Anita. Behav., 1973, 21, 160--163

EFFECTS OF CHICK VOCALIZATIONS ON ONGOING BEHAVIOUR

BY ANDREW LANGFORD & JERRY A. H O G A N Department of Psychology, University of Toronto

Abstract. Recorded feeding twitters, shrill calls, and tones of two intensities were presented to young chicks that were pecking a key for food on a variable interval schedule of reinforcement. The shrill calls and tones had an immediate inhibitory effect on pecking which dissipated in about 5 min. Feeding twitters had no effect on pecking rate.

Many investigators have used chick vocalizations as measures in the causal analysis of chick be- haviour, but relatively little work has been done to ascertain the functions of chick calls. In this paper we will be concerned with some effects on ongoing behaviour of two types of vocaliz- ations: feeding twitters that occur while chicks feed undisturbed, and shrill calls that occur when a chick is suddenly isolated from its com- panions. These calls may also play a role in development (see, for example, Konishi 1963; Stevenson 1969; Gottlieb 1971), but such functions are not considered here. For a general discussion of the functions of avian call notes see Thorpe 1961, Chapter 2 (see also papers in Hinde 1969).

Shrill calls are known to activate a mother- hen and direct her toward the calling individual (e.g. Briickner 1933; Collias 1952), and feeding twitters, as well as shrill calls, may provide stimuli that allow a hen to locate and recognize her chicks (cf. Beer 1970). Calls of a mother-hen strongly affect the behaviour of young chicks (e.g. Collias 1952; Snapp 1969), but whether chick vocalizations affect the behaviour of other chicks is not clear. Tolman (1967) found that young chicks showed much greater pecking when a pecking model made tapping sounds than when it pecked silently; feeding twitters might cause a similar enhancement of pecking. On the other hand, feeding twitters and other sounds associated with feeding chicks were not effective in attenuating fear reactions to a novel environment (Hogan & Abel 1971). General observations suggest that shrill calls have no effect on young chicks, but, once again, there is no experimental evidence on the matter.

The purpose of the experiments reported here was to see what effects feeding twitters and shrill calls might have on pecking behaviour in a feed- ing situation. We approached this problem by presenting recorded chick vocalizations and other sounds to chicks that were pecking a key

for food on a variable interval schedule of re- inforcement. This schedule is known to produce a very steady rate of responding, and is especially suitable for situations where experimental manipulations could either increase or decrease response rate (Ferster & Skinner 1957, Chapter 6). Use of this method gives very precise control of the chick's behaviour at the time the stimulus is presented.

Experiment 1 Methods

Subjects. Chicks of the Burmese red jungle- fowl (Gallus gallus spadieeus) were hatched in an incubator in the laboratory. At about 24 hr post-hatch they were removed to housing cages (50 • 40 cm 2) where they lived in groups of six for the duration of the experiment. Commercial chick starter crumbs and water were always available except as noted below. Eighteen chicks were used in the training phase of the experiment, and twelve of these chicks were used in the testing phase.

Apparatus, Training and testing were con- ducted in a 24 • 24 x 22-cm operant con- ditioning chamber. Three sides of the chamber were constructed of Masonite, and the fourth side of clear Plexiglas. The floor was covered with wire mesh. Access to the chamber was via the top which was covered with a piece of Masonite. On one wall of the chamber, a 1.8 cm diameter translucent Plexiglas Gerbrands pigeon key was located 7.5 cm above the floor. A 7 x 5-cm aperture, through which the chick could gain access to a Gerbrands pigeon food magazine, was located level with the floor and was centred 5 cm to the left of the key. The conditioning chamber was illuminated and heated by a 30-W carbon filament lamp sus- pended 8 cm from the floor next to the wall opposite that containing the key. A small lamp transilluminated the key, and another small

160

L A N G F O R D & H O G A N : CHICK VOCALIZATIONS A N D O N G O I N G BEHAVIOUR 161

lamp lighted the food magazine whenever it operated.

The conditioning chamber was partially isolated from extraneous sound by enclosing it in a 60 x 60 • 62-cm box made of 1-8 cm plywood. This box was insulated by an inner shell of 5-cm thick styrofoam; two sheets of clear Plexiglas covered a 30 x 36-cm hole in the door. Ventilation and a low-level masking noise were provided by a fan mounted on the outside of the box.

Auditory stimuli were recorded on Sony PR 150 polyester tape at a speed of 19 cm per s, using a Sony TC 630 tape recorder and a Sony cardiodid dynamic microphone. Tapes were prepared using 12-day-old chicks of the same hatch as the experimental subjects. Feeding twitters were recorded from a pair of chicks when they were given access to food following 12 hr of food deprivation. Shrill calls were re- corded from a single chick that had been isolated without light. Sound spectrograms of these calls can be seen in Collias & Joos (1953) and Guyo- marc'h (1966) for domestic chicks and in Kruijt (1964, p. 28) for junglefowl chicks.

The tapes were edited to remove extraneous noise and to provide a single tape of 5-min duration for each call type. These calls were presented to the experimental subjects through a Sony 16-ohm speaker located adjacent to the food magazine. The intensity of the calls was adjusted to approximate natural loudness as judged by the experimenter when the door to the box was open.

Standard relay equipment, located in a separ- ate room, was used to programme reinforcement contingencies and stimulus presentations, and to record key pecks.

Training procedure. When the chicks were 6 days old, food was removed from the home cages; for the next 8 days, chicks received food only during twice-daily training sessions in the conditioning chamber. A chick was shaped to peck the key for food; when pecking was estab- lished, it was gradually switched to a variable interval schedule of reinforcement in which food was presented for key pecking on the average of once each minute (VI 1 rain). By the end of training, reinforcement duration was 3 s. On the last day of training (day 14), the twelve chicks that showed the highest rate of responding were selected for testing. Each of these chicks received a final training session. One hour later it was allowed access to food for 15 rain in a

cage identical to its home cage. Ten hours later, testing began.

Testing procedure and design. Tests were conducted at 12-hr intervals. Each test session was 15 min in duration, divided into three 5-rain periods. During the entire test, food was avail- able on a VI 1-min reinforcement schedule. Additionally, during the middle 5-min period, the chick was exposed to one of three stimulus conditions. The number of key peeks made by each chick during each minute of the test session was recorded. Half an hour after the end of each session, a chick was allowed to feed for 15 min in a cage identical to its home cage.

Each chick was exposed to each stimulus condition three times, making a total of nine test sessions. The stimulus conditions were: (a) a tape recording of feeding twitters played continuously for 5 min; (b) a tape recording of shrill calls played continuously for 5 min; and (c) no additional stimulus. Sequence effects in the order of presenting the stimuli were partially balanced by treating the three conditions as two Latin squares. Chicks were randomly assigned to the resulting six sequences of stimulus conditions.

Results The data of primary interest are those for the

middle 5-rain period of the testing sessions, during which time the stimuli were presented; only those data will be considered here. Figure 1 presents the mean number of key pecks during each session of each of the three stimulus f0resentations averaged over the twelve subjects. It can be seen that, compared to control sessions in which no stimulus was presented, the first presentation of shrill calls caused the level of responding to be halved; by the second session in which shrill calls were presented, however, the level of responding was the same as for the controls. An analysis of variance of these data showed that the stimulus by session interaction was significant at a level of <0.001 (F=6.61, df 4/44). From Fig. 1 it can be seen that this interaction is due, in large part, to the very low rate of responding during the first presentation of shrill calls. In order to see what role the higher rate of responding during the second and third presentations of feeding twitters played in the interaction, a separate analysis of variance of data for control sessions and feeding twitter sessions only was carried out. The results of this analysis gave no hint of a significant stimulus by session interaction (F--l.18, df 2/22), nor

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were either of the main effects significant. In- spection of the data for the individual chicks showed that in the second session eight of the twelve chicks showed higher responding during feeding twitters than during no stimulus, and in the third session seven of the twelve showed higher responding during feeding twitters; whereas eleven of the twelve chicks showed less responding when shrill calls were presented for the first time. The breakdown of the data into 1-min intervals shows that the inhibitory effect of shrill calls decreased continuously during the first 5-min session; scores for respond- ing during shrill call presentation reached control levels by the second minute of the second session.

Discussion Feeding twitters apparently have little, if any,

effect on the pecking rate of young chicks. It may be that feeding twitters in interaction with the pecking movements of other chicks would facilitate pecking, as implied by the results of Tolman (1967); but, by themselves, the feeding twitters of other chicks would seem to be irrelev- ant to ongoing feeding behaviour. Of course, it is always possible that feeding twitters would affect other measures of feeding behaviour than the one we used (cf. Miller 1956). For

example, in young chicks, pecking food and swallowing food are not highly correlated (Hogan 1971); feeding twitters might well affect swallowing without having any noticeable effect on pecking. Feeding twitters might also attract the attention of non-pecking chicks; then, in interaction with the movements of other chicks, the feeding twitters might serve to initiate approach and/or pecking (cf. CoUias 1952). These and other possible functions of feeding twitters have not yet been investigated�9

Shrill calls have a dear, though temporary, inhibitory effect on pecking. This might reflect a specific inhibitory function of shrill calls on the behaviour of companion chicks. A simpler interpretation of these results is that shrill calls have the same effects on a chick's behaviour that any unexpected sound would have. This idea was tested in the following experiment�9

Experiment 2 This experiment is an exact replication of experi- ment 1, except that the stimuli presented during the test periods were artificially produced tones rather than recordings of chick vocalizations.

Methods Eighteen chicks of the junglefowl were trained

to key-peck for food on a VI 1 rain schedule of reinforcement as described above. On day 14, the twelve chicks that showed the highest rate of responding were selected for testing. The testing procedure and design were the same as in experiment 1. During the middle 5-rain period of the test session chicks were presented with either high intensity tones, low intensity tones, or nothing�9

Tapes were prepared by recording a 500-Hz tone produced by a tone generator. The tone was broken into an irregular train of pulses that, on the average, were 1 s in duration and �89 s apart. (Feeding twitters occur at a rate of about 4 per s, and shrill calls occur at a rate of about 2 per s; almost all the energy in both calls is above 2000 Hz: Collins & Joos 1953; Kruijt 1964.) Collias& Joos (1953) played organ tones of various dura- tions and various frequencies to domestic chicks and noted whether the chicks gave pleasure tones or distress calls. Their results suggest that the stimulus used in this experiment should evoke a minimal reaction in the chicks. During experi- mental sessions, the tones were played either at low intensity or at high intensity. These in- tensifies were determined by the judgment of the experimenter who matched the loudness of the

LANGFORD & HOGAN: CHICK VOCALIZATIONS AND ONGOING BEHAVIOUR 163

low intensity tones with the feeding twitters and the loudness of the high intensity tones with the shrill calls.

Results Figure 2 presents the mean number of key

pecks during each session of each of the three stimulus presentations averaged over the twelve subjects. It can be seen that both tones produce an inhibitory effect that disappears by the third

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session. The high intensity tone showed a greater inhibitory effect than the low intensity tone. An analysis of variance of these data showed that the stimulus by session interaction was significant at a level of less than 0.01 (F=5.72, df 4/44). A t-test showed, however, that the difference between the high and low intensity tones was not significant.

Discussion A comparison of Figs 1 and 2 shows that the

effects of shrill calls and the high intensity tone on ongoing pecking behaviour are essentially identical. This supports the notion that shrill calls have no specific effect on the feeding be- haviour of companion chicks beyond the effects any unexpected sound might have. The effects of the low intensity tone were also very similar to the effects of the high intensity tone, but considerably different than the effects of the

feeding twitters. This suggests that feeding twit- ters, even when unexpected, do not have the inhibitory properties of other unexpected sounds.

Acknowledgments We would like to thank R. A. Hinde, S. J. Shettleworth, and J. G. Stevenson-Hinde for helpful comments on the manuscript. This research was supported by a grant from the National Research Council of Canada.

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(Received 19 June 1972; revised 30 September 1972; MS. number: 1154)