Das Verhalten der Schneemaus : (Chionomys nivalis)

1. Biology of the snow vole
The snow vole (Chionomys nivalis) belongs to the family of voles (Arvicolidae). Within the
Microtus genus it constitutes its own sub-genus (Chionomys), of which it is the only representative.
The territory in which it appears is vast, ranging from the northwest of Spain to
Turkmenistan and from the Carpathian Mountains to Lebanon, but its appearance is generally
limited to small residual areas. The Alps constitute the largest area of cohesive
occurrence of the snow vole. As one of eight indigenous species of voles prevalent in
Switzerland, it appears exclusively in the Alps and their foothills, upwards of approximately
1000 m above sea level, where it inhabits the crevices of rock faces. Snow voles are highly
adapted to their habitat, which can be described as a three-dimensional labyrinth of rocky
clefts. They therefore dispose of prominent elongated vibrissae and a flattened skull as well
as very distinctive three-dimensional callosities on the soles of their feet. To date, most
research on this species has been conducted within the context of population biology. It is
therefore known that the species exhibits a variety of specific characteristics in comparison
with other voles, and because of this must be regarded as a K-strategist. These characteristics
include a comparatively long lifespan, low number of offspring and stable density of
population. Despite these remarkable facts, very little scientific attention has so far been
given to the behavioural biology of the snow vole. This paper aims at a thorough and comprehensive
investigation and documentation of the snow voles' behaviour.
2. Methods
As it is practically impossible to observe snow voles in the wild, specimen living on the
Churer Joch, an area situated approximately 7 km to the southwest of Chur at around 2000
m above sea level, are captured and transferred to the Zoological Institute of the University
of Basel for the purpose of this investigation. Here, they are kept in glass terrariums designed
specifically for this project. The terrariums are 100 cm high, with a basis measuring
up to 190 x 80 cm. They are furnished with soil and rocks of varying size, arranged to offer a
variety of places for both climbing and hiding. On the narrow side of the terrarium, a socalled
nesting box is added, a glass container roughly 30 cm deep and 20 cm high and
directly connected with the main terrarium. The nesting box is filled up with soil and stones
and has a removable glass top. It is surrounded by a construction of corrugated board to
keep out the light and thus simulate the area beneath a large rock, the preferred hiding and
nesting place of snow voles. The specific design of these terrariums allows to monitor the
behaviour of the animals both within the nesting place and abroad, without causing disturbance
to them.
Surveillance of the snow voles takes place more or less on a daily basis between July 2002
and February 2006. With the help of a camcorder, extensive video footage is obtained.
Long-term recordings, especially of the nesting box, are made in the absence of the researcher.
As snow voles tend to move about extremely rapidly, details of their behaviour
often go unnoticed during first-hand observation, which is why the evaluation of video
footage, particularly in slow-motion, is an instrumental tool.
3. Ethogram
The ethogram of the snow vole encompasses 242 patterns of behaviours and is divided into
the following chapters: posture, movement, food behaviour, comfort behaviour, resting behaviour,
marking behaviour, exploratory behaviour, curiosity behaviour, protective behaviour,
building behaviour, social behaviour, parturition behaviour, behaviour of the young
animal, vocal repertoire.
4. General behaviour
The snow vole spends on average 85% of the day resting in its nest. The remaining time is
spent on a variety of activities of which feeding takes up the largest portion at 7%. Periods of
rest last on average 1.5 hours, while an extended period of activity will typically last up to 45
minutes. The snow vole is diurnal as well as nocturnal, with periods of heightened activity at
dusk. During daytime, activities take place more or less exclusively underground and it is
usually during nightfall and at night that the snow vole leaves its cover.
The various postures of the snow vole are particularly sophisticated in connection with its
rock-dweller's habitat. Thus, the snow vole likes to brace its hands and feet on vertical or
elevated horizontal surfaces. In doing so, it displays all possible combinations, alternatively
propping itself up by one hand and/or foot or by both hands and/or feet at the same time. If a
crevice has the adequate width, snow voles are even capable of standing upright by bracing
their hands and feet against the crevice walls at a certain distance from the floor.
Out of cover, a snow vole typically moves about in a fitful and abrupt manner along the floor,
pausing for a moment after each step. Usually, however, it moves amongst rocks, where it
displays very varied patterns of movement. It crosses over stones of all sizes and even
scales perpendicular walls with great dexterity, as well as regularly performing horizontal or
vertical leaps. Most characteristic for the snow vole is the way in which it navigates narrow
cracks and crevices. As soon as the width of a fissure allows, the snow vole will bend its
extremities outwards, brace itself on the walls with its hands and feet and thus move in every
direction with great ease.
Snow voles are strict herbivores, feeding mainly on the green parts of plants but at times
also on roots and blossoms. They consume a great variety of herbs, of which representatives
of Asteraceae, Fabaceae and also Caryophyllaceae make up the largest part. Food is
practically always carried to safety and eaten there. Larger pieces of food are usually
dragged into cover or divided into two parts for transportation. The snow vole's use of its
hands during feeding is very marked, it usually holds its food with both hands and furthermore
often folds or layers leaves before consumption in order to eat from at least two layers
of food in one go. Snow voles employ food intelligence. Thus inedible plants are always left
aside and unknown plants consumed in small quantities to start with.
Snow voles eat excrement, which has passed through their appendix (caecotrophy), usually
by catching it as it exits and chewing it at length before swallowing.
For grooming, a snow vole will usually lick and nibble its coat as well as combing it with its
hands. Special attention and care are given to hands and feet. The snow vole grooms its
head by wetting its hands with saliva and running them over it.
Snow voles use both urine and excrement to mark their territory. The main markers are
typically situated in the four corners of the terrarium. Urine can also serve to highlight a path
with scent marks. Especially in unfamiliar territory, the snow vole will dispense small drops at
regular intervals along the way to create an odour trail. When a snow vole finds itself in new
surroundings, it will distribute its excrement evenly onto all exposed spots during the first few
days. After some time, this type of behaviour will abate and faeces be left at designated
places of defecation only. Male snow voles dispose of an additional substance used for
marking, the secretion of their preputial gland. This dark brown, semi-fluid secretion is only
produced by adult, sexually active males, is distributed in large quantities predominantly on
stones and gives off a strong musky scent. Glands situated around the cheeks are used to
mark the territory around the nest. Presumably, these greasy, tallowy secretions contain the
individual scent of a snow vole.
Snow voles perambulate the paths of their territory on a regular basis and commit each
detail to memory, so that they dispose of a clear mental picture of their surroundings.
Changes, like a new rock or the like, immediately attract their attention. Should they incur a
change of route, this will be rehearsed promptly, to facilitate a speedy and secure exit in the
case of danger. The snow vole displays high levels of inquisitiveness; unfamiliar objects or
new areas of the terrarium are usually discovered very quickly and investigated as soon as
an appropriate period of caution has passed.
Preferred nesting places of snow voles are usually situated underneath large, stable rocks.
Depending on the space available and the temperatures, a snow vole will either build a nest,
which is open at the top and surrounded by walls of appropriate height or indeed a spherical
nest with only one or two apertures on the side. Nesting material usually consists of dried
plant material preferably grass. Inside the nest, there is a shallow dent used for nesting and
lined with finely spliced plant material.
When burrowing, snow voles display a type of behaviour specific to their species. They
practically always dig vertically downwards along rocks and generally avoid digging up loose
soil. Thus, they create cavities beneath large stones as well as passageways between individual
rocks. When it encounters encumbering pebbles or twigs, the snow vole transports
them aside by use of its mouth and is able to carry objects weighing more than half of its
own body weight. Sometimes, snow voles do not only clear small stones away but incorporate
them into the design of the burrow by adeptly piling them up into small stonewalls.
These are normally used to border the nest, line pathways, stabilise exits and lend structure
to as well as decrease the size of large cavities, thus serving, to some extend, as protection
both from inclement weather conditions and potential intruders.
5. Social behaviour
The approach between a male and a female snow vole meeting for the first time can be
divided into several phases. During a first phase, the female will usually try to drive the male
out of her territory by following him around and attacking at random as well as involving him
in wrestling matches again and again. She will also repeatedly demonstrate her territorial
claim by showing off by means of intimidating behaviour. This normally takes place in front
of the entrance to the nest. The female faces the male and vigorously paws the ground with
both hands and feet, an action which is generally accompanied by a good deal of noise as
well as the raising of dust and material. At this point, the male will merely try to fend off the
female's attacks without ever displaying any signs of aggression himself. During a second
phase, the female will calm down somewhat and increasingly retreat to the nest. Now, the
male takes on a more active role, seeking time and again the close proximity of the female
and thus slowly reducing the distance as far as she is prepared to tolerate.
Courting may start as early as one week after the couple has begun to share a nest.
Quite often, however, a couple will cohabit in a friendly and affectionate manner for months
without any signs of courtship. The courting male approaches the female slowly and spends
a great deal of time sniffing at both sides of her face by turns. This is accompanied by soft
cooing. Unless the female asserts the distance by holding him at bay with paw cuffs, he will
gradually move his muzzle along her flank and eventually sniff her genital area. Following
this, the female usually walks away, followed by the male who will continue to sniff at her
from behind. If she stops, he will put his hands on her back from behind and copulation can
take place if she is indeed willing to mate. During mating, which lasts between a few
seconds and half a minute, the male often nibbles at the female's neck.
A pregnant snow vole usually starts to build one or several nests for littering about half way
through the gestation period, i.e. approximately 10 days before giving birth. These spherical
nests are thick walled and padded with much finely spliced nesting material. After 20-22
days, the female snow vole will give birth to 1-4 babies, but prevalently to litters of 2 or 3
young animals. An impending birth usually announces itself with the display of intensive
nesting behaviour, heightened restlessness and regular licking of the vagina. Later, the
onset of regular contractions can be observed through recurring sounds of pain. Shortly
before the birth, the contractions are accompanied by strong pushing motions on the part of
the mother. Immediately after the birth, the mother will lick the newborn and eat the
placenta. A birth involving three young lasts approximately 40 minutes, from the first
contraction until the arrival of the third baby.
If, during the first few days after the birth, the mother has to leave the nest for a short
period of time, she will cover her offspring with nesting material so that they become invisible
inside their nest. For suckling, she will at first stand or lie over the young and later, when the
babies have grown a little, she may also nurse them by lying down on her side. The young in
their turn usually drink in a position where they lie on their back with the torso underneath
the mother's belly. Nursing also presents the mother with an additional opportunity for
grooming her young, which she frequently does by licking and cleaning them, especially
around their genital region. A female snow vole suckles her young until they are 50 days old
and she is also capable of simultaneously nursing offspring stemming from two separate
litters.
The mother will return her young to the nest if they have been dragged out of it whilst
hanging on to her teats or whenever an older and increasingly more active baby tries to
leave the nesting area of its own accord. She carries them by holding on to their bellies with
her snout and with their backs ahead. The young snow vole will usually squeal loudly in
protest at first but then quickly become immobile (limp posture). Once they are heavier and
over short distances, the mother may simply drag them along the floor. Occasionally, or in
the case of a disturbance, the mother will transfer her young to another nest. Before the
transfer, she prepares the new abode and afterwards she returns to the abandoned nest to
carefully check that none has been left behind. Transportation by the mother ceases when
the young are 17 days old.
When the offspring is between 7 and 21 days old, the mother will increasingly carry food
into the nesting area in order to facilitate the young animals' contact with and understanding
of edible plants within the safe surroundings of the nest. A snow vole mother remains in
close and friendly contact with her offspring even after they have become more independent
and never displays any signs of wanting to drive them away.
The father makes first contact with his offspring just a few minutes after the birth by sniffing
and licking them. From the very beginning he also cuddles up to them inside the nest. His
behaviour towards his young is friendly and free from any signs of aggression throughout
their development and the relationship between the male and the female also remains close
and amicable while they jointly raise their young.
Upon the birth of a subsequent litter, young snow voles are usually about 6 weeks old. From
the start, they display a great deal of interest in their younger siblings by sniffing and licking
them as well as lying down next to them in the nest. While this pattern of behaviour
continues in the adolescent males, the young females will get ever more interested in the
babies as they approach adulthood. They will, in fact, appropriate more and more of the
mother's behaviour with respect to the rearing of the cubs and thus increasingly relieve her
from her care duties.
From about the age of 2-3 months, young male snow voles develop a strong urge for
territorial expansion. It can be supposed that under natural conditions, they would now begin
to wander about until eventually leaving the mother's territory to establish one of their own. A
young female snow vole, however, will display no urge to wander whatsoever. Even after the
daughter has reached maturity, the connection between mother and daughter remains
strong. It is likely that in the wild, the daughter will also remain in her mother's territory and
help her rear younger siblings. Later on, mother and daughter may even jointly raise their
respective litters and when the mother dies, the daughter takes over her territory.
Snow voles are naked at birth. Their bellies are pink, while their backs and the top of their
heads are pigmented grey. The eyes are closed and the earlaps folded to the head. Young
snow voles weight approximately 4.5 g at birth and have a head-body length of about 4.7 cm
as well as vibrissae that are already 0.4 cm long at birth. The newborn usually lies on its side
with its back curved and its tail between its hind legs. During the first post-natal days, the
young snow vole's movements are limited to bending and stretching the torso and flexing all
four extremities as well as a swinging movement of the head, which can be interpreted as a
searching automatism. Twitches affecting the body as well as the extremities are very
commonplace. If a litter consists of more than one animal, they will always lie huddled
closely together or even on top of each other. When the young snow voles are 4 days old,
they begin to grow a short grey fluff on the upper side of their bodies. The young animal is
now able to lie on its stomach for short periods of time. A day later, it will cover short
distances crawling on the floor, but the belly always maintains contact with the ground. After
8 days, the entire body, apart from the extremities and the tail, is covered with soft, light
brown fur and by the 11th post-natal day, the young animals have trebled their body weight.
They are by now quite accomplished crawlers, leave the nest of their own accord, and
investigate their surroundings with their noses. Young snow voles open their eyes at 12-13
days of age and will then begin to explore the entire nesting box, while some of the more
adventurous ones might even venture out into the open. They take their first nibble and
eventually consume small quantities of fodder. On the 14th post-natal day, the head-body
length measures approximately 8.7 cm. A day later the young snow voles are already fast
and adept runners, displaying the quick starts and abrupt changes of direction typical for that
age. Their fur has now assumed the characteristic more or less uniform slate grey colour of
adolescent snow voles. At the age of approximately 25 days, the young animals navigate
rocky areas and scale clefts as adeptly as fully grown adults. Between the 30th and the 85th
post-natal day, the young snow voles go through a period of molting, which usually starts at
the back end of the trunk and spreads to the front. Shortly afterwards, new fur also begins to
sprout on the head, spreading slowly towards the neck, where the two areas of growth will
meet. After this process, the coat has the mottled grey-brown colour, which generally
prevails in adult snow voles. During this period of time, young snow voles also display
heightened levels of inquisitiveness as well as a strong interest in building behaviour and
their periods of activity are markedly longer than those of adult animals. Finally, at the age of
approximately 80 days, they will adopt the behaviour of adult snow voles.
Playful behaviour in young snow voles occur between the 21st and 60th post-natal day and
must be divided into two different types: games played with the mother and games played
with siblings of the same litter. Young animals will challenge their mother to a game by
running up to her, nibbling or sniffing her and trying to climb and stand on top of her on all
fours. If the mother then gets up on her hind legs, a playful but tumultuous wrestling match
ensues, with the young lashing out at their mother with hands and feet, while she tries to
fend them off. The mother meets even the roughest games of her young with patience and
devoid of any show of aggression. She never initiates a game herself. Occasionally, two
distinctive types of games can be observed: firstly, the young chasing their mother around
and secondly a game where the young animals playfully jump over the sitting or reclining
mother. The latter appears to be characteristic to snow voles. Games between siblings
usually evolve after two animals greet each other by sniffing at each other’s snouts but it is
by biting and pulling a sibling's tail that a young snow vole clearly signals its willingness to
play. The games usually consist of wrestling and biting matches as well as chases and
preferably take place at dusk and during the early hours of night.
Encounters between non-related snow voles of the same sex usually result in violent
conflict. Male animals will carry out aggressive wrestling and biting fights, whereby they will
try to sink their teeth into the base of theirs adversary's tail. The inferior male is eventually
thrown on its back and pinned down with all fours by his superior opponent. The winner then
sniffs at the loser's genitals before letting him go. Fights between female snow voles are not
to the same extent characterised by biting and rituals of subordination but consist mainly of
the reciprocal dealing of blows and charges at the opponent as well as adept evasive
manoeuvres. After an initial confrontation, females tend to avoid open conflict and in the
event of a subsequent encounter, the inferior female will usually have to beat a retreat.
Summing up, it must be stated that on account of the close pair-bonding in couples,
extended adolescent development and the associated high rate of investment into offspring
as well as the close relationship between mother and daughter and the marked play
behaviour, hitherto undocumented in the Microtus genus, snow voles dispose of characteristic
and distinctive patterns of social behaviour.