Imitative pecking in chicks as a function of early social experience

JACK G. MAY, Jr. AND DARWIN DORR, DEPARTMENT OF PSYCHOLOGY, FLORIDA STATE UNIVERSITY, Tallahassee, Fla. 32306

Three groups of seven White Leghorn Chicks were reared for five weeks in one of three conditions of social stimulation. It was found that group reared chicks exhibited more imitative pecking than chicks reared in semi-isolation and that the semi-isolates imitated more than chicks reared in total social isolation.

It has been shown many times that socially isolating animals from birth can have a detrimental effect on their subsequent social behavior (Baron & Kish, 1960; Cross & Harlow, 1965; Folman & Drori, 1965). The purpose of this study was to investigate the influence of socially isolated rearing conditions on a social behavior, imitative pecking, in young chicks. In this case, imitative pecking was defined as a change in the frequency of pecking that is shown in the presence of other chicks already pecking. This is a form of imitation that Crawford (1939) called "social facilitation" and Bandura & Walters (1963) subsume under the "eliciting effects" of imitation.

Since imitation (in this case imitative pecking) is a kind of social behavior, it was expected that it would be adversely affected by early socially isolated rearing conditions. More specifically, chicks reared normally in a group would be expected to exhibit more imitative pecking than chicks reared in semi-isolation, and that semi-isolated chicks would imitate more than chicks reared in total social isolation.

Subjects and Apparatus. The Ss were 21 White Leghorn chicks hatched in the laboratory in two Oakes Model A 6 incubators.

The three kinds of rearing chambers are as follows. The group chamber consisted of a 34~ x 20~ x 8 in. unpainted pine box. One inch of dry, dark brown sawdust covered the floor of the chamber. Positioned directly overhead was a 20 x 1414 x 4~ in. aluminum alloy sheet metal hover. A 25 W G. E. heat lamp was suspended directly over the hover.

The semi-isolation chamber consisted of an unpainted white pine box divided into two rows of five compartments of the dimensions 714 x 12~ x 5~ in. One inch of sawdust of the type previously described was placed on the bottom of the compartments. A 40 x 17~ x 4 in. hover was positioned on the top of the box so that half of each chamber was covered with the hover. Five 15 W incandescent light bulbs were mounted in the top of the hover.

The seven isolation chambers were also constructed of unpainted pine board. The chambers were 9* x 7* x 6 in. Heat was provided by a IS W bulb which was inserted through a I ~ in. hole in the back of the box. The floor of the box was covered with approximately ~ in. of the type of sawdust previously described. In all conditions food was scattered on the cage floors and water was provided in small cups.

The test box consisted of an 8 x IO in. aquarium which was divided into two equal chambers by an 8 x IO in. piece of 14 in. wire mesh. The bottoms of the chambers were covered with one inch of dry, dark brown sawdust. A 2 x 8 in. strip of Plexiglas was placed at the bottom of the dividing screen to prevent sawdust and grain from being thrown from one chamber to the other. Observers recorded responses on silent push buttons which operated the pens of a Gerbrands event recorder located in another room.

Procedure. Fertilized eggs were procured at a local hatchery and placed under the incuhators. In the third week the eggs were separated by placing them in an egg-<:rate-type divider under the incubators. This was to insure that the chicks would be isolated at birth.

As each chick was hatched it was placed in one of the three rearing conditions. The rearing conditions were group, semi-isolated, and isolated. The group chicks were reared in a group such as they would be normally. The semi-isolated chicks never saw or came into physical contact with other chicks but could hear their vocalizations, scratching and general activity. The isolates were totally isolated from other chicks in individual boxes which were placed in separate rooms throughout the lab suite. It should be stressed that the isolates were not sensory deprived, but only socially isolated from other chicks.

The chicks were then maintained in their respective rearing conditions for five weeks. At this time testing was begun. The test procedure was as follows.

Psychon. Sci., 1968, Vol. II (5)

Each chick was placed alone in one side of the test chamber for 5 min. Food was never present in the imitator's compartment but was always present in the model's compartment, even in baseline periods when the model was not present. Two independent Os recorded pecking. Pecking was defined as striking objects with a quick, sharp stroke of the beak. Pecks were counted which were directed at the floor of the cage or at the divider. In the second 5 min period another chick was placed in the second compartment as a model. The models had been trained to eat off the bottom of the test cage. Three models were used and were rotated such that each model served all experimental conditions. In all cases the models pecked at the food constantly for 5 min. During this period the pecks of the test chicks were recorded. In the third 5 min period the model was removed, and the responses of the test chicks were recorded. One chick from each rearing condition was tested and then the order was repeated. Each animal was tested in this manner twice with one day intervening between test days.

Results and Discussion. The mean response rates per minute under the three conditions, baseline, imitation and baseline are shown in Fig. l. It can be seen, for each day, that while the group and semi-isolated chicks performed in the predicted manner, the isolates did not. The isolates' base rates were markedly higher than had been predicted, their rates dropped appreciably when pre­sented with the model, and finally their rates again increased when the model was withdrawn. An analysis of variance showed this Groups by Periods interaction to be significant at the .01 level (F = 9.96). The Groups by Periods by Days interaction was not significant (F = .77) indicating that the results were essentially the

[JAY I

MINUTES

DAY 2

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..........,SOLATE

• .. ··GROUP

<>---<>VIS.ISO

10 11 12 13 14 15

........ ,SOLATE

• .... GROUP

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Fig. I. Mean response rate per minute for each minute under the three conditions: baseline, imitation. baseline.

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same for each day. The Periods by Trials interaction was significant at the .01 level (F = 3.154) which reflects the general increase in responding over trials during the first two periods and the subsequent decline during the third period.

The results support the contention that social isolation will have a detrimental effect on the performance of an imitative response. However, while the behavior patterns of the group and semi­isolated chicks conformed with the expectation, the performance of the isolates was not expected. It was assumed that the isolates' rates would remain around zero during all three periods but this was clearly not the case. On the other hand, in view of the animals' respective reinforcement histories, the results are exactly what would be expected. While the group and semi-isolates had usually been reinforced for pecking (by finding food on the floor) when seeing or hearing other chicks engaged in pecking, the isolates had never been reinforced for responding in the presence of other chicks. Therefore there would be no reason for the isolates to respond when confronted with the model, while there would be adequate reason for the other two groups to do so. On the other hand the group and semi-isolates had never been reinforced when completely alone (since they had obviously never been alone) while the isolates had always been reinforced under

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these conditions, and therefore all groups again behaved in a manner consistent with their reinforcement histories.

There are other important variables to be considered such as the role that fear and novelty play in directing the behavior of the animals, but since this experiment was not specifically designed to examine these variables, discussion of them will have to wait until further investigations have been completed.

REFERENCES BANDURA, A., & WALTERS, R. H. Social learning and personality

development. New York: Holt, Rinehart, & Winston, 1963. BARON, A., & KISH, G. B. Early social isolation as a determinant of

aggregative behavior in the domestic chicken. J. compo physiol. Psychol., 1960,53,459463.

CRAWFORD, M. P. The social psychology of the vertebrates. PsychoL Bull., 1939,36,407447.

CROSS, H. A., & HARLOW, H. F. Prolonged and progressive effects of partial isolation on the behavior of macaque monkeys. J. expo Res. in Pers., 1965, 1,3949.

FOLMAN, Y., & DRORI, D. Normal and aberrant copulatory behaviors in male rats (R. norvegious) reared in isolation. Anim Behav., 1965, 13, 427429.

Psychon. Sci., 1968, Vol. 11 (5)