Stereotypies in polar bears

Zoo Biology 10:177-188 (1991)

Stereotypies in Polar Bears Beat Wechsler

Tiergatfenbiologische Abteilung, Universitat Zurich, Zurich, Switzerland

The spatial and temporal patterns of stereotypies in three captive polar bears (Ursus maritimus) were analysed. There was considerable variation in the time budgets of the three animals: stereotypies made up 16.0%, 24.4%, and 76.5% of the observation time between 8.00 A.M. and 4.00 P.M. Stereotyped walking or swimming bouts were of significantly longer duration than variable walking or swimming bouts. Seventy-five bouts of stereotyped walking were observed in detail to test the hypothesis that stereotypies can reduce arousal level. The bouts were composed of regular laps. At a given site, each lap consisted of a fixed number of steps, and there was little variation in the duration of a lap. In one individual the walking speed decreased significantly in the course of stereotyped walking bouts. Generally, however, stereotyped walking bouts were not preceded by high activity levels and followed by low activity levels. Stereotyped walking was regularly associated with yawning and tongue-flicking. Qualitative observations suggest that polar bears remain attentive while stereotyping. It is hypothesized that stereotyped walking in polar bears does not originate from frustrated migratory activity, but from frustrated appetitive behavior.

Key words: stereotypy, abnormal behavior, arousal, coping, appetitive behavior

INTRODUCTION

Stereotypies are regularly associated with animal housing conditions that devi- ate fundamentally from the species’ natural environment. They are widespread in intensive farm animal husbandry systems characterized by extreme spatial confinement and a monotonous environment [Kiley-Worthington, 1977; Sambraus, 1985bl. They are also frequently observed in isolation-reared primates lacking the social part of a species-specific environment [Berkson, 1968; Davenport, 19791. Stereotypies have been described in a wide variety of zoo animals [Boorer, 1972; Hediger, 1950; Meyer-Holzapfel, 1968; Morris, 19641.

Stereotypies develop and are performed in situations characterized by motivational conflict [Kiley-Worthington, 1977; Meyer-Holzapfel, 1968; Odberg, 19781. Tinbergen and Tinbergen [ 19721 , for example, hypothesized that the stereotyped

Received for publication May 3, 1990; revision accepted December 12, 1990.

Dr. Beat Wechsler is now at Ethologie und Wildforschung, Zoologisches Institut, Universitat Zurich- Irchel, Winterthurerstr. 190, 8057 Zurich, Switzerland. Address reprint requests there.

0 1991 Wiley-Liss, Inc.

178 Wechsler

movements often observed in autistic children are based on a motivational conflict between avoiding and approaching. Unsolvable conflict situations are especially likely to induce stereotypies [Wiepkema, 19821. Duncan and Wood-Gush [ 19721 described the development of stereotyped pacing in domestic hens frustrated by food presented under a plexiglass cover. Once established, stereotypies are readily trans- ferred to other conflict situations. Therefore, a situation that releases stereotyped behavior does not have to be the one that initially shaped the stereotypy [Hinde, 1966; Kiley-Worthington, 19771.

Situations of conflict, thwarting, and frustration are associated not only with stereotyped behavior, but also with high levels of arousal [Berlyne, 19601. The arousal theory assumes that arousal “is a variable which has clear effects on general behavior and which varies along a single continuum from sleep through full wake- fulness to states of high excitement or emotion” [Andrew, 1974, p. 1351. Arousal levels can be measured by various physiological and behavioral variables. High arousal levels are related to high levels of activity and responsiveness [Andrew, 19741, and to high rates of information processing in the nervous system [Delius, 19701. Amphetamine, which causes the release of noradrenaline and produces increased activity, is known to induce stereotypies [Ridley and Baker, 19821.

Berkson and Mason [ 19641 found that rocking and swaying in chimpanzees are related to high levels of arousal. Hutt and Hutt [1968] reported that bursts of stereotypy in autistic children occurred together with a desynchronisation of the EEG, which indicates a high level of arousal. They hypothesized that “stereotypies sub- serve a neurophysiological system whose function is to regulate level of arousal” [Hutt and Hutt, 1968, p. 2831. A similar conclusion was drawn by Delius [1967, 19701 for displacement activities, which are also observed in situations of conflict, thwarting, or frustration. He assumed that displacement activities form part of a de-arousal process to reduce the information processing rate in the nervous system below its limited channel capacity. Stereotyped behavior patterns could also serve this function, as they “require less processing capacity than the more complex and less often repeated patterns of behavior” [Fentress, 1976, p. 1581.

There is some evidence that stereotyped behaviors may lower the arousal level. Soussigan and Koch [ 19851 found a decrease in the heart rate during rhythmical leg swinging in normal school children. Dantzer and Mormede [I9831 reported that stereotyped chain pulling in pigs was accompanied by decreased pituitary-adrenal activity, as indicated by a reduction in plasma corticosteroid concentrations. These results confirm the view that there is a connection between the arousal system and the stress system [Hennessy and Levine, 19791. Accordingly, the injection of a tranquilizer delayed the onset of stereotyped movements and reduced the frequency of established stereotypies in hens frustrated by a food thwarting situation [Duncan and

Stereotypies in polar bears are proverbial. In the Dutch language there is the verb ijsberen (“to polar-bear”), which is translated as walking up and down restlessly. The aim of this study was to analyse the spatial and temporal patterns of walking stereotypies in polar bears with respect to the arousal level of the stereotyping animals, as well as changes in the arousal level during stereotyped walking. It was hypothesized that polar bears start to walk stereotypically when a critical level of arousal is exceeded, and that stereotyped walking reduces their arousal level. The hypothesis is tested by a comparison of activities preceding and following stereotyped

Wood-Gush, 19741.

Stereotypies in Polar Bears 179

walking bouts, and an analysis of changes in the walking speed during stereotyped walking.

MATERIALS AND METHODS Subjects and Housing

The study is based on behavioral observations of three polar bears (Ursus maritimus) living as a group at Zurich Zoo. Ludmilla, an old female, was born at Zurich Zoo in 1964 and was hand-reared. Malka, a subadult female, was wild-born in 1985 and Majno, a male, was born at Munster Zoo in 1984. Both Malka and Majno were brought to Zurich Zoo and grouped with Ludmilla in 1986.

The subjects were housed in an outdoor cage of 15.0 m X 12.0 m built in 1934. The cage included a moat of 15.0 m X 6.6 m situated between the visitors’ path and an artificial rock. The rock consisted of a rather steep ascent and a plateau 3.4 m above the water surface of the moat and on level with the visitors’ path. In the steep part of the rock there were two caves, one 80 cm above the water surface (3.7 m X 3.1 m X 2.0 m high), the other one just below the plateau (2.5 m X 1.7 m X 1.2 m high). The plateau was surrounded by walls on three sides. On the left side of the rear wall, 35 cm above the plateau level, there was a third cave (3.8 m X 1.9 m X 1.4 m high). The plateau itself had a surface of 50 m2. At the right end of the plateau there were three indoor cages. The polar bears were fed in two of these indoor cages once a day between 4.00 P.M. and 5.30 P.M. The rest of the day they spent in the outdoor cage.

Data Collection

Data were collected in July and August 1989. Time budgets were obtained using a continuous sampling method. All three animals were observed simultaneously as focal animals, and transitions between different activities were recorded with a keyboard data collection system (Zirelco Datapad). The following activities were scored: lying, sitting, swimming variably, swimming in stereotyped laps, walking on stereotyped paths or walking variably (including standing as well as sniffing, scratching, or socially interacting while standing). At every moment each individual could be as- signed to one of these activities, and the animals were always visible.

The stereotyped walking or swimming bouts were in accordance with the op- erational definition of Fraser and Broom [ 19901: “a stereotypy is a repeated, rela- tively invariate sequence of movements which has no obvious purpose” (p. 307). They were composed of regular laps (or to-and-fros), and each individual stereotyped at particular sites of the cage. The transition from a variable to a stereotyped walking or swimming bout was recorded when the animal had finished a first complete stereotyped lap. As soon as the animal left the typical stereotyped path, the bout was recorded as terminated. Thirty-two one-hour observations were evenly distributed between 8.00 A.M. and 4.00 P.M.

A second data set was collected independently of the time budget study. It consisted of 75 stereotyped walking bouts that were observed in detail. A variably walking individual was chosen as focal animal, and a protocol was started when the animal had completed one stereotyped lap. The duration of each following lap was recorded with the keyboard data collection system. The start of a new lap was recorded whenever the focal animal put its paw on a defined spot of the stereotyped

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TABLE 1. Percentage of time spent at different activities by three captive polar bears

Individual

Activity Ludrnilla Malka Majno

Lying 47.7 57.5 1.3

Variable walking 6.2 7.3 13.1 Variable swimming 4.2 5.1 8.1 Stereotyped walking 1 .o 16.0 61.3 Stereotyped swimming 2.8 0.0 15.2 Paw-sucking-scratching stereotypy 20.6 0.0 0.0

Sitting 17.5 14.1 1 .o

path. The occurrence of breaks in the walking speed (the animal stops walking for at least one second), deviations from the typical stereotyped path, and all occurrences of yawning or tongue-flicking were also recorded.

Qualitative observations were noted ad libitum during the data collection pe- riod, as well as during the preparation of the study in May and June 1989.

RESULTS Time Budgets

All three polar bears showed stereotyped walking bouts. Each individual performed these bouts at particular sites, repeating an equal number of steps over and over. Ludmilla was seen to walk in stereotyped laps on the left and on the right side of the plateau, as well as in the lowest cave. Malka stereotyped either on the left side or in the center of the plateau. Majno was the most variable with regard to sites of stereotyped walking. He had three stereotyped paths on the right side of the plateau, one in the center of the plateau, one on the left side of the plateau, and one in the lowest cave. Ludmilla and Majno also stereotyped while swimming. Ludmilla had only one stereotyped swimming lap on the right side of the moat, whereas Majno had two laps, one at each end of the moat. Malka was never seen to swim stereotypically. Ludmilla also showed a paw-sucking-scratching stereotypy. It consisted of sucking the palm of the right paw and licking the fingers alternating with scratching of the snout, head, or neck.

The individuals differed greatly in their time budgets (Table 1). Ludmilla was very inactive, lying or sitting most of the time. Majno, however, was hardly ever quiet. During 76.5% of the observation time, he either walked or swam stereotypically .

Majno and Ludmilla performed their stereotypies evenly throughout the day, whereas Malka stereotyped increasingly in the course of the afternoon (Fig. 1). All three animals would, however, sit down in front of the slides and wait quietly during the last minutes before these were opened for feeding. On occasional observations at 7.00 A.M. and 8.00 P.M., all three polar bears were lying down.

The time budget protocols were used to compare the length of stereotyped and non-stereotyped bouts (Table 2). Incomplete bouts at the beginning or end of a protocol were omitted from this analysis, and Ludmilla was not included, as the sample sizes of her stereotyped walking or swimming bouts were less than five. There was considerable variation in bout length, but for both individuals stereotyped walk-


V Ludmilla

I Malka - Majno

60

Daytime .f feeding time

Fig. 1. Distribution of stereotyped activities of three captive polar bears over daytime.

TABLE 2. Mean duration and range of stereotyped and variable activity bouts in polar bears

Bout length (secl

Individual Activity Mean (N) Minimal Maximal

Malka Stereotyped walking 291.2 (40) 11.9 1182.1 Variable walking 61.7 (124) 6.1 315.9

Majno Stereotyped walking 257.6 (192) 8.4 1644.1 Variable walking 54.8 (250) 3.6 855.3

Majno Stereotyped swimming 250.7 (45) 14.8 1554.5 Variable swimming 110.3 (81) 10.4 1276.7

ing bouts were significantly longer than variable walking bouts (P < .001, Mann- Whitney U-test) . Majno’s stereotyped swimming bouts were significantly longer than his variable swimming bouts (P < .005, Mann-Whitney U-test). The longest variable walking bouts observed in Malka and Majno lasted for less than 15 min.

By definition (see Materials and Methods) each stereotyped walking bout was preceded by a variable walking bout. It was assumed that the transition from a variable to a stereotyped walking bout occurred whenever a critical arousal level was exceeded. It was further assumed that an inactive polar bear (lying or sitting) was at a lower arousal level than an active polar bear (walking or swimming), and that an inactive polar bear needed more time to reach the critical arousal level than an active polar bear. Based on these assumptions, one would predict that a variable walking bout immediately preceding a stereotyped walking bout of a previously inactive polar bear should last longer than a variable walking bout of a previously active one. No significant difference was found, however, for either Malka or Majno ( P > .05, Mann-Whitney U-test). For both animals there was also no significant difference in the duration of stereotyped walking bouts, whether the individual was inactive or active before stereotyping ( P > .05, Mann-Whitney U-test).

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TABLE 3. Frequencies of activities preceding or following stereotyped walking bouts (N = 257) in polar bears

Temporal position relative to stereotyped Stereotyped

Activity

Individual walking walking Sitting Lying Swimming

Ludmilla Preceding 1 1 0 I Following 1 0 0 1

Following 15 18 3 7 Majno Preceding 155 14 5 33

Malka Preceding 15 20 5 6

Following 155 19 3 31

If there were a change in the arousal level from the beginning to the end of a stereotyped walking bout, one might expect a difference in the kind of activities preceding and following stereotyped walking bouts. Table 3 shows the second-order transitions of activities preceding and following a stereotyped walking bout. The transitions are called second-order, as all variable walking bouts, which by definition immediately preceded or followed a stereotyped walking bout, were omitted. In all three animals there was no obvious difference in the distribution of activities preceding or following a stereotyped walking bout.

Stereotyped Walking Bouts

Seventy-five stereotyped walking bouts were observed in detail (Table 4). The analysis is restricted to the most frequently used stereotyped paths. It includes one stereotyped walking site of Malka and three sites of Majno. There was considerable variation in the number of laps per bout, but the duration of a single lap was very constant for a given stereotyped path. All incomplete laps, i.e., all laps during which there was either a break in the walking speed or a deviation from the typical stereotyped path, were excluded form the analysis of lap duration. Seventeen percent of Malka’s and 9% of Majno’s laps were incomplete. The longest stereotyped walking bout observed in Majno consisted of 285 laps and lasted for 74 min. The number of steps per lap was fixed at every site, and the paws regularly touched the ground on the same spots. Malka’s stereotypy had two slightly different versions (32 or 34 steps), resulting in a greater standard deviation of the mean duration of a lap. She typically repeated one version several times before switching to the other version.

A change in the arousal level during a stereotyped walking bout could be reflected by a change in the walking speed. In order to test this hypothesis, durations of complete laps of the first and the second halves of stereotyped walking bouts were compared. Only bouts consisting of at least 20 complete laps were included in this analysis. There was a significant slow down effect with Majno. In 21 out of 29 stereotyped walking bouts, his mean lap duration was shorter in the first than in the second half of the bout ( P < .05, Binomial test, two-tailed). There was no such tendency with Malka (4 out of 10 bouts), but her lap durations were strongly biased by the fact that a lap consisted of either 32 or 34 steps.

Yawning and tongue-flicking were regularly observed during stereotyped walking. Malka yawned in 6% of the stereotyped laps and tongue-flicked in 48% of the


TABLE 4. Characteristics of Stereotyped walking bouts in polar bears

Individual

Characteristic Malka

Site of the stereotype

Laps per bout

Plateau left No. of bouts analysed 22

Mean 37.4 Min-Max 6-124

Duration of lap Mean (sec) 23.1 SD 0.81 N 685

Steps per lap 32 or 34

Majno

Plateau left 10

40.5 7-285

15.9 0.34

424 24

Maino

Plateau center 18

34.6 6-175

13.7 0.34

566 20

Majno

Plateau right 25

59.6 11-273

10.9 0.33

1383 16

laps. The respective values for Majno were 7% (yawning) and 33% (tongue-flicking). Tongue-flicking was sometimes shown two or three times during a lap, whereas yawning only occurred once per lap. Both behavior elements were not evenly distributed over the stereotyped path, but were clearly, though not exclusively, associated with certain parts of the path. This is also true for the head waving movements shown during stereotyped walking. They were typical for a given individual, and a given stereotyped path, but most developed in Ludmilla’s walking stereotypies. Con- trary to yawning and tongue-flicking, the head waving movements were regularly shown in every lap.

The incidence of yawning and tongue-flicking was not independent. During a given lap, typically either both or neither of these behavior elements occurred (Malka: x2 = 10.2, df = 1, P < .001, N = 823 laps; Majno: x2 = 13.7, df = 1, P < .001, N = 2,609 laps). It was hypothesized that the two behavior elements could be interpreted as conflict behavior and that motivational conflicts would mainly occur after the disruption of a stereotyped bout. The first lap following an incomplete lap, however, was not more frequently associated with yawning or tongue-flicking (Malka: x2 = 0.2, df = 1, P > .05; Majno: x2 = 2.5, df = 1, P > .05). Yawning was not significantly more frequent in laps of the first than of the second half of stereotyped bouts, either with Malka (x2 = 0.06, df = 1, P > .05) or with Majno (x2 = 0.4, df = 1 , P > .05), whereas tongue-flicking was more frequently associated with laps of the second half with Majno (x2 = 9.0, df = 1, P < .005), but not with Malka (x2 = 0.3, df = 1, P > .05).

Qualitative Observations

The polar bears were not at all inattentive while walking stereotypically. They stopped and looked up at once when a caretaker passed on the visitor’s path, or when a visitor threw a leaf or a small branch into the moat. They also spontaneously broke their stereotypies to sniff on the ground or to look around. Altogether, 15% of Malka’s stereotyped laps and 6% of Majno’s laps were interrupted.

In 5% of Malka’s laps and 5% of Majno’s laps there was a deviation from the normal stereotyped path. The most common type of deviation was a shift of the turning-point of stereotyped to-and-fros, resulting in a smaller number of steps for that lap. Usually there was no obvious reason for this shortening of the path, but

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sometimes the stereotyping animal clearly turned in advance to prevent a collision with a cage mate passing the stereotyped path. This was seen especially often when Malka and Majno stereotyped simultaneously on the left side of the plateau. Inter- estingly, it was always Majno who adapted his path, whereas Malka rigidly followed her stereotyped path. Majno normally went off after a while and stereotyped at one of his other sites.

Majno selected his site of stereotypy according to the position of his cage mates. If Ludmilla and Malka were on the left side of the plateau, he stereotyped on the right side, and vice versa. He clearly preferred stereotyping undisturbed over adapting the number of steps per lap. Whenever Ludmilla or Malka sat or lay down on his actual stereotyped path, he soon left and continued at another site. As Majno performed stereotyped walking for 61.3% of the observation time, such disturbances occurred very often. Nevertheless, he was never seen to react aggressively to the interrupting cage mate.

Majno frequently changed from stereotyped walking to swimming and back with only short bouts of variable walking in between. Soon after entering the water he used to change from variable to stereotyped swimming. He then swan in stereotyped laps, pushing off the wall, diving and emerging always within the same part of the lap. This was also true for the stereotyped swimming laps of Ludmilla. Sometimes Ludmilla and Majno simultaneously swam stereotypically on the right side of the moat, and they both avoided collisions by slightly adapting their stereotyped laps.

Situational adaptation of a stereotyped walking path has also been observed anecdotally. Majno was stereotyping in the center of the plateau (10 steps to and 10 steps fro) when he was disturbed by Malka, who defecated on the right end of his stereotyped path. He first moved off, but soon returned and started stereotyping again, 9 steps to and 9 steps fro, properly avoiding the feces. This example illustrates again that polar bears remain attentive while Stereotyping.

DISCUSSION

Stereotyped walking in polar bears is more than walking up and down restlessly at sites within the cage. The stereotyped laps consist of a fixed number of steps, the paws regularly touch the ground on the same spots and there is little variation in the duration of a stereotyped lap at a given site. The spatial and temporal fixation gives the impression that there is something compulsory in these stereotyped movements. They seem to be “pre-organized” [Fentress, 19761 in the nervous system so that, once released, they do not have to be guided by the environment [Morris, 1964, 19663.

It has been hypothesized that stereotypies are accompanied by a reduced sensitivity to extraneous inputs [Fentress, 1976; Odberg, 1978; Wiepkema, 19821. This is not confirmed by my observations. The polar bears readily interrupted their stereotyped walking to react to relevant cues (caretaker passing, object thrown into the cage), and they were able to abandon the rigidity of their stereotyped paths in adaptation to special situations. The sensitivity to extraneous inputs, however, may vary in relation to the intensity or the age of a stereotypy. Fentress [ 19761 observed a Cape hunting dog (Lycnon pictus) adapting its figure-eight stereotyped path to avoid a chain that was newly placed at its crossing point. The animal stumbled over the chain


several times, however, when it raised its speed of pacing because of external disturbances.

The fact that the polar bears remained attentive while stereotyping does not contradict the theory that stereotypies may lead to self-generated increased sensory input [Hinde, 1966; Kiley-Worthington, 19771, and that this input may reduce a motivational conflict, as it is highly predictable [Forrester, 19801. But stereotyped walking in polar bears does not seem to serve as “cut-off” behavior [Chance, 19621 in order to control the arousal level by switching attention to self-generated, repetitive stimuli of little novelty [Delius, 1967; Hutt and Hutt, 19651.

The reduction in walking speed in the course of Majno’s stereotyped bouts suggests that walking stereotypies reduce his arousal level. Other results, however, speak against this interpretation. There was no general pattern in which high activity levels mainly preceded and low activity levels mainly followed stereotyped walking bouts. The activity level before stereotyping also had no significant influence on the duration of the variable walking bout immediately preceding a stereotyped walking bout. Still, it remains possible that walking stereotypies reduced the arousal level in polar bears from yet higher levels. To test this hypothesis, the polar bears should be prevented from stereotyping. When such tests were carried out on tethered sows by applying naloxone, which blocks opioid brain receptors, the per- formance of stereotypies was reduced and the sows showed high arousal levels, even attempting to attack neighboring sows and to escape the tether [Wiepkema et al., 19841.

Stereotyped walking in polar bears was associated with yawning and tongue- flicking. These behavior elements may be interpreted as displacement activities and indicators of a high arousal level [Delius, 19671. It was therefore surprising to find tongue-flicking preferentially associated with the slower laps of the second half of Majno’s stereotyped walking bouts. Duncan and Wood-Gush [ 19741, however, found a similar result in frustrated hens. They reported that after the injection of a tranquil- lizer there was a significant decrease in the frequency of stereotyped pacing, but also a significant increase in the frequency of preening. Possibly, displacement activities are related to a lower arousal level than stereotyped movements.

Stereotypies made up a considerable portion of the time budgets of the three polar bears observed. They were distributed over the daily activity, and were not released by external disturbances. This gives the impression that polar bears regularly get in a motivational state that forces them to perform stereotyped behavior. That impression was especially strong with Majno, who just “could not” stop being active, and for whom stereotyped behavior seemed to be a “better” form of activity than variable behavior. But why do polar bears walk and swim stereotypically ?

The behavioral organization of a species has been shaped by an evolutionary process in adaptation to the natural environment. Stereotypies, like other abnormal behaviors, must be considered as an animal’s attempt to cope with an unnatural environment. Functionally they seem useless or purposeless [Odberg, 19781, but on the proximate level they represent behavioral strategies to reach motivational homeostasis in housing conditions that exceed the possibilities of normal coping behavior [Stolba et al., 1983; Wiepkema, 19831. The concept of coping refers to the animal’s behavioral strategies to react to aversive situations (e.g., flight, attack, exploration), and is related to the concept of stress [Levine et al., 19781.

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Stereotyped pacing is often observed in species that are active by nature [Meyer- Holzapfel, 19681 or species that patrol a territory in the wild [Morris, 19641. In farm animals various kinds of mouth-based stereotypies have been described [Sambraus, 1985al. It has been argued that locomotion and ingestion are essential activities for a wild animal and that the frustration of these two activities by spatial confinement or concentrated food results in stereotyped locomotory and mouth-based behaviors [ Sambraus , 1 985 b] .

Polar bears are known to travel for long distances. Marked individuals have been recaptured up to 1000 km away from the capture location after one or two years [Lentfer, 1983; Schweinsburg et al., 19821. Lentfer [1983] computed an average travel speed of 10.7 km per day, requiring 2 hours walking each day [Larsen et al., 19831. Perhaps the stereotyped walking observed in captive polar bears corresponds to the migratory activity of wild polar bears. Time budget studies in wild polar bears, however, indicate that this explanation may not be sufficient. Stirling [ 19741 reported 25% traveling in polar bears kept under continuous observation in July and August. Martin and Jonkel [1983] found 13%, 18%, and 35% traveling per day at three different sites from May to July. Knudsen [ 19781, observing polar bears from July to October and mainly between 10.00 A M. and 6.00 P.M., recorded only 11.2% traveling, whereas Majno walked variably or stereotypically during 74.4% of the time between 8.00 A.M. and 4.00 P.M.

The explanation that stereotypies originate from frustration of locomotion or eating behavior [Sambraus, 1985bl neglects the fact that walking and food handling (licking, biting, gnawing, pecking) also form part of the appetitive behavior. In a specie’s natural environment, it is adaptive for a highly motivated animal to show appetitive behavior to find the adequate releasing stimuli [Lorenz, 19781. Two different strategies of appetitive behavior can be distinguished. Either an animal moves to other places with potentially releasing stimuli, or it explores the place in which it is to discover hidden releasing stimuli. Neither strategy is feasible in barren animal housing conditions: locomotion is restricted and exploration is useless, as everything within the cage is already familiar. Nevertheless, the animals continue to show appetitive behavior. They redirect their behavior to inadequate objects [Sambraus, 1985al and they perform repetitive sequences of locomotory and exploratory behavior [Morris, 19641.

Stereotypies are known to be related to monotonous environments and boredom [Kiley-Worthington, 1977; Sambraus, 1985b; Wemelsfelder, 19851. An adaptive way to cope with boredom is to exhibit appetitive behavior, which may gradually develop into stereotyped behavior. Cronin et al. [ 19841 differentiated four stages of coping strategy in newly tethered sows. After an initial stage of frantic resistance, the sows went through a stage of increased drowsiness. They then started to show short bursts of repetitive exploratory elements (sniff, lick, touch, bite), and finally developed individual-specific stereotypies . Morris [ 19661 compared the rigidification of appetitive behavior in zoo animals with the evolution of ritual displays. Finally, stereotyped behavior may completely replace appetitive behavior and the animals stereotype whenever “they feel they should do something but do not know what to do” [Fentress, 1976, p. 1611. To summarize, there is evidence supporting the hypothesis that the most invariate behavior, stereotyped behavior, develops from the most variable behavior, appetitive behavior.


CONCLUSIONS

1. Stereotypies can make up a considerable portion of the time budgets of captive polar bears. They seem to refer to recurring motivational states, as they are distributed over the daily activity and not released by external disturbances.

2. Walking stereotypies in polar bears are fixed both spatially and temporally. At a given place an equal number of steps is repeated over and over, the paws regularly touch the ground on the same spots, and the duration of a lap hardly varies.

3 . A reduction in walking speed during stereotyped walking observed in one individual could indicate that this activity reduces the level of arousal.

4. A comparison with time budgets of wild polar bears suggests that the interpretation that stereotyped walking in captive polar bears corresponds to the migratory activity of wild bears may not be sufficient. It is hypothesized that walking stereotypies do not develop from frustrated traveling, but from frustated appetitive behavior.

ACKNOWLEDGMENTS

I am grateful to Marina Cords and Christoph Wiedenmayer who commented on the manuscript.

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Stereotypies in polar bears