Agricultural and Food Science, Vol. 17 (2008): 41-52

A G R I C U L T U R A L A N D F O O D S C I E N C E

Vol. 17 (2008): 41-52.

Water baths for farmed mink: intra-individual
consistency and inter-individual variation in

swimming behaviour, and effects on stereotyped
behaviour

Jaakko Mononen, Maarit Mohaibes, Sakari Savolainen and Leena Ahola
University of Kuopio, Department of Biosciences, PO Box 1627, FI-70211 Kuopio, Finland

e-mail: jaakko.mononen@uku.fi

Swimming behaviour and effects of water baths on stereotyped behaviour in farmed mink (Mustela vison)
were studied in three experiments. The singly-housed mink had access from their home cages to extra cages
with 20.5 litre water baths. Two short-term experiments aimed to investigate how quickly adult and juvenile
mink start using and how consistently they use water baths over 10 days, and whether the extent of the use
correlates between dams and their females kits. A four-month experiment was designed to compare the
development of stereotyped behaviour in juvenile mink housed with and without swimming opportunity. The
behavioural analyses were based on several 24-hour video recordings carried out in all three experiments.
There were obvious inter-individual differences and intra-individual consistency in swimming frequency
and time. Farmed mink’s motivation to swim can be assessed in short-term experiments, and measurement
of water losses from the swimming baths and use of instantaneous sampling with 10 min sampling intervals
provide quite reliable measures of the amount of swimming. The bath use of the juveniles correlated with
that of their dams, indicating that an individual mink’s eagerness to swim may have a genetic component.
The lower amount of stereotyped behaviour in mink housed with water baths indicates that long-term access
to baths may alleviate frustration in singly-housed juvenile farmed mink.

Key-words: mink, Mustela vison, fur farming, swimming, stereotyped behaviour, behavioural need, animal
welfare

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Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

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Vol. 17 (2008): 41-52.

Introduction

Charles Darwin was challenged by his opponents
with the question of how aquatic carnivores could
have evolved from terrestrial carnivores (see Dun-
stone 1993, pp. 1-2). The opponents doubted the
ability of an intermediate species to cope in either
environment. Darwin used American mink (Mustela
vison) as an example of a successful intermediate
species. The semi-aquatic nature of mink (see also
Birks 1986) and how it copes in different environ-
ments is still a controversial issue today, but in a quite
different sense. Mink have been farmed for their fur
since the 1860s (European Commission 2001), but
farmed mink are not provided with the opportunity
to swim, and it has been argued that this might be
detrimental to their welfare (e.g. Nimon and Broom
1999, European Commission 2001).

Whether mink need swimming water has been
investigated quite intensively in many countries
recently, using various methods. Cooper and Ma-
son (2001) discovered in a demand study that
mink valued swimming water (and food) over
many other resources. Other demand studies
have not confirmed these findings, but it has been
found that mink value swimming water and run-
ning wheels equally (as measured by the demand
elasticity, Hansen and Jensen 2006). In addition,
the mink used the running wheel much more than
the water. Furthermore, studies comparing mink
that are housed with and without water baths have
not shown that baths have any long-term positive
welfare effects (Skovgaard et al. 1997, Hansen and
Jeppesen 2000a and b, Hansen and Jeppesen 2001a,
Vinke & Spruijt 2001, Vinke et al. 2004). On the
other hand, it has been reported that if mink have
water baths and then are deprived of them, they
show signs of stress (Mason et al. 2001, Korhonen
et al. 2003). Here it is noteworthy that many mink
farms are located in areas where winter is cold (e.g.
Finland and Canada), where water freezes if not
warmed, which would lead to “natural deprivation”
of the baths.

There is clearly not enough scientific evidence
yet to support either the view that farmed mink
need swimming water or the view that they do not.

Furthermore, it is highly possible that the relaxa-
tion of natural selection (e.g. Price 1999) during the
domestication process of mink may have led to an
increase in inter-individual differences in their atti-
tude towards swimming water. If this is true, some
mink might suffer more than others when deprived
of water. It is also important to identify inter-in-
dividual differences because they cause noise in
experiments and, perhaps even more importantly,
may lead to discrepancies between results from dif-
ferent farm mink populations.

In this paper we report three experiments from a
longer series of studies focusing on farmed mink’s
need for water baths. In the first two experiments
we assessed how quickly an individual mink es-
tablishes its use of a water bath, and whether there
are differences between juveniles and adults in
this. Furthermore, we studied the extent of inter-
individual and intra-individual variation in the use
of the bath in the short and long term, and the cor-
relation in bath use between females and their prog-
eny. Different ways of measuring the amount of
swimming were also evaluated in the first and third
experiment. In the third experiment we studied the
short-term and long-term behavioural effects of
deprivation of access to a water bath. Deprivation
included “natural deprivation”, i.e. the freezing of
water in late autumn. We also assessed whether the
deprivations affect differently mink that use baths
frequently and those that use them less.

Material and methods

Three experiments were carried out in an unheated
animal barn at the Research Station of the Univer-
sity of Kuopio, Finland. Female mink of scan-glow
colour-type were used in all experiments, which
were approved by the Institutional Animal Care
and Use Committee of the University of Kuopio
(licence number 01-34).

The mink were housed singly in standard
mink cages (85×30×45 cm, L×W×H) with stand-
ard nest boxes (27×31×39 cm) with bedding. The
mink housed with water baths, i.e. all mink in

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Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

A G R I C U L T U R A L A N D F O O D S C I E N C E

Vol. 17 (2008): 41-52.

Experiment 1 and Experiment 2 and the mink in
the bath group in Experiment 3, had access to a
neighbouring standard cage (without a nest box)
where a 20.5-litre water bath was available. The
water depth was 17 cm. The mink in the control
group in Experiment 3 had access to an empty cage
of the same size. The behaviour of the mink was
video-recorded with a wide-lens video-camera (Pa-
nasonic WV-BP330), a time lapse recorder (Hitachi
VT-L2600E) and a Video Quad Splitter (VT-6040).
The extent of bath use was analysed from the vid-
eotapes with continuous recording (Martin and
Bateson 1993) in all experiments. Bath use was
defined as the time the mink spent in the water (all
four limbs in the water).

Experiment 1

In Experiment 1, 18 naïve juvenile mink were given
access to swimming water for 10 days to investigate
how quickly they would start using it, how consist-
ently they used it over the 10 days, and whether a
proxy measure of swimming, i.e. the decline of water
levels in the baths, could be validated.

The experimental animals had been born in
May, weaned into sister-pairs at the age of eight
weeks, moved to the experimental cages at the age
of twelve weeks, and housed singly during the ten-
day experiment in August-September. The behav-
iour of the mink was video-recorded on days 1, 2
and 10 of the experiment. The water loss from the
baths over 24 hours was also measured after each
24-hour video-recording.

Intra-individual consistency in bath use between
days 1, 2 and 10, and correlation between bath use
and water loss from the baths were analysed with
the Spearman rank-order correlation (henceforth
the Spearman correlation) (Siegel and Castellan
1988). The differences in bath use between days 1,
2 and 10 were compared with the Friedman two-
way analysis of variance by ranks (henceforth the
Friedman test) followed by a post hoc test. The dif-
ferences between days 1, 2 and 10 in the percentage
of animals not swimming were compared with the
Cochran Q test.

Experiment 2

In Experiment 2, two groups of adults and one
group of juveniles were given ten days’ access to
swimming water in August. The two adult groups
differed in water bath experience: the adults in one
group had had prior experience with water (ten
days during Experiment 1, experienced adults, n =
8), while the adults in the other group were naïve
(naïve adults, n = 11). The juveniles had no earlier
water bath experience (naïve juveniles, n = 27). This
experiment thus allowed comparison of bath use
between naïve adults and juveniles, and between
experienced and naïve adults. Furthermore, since
the juveniles were the offspring of the adults, their
bath use could be compared with that of their dams,
in order to see if individual differences in bath use
might have a genetic component. Also, day-to-day
(all groups) and year-to-year (experienced adults
only) intra-individual consistency in bath use could
be compared.

The adults had been born in May in the previous
year (experienced adults) or one or two years earlier
(the naïve adults), weaned at the age of eight weeks
into male-female pairs, pair-housed until their first
December and kept singly thereafter, except dur-
ing the breeding season when they had kits. The
juveniles had been born in May of the year of the
experiment, weaned at the age of eight weeks into
sister-pairs, moved to the experimental cages at the
age of twelve weeks and housed singly through the
experiment. The naïve juveniles were offspring of
the adult females of both experienced and naïve
adults.

The video-recordings were carried out on days
2 and 10 of the experiment. In addition to the time
spent in the bath, the time spent on the edge of the
bath was also recorded with continuous recording
(Martin and Bateson 1993).

Intra-individual consistency in bath use from
day 2 to day 10 (all groups) and from year to year
(for the experienced adults only), correlation in bath
use between females and their progeny (data from
days 2 and 10 pooled), and correlation between
swimming behaviour and staying on the edge of
the bath (for the naïve juveniles only) were ana-
lysed with the Spearman correlation. There were

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Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

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Vol. 17 (2008): 41-52.

seven dams with one kit and ten dams with two
kits in the experiment, and in the latter case the
mean value for the two kits was calculated and
used in analysing the correlation in swimming be-
haviour between the dams and their daughters to
avoid pseudo-replication. The differences in bath
use (time spent swimming, frequency of swimming
bouts, mean swimming bout length, time spent on
the edge of the bath) between the three groups were
analysed with the Kruskall-Wallis one-way analysis
of variance (henceforth the Kruskall-Wallis test),
and the pair-wise comparisons were performed with
a post hoc test described in Siegel and Castellan
(1988). The differences between the two recording
days were analysed with the Wilcoxon signed-ranks
test (henceforth the Wilcoxon test). In addition, the
number of animals not swimming at all was com-
pared between the groups with Fisher’s exact test.

Experiment 3

Experiment 3 was a longer-term study of 36 juvenile
mink. Stereotypic behaviour was used to investigate
whether control mink have poorer welfare than the
mink in the bath group; whether artificial and natural
thwarting of swimming have similar or different
effects on stereotypies; and whether individual dif-
ferences in bath use predict frustration when swim-
ming is prevented.

The experimental animals had been born in May,
weaned at the age of eight weeks into sister-pairs,

allotted randomly to the bath group or the control
group and moved to the experimental cages at the
age of twelve weeks and housed singly through the
experiment from August to December.

The mink in the bath group (n = 18) were given
18 weeks of access to swimming water, broken
by two periods of deprivation: an artificial one in
which access was prevented experimentally for two
weeks, and a natural one in which the water froze
over with the arrival of winter (Table 1). The mink in
the control group (n = 18) were housed in bath-free
double-cages for 18 weeks, broken only by a two-
week period of bath access (when the bath group
were artificially deprived of the baths).

Twenty-four-hour video-recordings were carried
out on days 1, 2 and 10 of each of four two-week
observation periods. In addition to continuous re-
cording of the swimming behaviour, instantaneous
sampling with 10 min sampling intervals (Martin
and Bateson 1993) was used to record general activ-
ity (measured as the time spent outside the nest box),
stereotyped behaviour and swimming behaviour.

The differences in activity and stereotyped
behaviour between the two groups were analysed
separately for each month with the Wilcoxon-Mann-
Whitney test. The percentage of stereotyped behav-
iour between the months was compared group-wise
with the Friedman test with a post hoc test described
in Siegel and Castellan (1988). The relation between
the frequency of stereotyped behaviour in the artifi-
cial and natural deprivation periods and bath use in
the observation periods before each of the two depri-
vation periods were analysed with the Spearman cor-

Study
weeks

Observation weeks (month) Ta
Group and circumstances

Bath Control

1 - 5 1 - 2 (Aug) +11 - +14°C Bath No bath
6 - 7 6 - 7 (Sep-Oct) +1 - +10°C No bath

(artificial deprivation)
Bath

8 - 16 10 - 11 (Oct) +0 - +11°C Bath No bath
17 - 18 17 - 18 (Nov-Dec) -13 - +1°C Bath frozen

(natural deprivation)
No bath

Table 1. The schedule of Experiment 3. Study week 1 started on 12 - 18 August. Ta = the range of
ambient temperature during the observation weeks.

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Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

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Vol. 17 (2008): 41-52.

relation. In addition to the frequency of stereotyped
behaviour during the deprivation, the change in the
frequency from the period preceding the depriva-
tion to the deprivation period was also used in these
analyses in order to take into account the individual
baseline levels in stereotyped behaviour. The Spear-
man correlation was also used for analysing short-
term intra-individual consistency (i.e. consistency
between observation days 1, 2 and 10 within each
month) and long-term intra-individual consistency
(consistency between months; data pooled from
the three observations in each month) of bath use,
as well as for comparing the swimming behaviour
data from the continuous recording and instantane-
ous sampling (data from the six 24-h recordings of
the bath group in August and October).

Notes on statistical analyses and presen-
tation of the data

Despite transformation attempts, many variables
(e.g. those related to stereotyped behaviour) never
met the assumptions of parametric statistics. There-
fore, statistical analyses were performed using non-
parametric statistics (Siegel and Castellan 1988).
Due to this non-normality of most of the variables,
the results are presented not only as mean ±standard
deviation (SD), but also with median and/or mini-
mum and maximum values. The level of statistical
significance was set at the conventional 0.05, but
to facilitate readers’ opportunities to do their own
interpretations of the results the exact p-values are
indicated every time the value is between 0.05 and
0.1 (whenever this is possible).

Results

Experiment 1
In the juvenile mink, the number of swimming bouts
was at its highest on day 2, whereas the amount of
swimming time decreased and the length of the

swimming bouts became shorter from days 1 and
2 to day 10 (Table 2). Water loss from the bath had
also decreased by the tenth day. The number of
mink that did not swim at all did not change from
day to day. Twelve out of 18 mink were observed
to swim on all observation days, and all animals
swam at least on one observation day.

There was intra-individual consistency in the
swimming time and the number of swimming bouts
from day to day: the Spearman correlation coef-
ficients (rs) for these variables between the days
ranged from 0.70 to 0.83 (p < 0.001, n = 18). There
was a strong correlation between the swimming
time and the number of swimming bouts on days
1, 2 and 10 (rs = 0.88–0.98, p < 0.001). Water loss
from the bath correlated with both the number of
swimming bouts and the swimming time on all ob-
servation days (rs = 0.80–0.87, p < 0.001).

Experiment 2

The experienced adult mink swam the most and
the naïve adult mink the least, with the naïve ju-
veniles intermediate between these two (Table 3).
These differences were clearer on the 2nd than on
the 10th day of the experiment, since both the daily
swimming time and frequency tended to increase
in the naïve adults from day 2 to day 10. The mean
swimming bout length tended to be the shortest in
the naïve adults, but only on day 2. The percentage
of animals that did not swim at all was highest in
the naïve adult mink and lowest in the experienced
adults, with the naïve juveniles intermediate between
these two, but this difference did not reach statistical
significance. In addition to being in the bath for an
average of 5–23 min/24 hours, the mink spent 2–4
% of observations, corresponding to approximately
30–60 min/24 hours, on the edge of the bath. There
was no difference in the time spent on the edge of
the bath between the three groups.

Swimming behaviour between days 2 and 10
correlated in juvenile (rs = 0.60 for the time spent
swimming and rs = 0.63 for swimming frequency;
p < 0.01, n = 27, Spearman correlation) and expe-
rienced adult mink (rs = 0.83 and 0.74, respectively;

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Vol. 17 (2008): 41-52.

Day 1 Day 2 Day 10 p
Time spent swimming (min/24h)
Mean±SD 60±61A 66±5A 21±28B < 0.01
Median 39 63 8
Minimum-maximum 0-163 0-169 0-82
Number of swimming bouts
Mean±SD 101±101AC 163±118B 68±81AC < 0.001
Median 82 149 41
Minimum-maximum 0-285 0-336 0-271
Mean bout length (s)
Mean±SD 22.2±18.3a 24.7±10.5a 15.0±9.4b < 0.05
Median 29.8 25.7 15.4
Minimum-maximum 0-44.4 0-45.9 0-33.0
Number (and %) of animals not swimming 4/18 (22%) 1/18 (6%) 2/18 (11%) NSx
Water loss from the bath (l)
Mean±SD 9.7±4.7a 10.6±4.6a 7.2±5.7b < 0.05
Median 9.8 12.0 5.7

p: The Friedman two-way analysis of variance by ranks or xCochran Q test. Values without a common superscript differed from each
other in a post hoc test at the level of p < 0.05 (upper case) or p < 0.1 (lower case)
NS: p > 0.1

Table 2. Swimming behaviour of juvenile mink (n=18) and water loss from the baths in Experiment 1.

Naïve juveniles
(n = 27)

Naïve adults
(n = 11)

Experienced
adults (n = 8)

Time spent swimming (min/24h)

Day 2 6.2±8.0
ab

(3.4; 0-25.8)
1.4±2.1a
(1.0; 0-5)

23.3±24.8b
(12.4; 1.2-60.6) < 0.05

Day 10 6.5±11.6(3.5; 0-57.6)
4.8±6.0
(2.8; 0-16.5)

18.5±22.4
(9.4; 0.2-54.3) NS

p 2 NS = 0.06 NS
Number of swimming bouts

Day 2 12±15
a

(8; 0-53)
5±7a
(1; 0-18)

83±94b
(24; 7-220) < 0.01

Day 10 17±26(8; 0-105)
19±22
(12; 0-63)

77±83
(48; 1-196) NS

p 2 NS = 0.05 NS
Mean bout length (s)
Day 2 23±21 8±12 21±14 = 0.07
Day 10 19±16 9±9 13±5 NS
p 2 NS NS NS
On the edge of the bath
(% of observations)

Day 2 4±2(3; 0.7-9.7)
4±4
(3; 0-11.0)

3±2
(4; 0.7-5.5) NS

Day 10 4±3(4; 0-14)
2±3
(0.7, 0-9)

3±2
(2.1; 0.7-7) NS

p 2 NS NS NS
Number (and %) of animals
not swimming
Day 2 7 (26%) 5 (45%) 0 (0%) = 0.09
Day 10 4 (15%) 3 (27%) 0 (0%) NS
Days 2 and 10 3 (11%) 2 (18%) 0 (0%) NS
p 1: The Kruskall-Wallis one-way analysis of variance by ranks or Fisher’s exact test between the groups;

ab = values without a com-
mon letter differ from each other at the level of p < 0.05
p2 : The Wilcoxon signed-ranks test between days 2 and 10 within the groups
NS: p > 0.1

Table 3. Bath-related behaviour of mink in Experiment 2. Mean±SD (median; minimum-maximum) or number (and
percentage) of animals.

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p < 0.05, n = 8) but not in naïve adults (rs = 0.30
and 0.22, respectively; p > 0.1, n = 11). There was
a moderate correlation between the two years in the
frequency of swimming bouts in the experienced
adults, but the correlation for time spent swimming
between the years was not statistically significant
(Fig. 1). There was a moderate correlation in the
time spent swimming between the dams and their
daughters (Fig. 2).

Experiment 3

In the bath group, the time spent in the bath decreased
from August (mean ±SD 1.1 ±1.1% of time, range
0-52 min/24 h; data pooled from days 1, 2 and 10
of a two-week period ) to October (0.1 ±0.2 %,
0–10 min), and the baths were used the most in
November-December (4.8 ±2.1 %, 38–162 min),
when they were frozen (the Friedman test: p < 0.05
for all three pair-wise comparisons in a post hoc
test, n = 17). The time spent in the bath correlated
between days 1, 2 and 10 within the two-week
observation periods in August and October (0.48 <
rs < 0.66, 0.06 > p > 0.003, Spearman correlation,
n = 17–18) whereas the correlation was weaker in
November-December (0.29 < rs < 0.52, 0.26 > p >
0.03, n = 17–18). The time spent in the bath (data
from days 1, 2 and 10 pooled within each month)
correlated between August and October (rs = 0.58, p
< 0.05, n = 17), tended to correlate between October
and November-December (rs = 0.47, p = 0.06, n
= 17), and did not correlate between August and
November-December (rs = 0.18, p > 0.1, n = 17).
The control group spent 0.2 ±0.3 % (0–15 min) of
their time in the bath in September-October, i.e.
in the only two week period that they had baths
available.
The mink in the bath group showed less stereotyped
behaviour than the control mink, except during the
artificial deprivation period (when the bath group did
not have the baths and the control group did) (Fig. 3:
top). The control animals were more active (outside
the nest box) than those with the bath in August and
October (Fig. 3: bottom). The situation was reversed
for activity in the artificial deprivation period, i.e.

Fig. 1. Correlation in the frequency of swimming bouts
(top) and the time spent in the water bath (bottom) be-
tween two consecutive years in eight female mink (ex-
perienced females). The data are based on the mean of
two 24-hour recordings per year. rs = Spearman corre-
lation coefficient.

Fig. 2. Correlation in the time spent in the water pool
between mink dams and their female kits. The data are
based on the average time spent in the water bath dur-
ing two 24-hour recordings. rs = Spearman correlation
coefficient.

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Vol. 17 (2008): 41-52.

when the bath group did not have the baths and the
control group did. There was no difference in activity
between the groups in November-December when
the baths were frozen.
The Friedman test revealed differences (p < 0.001)
between the months in the percentage of stereotyped
behaviour in both groups (Figure 3: top). The
pair-wise post hoc comparisons for the bath group
showed increases only from August to November-
December, whereas in the control group increases
were found from August to November-December,

from September-October to October, and from
September-October to November-December.
The bath group mink which swam more in August
and October, i.e. the observation periods before
the deprivations, did not show more stereotyped
behaviour than the less active bath users during the
artificial or natural deprivation: rs = 0.12 (p = 0.65,
n = 18, Spearman correlation) and rs = 0.11 (p =
0.69, n = 17), respectively. Neither did the changes
in the percentage of stereotypies from the observa-
tion period preceding the deprivation period to the
deprivation period correlate with swimming time
in August (rs = 0.09, p = 0.73, n = 18) or October
(rs = 0.07, p = 0.79, n = 17).
The two recording methods for the amount of
swimming, continuous recording and instantane-
ous sampling, produced more similar results in
August (when swimming was more frequent) than
in October (when swimming was less frequent): the
Spearman correlation coefficients (rs) between the
two recording rules were 0.95 (p < 0.001), 0.84 (p
< 0.001) and 0.60 (p < 0.01) in August (n = 18),
and 0.36 (p > 0.1), 0.34 (p > 0.1) and 0.73 (p <
0.001) in October (n = 17–18) for observation days
1, 2 and 10, respectively.

Discussion

In the present three experiments the mean lengths
of swimming bouts varied from a few to tens of
seconds, which is in accordance with earlier stud-
ies in farmed mink (de Jonge and Leipoldt 1994
cited in Vinke 2004, Hansen and Jeppesen 2001b),
and the behaviour of mink in the wild (Birks 1986,
Dunstone 1993). Mink naïve in regard to the water
baths established their swimming in a few days,
especially in the case of juvenile animals. The
intra-individual consistency in swimming behaviour
was obvious from day to day, week to week, month
to month and year to year. The fast establishment
together with the consistency in bath use implies
that an individual mink’s motivation to swim can
be assessed in fairly short-term experiments. (By
motivation to swim we mean the internal process

Fig. 3. Stereotyped behaviour and activity (% of observa-
tions, mean ±SD) in juvenile mink housed with and with-
out water baths. °In September-October the bath group did
not have and the control group had the baths for a two-
week period. *p < 0.05, ** p < 0.01, NS p > 0.1: differ-
ence between the groups within an observation period
(Wilcoxon-Mann-Whitney test). Letters below the col-
umns indicate differences (p < 0.05) between the obser-
vation periods within a group (upper case = bath group,
lower case = control group): columns without a com-
mon letter differ from each other (Friedman test with a
post hoc test).

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that underlies swimming behaviour and that is
reflected by a mink’s tendency, or ‘eagerness’, to
show swimming behaviour [cf. Toates 2002]: i.e.
the frequency of swimming bouts and the total time
spent in a water bath are interpreted to be measures
of motivation.)

The daily time spent in the bath had a high cor-
relation with the frequency of swimming bouts and
water loss from the baths. The results indicate that
the amount of swimming can be evaluated quite
easily by measuring these parameters. The use of
water loss as a measure of the amount of swim-
ming behaviour in mink has also been reported
earlier (Hansen and Jeppesen 2001b, Korhonen
and Niemelä 2002, Korhonen et al. 2003). The un-
derlying mechanism, i.e. the fairly constant amount
of water carried away from the bath after each
swimming bout, has been described in detail in
Korhonen and Niemelä (2002). Compared with the
more laborious continuous recording, instantane-
ous sampling with 10 min sampling intervals also
provides a fairly reliable estimation of the amount
of swimming (provided that the mink use the baths
for at least tens of minutes per day).

It has been strongly argued that swimming is es-
sential for the welfare of farmed mink (Nimon and
Broom 1999, European Commission 2001). This
argument has been justified with reference to the
behaviour of mink in the wild. The wild mink has
been characterised as a semiaquatic animal (Dun-
stone 1993), and we have not found any reports
that mink in the wild thrive if totally terrestrial,
although increased competition for aquatic prey
may make mink “more terrestrial” (Bonesi et al.
2006). Thus, it can be supposed that motivation to
swim is deeply rooted in mink’s genes, and indeed,
we found a moderate correlation in swimming be-
haviour between dams and their kits. However,
although age and experience did not affect mink’s
first hand interest in water baths, i.e. tendencies to
stand at the edge of the bath, they did affect the
actual immersion in the bath. Naïve adults were
slower to start swimming than naïve juveniles, but
by the end of the ten days both groups swam to
a rather similar extent. These results indicate that
despite the putative genetic component, experience

also plays a role in an individual mink’s motiva-
tion to swim.
The inter-individual variation in swimming was
remarkably large in the present study, as has been
observed in earlier studies (Hansen and Jeppesen
2001b, Korhonen et al. 2003). It is also worth em-
phasising that earlier reports (e.g. Korhonen et al.
2003) as well as our present results show that some
farmed mink make little or no use of water baths.
Accordingly, the data from the wild support the
view that swimming fulfils an important feature of
a behavioural need in the mink, i.e. all individuals
of the species perform the behaviour frequently
and regularly or seek for water as a key stimulus to
release swimming and/or foraging behaviour (Stolba
and Wood-Gush 1984, Vinke 2004), but data from
farmed mink and findings in the wild are to some
extent contradictory.

There is a consensus that the domestication
process does not delete behaviours but rather af-
fects the threshold to perform various behavioural
patterns (Price 1999, Jensen 2002 pp. 27-29). In-
creased inter-individual variation in the strength
of the motivation to perform a behavioural pattern
may be due to the relaxation of natural selection
during domestication (e.g. Price 1999). This could
explain the large inter-individual variation in the
swimming motivation of mink: swimming has
not been essential for survival during the approxi-
mately 80-generation-long (European Commission
2001) domestication process of farmed mink kept
in cages mostly without a swimming opportunity.
It can, then, be hypothesised that farmed mink with
a stronger motivation to swim would be more frus-
trated when deprived of the opportunity to swim
than mink with a weaker motivation to swim, and
show more stereotyped behaviour due to this frus-
tration (see e.g. Fraser and Broom 1990, Mason
and Latham 2004). However, in our small-scale
study we found no indication that the mink which
swam more had more stereotyped behaviours when
they were deprived of baths than those that swam
less.

Instead, we found that the juvenile mink housed
with swimming baths had less stereotypies than
those housed without baths, indicating that the
baths may have alleviated frustration. This result is

A G R I C U L T U R A L A N D F O O D S C I E N C E

Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

A G R I C U L T U R A L A N D F O O D S C I E N C E

Vol. 17 (2008): 41-52.

in conflict with those of earlier studies (Skovgaard
et al. 1997, Hansen and Jeppesen 2000b, Korhonen
et al. 2003), which may be due to differences in the
age of the experimental animals and the methods
used to analyse behaviour. We provided baths to
juvenile animals, who may not yet have established
stereotyped behaviour (cf. Mason 1993), whereas
many other studies have been carried out with
adults (Warburton and Mason 2003, Korhonen et
al. 2003, Hansen and Jensen 2006). Developing
stereotypies are easier to attenuate by enriching the
housing environment than already established ster-
eotypies (Mason and Latham 2004). The difference
in stereotypies between the experimental and con-
trol groups was observed already in August during
the first two weeks after providing the bath group
with the swimming opportunity. Furthermore, in
the control group the otherwise steady increase in
the frequency of stereotypies in the course of the
autumn was interrupted by the two week period in
September-October when they had the baths. These
findings support the conclusion that stereotypies
were not firmly established during our study with
juvenile animals.

We also measured stereotypies on a 24-hour
basis, whereas in most other studies behavioural
observations have been limited to day-time (Sko-
vgaard et al. 1997, Hansen and Jeppesen 2000b).
Farmed mink are most prone to perform stereotyped
behaviour before and after feeding (Mason 1993),
and they are fed during the day-time. Therefore,
it can be assumed that most mink may perform
stereotypies during the day-time, and only 24-hour
observations can reveal the true differences in the
occurrence of stereotypies between experimental
groups in M. vison, which is active also at night
(wild animals, Birks 1996; farmed animals, Hansen
et al. 1994).

It is important to emphasise that the baths cer-
tainly had enrichment value for the mink. In addi-
tion to swimming, the mink spent a lot of time on
the edge of the baths, which has also been observed
earlier in farmed mink (Korhonen et al. 2003). This
behaviour corresponds well with that of mink in
the wild: they stare into the water before diving to
catch their prey (Dunstone 1993). The mink were
also particularly interested in the baths when they

were frozen in November-December. The use of
the frozen bath tended to correlate with swimming
time earlier in the autumn, indicating that the in-
terest in the baths was sustained even though its
properties changed radically. The difference in the
amount of stereotypies between mink housed with
a bath and those without was also greatest in No-
vember-December, which may either indicate that
the frustration-alleviating effects of the baths were
greatest then or simply result from the difference
between the groups in the rate at which stereotypies
developed in the course of the autumn.

On the other hand, we cannot be absolutely
sure that the higher number of stereotypies in the
control group in Experiment 3 was due to the lack
of swimming opportunity per se. It is possible that
the frustration resulted from seeing or hearing the
bath group mink swimming (cf. Vinke 2004). The
two groups in the present study were in cage rows
on two sides of a 100 cm wide corridor in the ex-
perimental animal barn. The view from the cages in
one row to the cages in the opposite row was not to-
tally obstructed by the two nest box rows between
the cages, and a mink looking over its nest box
might be able to see parts of the swimming pools
in the opposite cage row. However, being able to
see water may have little effect on mink’s motiva-
tion to work for access to water baths (Warburton
and Mason 2003).

Conclusions

There were very large inter-individual differences
in the frequency of swimming bouts and time spent
swimming in farmed mink, but due to the intra-
individual consistency in swimming behaviour,
farmed mink’s swimming behaviour can be assessed
in short-term experiments, especially in juvenile
animals. Furthermore, measuring water losses from
the swimming baths and instantaneous sampling
with a 10 min sampling interval proved to be less
laborious than continuous recording, while still
providing quite reliable measures of the amount
of swimming behaviour.

A G R I C U L T U R A L A N D F O O D S C I E N C E

Mononen, J. et al. Water baths for mink: swimming behaviour and effects on stereotypies

A G R I C U L T U R A L A N D F O O D S C I E N C E

Vol. 17 (2008): 41-52.

The bath use of the juveniles correlated with
that of their dams, which may indicate that an in-
dividual mink’s eagerness to swim has a genetic
component.

A long-term experiment showed that mink
housed without a water bath displayed more stere-
otypic behaviour than mink housed with a bath.
This suggests that water baths might have posi-
tive effects on the welfare of singly-housed mink.
However, preventing access to water baths experi-
mentally or naturally via freezing did not increase
stereotypic behaviour statistically significantly.
Furthermore, individual differences in the amount
of swimming did not predict individual differences
in stereotypic behaviour during thwarting.

Acknowledgements. The study was carried out at the
Research Station of the University of Kuopio (Juankoski,
Finland). We are grateful to the staff of the research station
for taking care of the animals and helping in carrying out
the experiments. We thank the two anonymous referees for
their constructive comments on this paper. This study was
supported by the Fur Animal Welfare Research Committee
and the Emil Aaltonen Fund.

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SELOSTUS

Uima-altaat tarhatuilla minkeillä: yksilölliset erot uimakäyttäytymisessä ja
vaikutukset hyvinvointiin

Jaakko Mononen, Maarit Mohaibes, Sakari Savolainen ja Leena Ahola
Kuopion yliopisto

Tutkimme turkistiloilla kasvatettavien minkkien (Mus-
tela vison) uimakäyttäytymistä ja sen mittaamista,
uimakäyttäytymisessä esiintyvää yksilöllistä vaihtelua
sekä uimismahdollisuuden vaikutusta stereotyyppiseen
käyttäytymiseen kolmessa erillisessä kokeessa. Minkit
kasvatettiin kaikissa kokeissa yksin kotihäkeissään,
joista niillä oli pääsy toiseen häkkiin, jossa oli 20,5 litran
uima-allas. Kahdessa lyhytkestoisessa (10 vuorokautta)
kokeessa tutkittiin yksilöllistä vaihtelua uimisen mää-
rässä sekä nuorilla että aikuisilla naarasminkeillä. Yh-
dessä pitkäkestoisessa (4 kuukautta) kokeessa verrattiin
käyttäytymistä nuorilla naarasminkeillä, joilla ei ollut
ja joilla oli käytettävissään uima-allas. Käyttäytymisen
analysoinnit tehtiin 24 tunnin videonauhoituksista, joita
tehtiin lyhytkestoisissa kokeissa kaksi tai kolme kertaa
ja pitkäkestoisessa kokeessa neljä kertaa. Yksilöiden

väliset erot uimakäyttäytymisessä olivat suuria, mutta
yksilöiden uimakäyttäytyminen ei kuitenkaan vaihdellut
paljoa eri mittauskertojen välillä, ja minkkien uimamo-
tivaatiota voidaankin siten mitata luotettavasti myös
lyhytkestoisissa kokeissa (etenkin nuorilla eläimillä).
Minkkien turkin mukana uima-altaasta poistuneen ve-
den määrä oli melko luotettava uimisen määrän mittari.
Samoin käyttäytymisseurannoissa kymmenen minuutin
tarkkailuväli riitti melko luotettavan kuvan saamiseen
vuorokautisesta kokonaisuintimäärästä. Pitkäkestoisessa
kokeessa havaittiin, että uima-altaiden kanssa eläneillä
minkeillä oli vähemmän stereotyyppistä käyttäytymistä
kuin ilman uima-altaita eläneillä minkeillä. Tämä osoit-
taa, että uima-altaat saattavat vähentää yksin kasvatet-
tujen nuorten minkkien turhautumista ja parantaa siten
niiden hyvinvointia.

Water baths for farmed mink: intra-individual consistency and inter-individual variation in swimming behaviour, and effects on stereotyped behaviour
Introduction
Material and methods
Results
Discussion
Conclusions
References
SELOSTUS