Bulletin of the Psychonomic Society 1977, Vol. 9 (3),186-188 Interspecific attack on mice and frogs by golden ( auratus)

PAUL E. VAN HEMEL Franklin and MarshaU College, Lancaster, Pennsylvania 17604

When tested for their reactions to mice, most male and female hamsters attacked with a pattern typical of attacks on conspecifics_ Females attacked with shorter latency than did males, and the very few hamsters that consistently killed mice were all females. Latencies of attack decreased with repeated testing, even though most attacks were not followed by killing. When tested with frogs, hamsters typically avoided the frogs, although a few showed long-latency attacks and kills. A detailed description of the topography of interspecific attack by hamsters and other closely related groups would be useful as a beginning step in analysis of the function of interspecific attack.

Psychologists investigating mouse-killing behavior in If hamsters attack mice and frogs, as rats do (Bandler rats have been primarily concerned with the causation & Moyer, 1970), then a comparison of behavioral and ontogeny of the behavior (polsky, 1975a). Studies phenotypes would be useful as a beginning step for that concentrate on such proximate determinants of functional analysis. Hamsters are known to attack behavior focus on issues quite different from those locusts (polsky, 1974, 1976) and may catch and raised by studies concerned with ultimate questions consume insects (Jacobs, 1945). There has even been about the function, or ecological significance, and the a report of spontaneous attacks by hamsters on mice evolution of behavior (Alcock, 1975). Some authors (Wnek & Leaf, 1973). The present studies were con­ have nonetheless been willing to attribute function to ducted as a preliminary investigation of the reactions mouse killing, characterizing it as an element of a of golden hamsters to mice and frogs. Hamsters of predatory sequence (O'Boyle, 1974), although it could both sexes were used to determine if the reputed greater as easily be considered a form of aggression (Moyer, pugnacity of the female (Short & Woodnott, 1969) 1968) which provides an intrinsic source of reinforce­ would appear in interspecific encounters. ment in its species-typical attack pattern (Van Hemel, 1972, 1975). In the absence of comparative data, EXPERIMENT 1 statements about the function and evolution of behavior are of questionable validity (Hinde, 1970). Method The subjects in studies of interspecific attack in Subjects. The subjects were 30 male and 30 female experi­ have represented a rather wide range of mentally naive outbred golden hamsters, Mesocricetus auratus, obtained from Lakeview Hamster Colony, Newfield, New species (see Polsky, 1975a, b for reviews), but compara­ Jersey. During a 10-day adaptation period before the experiment tive studies (e.g., Kruuk & Turner, 1967; Thomas, and throughout experimental testing, subjects were individually 1969; Wnek & Leaf, 1973) are rare. Cross-species com­ housed in standard suspended rat cages with food and water parison of behavioral phenotypes is the desirable way to continuously available. Procedure. Daily testing for the hamsters' reactions to mice begin species comparisons of similarities and differences began 10 days after the hamsters' arrival at the laboratory. Each in a unit of behavior (Gottlieb, 1976). For such com­ day an adult albino mouse was placed in each hamster's cage. parison, it is preferable to use species believed to be Latencies of any attacks and kills were measured with a stop­ closely related phylogenetically, thus reducing the watch. Attack latency was defined as the time elapsed between likelihood that apparently close similarities between presentation of the mouse and the first seizure of the mouse by the hamster. Killing latency was dermed as the time between species may tum out to be only parallel evolutionary presentation of the mouse and cessation of movement by the adaptations to similar environmental demands (Hinde, mouse. Except on the final test day for each hamster, bodies of 1970). killed mice were removed within 1 miR of the kill, and mice Hamsters and rats are both muroid ; hamsters that were not killed were removed after 1 h. Testing continued at daily intervals for each hamster until that reached fall in the family , rats in the family Muridae. a criterion of consistent reaction, either killing or failing to kill on 10 successive days. On the last test for each animal, the mouse was left with the hamster overnight, whether or not The author is grateful to the Franklin and Marshall College it was killed, and the conditon of the mouse was noted the Committee on Grants for financial support, to Vincent M. next day. Colucci for wondering whether hamsters attack mice, and to Susan B. Van Hemel for helpful criticism of an earlier draft of the paper. Requests for reprints should be sent to Paul E. Results and Discussion Van Hemel, Department of Psychology, Franklin and Marshall For one familiar with studies of mouse killing by rats, College, Lancaster, Pennsylvania 17604. several features of the behavior of hamsters toward

186 INTERSPECIFIC AGGRESSION IN HAMSTERS 187 mice were salient. Only 8 of the 60 hamsters killed on When mice were left overnight with the hamsters at 10 successive days to reach criterion, and all 8 of them the end of testing, seven kills occurred after the end of were females. All of the males and 22 females reached the I-h test. Counting the eight kills by the consistent the nonkilling criterion. However, the nonkillers did not killers, that left 15 hamsters in the presence of dead ignore the mice. Every hamster attacked at least one mice for an extended period. Parts of only two of the mouse, and most hamsters energetically attacked every dead mice were chewed by the next day. Although mouse, persistently biting at flank and tail and chasing many hamsters attacked mice, and some killed con­ when the mouse retreated, a characteristic hamster sistently during the experiment, few ate killed mice attack pattern (Lerwill & Makings, 1971). In one inter­ when the opportunity was given. esting and frequently occurring pattern, the hamster .repeated1y attacked from the sideways offensive posture EXPERIMENT 2 described by Grant and Mackintosh (1963), followed by a lengthy period of lying motionless on its side, with a Method SUbjects. Forty experimentally naive golden hamsters, 20 subsequent resumption of the vigorous chase. Serious of each sex, were obtained from Lakeview Hamster Colony. or fatal injury to the mouse was the exception rather As in the fust experiment, they were housed individually with than the rule, although many hamsters killed some mice continuous access (0 food and water before and during experi­ and a few were consistent killers. Twenty males and mental testing. 18 females showed reversals of reaction before becoming Procedure. Rather than testing to a criterion of consistent killing or nonkilling for 10 successive days, daily for 20 days consistent killers or nonkillers. Eight of those males and each hamster received one test of 1-h maximum duration with 10 of the females required 15 or more trials to reach a stimulus animal. Latencies of any attaCks and kills were meas­ criterion. Thirty-two of the 52 nonkillers killed some ured with a stopwatch, and bodies of any killed stimulus mice before failing to kill on 10 successive days. It were removed within 1 min of the kill. During the fust 10 test days, half the males and half the females were tested with frogs, remains to be determined whether the variable reactions and the other half were tested with mice. For the second 10 test of the hamsters to the mice resulted from some par­ days, hamsters that had been tested with frogs were tested with ticular developmental experience of the hamsters, or mice and hamsters that had been tested with mice were tested from variations in the behavior of the mice in the with frogs, until each hamster had received 10 tests with each test situation. of the two types of stimulus animal. Possible order effects in testing were thus counterbalanced, with the exception that one Figure 1 shows the median attack latency during the male and ..one female died of unknown causes before testing was last 5 days of testing for 23 males and 23 females that completed. Their data were excluded from the analysis. each attacked at least 10 mice during the experiment. Analysis of the latencies of the first 10 attacks by these Results and Discussion animals showed a significant decline in latency for both Every hamster in this experiment attacked at least sexes (sign tests, p < .001), but high variability obscured half of the 10 mice presented, but only 53% of them any differences between males and females in latencies attacked any frogs. Nine males and nine females never of these early attacks. However, the median test (Siegel, attacked any of the 10 frogs presented, and 11 of those 1956) showed that the faster attack by females during hamsters that did attack frogs attacked on only 1 or the last 5 days, evident in the figure, was reliable 2 of the 10 opportunities. Because there were no (X 2 = 5.565, P < .02). discernible significant differences in attack latencies between the group tested with frogs first and the group 90 tested with mice first, the data were pooled for further .., .---~ ""? analysis . u ~7S Figure 2 shows the median attack latency for males and females during the last 5 days of testing with mice :> u and during the last 5 days of testing with frogs. la­ Z60 ///\\ UJ tencies of attack on frogs were far longer than the .0 .. latencies of attack on mice, and the difference was ~ .•.. ..J4S .. reliable (Mann-Whitney U test, Z = -5.76, P < .001) . ~ As in the first experiment, females attacked mice sig­ U ...... •...... nificantly faster than did males (Mann-Whitney U test, ~30 .. p < .025). The apparent differences between males ~ ...... •...•.. and females in latency of attack on frogs, based on fewer Z IS ~ o~~o ___ •••• animals attacking, was not statistically reliable. C -0--=-__- 0 The behavior of the hamsters in the presence of frogs UJ ~ was highly variable. Initial exploration quickly gave 2 3 .. 5 way to avoidance in most cases, with the hamster DAYS actively moving to the opposite end of the cage from the Figure l. Median attack latency as a function of days during frog, often emitting a rasping vocalization in so doing. the last 5 days of testing for 23 males and 23 females that each Several hamsters attacked frogs on 5 or 6 days, and on attacked at least 10 mice during Experiment 1. occasion a sustained biting attack resulted in killing. 188 VAN HEMEL

REFERENCES

>- ALCOCK, 1. Animal behavior: An evolutionary approach. ~ Sunderland. Mass: Sinauer. 1975. UJ BANDLER, R., & MOYER, K. E. Animals spontaneously attacked by rats. Communications in Behavioral Biology, ~ 1000 ~ 1970.5,177-182. ~ GOTTLIEB, G . Comparative psychology. American u Psychologist, 1976, 31, 295-297. 750 GRANT, E. C., & MACKINTOSH, J. H. A comparison of the 4~ social postures of some common laboratory rodents. z Behaviour, 1963, 21, 246-259. « HINDE. R. A. Animal behaviour: A synthesis of ethology and 0 comparative psychology. New York: McGraw-Hili, 1970. UJ JACOBS, D. L. Food habits of the . Journal of ~ Mammalogy, 1945, 26, 199. KARLI. P. The Norway rat's killing response to the white mouse: An experimental analysis. Behaviour. 1956. 10.81-103. KRUUK. H .• & TURNER, M. Comparative notes on predation by lion. leopard. cheet~h. and wild dog in the Serengeti area, MICE FROGS East Africa. Mammalia, 1967. 31. 1-27. TEST STIMULUS LERWILL, C. 1.. & MAKINGS, P. The agonistic behaviour of the golden hamster (Mesocricetus auratus). Animal Figure 2. Median attack latency, in seconds, for males and Behaviour. 1971. 19.714-721. females during the last 5 days of testing with mice and during MOYER, K. E. Kinds of aggression and their physiological the last 5 days of testing with frogs in Experiment 2. basis. Communications in Behavioral Biology, 1968. 2. 65-87. MYER. J. S. Stimulus control of mouse-killing rats. Journal of However, most of the frogs were not approached or Comparative and Physiological Psychology. 1964. 58. attacked. 112-117. MYER. 1. S. Experience and the stability of mouse killing by rats. Journal of Comparative and Physiological Psychology. GENERAL DISCUSSION 1971. 75. 264-268. O'BOYLE; M. Rats and mice together: The predatory nature In these experiments, some hamsters attacked and killed of the rat's mouse-killing response. Psychological Bulletin, mice and frogs. A greater percentage of hamsters attacked mice 1974. 81. 261-269. than attacked frogs, which is the reverse of the pattern seen POLSKY. R. H. Effects of novel environment on predatory when rats are tested with these stimulus animals (Bandler & behavior of golden hamsters. Perceptual and Motor Skills. Moyer, 1970). Female hamsters attacked mice faster than did 1974. 39. 55-58. males, confirming in interspecific attack the reputed greater POLSKY, R. H. Developmental factors in mammalian aggressiveness of females (Short & Woodnott, 1969). predation. Behavioral Biology. 1975. 15. 353-382. (a) With repeated testing, hamsters showed a decrease in latency POLSKY. R. H. Hunger. prey feeding. and predatory of attack on mice. A similar decline in latency of attacking or aggression. Behavioral Biology. 1975. 13. 81-93 . (b) killing has been a consistent rmding in studies of mouse killing POLSKY, R. H. Con specific defeat. isolation/grouping. and by rats (Karli, 1956; Myer, 1964; Van Hemel & Colucci, 1973), predatory behavior in golden hamsters. Psychological and has been taken as evidence for the reinforcing nature of Reports, 1976. 38. 571-577. killing behavior. The decrease in latency of attack on mice with SHORT. D. 1.• & WOODNOTT. D. P. The I.A. T. manual of repeated testing in the present experiment is particularly note­ laboratory animal practice and techniques. Springfield: worthy because a large portion of the attacks were not followed Charles C Thomas. 1969. by killing. This rmding is consistent with the view that reinforce­ SIEGEL, S. Nonparametric statistics, New York: McGraw­ ment is intrinsic to the attack itself (Van Hemel, 1972). How­ Hill. 1956. ever, especially given that the relative size difference between THOMAS. K. Predatory behavior in two strains of laboratory hamsters and mice or frogs is less than that between rats and mice. Psychonomic Science. 1969, IS, 13-14. mice or frogs, it is possible that the attacks by hamsters in VAN HEMEL, P. E. Aggression as a reinforcer: Operant these experiments were primarily defensive. Research is needed behavior in the mouse-killing rat. Journal of the to determine if hamsters would perform an arbitrary response Experimental Analysis of Behavior, 1972. 17. 237-245. followed by the opportunity to attack mice. V AN HEMEL, P. E. Rats and mice together: The aggressive Because latencies of attack and kill were the primary de­ nature of mouse killing by rats. Psychological Bulletin, pendent measures in these experiments, there was no objective 1975. 82.456-459. record of such interesting aspects of the attack behavior as VAN HEMEL. P. E .. & COLUCCI. V. M. Effects of target intensity and duration or accompanying postures and vocaliza­ movement on mouse-killing attack by rats. Journal of tions. A more detailed analysis of interspecific attack in ham­ Comparative and Physiological Psychology. 1973. 85. sters, with emphasis on the topograpy of the attack, is needed, 105-110. along with similar careful analysis of such spontaneously oc­ WNEK. D. 1.. & LEAF. R. C. Effects of cholinergic drugs on curring attack patterns in other closely related groups. Then we prey-killing by rodents. Physiology and Behavior. 1973, 10. will be in a position to begin comparing the similarities and 1107-1113. differences in controlling stimulus conditions for these behavior patterns among various animal groups, with a view toward understanding the function of these behaviors. (Received for publication September 24. 1976.)