STIMULUS COMMUNICATION
INTENSITY AND ACOUSTICAL IN YOUNG DOMESTIC CHICKS by
ROGER M. EVANS 1) (Department of Zoology, University of Manitoba, Winnipeg, Canada) (With 2 Figure) (Rec. 10-X-1974)
When a young chick is isolated from its parent, it tends to emit high intensity vocalizations called "distress calls" or "peeps" (COLLIAS, 1952; ANDREW, 1964), and may move about as if appetitively searching for suitable stimulation (BATESON, 1971). Under natural or semi-natural rearing conditions, the loud peeps emitted by an isolated chick function to attract the mother and to elicit maternal clucks, which in turn function to attract the chick and inhibit its high intensity peeps (BRÜCKNER, 1933; COLLIAS, 1952; McBsRrDE et al., 1969). The acoustical aspects of this system apparently provide the primary communication link between parent and young whenever the combined effects of distance and habitat density are sufficient to reduce or cut off visual signals. The salient features of the above described acoustical communication link between parent and chick are illustrated in Fig. I. Considered functionally, it is important to note that whereas chick peeps tend to increase the output of parental clucks (as indicated by the lower arrow and "plus"' sign in Fig. r), clucks tend to inhibit the production of peeps by the chicks (upper
Fig. i. Relationship between parental clucks and chick peeps. ( + ) indicates facilitation, (-) indicates inhibition. arrow
and minus
sign).
This inhibition
introduces
an important
negative
I) This study was financed by grants from the University of Manitoba Research Board and the National Research Council of Canada. I thank Peter COWANfor his comments on the manuscript.
74 component into the system that should theoretically allow for a stabilizing of call rates or intensities at some more or less optimum level. to external Whether the system is also able to respond homeostatically in effective disturbances, such as those produced by noise or the reduction signal intensity when parent and chick become widely separated in space, is apparently unknown. Since the effect of parental clucks on peeps is negative in sign (Fig. I), it is evident that one form of homeostatic response to distance or noiseinduced variations in effective stimulus intensity could arise if the inhibition of peeps were itself graded according to the intensity of clucks received by the chick, with weaker clucks producing less inhibition of peep calls. An analogous intensity grading of approach responses to parental calls in the presence of a conspicuous visual stimulus has been shown in domestic chicks (FISCHER & GILMAN, ig6g; Cf SCHNEIRLA, 1965), but such intensity effects have received surprisingly little attention in studies of avian acoustical communication (LANYON & TAVOLGA, ig6o; MARLER & HAMILTON, 1966; 1-iusNEL, 1968, HINDE, ig6g). The possibility that inhibition of peeps is influenced by this variable was examined in the present study by testing chicks from two age groups with three different intensity levels of maternal clucks presented in the absence of conspicuous visual stimuli. For comparison, approach responses were also measured. feedback
METHODS Subjects. All subjects consisted of White Rock X Cornish domestic chicks hatched in the laboratory from eggs obtained locally from a commercial hatchery. Chicks of known age (usually within -L i hr) were color marked for individual identification and removed to rearing pens within the first few hours after hatching. Chicks were reared communally, in groups of up to approximately one dozen, in wooden pens measuring 35 X 45 X 25 cm high that were equipped with a T5 «·att light bulb to provide continuous light and heat. Food and water were withheld until after the termination of testing. Apparatus. All chicks were tested in standard "tip-floor" pens described in detail elsewhere (EVANS,i972). These pens consisted of two end compartments, each measuring 30 X 40 X 3o cm high which were equipped with loudspeakers to provide auditory test stimuli, and a central compartment, measuring 57 X 40 X 30 cm high for the test subject. The central compartment was fitted with a movable floor that tipped down at either end according to the location of the test chick at any given time. Switches under the tip-floor were connected to the loudspeaker control circuits so that when a chick moved towards the active loudspeaker at one end, the speaker became deactivated and the loudspeaker at the other end simultaneously became activated. Any tendency for the test subject to approach the test stimulus thus resulted in locomotion back and forth, from one end to the other of the central compartment. The number of such crossings was recorded by means of a remotely positioned event recorder. A microphone, placed above
75 the tip-floor pen and connected to a voice-operated relay and event r.ecorder provided a count of high-intensity vocalizations. The voice-operated relay was set by advancing the sensitivity setting until the relay was activated by peeps but not by the most intense (85 dB) clucks used as auditory test stimuli. stimuli. Auditory stimuli consisted of "clucks" recorded earlier in the laboratory from broody White Rock X Cornish hens with newly hatched chicks. A Sony model TC 8co tape recorder equipped with omnidirectional Uler microphone was used. A continuous loop of one individual cluck played back at the rate of approximately 110 clucks per minute w-as used for all tests (see EVANS & MATTSON,1972, for additional description of cluck stimulus). Test
Procedure. Seventy two chicks were randomly assigned in equal numbers to each of three groups. The chicks in one group were tested with clucks presented at a level of 65 dB (B fast scale, General Radio Co. type 1565-A sound level meter), another group was tested with the same stimulus at 75 dB, while the third group was tested at 85 dB. Half of the chicks in each group were tested at from 10-12 hr post hatch, half at from 18-2o hr min bouts of auditory stimulation post hatch. A given test consisted of alternating min control bouts in which no stimulus was given, in an abababab order for with a total of 20 min. Test order (ab vs ba) was balanced between chicks for each sub?;roup tested. Ambient noise levels were maintained at approximately 55 dB (B fast scale) by Grason-Staddler white noise generators. RESULTS Mean number of peeps and approach responses over successive 5-min blocks are plotted in Fig. 2 for both age groups at each of the three test dB levels. For all groups, there was a significant inhibition of distress calls when the auditory stimulus was presented (S+ curves in Fig. 2) compared to silent control periods (S- curves). As expected, ther was also a significant increase in approach responses in the presence of the auditory stimulus (lower half of Fig. 2). The probability levels associated with these effects of stimulation are shown adjacent to the appropriate curves in Fig. 2. Effects due to age were slight (Fig. 2), and failed to reach statistical significance (p> .05) during stimulus presentation (S+) for either response measure at any of the three dB levels used for testing. Differences due to age also failed to reach statistical significance during silent (S-) periods, even when all 36 chicks of each age were combined for analyses. In the absence of significant age effects, age groups are pooled for the remaining analyses. Auditory stimulation with increased dB levels tended to decrease the frequency of both peeping and approach responses (S+ curves of Fig. 2). For peeps, the relatively high levels present at 65 dB decreased significantly U test) at both 75 and 85 dB. For approach (p.2). The decrease was significant (p.3) during silent periods. The maximum difference in the rate at which chicks crossed the tip-floor during silent periods was between the 65 and 85 dB groups, and it also was not significant (p>.2) Peeps tended to increase during the 20-min test period (Fig. 2). This effect was most pronounced during presentation of the stimulus (S+). Comparison (X2) between the first and last 5-min blocks indicated a significant and at 85 dB (p
INTENSITY AND ACOUSTICAL IN YOUNG DOMESTIC CHICKS by
ROGER M. EVANS 1) (Department of Zoology, University of Manitoba, Winnipeg, Canada) (With 2 Figure) (Rec. 10-X-1974)
When a young chick is isolated from its parent, it tends to emit high intensity vocalizations called "distress calls" or "peeps" (COLLIAS, 1952; ANDREW, 1964), and may move about as if appetitively searching for suitable stimulation (BATESON, 1971). Under natural or semi-natural rearing conditions, the loud peeps emitted by an isolated chick function to attract the mother and to elicit maternal clucks, which in turn function to attract the chick and inhibit its high intensity peeps (BRÜCKNER, 1933; COLLIAS, 1952; McBsRrDE et al., 1969). The acoustical aspects of this system apparently provide the primary communication link between parent and young whenever the combined effects of distance and habitat density are sufficient to reduce or cut off visual signals. The salient features of the above described acoustical communication link between parent and chick are illustrated in Fig. I. Considered functionally, it is important to note that whereas chick peeps tend to increase the output of parental clucks (as indicated by the lower arrow and "plus"' sign in Fig. r), clucks tend to inhibit the production of peeps by the chicks (upper
Fig. i. Relationship between parental clucks and chick peeps. ( + ) indicates facilitation, (-) indicates inhibition. arrow
and minus
sign).
This inhibition
introduces
an important
negative
I) This study was financed by grants from the University of Manitoba Research Board and the National Research Council of Canada. I thank Peter COWANfor his comments on the manuscript.
74 component into the system that should theoretically allow for a stabilizing of call rates or intensities at some more or less optimum level. to external Whether the system is also able to respond homeostatically in effective disturbances, such as those produced by noise or the reduction signal intensity when parent and chick become widely separated in space, is apparently unknown. Since the effect of parental clucks on peeps is negative in sign (Fig. I), it is evident that one form of homeostatic response to distance or noiseinduced variations in effective stimulus intensity could arise if the inhibition of peeps were itself graded according to the intensity of clucks received by the chick, with weaker clucks producing less inhibition of peep calls. An analogous intensity grading of approach responses to parental calls in the presence of a conspicuous visual stimulus has been shown in domestic chicks (FISCHER & GILMAN, ig6g; Cf SCHNEIRLA, 1965), but such intensity effects have received surprisingly little attention in studies of avian acoustical communication (LANYON & TAVOLGA, ig6o; MARLER & HAMILTON, 1966; 1-iusNEL, 1968, HINDE, ig6g). The possibility that inhibition of peeps is influenced by this variable was examined in the present study by testing chicks from two age groups with three different intensity levels of maternal clucks presented in the absence of conspicuous visual stimuli. For comparison, approach responses were also measured. feedback
METHODS Subjects. All subjects consisted of White Rock X Cornish domestic chicks hatched in the laboratory from eggs obtained locally from a commercial hatchery. Chicks of known age (usually within -L i hr) were color marked for individual identification and removed to rearing pens within the first few hours after hatching. Chicks were reared communally, in groups of up to approximately one dozen, in wooden pens measuring 35 X 45 X 25 cm high that were equipped with a T5 «·att light bulb to provide continuous light and heat. Food and water were withheld until after the termination of testing. Apparatus. All chicks were tested in standard "tip-floor" pens described in detail elsewhere (EVANS,i972). These pens consisted of two end compartments, each measuring 30 X 40 X 3o cm high which were equipped with loudspeakers to provide auditory test stimuli, and a central compartment, measuring 57 X 40 X 30 cm high for the test subject. The central compartment was fitted with a movable floor that tipped down at either end according to the location of the test chick at any given time. Switches under the tip-floor were connected to the loudspeaker control circuits so that when a chick moved towards the active loudspeaker at one end, the speaker became deactivated and the loudspeaker at the other end simultaneously became activated. Any tendency for the test subject to approach the test stimulus thus resulted in locomotion back and forth, from one end to the other of the central compartment. The number of such crossings was recorded by means of a remotely positioned event recorder. A microphone, placed above
75 the tip-floor pen and connected to a voice-operated relay and event r.ecorder provided a count of high-intensity vocalizations. The voice-operated relay was set by advancing the sensitivity setting until the relay was activated by peeps but not by the most intense (85 dB) clucks used as auditory test stimuli. stimuli. Auditory stimuli consisted of "clucks" recorded earlier in the laboratory from broody White Rock X Cornish hens with newly hatched chicks. A Sony model TC 8co tape recorder equipped with omnidirectional Uler microphone was used. A continuous loop of one individual cluck played back at the rate of approximately 110 clucks per minute w-as used for all tests (see EVANS & MATTSON,1972, for additional description of cluck stimulus). Test
Procedure. Seventy two chicks were randomly assigned in equal numbers to each of three groups. The chicks in one group were tested with clucks presented at a level of 65 dB (B fast scale, General Radio Co. type 1565-A sound level meter), another group was tested with the same stimulus at 75 dB, while the third group was tested at 85 dB. Half of the chicks in each group were tested at from 10-12 hr post hatch, half at from 18-2o hr min bouts of auditory stimulation post hatch. A given test consisted of alternating min control bouts in which no stimulus was given, in an abababab order for with a total of 20 min. Test order (ab vs ba) was balanced between chicks for each sub?;roup tested. Ambient noise levels were maintained at approximately 55 dB (B fast scale) by Grason-Staddler white noise generators. RESULTS Mean number of peeps and approach responses over successive 5-min blocks are plotted in Fig. 2 for both age groups at each of the three test dB levels. For all groups, there was a significant inhibition of distress calls when the auditory stimulus was presented (S+ curves in Fig. 2) compared to silent control periods (S- curves). As expected, ther was also a significant increase in approach responses in the presence of the auditory stimulus (lower half of Fig. 2). The probability levels associated with these effects of stimulation are shown adjacent to the appropriate curves in Fig. 2. Effects due to age were slight (Fig. 2), and failed to reach statistical significance (p> .05) during stimulus presentation (S+) for either response measure at any of the three dB levels used for testing. Differences due to age also failed to reach statistical significance during silent (S-) periods, even when all 36 chicks of each age were combined for analyses. In the absence of significant age effects, age groups are pooled for the remaining analyses. Auditory stimulation with increased dB levels tended to decrease the frequency of both peeping and approach responses (S+ curves of Fig. 2). For peeps, the relatively high levels present at 65 dB decreased significantly U test) at both 75 and 85 dB. For approach (p.2). The decrease was significant (p.3) during silent periods. The maximum difference in the rate at which chicks crossed the tip-floor during silent periods was between the 65 and 85 dB groups, and it also was not significant (p>.2) Peeps tended to increase during the 20-min test period (Fig. 2). This effect was most pronounced during presentation of the stimulus (S+). Comparison (X2) between the first and last 5-min blocks indicated a significant and at 85 dB (p
