The Dancing Mouse by Robert M. Yerkes

R >> Robert M. Yerkes >> The Dancing Mouse

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21

[Footnote 1: A cereal food.]

Success in keeping and breeding dancing mice depends upon three things:
cleanliness, warmth, and food supply. The temperature should be fairly
constant, between 60 deg. and 70 deg. Fahr. They cannot stand exposure to cold or
lack of food. If one obtains good healthy, fertile individuals, keeps them
in perfectly clean cages with soft nesting materials, maintains a
temperature of not far above or below 65 deg., and regularly supplies them
with pure water and food which they like, there is not likely to be
trouble either in keeping or breeding these delicate little creatures.
Several persons who have reported to me difficulty in rearing the young or
in keeping the adults for long periods have been unable to maintain a
sufficiently high or constant temperature, or have given them food which
caused intestinal trouble.

The males are likely to fight if kept together, and they may even kill one
another. A male may be kept with one or more females, or several females
may be kept together, for the females rarely, in my experience, fight, and
the males seldom harm the females. Unless the male is removed from the
cage in which the female is kept before the young are born, he is likely
to kill the newborn animals. When a female is seen to be building a nest
in preparation for a litter, it is best to place her in a cage by herself
so that she may not be disturbed.

The sex of individuals may be determined easily in most cases, at the age
of 10 to 12 days, by the appearance of teats in the case of females.

The period of gestation is from 18 to 21 days. The maximum number born by
my dancers in any single litter was 9, the minimum number 3. In 25 litters
of which I have accurate records, 135 individuals were born, an average of
5.4. The average number of males per litter was precisely the same, 2.7,
as the number of females.

On the birth of a litter it is well to see that the female has made a nest
from which the young are not likely to escape, for at times, if the nest
is carelessly made, they get out of it or under some of the pieces of
paper which are used in its construction, and perish. Several times I have
observed nests so poorly built that almost all of the young perished
because they got too far away to find their way back to the mother. It is
surprising that the female should not take more pains to keep her young
safe by picking them up in her mouth, as does the common mouse, and
carrying them to a place where they can obtain warmth and nourishment.
This I have never seen a dancing mouse do. For the first day or two after
the birth of a litter the female usually remains in the nest box almost
constantly and eats little. About the second day she begins to eat
ravenously, and for the next three or four weeks she consumes at least
twice as much food as ordinarily. Alexander and Kreidl (3 p. 567) state
that the female does not dance during the first two weeks after the birth
of a litter, but my experience contradicts their statement. There is a
decreased amount of activity during this period, and usually the whirling
movement appears but rarely; but in some cases I have seen vigorous and
long-continued dancing within a few hours after the birth of a litter.
There is a wide range of variability in this matter, and the only safe
statement, in the light of my observations, is that the mother dances less
than usual for a few days after a litter is born to her.

The development of the young, as I have observed it in the cases of twenty
litters, for ten of which (Table I) systematic daily records were kept,
may be sketched as follows. At birth the mice have a rosy pink skin which
is devoid of hair and perfectly smooth; they are blind, deaf, and
irresponsive to stimulation of the vibrissae on the nose. During the first
week of post-natal life the members of a litter remain closely huddled
together in the nest, and no dance movements are exhibited. The mother
stays with them most of the time. On the fourth or fifth day colorless
hairs are visible, and by the end of the week the body is covered with a
coat which rapidly assumes the characteristic black and white markings of
the race. For the first few days the hind legs are too weak to support the
body weight, and whatever movements appear are the result of the use of
the fore legs. As soon as the young mice are able to stand, circling
movements are exhibited, and by the end of the second week they are
pronounced. Somewhere about the tenth day the appearance of the teats in
the case of the females serves to distinguish the sexes plainly. Between
the tenth and fifteenth days excitability, as indicated by restless jerky
movements in the presence of a disturbing condition, increases markedly;
the auditory meatus opens, and, in the case of some individuals, there are
signs of hearing. On or after the fifteenth day the eyes open and the
efforts to escape from the nest box rapidly become more vigorous. About
this time the mother resumes her dancing with customary vigor, and the
young, when they have opportunity, begin to eat of the food which is given
to her. They now dance essentially as do the adults. From the end of the
third week growth continues without noteworthy external changes until
sexual maturity is attained, between the fourth and the sixth week. For
several weeks after they are sexually mature the mice continue to increase
in size.

TABLE I

DEVELOPMENT OF THE YOUNG

NUMBER JERKY REACT
IN HAIR TEATS MOVE- EARS TO EYES
PARENTS LITTER VISIBLE VISIBLE MENTS OPEN SOUND OPEN
M F APPEAR

152+151 5 0 4th day -- 13th day 14th day 14th day 16th day
152+151 1 3 4th day 9th day 10th day 12th day 13th day 15th day
410+415 4 1 5th day 11th day 14th day 15th day 15th day 17th day
410+415 2 4 5th day 10th day 13th day 14th day 14th day 16th day
420+425 0 2 4th day 10th day 12th day 14th day 14th day 16th day
210+215 4 1 -- -- 17th day 13th day 17th day 15th day
210+215 3 3 5th day 11th day 11th day 14th day No 16th day
212+211 1 3 4th day 10th day 15th day 14th day No 15th day
220+225 2 4 4th day 10th day 16th day 14th day No 15th day
220+225 3 3 4th day 10th day 17th day 13th day No 15th day

A course of development very similar to that just described was observed
by Alexander and Kreidl (3 p. 565) in three litters of dancing mice which
contained 3, 5, and 7 individuals respectively. These authors, in
comparing the development of the dancer with that of the common mouse, say
that at birth the young in both cases are about 24 mm. in length. The
young common mouse grows much more rapidly than the dancer, and by the
ninth day its length is about 43 mm. as compared with 31 mm. in the case
of the dancer. According to Zoth (31 p. 148) the adult dancer has a body
length of from 7 to 7.5 cm., a length from tip of nose to tip of tail of
from 12 to 13 cm., and a weight of about 18 grams. The movement of the
dancer from the first tends to take the form of circles toward the middle
of the nest; that of the common mouse has no definite tendency as to
direction. When the common mouse does move in circles, it goes first in
one direction, then in the other, and not for any considerable period in
one direction as does the true dancer. Neither the young dancer nor the
common mouse is able to equilibrate itself well for the first few days
after birth, but the latter can follow a narrow path with far greater
accuracy and steadiness than the former. The uncertain and irregular
movements of the common mouse are due to muscular weakness and to
blindness, but the bizarre movements of the young dancer seem to demand
some additional facts as an explanation.

A brief account of the development of the dancer given by Zoth (31 p. 149)
adds nothing of importance to the description given by Alexander and
Kreidl. As my own observations disagree with their accounts in certain
respects, I shall now give, in the form of a diary, a description of the
important changes observed from day to day in a normal litter. The litter
which I have selected as typical of the course of development in the
dancer grew rapidly under favorable conditions. I have observed many
litters which passed through the various stages of development mentioned
in this description anywhere from a day to a week later. This was usually
due to some such obviously unfavorable condition as too little food or
slight digestive or bowel troubles. According to the nature of the
conditions of growth the eyes of the dancer open anywhere from the
fourteenth to the twentieth day. This statement may serve to indicate the
degree of variability as to the time at which a given stage of development
is reached by different litters.

On July 14, 1906, No. 151 (female) and No. 152 (male) were mated, and on
August 3 a litter of six was born to them. The course of the development
of this litter during the first three weeks was as follows:--

_First day_ The skin is pink and hairless, several vibrissae are visible
on the nose and lips, but there is no definite response when they are
touched. The mice are both blind and deaf, but they are able to squeak
vigorously. The mother was not seen to dance or eat during the day.

_Second day_. There is a very noticeable increase in size. The vibrissae
are longer, but touching them still fails to cause a reaction. No hairs
are visible on the body. The mother danced rapidly for periods of a minute
several times while the record was being made. She ate very little to-day.

_Third day_. Scales began to appear on the skin to-day. The animals are
rapidly increasing in strength; they can now crawl about the nest easily,
but they are too weak to stand, and constantly roll over upon their sides
or backs when they are placed on a smooth surface. Because of their
inability to progress it is impossible to determine with certainty whether
they have a tendency to move in circles. The mother was seen out of the
nest dancing once to-day. She now eats ravenously.

_Fourth day_. One of the six young mice was found under a corner of the
nest this morning dead, and the others were scattered about the nest box.
I gathered them together into a nest which I made out of bits of tissue
paper, and the mother immediately began to suckle them. They are very
sensitive to currents of air, but they do not respond to light or sound
and seldom to contact with the vibrissae.

_Fifth day_. When placed on a smooth surface, they tend to move in
circles, frequently rolling over. When placed on their sides or backs,
they immediately try to right themselves. They do not walk, for their legs
are still too weak to support the weight of the body; instead they drag
themselves about by the use of the fore legs. Fine colorless hairs are
visible over the entire body surface. When the vibrissae are touched, the
head is moved noticeably. The mother dances a great deal and eats about
twice as much as she did before the birth of the litter.

_Sixth day_. Certain regions of the skin, which were slightly darker than
the remainder on the fourth and fifth days, are now almost black. It is
evident that they are the regions in which the black hair is to appear.
The movement in circles is much more definite today, although most of the
individuals are still too weak to stand on their feet steadily for more
than a few seconds at a time. Most of their time, when they are first
taken from the nest, is spent in trying to maintain or regain an upright
position. The hair is now easily visible, and the skin begins to have a
white appearance as a result.

_Seventh day_. Although they are strong enough to move about the nest
readily, none of the young has attempted to leave the nest. They huddle
together in the middle of it for warmth. The epidermal scales, which have
increased in number since the third day, are dropping off rapidly. Contact
with the vibrissae or with the surface of the body, frequently calls forth
a motor reaction but neither light nor sound produces any visible change
in behavior. The black and white regions of the skin are sufficiently
definite now to enable one to distinguish the various individuals by their
markings. The mother was seen to dance repeatedly today, and she ate all
the food that was given to her.

_Eighth day_. A fold is plainly visible where later the eyelids will
separate. The black pigment in the skin has increased markedly.

_Ninth day_. The eyelids are taking form rapidly, but they I have not
separated. The body is covered with a thick coat of hair which is either
pure white or black. Standing on the four legs is still a difficult task.

_Tenth day_. To-day teats are plainly visible in the case of four of the
five individuals of the litter. Up to this time I had thought, from
structural indications, that there were three males and two females; it is
now evident that there are four females and one male. The external ear,
the pinna, is well formed, and has begun to stand out from the head, but
no opening to the inner portion of the ear is present. The eyelids appear
to be almost fully formed.

_Eleventh day_. There are no very noticeable changes in appearance except
in size, which continues to increase rapidly. They are able to regain
their normal upright position almost immediately when they happen to roll
over. The mother dances as usual.

_Twelfth day_. It appears to-day as if the eyes were about to open. The
ears are still closed, and there is no evidence of a sense of hearing.
They squeaked considerably when in the nest, but not at all when I took
them out to note their development. The mother stays outside of the nest
box much of the time now, probably to prevent the young ones from sucking
continuously.

_Thirteenth day_. One of the little mice came out of the nest box while I
was watching the litter this morning, and was able to find his way back
directly despite the lack of sight. The mice are still dependent upon the
mother for nourishment. I have not seen any of them attempt to eat the
food which is given to the mother. They are extremely neat and clean. I
watched one of them wash himself this morning. Each foot was carefully
licked with the tongue. There seems to be special care taken to keep the
toes perfectly clean.

_Fourteenth day_. An opening into the ear is visible to-day. When tested
with the Galton whistle, all five responded with quick, jerky movements of
the head and legs. They evidently hear certain tones. During the past two
days the ears have changed rapidly. In one of the females, which seems to
be a little in advance of the others in development, certain peculiarities
of behavior appeared to-day. She jumped and squeaked sharply when touched
and sprang out of my hand when I attempted to take her up. This is in
marked contrast with her behavior previously.

_Fifteenth day_. The eyes are partly opened. All of the members of the
litter came out of the nest box this morning and ran around the cage,
dancing frequently and trying to eat with the mother. Three out of the
five gave auditory reactions on first being stimulated; none of them
responded to repetitions of the stimulus. All appeared to be less
sensitive to sounds than yesterday. The quick, nervous, jerky movements
are very noticeable.

_Sixteenth day_. The eyes of all five are fully opened. They dance
vigorously and are outside the nest much of the time.

_Seventeenth day_. No reactions to sound could be detected to-day. The
sense of sight gives evidence of being well developed. The nervous jumping
movements persist.

_Eighteenth day_. The young mice continue to suck, although they eat of
the food which is given to the mother. They are now able to take care of
themselves.

_Nineteenth day_. There are no noteworthy changes except increase in size
and strength.

_Twentieth day_. No auditory reactions were obtained today, but other
forms of stimulation brought about unmistakable responses.

_Twenty-first day_. They are now about half grown and there is no other
change of special interest to be recorded. Growth continues for several
weeks. The statement made by Alexander and Kreidl to the effect that the
dancer is almost full grown by the thirty-first day of life is false. At
that age they may be sexually mature, but usually they are far from full
grown.

CHAPTER III

BEHAVIOR: DANCE MOVEMENTS

The peculiarities of behavior of the dancing mouse are responsible alike
for the widespread interest which it has aroused, and for its name. In a
little book on fancy varieties of mice, in which there is much valuable
information concerning the care of the animals, one who styles himself "An
old fancier" writes thus of the behavior of the dancer: "I believe most
people have an idea that the waltzing is a stately dance executed on the
hind feet; this is not so. The performer simply goes round and round on
all fours, as fast as possible, the head pointing inwards. The giddy
whirl, after continuing for about a dozen turns, is then reversed in
direction, and each performance usually occupies from one to two minutes.
Whether it is voluntary or not, is difficult to determine, but I am
inclined to think the mouse can refrain if it wishes to do so, because I
never see them drop any food they may be eating, and begin to waltz in the
midst of their meal. The dance, if such it can be called, generally seizes
the mouse when it first emerges from its darkened sleeping place, and this
would lead one to suppose that the light conveys an impression of shock to
the brain, through the eyes, which disturbs the diseased centers and
starts the giddy gyrations. The mice can walk or run in a fairly straight
line when they wish to do so." Some of the old fancier's statements are
true, others are mere guesses. Those who have studied the mice carefully
will doubtless agree that he has not adequately described the various
forms of behavior of which they are capable. I have quoted his description
as an illustration of the weakness which is characteristic of most popular
accounts of animal behavior. It proves that it is not sufficient to watch
and then describe. The fact is that he who adequately describes the
behavior of any animal watches again and again under natural and
experimental conditions, and by prolonged and patient observation makes
himself so familiar with his subject that it comes to possess an
individuality as distinctive as that of his human companions. To the
casual observer the individuals of a strange race are almost
indistinguishable. Similarly, the behavior of all the animals of a
particular species seems the same to all except the observer who has
devoted himself whole-heartedly to the study of the subject and who has
thus become as familiar with their life of action as most of us are with
that of our fellow-men; for him each individual has its own unmistakable
characteristics.

I shall now describe the behavior of the dancing mouse in the light of the
results of the observation of scores of individuals for months at a time,
and of a large number of experiments. From time to time I shall refer to
points in the accounts of the subject previously given by Rawitz (25 p.
236), Cyon (9 p. 214), Alexander and Kreidl (1 p. 542), Zoth (31 p. 147),
and Kishi (21 p. 479).

The most striking features of the ordinary behavior of the dancer are
restlessness and movements in circles. The true dancer seldom runs in a
straight line for more than a few centimeters, although, contrary to the
statements of Rawitz and Cyon, it is able to do so on occasion for longer
distances. Even before it is old enough to escape from the nest it begins
to move in circles and to exhibit the quick, jerky head movements which
are characteristic of the race. At the age of three weeks it is able to
dance vigorously, and is incessantly active when not washing itself,
eating, or sleeping. According to Zoth (31 p. 149) the sense of sight and
especially the sense of smell of the dancer "seem to be keenly developed;
one can seldom remain for some time near the cage without one or another
of the animals growing lively, looking out of the nest, and beginning to
sniff around in the air (_windet_). They also seem to have strongly
developed cutaneous sensitiveness, and a considerable amount of curiosity,
if one may call it such, in common with their cousin, the white mouse." I
shall reserve what I have to say concerning the sense of sight for later
chapters. As for the sense of smell and the cutaneous sensitiveness, Zoth
is undoubtedly right in inferring from the behavior of the animal that it
is sensitive to certain odors and to changes in temperature. One of the
most noticeable and characteristic activities of the dancer is its
sniffing. Frequently in the midst of its dancing it stops suddenly, raises
its head so that the nose is pointed upward, as in the case of one of the
mice of the frontispiece, and remains in that position for a second or
two, as if sniffing the air.

The restlessness, the varied and almost incessant movements, and the
peculiar excitability of the dancer have repeatedly suggested to casual
observers the question, why does it move about in that aimless, useless
fashion? To this query Rawitz has replied that the lack of certain senses
compels the animal to strive through varied movements to use to the
greatest advantage those senses which it does possess. In Rawitz's opinion
the lack of hearing and orientation is compensated for by the continuous
use of sight and smell. The mouse runs about rapidly, moves its head from
side to side, and sniffs the air, in order that it may see and smell as
much as possible. In support of this interpretation of the restlessness of
the dancer, Rawitz states that he once observed similar behavior in an
albino dog which was deaf. This suggestion is not absurd, for it seems
quite probable that the dancer has to depend for the guidance of its
movements upon sense data which are relatively unimportant in the common
mouse, and that by its varied and restless movements it does in part make
up for its deficiency in sense equipment.

The dancing, waltzing, or circus course movement, as it is variously
known, varies in form from moment to moment. Now an individual moves its
head rapidly from side to side, perhaps backing a little at the same time,
now it spins around like a top with such speed that head and tail are
almost indistinguishable, now it runs in circles of from 5 cm. to 30 cm.
in diameter. If there are any objects in the cage about or through which
it may run, they are sure to direct the expression of activity. A tunnel
or a hole in a box calls forth endless repetitions of the act of passing
through. When two individuals are in the same cage, they frequently dance
together, sometimes moving in the same direction, sometimes in opposite
directions. Often, as one spins rapidly about a vertical axis, the other
runs around the first in small circles; or again, both may run in a small
circle in the same direction, so that their bodies form a living ring,
which, because of the rapidity of their movements, appears perfectly
continuous. The three most clearly distinguishable forms of dance are (1)
movement in circles with all the feet close together under the body, (2)
movement in circles, which vary in diameter from 5 cm. to 30 cm., with the
feet spread widely, and (3) movement now to the right, now to the left, in
figure eights ([Symbol: figure eight]). For convenience of reference
these types of dance may be called _whirling, circling_, and the _figure
eight dance_. Zoth, in an excellent account of the behavior of the dancer
(31 p. 156), describes "manege movements," "solo dances," and "centre
dances." Of these the first is whirling, the second one form of circling,
and the third the dancing of two individuals together in the manner
described above.

Both the whirling and the circling occur to the right (clockwise) and to
the left (anticlockwise). As certain observers have stated that it is
chiefly to the left and others that it is as frequently to the right, I
have attempted to get definite information concerning the matter by
observing a number of individuals systematically and at stated intervals.
My study of this subject soon convinced me that a true conception of the
facts cannot be got simply by noting the direction of turning from time to
time. I therefore planned and carried out a series of experimental
observations with twenty dancers, ten of each sex. One at a time these
individuals were placed in a glass jar, 26 cm. in diameter, and the number
of circle movements executed to the right and to the left during a period
of five minutes was determined as accurately as possible. This was
repeated at six hours of the day: 9 and 11 o'clock A.M., and 2, 4, 6, and
8 o'clock P.M. In order that habituation to the conditions under which the
counts of turning were made might hot influence the results for the group,
with ten individuals the morning counts were made first, and with the
others the afternoon counts. No attempt was made in the counting to keep a
separate record of the whirling and circling, although had it been
practicable this would have been desirable, for, as soon became evident to
the observer, some individuals which whirl in only one direction, circle
in both.

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21