering the exploration or

even discovery of the burrows more difficult than we had before

experienced; and the thick grass afforded shelter for venomous

reptiles, among which black and brown snakes were numerous, rendering

the process not a little dangerous.”

On pp. 130-131 another burrow is described:--

“I left Yas on the 23rd of December, and arrived at Lansdown Park,

Goulburn Plains, on the 24th. On the 28th of this month, with a

small party of aborigines, we visited a very beautiful part of the

Wollondilly River, which passes near this estate, and which has the

native name of Koroa. It was a noble sheet of water, extending to

some distance, and abounding in wild ducks of various species. We

then proceeded to explore the burrow of an _Ornithorhynchus_ which

had been discovered. The aborigines used their hard-pointed sticks,

called _kiar_ by them (the same name is applied to our spade in

their language); and although the ground was firm, they succeeded as

quickly as we could have done with our spades. The method of laying

open the burrow was by holes dug at about 4 or 5 feet apart, a stick

being passed up to ascertain the direction of the excavation.

“As we proceeded in exploring, there were abundant good omens to

encourage us; for, besides fresh tracks of the feet of the animal,

pieces of grass, weeds, etc. (such as they strew at the bottom of

the termination of the burrow to form a warm nest for their young),

were seen. On every indication of the presence of the inmate, the

older blacks quietly passed either the earth from the under surface

of the burrow bearing recent impressions of its feet or tail, or the

pieces of grass, reeds, etc., to one another, for the opinion of

each, and if in favour of the presence of the occupant, the digging

up of the burrow was continued, the indications so well known to them

giving fresh hopes and renewed vigour to the diggers. The extent to

which this burrow was continued up the bank in a serpentine form

was very great; and after a most laborious task in exploring it,

in consequence of the hardness of the ground, the termination was

attained at a distance of 35 feet from the entrance. Extensive as

this may appear, burrows have been found of even 50 feet in length.

“On arriving at the extremity of this very large burrow, a growling

was distinctly heard: this I at first thought proceeded from the old

one, which I now believed I should have an opportunity of viewing

with her young; but, on reconsideration, thinking it more probable

that the old one had forsaken them (as I noticed during the course

of laying open the burrow that we had not seen her come down, in

the usual manner, to ascertain why we destroyed her habitation), I

could not account for it, more especially when, on the termination

of the burrow being laid a little more open, the fur of the animal

or animals was seen. What then surprised me was, that although there

was abundance of growling, there was no movement of the animals to

escape. On being taken out, they were found to be full-furred young

ones, coiled up asleep, and they growled exceedingly at being exposed

to the light of day. There were two of them, a male and a female,

of the dimensions of 10 inches from the extremity of the beak to

that of the tail. They had a most beautiful, sleek and delicate

appearance, and seemed never to have left the burrow. The nest, if

it may be so termed, consisted of dry river-weeds, the epidermis of

reeds, and small dry fibrous roots, strewed over the floor of the

cavity, which was of sufficient size to contain the mother and her

young.”

The only further reference to the burrow which need concern us here

occurs on p. 146:--

“I have no doubt the Water-Moles make their burrows high in the

banks--at such a height as to be out of the reach of the floods

which occasionally prevail: if they did not adopt some plan of the

kind, they would be destroyed, or drowned in their burrows by the

floods; for although very amphibious in their habits, they require to

repose on the dry land, and also to respire atmospheric air at short

intervals of time.”

George Bennett maintained his interest to the very end of his long

life. But the pioneer discoverer rarely wins through to complete and

adequate knowledge of his discovery; and Bennett, owing to the fact

that he adopted the aboriginal method of opening up the burrows, and

did not follow them along their full length, missed several important

features in the structure of the burrow.

The next description of the burrow is that of Verreaux (1848, pp.

128-9), who observed the platypus in Tasmania. His account is passably

accurate. He makes no specific claim to have opened up burrows himself,

but mentions (p. 131) that a Dr. Casy found two nests, one with one

young one, the other with two; so it may be that his description is

founded on Casy’s observation rather than on his own. However that may

be, the translation of the account is as follows:--

“The _Ornithorhynchus_ dwells by preference in marshy places, but

is nevertheless not so wholly aquatic as one might suppose from its

structure. It digs deep burrows, that is to say, of considerable

extent, which are at most fifteen to eighteen inches below the

surface of the ground. These burrows have two or three outlets, and

are usually divided into twelve or fifteen branches; usually one

of these outlets is placed beneath, or at the level of, the water,

to facilitate retreat in case of danger. Although these burrows,

which are dug in clayey banks, have a great number of passages,

they ordinarily include but a single nest, placed right at the end

farthest from the water, and in an enlarged space; this space seems

able to hold three or four of the animals. The nest is composed of

débris of reeds and other aquatic plants, and forms a bed thick

enough to protect the _Ornithorhynchus_ from the damp produced by the

constantly percolating water.... It is ... an excellent digger; and I

have watched one, in very gravelly and very hard ground, successfully

dig a hole more than two feet deep in less than ten minutes. For

the purpose of this operation, the webs of the fore-feet, which are

so highly developed for swimming, undergo a curious transformation,

disappear, and leave visible only the powerful claws, which are

equally useful for climbing when it is a question of surmounting an

obstacle. In the attitude which it assumes when burrowing, one might

take this animal for a mole rather than a swimmer. I have witnessed

the quickness with which they can dig in the muddy places which they

prefer. The beak is first used to dig the earth, then the claws are

brought into play.

“One observation worthy of note, which shows a resemblance between

_Ornithorhynchus_ and the beaver, is that, as it digs, it uses its

tail to beat and consolidate the earth. During this work the animal,

twisted in the shape of an auger, turns upon itself. The tail, moved

by powerful muscles, follows the movement. I have observed this fact

with several live individuals, which I placed in a box filled with

moist earth, and have been able to study at all times.”

The account of _Ornithorhynchus_ in Gould’s beautiful folio _Mammals

of Australia_ (1863) is based very largely upon the observations of

Bennett and Verreaux, supplemented by those of the author himself.

He writes, on p. 1, of the burrow as--“a retreat to which it resorts

during the day or on the approach of danger.” No distinction is made

between resting- and nesting-burrows; nor does Gould add anything from

personal observation to the sum of knowledge of the burrowing habits.

The first precise description, with measurements, of nesting-burrows

is that of Mr. G. F. Bennett (1877, pp. 161-166), son of Dr. George

Bennett, who examined three burrows on Lockyer Creek, a tributary of

the Bremer River, near Helidon in southern Queensland. The first one

opened was twenty feet in total length, with cross-section four inches

by three. The entrance is shown as just under water; five feet from

it a chamber measuring twelve by eight by six inches opened off the

burrow on the right side. Five feet farther on, and also on the right

side, a second chamber occurred; ten feet beyond that, the nest. The

nesting-chamber measured eighteen inches by ten, with a height of eight

inches; in the nest, which was composed of dried grass, reeds, and

gum-leaves--all, from their blackened appearance, evidently collected

under water--were two young ones, estimated to be a month old. This

nest was opened on 27 October, 1876.

Almost a month later a second burrow was found, eleven feet in length,

with two offset chambers, one on each side, and with a nesting-chamber

excavated but containing no nest. A third contained three offset

chambers, and two young in a nest, which was four feet underground--a

very unusual depth--and twenty-two feet above the level of the entrance.

Caldwell has nothing to say about the burrows. His only reference

(1887, p. 466) is as follows:--

“In September my friend Bloxsome superintended the transfer of the

camp to the colder river Mole, further south, where we hoped to

dig out the later stages of _Ornithorhynchus_ from their nests. I

employed some white navvies, who opened up a large number of burrows,

but the renewed exposure in Queensland had brought on my fever

again, and this seriously interfered with the completion of the

_Ornithorhynchus_ series.

“The later stages of Monotreme development have, therefore, to be

worked out, mainly with _Echidna_ material.”

The last sentence might imply that some later platypus material was

obtained; but, if this were the case, it is remarkable that Caldwell

has made no mention of it. His remarks are so non-committal as to

justify a suspicion that he got neither eggs nor young from the burrow.

Semon (1899, p. 42) describes the burrows thus:--

“These burrows have one entrance above and one below the water,

uniting in a tube of 20 to 50 feet, which leads slantingly upwards

from the river-surface and ends in a little cave. I have never found

burrows with a greater number of tubes labyrinthically entwined, and

believe that their existence may be regarded as exceptional.”

Semon here repeats the popular belief that there are two entrances,

one below, and one above the level of the water. This does happen

occasionally, and the reason will be explained later; but it is the

exception rather than the rule.

Lucas and Le Souef (1909, p. 145) allow the burrow one paragraph:--

“The home of the Platypus is a long narrow tunnel-like burrow, which

begins with an entrance under the surface of the water, and then

runs obliquely upwards in the bank for a distance of 20-50 feet. It

eventually terminates in a rounded chamber or living apartment, lined

with grass and leaves, and situated not very far below the surface

of the ground. Very often the main burrow gives off at intervals

lateral branches also terminating in chambers. Sometimes the burrow

is provided with an additional opening above the level of the water,

though this is certainly not always present.”

Despite its brevity, this paragraph contains some minor errors.

The burrow does not begin with an entrance below water-level; the

nesting-burrow is not a ‘home;’ and the lateral chambers (pug-pits) are

excavated in the side walls of the main tunnel, and are not connected

with it by branches.

[Illustration: A NEWLY-OPENED NESTING-CAVITY.

1. Asleep; 2. Awake; 3. Away.

_Plate 17_]

To Kershaw (1912, pp. 102-105) must be given the credit of the first

adequate account of the nesting-burrow, several examples of which he

carefully examined in the banks of the Hopkins River near Mortlake in

Victoria. He writes:--

“The river, at the spot visited, is a fairly broad, quiet stream,

winding about through an extensive grassy flat, margined and shaded

with large old red-gum trees. The banks in places are steep; in

others they slope rapidly to the water’s edge. At the time of my

visit the river was low, but when in flood it rises fully ten or

twelve feet.

“After a careful search along the banks several burrows were located,

places where the soil is easily worked being usually selected. The

entrances to the burrows, when once seen, may always be easily

recognised. In every instance these were situated some feet above the

level of the water, varying from four to fully twelve feet above the

present level. In no case did the burrows open out below the water,

though during heavy floods several of those seen would certainly be

covered. In nearly every instance there was an opening to the surface

higher up the bank, and in one case a double opening was found in

the same burrow--one immediately beyond the other--the narrow ridge

of earth separating the two holes being worn smooth, as though the

animal, when passing up, came out of one and immediately entered the

other. These surface-holes are probably for use during flood times,

when the entrance is under water.

“Along the steep, muddy bank, close to the water’s edge, the tracks

made by the animals when passing to and from the water through the

grass tussocks were easily recognised, being worn flat and smooth

by the animal’s wet bodies. Claw marks could also be seen here and

there. Such places where the projecting roots of the gum-trees run

into the water are, apparently, most favoured for landing.

“The entrances to the burrows varied from four to five inches wide

and three inches high. They are always arched above and quite flat

below, following the shape of the animal’s body. This form is

followed throughout the whole length of the burrow, though the latter

may be enlarged here and there. The entrance is occasionally blocked

up with earth.[13]

“The burrows do not follow a direct line, but wind about, at times

very considerably. They always follow up the slope of the bank,

parallel to and rarely more than a foot below the surface. In no

instance was one found deeper than fifteen inches, while here and

there they approach within a few inches of the surface. A short

branch, from one to three feet long, is frequently made on either

side of the main burrow; in one instance four were seen--two on

either side. These end abruptly, without any apparent cause. Although

in the same class of soil, the length of the burrows varies, the

shortest examined being ten feet, and the longest, carefully

measured, thirty-five feet. While usually terminating in the

nest-chamber, the burrow is occasionally continued beyond the nest

for a foot or two.

“A peculiarity which, I believe, has not been noted before is that

when the burrow is occupied it is completely blocked with earth for

about a foot. This occurred in three places in one burrow, and is

apt to lead one to conclude that the end has been reached. From this

it is also assumed that the female does not leave the nest for some

time after the eggs are laid or the helpless young are hatched, and

during the time the latter are attached to the mother. The object

in so securely blocking the burrow is, probably, for protection

against flood water in the event of a sudden rise of the river, or

from possible enemies. Unless the block is removed from time to

time, however, it is difficult to conceive how the animal obtains

sufficient air during her lengthened seclusion.

“The nest-chamber is rounded in form, the bottom always being much

lower than the floor of the burrow, which enters about its centre.

All those examined were of about the same dimensions, the two

carefully measured being each twelve inches deep, thirteen inches

wide, and eleven inches from the entrance.

“The nest itself is composed of fine grass and gum-leaves, and

completely fills the cavity. The bottom of the chamber is first

covered with a thin layer of grass, followed by a thick layer of

gum-leaves about four inches deep, which is continued up the sides,

and--at least in one case--completely encircles the cavity, forming

a compact circular nest, with the entrance in the side opposite

the tunnel. It was noticeable that many of the leaves were green,

and appeared to be quite fresh. The bottom of the chamber in every

instance was wet, owing to surface soakage, and it is apparently

with the object of avoiding this that the bottom of the chamber is

excavated below the level of the burrow and so thickly lined with

leaves.

“The first burrow examined had been opened up by Mr. Hood on the

17th October (nine days prior to my visit), and from the nest two

fresh eggs were taken. These, when found, were attached to one

another, and had been kept in a small box; but in two or three days

they collapsed. When I received them on the 26th October they were

flattened and dry. Several other burrows close by, though having the

appearance of recent occupation, were untenanted, but each contained

a nest, more or less complete. From one of these the shrivelled

remains of two eggs were obtained.

“Later in the day a burrow was discovered which had every appearance

of being occupied. It was situated on the sloping side of the bank,

fully twenty-five feet from the water, and was the only one I saw

with recently scratched earth at the entrance. The burrow followed

up the slope of the bank for about twenty-five feet, terminating

in a nest-chamber, some ten or twelve feet above the level of the

river. This one was blocked up in three separate places, the last

within three feet of the nest. When about a foot from the nest a

peculiar grating growl was heard, and the next shovelful of earth

exposed the side of the very compact structure, through which the

old one hurriedly forced her way. She was permitted to traverse

the excavation for a couple of feet to a depression, where she was

covered with clods of earth, while a careful examination of the nest

was made. This proved to be the most complete of all those examined,

the whole cavity being completely filled with leaves. No opening

into the interior of the nest could be seen, the entrance being

evidently closed by the animal during occupation. As was the case

in all those examined, it was composed of gum-leaves, with a small

layer of grass at the bottom of the chamber. The lower portion was

tightly compressed from the weight of the animal, while those forming

the sides and top were loosely interwoven. The interior measured six

inches across and four and a half inches deep. The shrunken remains

of one egg were found in the nest.”

With the exception of the blocking of entrances, and two or three

other minor matters, I can confirm Kershaw’s statements after a long

term of practical experience in the field. What this has involved in

labour alone may best be judged from the remarks of Professors Wilson

and Hill (1908), who, like myself, spent a number of years getting

together material for embryological study. They write:--

“The records of Australian biology bear sufficient witness to the

fact that it is extremely difficult, even for residents in Australia,

to procure the material necessary for an investigation into the

development of the eggs of _Ornithorhynchus_. It is only through the

organisation of special expeditions, with ample resources both of

time and money, that any large measure of success in this direction

can be hoped for.

“The animal itself, though pretty widely distributed, and probably

still far from becoming extinct, is to be found, in any one locality,

only in comparatively small numbers. It is now much less plentiful

than formerly, owing to the demand for its fur--a demand which is

still satisfied in spite of the measure of legal protection which

the animal has obtained in the various Australian states. The

depredations of the fur-hunter are not easily repaired, since the

animal breeds only once in the year and produces but two eggs at a

time.

“The eggs, when laid, are deposited in a burrow which it is far from

easy to locate, and whose opening up involves a considerable amount

of labour, since, apart from its great length, the river-bank in

which it is situated is commonly enough permeated by tree-roots. And

when at length the actual dwelling chamber or nest is successfully

opened up, no reward at all may be forthcoming, or the material which

is obtained may be unsuitable for the immediate purpose in view....

[Illustration: (1) NEST COMPOSED OF GUM-LEAVES AND GRASS STEMS.

The earth has been removed, leaving cavity and nest undisturbed.

_Plate 18_]

“We have only to a very limited extent been able to superintend

personally the work of collection, and have found it necessary

to rely largely upon the efforts of the scientifically untrained

collector in the accumulation of the material for our investigations.

Unfortunately, the material result of the work of such a collector

during an entire season is so meagre that he requires considerable

inducement to carry on the work at all; whilst the product to

the investigator may be practically nil. The genuineness of the

difficulty in procuring this kind of material is sufficiently

indicated by the fact that whilst Semon, in his expedition, was

successful in obtaining a very considerable number of eggs and

foetal specimens of Echidna, his collection of _Ornithorhynchus_ and

embryos would appear to have been limited to a small number of early

intra-uterine eggs.

“Our own collection is very far indeed from being complete, though

the work of collection has been going on for quite a number of years.”

[Illustration: (2) BROODING FEMALE PLATYPUS, SHOWING SEPARATION OF FUR

AND SLIGHT INDENTATION OF ABDOMEN IN LIEU OF POUCH.

_Plate 18_]

Semon (1894, p. 13) tells a similar story:--

“Concerning the development of the eggs after being laid and

concerning the young after hatching I can unfortunately make no

statements. I had not the good fortune even to find eggs or young

in the numerous burrows which I and my white companions opened. My

blacks showed the greatest dislike for this work, and were averse

to troubling about _Ornithorhynchus_ at all: we ourselves were too

absorbed with the several other works in hand ... to be able to

give our whole time and zeal to the wearisome and for the most part

disappointing work of digging out _Ornithorhynchus_ nests.”

The two great expeditions of Caldwell and Semon failed to secure eggs

and young of the platypus from the nest. Wilson and Hill, after many

years of endeavour, obtained only a very limited number, most of which

have not yet been described. Since the eggs and young, which cannot

escape from the nest, are so difficult to get, it may well be imagined

that the doings of the elusive female, hidden in the darkness of her

burrow, are infinitely more difficult to observe.

The interest attaching to precise observations of the actual burrowing

method is great, the chief point being to determine the relative extent

to which the highly sensitive muzzle and the powerful claws of the

fore-paws are used in the process. I therefore experimented with a

single female platypus which I had in captivity at my home.

The creature was placed in a specially contrived enclosure, of which

the essential features were a plate-glass front and a wooden back,

four inches apart at the bottom, widening to six inches at the top.

This enclosure was filled with sifted soil, which was put in a

bucketful at a time, each bucket of soil being followed by a bucket

of water, until the frame was full, when the whole was tamped and

thoroughly flooded with water. The object of the taper was to cause

the soil to wedge, and so prevent it from collapsing on the burrowing

animal. Water was used to consolidate the soil to something like the

consistency of the banks in which the platypus burrows naturally in the

wild state.

The enclosure thus prepared was allowed to stand for twenty-four hours,

and the animal was then introduced at one side, where a portion of the

earth was removed to make room for it, at 2 p.m. No attempt was made to

burrow until about 5.30 p.m.; but I am not certain whether this time

bears any relation to what normally happens. The observations which

follow were made during a period of about an hour, by means of the

plate-glass front, and during this time I kept myself concealed as far

as possible from the animal.

The platypus, in order to obtain the greatest purchase before beginning

to burrow, tucked the tapering end of its pliable tail between its

hind legs and simultaneously hooked its out-turned hind-claws into the

earth at each side. While in this crouching attitude, with stiffened

top lip and splayed fore-claws it proceeded smartly to break away

the earth. After burrowing for several inches it rested awhile;

then it energetically contorted its neck and body so as to tamp the

freshly-loosened earth tightly into the hollow surrounding it.

While stationary, the creature occasionally beat the walls with its

trowel-like tail; but whether this action was deliberately intended

as part of the tamping process, or was due to muscular reaction as

the result of the strenuous exertion, or both, I do not profess to

know. Nevertheless, it certainly did not distort or tend to break

away the true design of the burrow by its spasmodic action. In fact,

the structure and shape of the tail suggest that it is designed as an

actual modelling-tool.

After a few minutes’ rest, during which the breathing was laboured

and was accompanied by an apparently involuntary gulping, the animal

again deliberately shovelled the earth over its head with the end of

its snout. In this way it created a crude cavity in which to loll its

head to one side, while, with neck shortened, it reached to the utmost

with one web-palmed paw, and scratched a hemispherical hollow to one

side of the tunnel, contorting its shoulders the while. The energetic

digger then placed its head in the recess so made, and, without any

hesitation, performed a similar operation on the opposite side with the

other splayed paw. Then, to dislodge the partition separating the two

recesses, it probed its muzzle vigorously into it, and then proceeded

as far as the out-stretched neck permitted, to form another “loll-hole”

to one side with its muzzle, in readiness for its head in burrowing a

further section. Meanwhile, the well-worked earth trickled round the

wriggling creature’s body, principally about the powerful shoulders,

whence a portion eventually filtered down as far as the hips.

While the fore-paws and rooting muzzle were working at high tension,

the hind legs were alternately keeping the specialized fore-parts

well up to their work by clinging tenaciously to the solid earth. In

their struggle to do this, the hind-claws actually aided the process

of excavation by cutting the lateral angles which complete the arched

design of the burrow.

A remarkable feature of the burrow is that no soil is ejected, but

the whole of it is reduced to a consistency suitable for packing into

the sides of the burrow, and even the soil dislodged when commencing

a burrow is consolidated into the river-bank. When the platypus has

burrowed about six inches, it packs the loose soil by contorting its

body and pressing against the sides, at the same time beating the floor

with its tail. The width of the excavation is about double that of the

finished burrow, that is to say, the earth excavated is tamped into

about half its original bulk. The whole of the earth taken from each

section is not always beaten in before a new section is commenced; but

the animal appears to work very systematically, and, according to

the consistency of the soil, it moves backward from time to time and

adds the finishing touches. In the experiment the captive repeated the

burrowing and tamping alternately, until it eventually broke through

the surface.

The powerful claws of the fore-paws do practically all the burrowing,

the only help they receive being a probing or lateral shearing movement

of the muzzle (when the earth is not too hard) and the pressure exerted

by the hind feet. Although apparently preferring to burrow in the

normal position, the platypus will readily lie on its back, or on

either side, and at times will work in a spiral fashion, either while

excavating or while tamping the tunnel, even in the absence of any

serious obstacle; but eventually it reverts to the normal position

for the purpose of finally shaping the burrow. The position in which

it works does not affect the rate of its progress in the least. When

confronted with temporary obstacles, such as impoverished or caked

earth between the roots of trees, etc., the platypus will, miner-like,

in order to avoid retracing its steps or branching off in another

direction, throw itself into the required position and follow, not the

line of least resistance, but of favourable soil.

The thickness of the pug or pugs tamped into position with the tail by

the female prior to retiring to the nest for the purpose of laying and

incubating the eggs, is about six inches, and it is packed so closely

as to be indistinguishable from the surrounding soil.

[Illustration: MODEL OF NESTING-BURROW.

Note rocky obstruction above nesting cavities. The cavity nearer to the

entrance has been abandoned.

_Plate 19_]

During the process of dragging back and packing into the sides of

the burrow the soil scratched out by the fore-paws and muzzle, the

platypus exhibits its remarkable ability to reverse the action of its

hind legs, and actually “advances” backwards. Students of anatomy

will have observed, no doubt, that the hind feet of a platypus have

a tendency to turn outwards from the flanks, and that the grooved,

curved claws continue in that trend towards the tail. This is as it

should be for the purpose of gripping and scratching back surplus soil

while tunnelling ahead. It is also as it should be when reversing.

Especially is this so when burdened with a packing of adhesive pug, and

when, incidentally, the fore-paws are practically out of action. The

muscular contortions of the body at that time certainly afford great

assistance. Nevertheless the hind quarters and cumbersome tail would

during one of its essential functions become useless, if not a burden,

to the platypus, but for the natural provision of a “two-way” action of

the hind limbs. Preparatory to pulling backwards, the trend of the hind

feet continues until the sets of claws are facing one another beneath

the tail. This contortion enables the animal to take a firm grip of

the flattened earth-floor; it then pulls the body backwards step by

step, while the fore-paws, when freed, do the shoving. The alternate

action of the fore-legs in walking forward is imitated exactly by the

hind legs in the reverse direction, and the platypus can thus, at will,

reverse the direction of its movements. It is rather amusing to witness

this act, for, at the outset, the fore-parts are usually obliterated

with earth, and the tail, which in contour and elevation somewhat

resembles the head, sometimes puts one at a loss to guess whether the

creature is really coming or going.

In addition to the uses of the hind-claws and to the reversible nature

of the entire limb, the hind foot of the platypus, especially of the

male, is just as versatile in its actions as that of a chimpanzee,

even to the power of deliberately gripping. During a backward march

it resembles, in action and general appearance, the fore-limb of a

grizzly bear, or, more nearly still, that of a long-clawed sloth.

Is it possible that this versatility is reptilian in origin? What

other mammal in the world is able thus to interchange the functions

of its hind- and fore-legs to such advantage? Such ability may be

characteristic of moles, etc., but it is certainly a remarkable

adaptation.

I have already mentioned the stiffening of the top lip, and, when one

realizes its extreme limpness when not employed in burrowing, it will

be obvious that stiffening is necessary in order that a groove may be

made in earth by lateral oscillation (“lipped-in,” so to speak). While

this groove is being formed, and until it is sufficiently deep for the

bony prong of the upper jaw to be used for shovelling the earth away,

the direction of the stiffened lip is maintained by the earth above and

below it.

Given favourable conditions, a platypus can excavate a cavity of

approximately 6 × 5 × 5 inches in five minutes. It can tamp loosened

earth completely into a six-inch section of a tunnel in fifteen

minutes. This makes twenty minutes in all to a shift. Therefore, if the

tunneller continued unceasingly in this manner, in sixteen hours it

would have completed a tunnel twenty-four feet in length. This is the

average length of a breeding-burrow.

Quite possibly the spasmodic gulping observed in the throat of a

burrowing platypus is due to involuntary exhalations of spent air,

corresponding to the periodical bubbling when the creature blows

beneath water. Under open conditions, normal breathing may be

reasonably governed at will, but this exhaust spasm appears to be

quite beyond control. This is probably so that it may collect its food

unhampered beneath water, and that it may also delve freely while

tunnelling, without having to relinquish such immediate business for

the purpose of replenishing spent air. The breathing observed while

the platypus was tunnelling was at the rate of thirty respirations

per minute, and the gulps in the throat approximately at intervals of

twenty-five seconds. The normal breathing of a sleeping platypus I have

found to be fifteen respirations per minute.

During the experiment the animal apparently kept the facial furrows,

embracing the orifices of the eyes and ears, tightly closed, as when

swimming under water.

Accounts of the bionomics of the platypus in current works on natural

history invariably assume that the nesting-burrow is the home of the

animal, in the same sense in which a rabbit-warren is the home of

the colony that it contains. As has already been stated, this is not

so, each burrow being inhabited by a single female, and that only

during the nursing period. The usual statement that the burrow has two

entrances, one under water and one above, is also erroneous. It is true

that such a condition often exists; but this merely indicates that

a rise in the river has covered the original entrance, which is always

put in above water-level, and that a new entrance has been broken out,

or that the secondary under-water “getaway” has been formed later by a

washaway at the root of an adjacent tree.

[Illustration: Bird’s-eye view of river-bank, showing platypus burrow

winding 40 feet from entrance to nesting-cavity. (Scale about ¾-inch to

1 foot.)

From model by H. Burrell.

_Plate 20_]

The female excavates her burrow unaided. She selects a suitable site,

preferably in a high sloping bank, well held together by the roots

of trees; it is all the better if a fringe of reeds adorns its edge,

so that she may come and go as safe from observation as possible.

The entrance is made above water, at a height varying from nearly

water-level to as much as twelve feet. When fresh, it has a definite

shape--low-arched above and flat below--and measures from four to six

inches in width, and from three to four inches in height, corresponding

pretty accurately to the cross-section of the occupant. On account of

this definite shape, it is easily distinguishable from the burrows

of water-rats (_Hydromys_) and rabbits found in similar localities.

But after a time this entrance may become adventitiously enlarged and

altered in shape, so that the distinction is not always completely

maintained. Bennett suggests that the entrance is usually concealed

among the vegetation of the bank; but, though this may happen where

banks are covered with a lush vegetation, my observations agree with

those of Kershaw that there is no attempt actually to ‘camouflage’ the

entrance, even though ample vegetation may be found growing close by.

The entrance is usually quite obvious, and, in any case, attention

directed to it by the runs of the animal, worn smooth and hard by the

dragging of its wet body over them. Upon these runs the impress of the

tail is usually to be seen, and the pricked tracks made by the claws of

the hind feet are unmistakable.

[Illustration: Nesting-burrow with two openings. Nest marked N.]

The burrows exhibit an infinite variety of form and length, but all

show the arched roof and flat floor adapted to the size of the female

which has constructed them. This size may therefore be gauged with

reasonable accuracy during the process of digging the creature out.

Here and there, however, there may be, in the calibre of the tunnel,

some irregularity apparently due to the adoption of an unusual position

during digging in order to deal with some particular obstruction.

The tunnel usually follows a sinuous course, but invariably keeps at

about the same distance (from 12 to 18 inches) below the surface.

This power of the platypus to judge how far it is below the surface

is as remarkable as that sense which warns it when it is approaching

another burrow, whether of its own kind, or of some other animal.

In constructing its tunnel, it sometimes circles round, so that, if

it continued on its course, it would break into an earlier section

of its own burrow. This, however, never happens. In one case it was

observed that the platypus stopped a foot from this earlier section,

and forthwith constructed its nesting-chamber. In a number of others,

it avoided breaking into its own burrow by passing under it at a

distance of a foot, coming up on the other side to the usual distance

below the ground-level (see page 127 and Plate 20). In the same way

it avoids the burrows of water-rats and rabbits by tunnelling clear

of them. I have known it go down to the very unusual depth of four

feet to avoid a rabbit-burrow. In some cases, instead of going under

an obstructing burrow, it turns aside, and continues its tunnel in a

different direction. One more example of this uncanny sense may be

quoted. Plate 19 illustrates a model of a burrow made to scale. In

this the nesting-cavity is shown at a vertical depth of about three

feet. The animal burrowed in at the usual level below the bank

where it sloped, until it came to a place where the bank suddenly rose

steeply. Here two alternatives were open to it. Either it must go

straight upwards through rocky soil for more than two feet, or it could

construct its nest where it found itself, three feet below the level of

the upper bank, but still the normal distance from the lower face. It

chose the latter alternative.

[Illustration: VARIETY IN NESTS.

1. Couch grass stems, and a few gum-leaves; 2. Willow “swishes,” willow

rootlets, and reed flags; 3. River reed roots, entirely; 4. Couch grass

stems, and gum-leaves; 5. Fuzzed reed stalks, and reed flags.

_Plate 21_]

A great amount of discrimination is necessarily displayed in selecting

a suitable soil in which to burrow. Burrows commenced in soil that

ultimately proves unsuitable because of its friable nature, are--as

often--promptly deserted. Although a preference for soft soil is

indicated, I noticed that in one burrow which I investigated the animal

had removed three inches of compacted river-gravel from the face of the

bank before reaching the ideal earth behind, which she evidently knew

was to be found by perseverance. Sandy banks, unless reinforced with

lengthy lucerne or similar roots, are left severely alone, since the

burrows tend so easily to collapse.

No general statement can be made as to the length and direction of

the nesting-burrows, since both are infinitely variable. The length

varies from five feet to upwards of sixty in one season’s burrowing;

but all the short lengths recorded are probably abnormal, and due to

exigencies brought about by flood-conditions. From fifteen to twenty

feet would appear to be a fairly adequate length, though that is under

the average, which is raised by a number of extraordinary length.

What it is that impels the animal sometimes to go on burrowing up

to the amazing distance of 100 feet, I will here explain. These

abnormalities occur only in ground that has been occupied undisturbed

by platypus for many years. Indirectly, floods are responsible for the

trouble that compels platypus to enlarge and renovate. These shy and

timid creatures naturally do not wish to make their ideal breeding-bank

more conspicuous to their enemies than is necessary; they therefore

prefer to use the same entrance (when convenient) year after year,

rather than perforate the face of the bank with tell-tale porches for

which there is no necessity. Leave well alone, is their motto. Now

suppose that a platypus puts in a burrow in any one season, and that it

is, at some later time, covered by flood waters. Being in soft soil,

it soon becomes silted up--at least, here and there. The following

year, the same or even another female enters the porch and traverses

the tunnel, as far as it is habitable, to investigate. If she approves

of it up to a certain distance, she will cut a pit in the side wall

there and then, and plug up the section which is not to her liking;

then she will tunnel anew in another direction to the average distance,

as if commencing from the original porch. This may go on year after

year, with flood after flood, until the enormous length of 100 feet is

recorded by the collector as the longest breeding-burrow discovered.

Peter Yates, my able assistant, can vouch for that fact.

The nesting-chamber is generally placed at the extreme end of the

burrow, though sometimes a blind branch is carried on beyond it. It

varies somewhat in size, but is usually more wide than high, and

measures on an average about twelve inches by eleven. In this chamber

a nest is constructed, a variety of materials being used, the nature

of which depends upon the locality. In the New England district the

commonest type of nest is composed almost entirely of eucalyptus

leaves and the rhizomes of couch grass, but I have also found willow

“swishes,” roots, branchlets, and leaves; roots and stems of the reed

_Arundo phragmites_; and the leafless branches of she-oaks (_Casuarina

spp._). These materials are arranged as a lining of the cavity, except

for the opening where the burrow enters, and are of even thickness,

except on the floor, where the lining is distinctly thicker. I have

been informed by an aboriginal that he has seen a male carrying

nesting-material by means of his spurs, but am not disposed to believe

it, although I am quite sure he could do so. All my own observations

suggest that the female alone digs the burrow and makes the nest. They

also show that the amount of nesting-material never more than half

fills the cavity until the babies begin to grow and toss the litter

about. For instance, where triplets are concerned one is apt to find

the nest-cavity crammed to the dome with such material.

In all the years during which I have been making observations I

have never once actually seen the female in the act of carrying in

nesting-material. It seems likely, therefore, that nest-building is

done at night. The materials used are those closest to hand. As the

foundation of one nest I found a willow “swish” more than five feet in

length. It would surely be awkward to drag such a thing to the end of

a long burrow. It seems likely that the animal collects a great deal

of material that is lying loose upon the ground, or even in the water.

But there is no doubt that it is also able to cut off reeds and grass

rhizomes by means of the elongate horny ridges in the anterior part

of the mouth. These ridges are also used to shred the stems of reeds,

reducing them to a mass of soft fibres (see Plate 3).

As soon as the nest is completed, and before the eggs are laid, the

most remarkable habit of all comes into evidence--that of plugging

the burrow. G. F. Bennett (1877) was the first to observe the lateral

pits from which the earth to form these plugs is drawn; but he did not

observe the plugs, and therefore missed the import of the pits. Kershaw

(1912, p. 103) saw the plugs, but did not connect them with the lateral

pits. He writes:--