Reinforcing effects of chaffinch song

Anim . Behav., 1967,15,427-432

REINFORCING EFFECTS OF CHAFFINCH SONG BY JOAN G . STEVENSON Sub-Department of Animal Behaviour, Madingley, Cambridge

In the wild, the song of the chaffinch (Fringilla coelebs) is important in territorial defense ; territory-owning males attack intruders that sing, and song played through a loudspeaker induces aggressive display (Marler, 1956) . In the laboratory, song played through a loudspeaker can be learned . While birds caught when about 5 days old and kept isolated from adult song develop only a simple song, they can learn a normal song, a rearranged song, or even a Tree Pipit (Anthus trivialis) song from a loudspeaker . Birds caught in the autumn are more restricted in what they will learn, having already learned some aspects of normal song in the wild before they themselves are singing (Thorpe, 1958) . Once song has developed, playback of that song from the repertoire which is sung most frequently is more likely to induce singing than less frequently sung types . Birds thereby show a selective responsiveness to a particular song type (Hinde, 1958) . These effects of song on subsequent behaviour suggest that song might be a reinforcer for behaviour which precedes it . Just as stimuli that elicit aggressive behaviour from Siamese fighting fish and fighting cocks can act as reinforcers for operant responses (Thompson, 1963, 1964), so also might song act as a reinforcer in the case of the chaffinch . The present experiment investigates this possibility for first-year, autumncaught chaffinches injected with testosterone to make them begin to sing .

dual-cone speaker mounted on a 24 x 15 in . baffle . The speaker received input from a tape loop on which was recorded either one adult chaffinch song or a burst of white noise of approximately the same duration and loudness (Fig. 1, Plate VIII) . At the centre of the cage the song intensity varied around 64 dB and the noise intensity 74 dB re : 0 . 0002 dynes/cm 2 . The micro-switch on one of the end perches controlled the driving of the tape loop, which went round once and only once, regardless of response duration (Lowe & Stevenson, 1966) . Procedure Each bird was injected with 2 . 0 mg of testosterone phenylacetate in aqueous suspension and placed in the experimental cage in the soundproof chamber, where he lived until the end of testing. Further injections were given on days 3, 7 and 14, with the result that all birds were singing during testing . On the 7th day, responses to each end perch were recorded, and testing began on the 8th day . Throughout testing, the perch which had received the fewer responses on the 7th day was the `active' perch . Each testing block consisted of : (1) 10 min of `no stimulus', when perching responses were merely recorded . (2) 20 min of `stimulus', when both cue lights were on and every fifth or sixth response (alternatively) to the `active' perch operated the tape . (3) 10 min of `no stimulus', when responses were again merely recorded . Response counters were read every 10 min over six blocks a day from 9 a .m . to 1 p .m . until a total of seventy-two blocks, each having at least eleven responses, was reached . In the `noise group' eight birds operated the white noise tape during the `stimulus' condition ; and in the `song group' eight birds operated the song tape . The ages at which the birds were tested did not differ between groups . The above method, which might seem unorthodox, evolved during pilot studies . Because chaffinches take time to settle in a new situation, they had to live in the testing cages . In order to avoid giving different amounts of song or noise while shaping the response and to insure some

Method Subjects and Apparatus The subjects were sixteen first-year male chaffinches, trapped in November 1965 and kept on a 6-hr day (8 .30 a .m . to 2 .30 p.m .) . During testing, which lasted about 3 weeks, each subject lived in an experimental cage, 23 x 10 x 15 in., contained in a sound-proof chamber . The cage had four parallel perches, the two centre ones 10 in . and the end ones 7 in . from the floor . The two end perches activated micro-switches, so that each time the bird alighted on one, a digital counter operated . Two small red neonlights were mounted at the back of the cage, 3 in . above each end perch . In the sound-proof chamber, 12 in . from the back of the cage, was an 8-in . 427

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ANIMAL BEHAVIOUR, 15, 4

responding from each bird tested, a response with a high operant level was chosen . But because the frequency of perching varied both within and between days, no reliable base-line rate could be established, and control conditions were inserted in each day, giving an arrangement of blocks of stimulus conditions surrounded by no stimulus conditions . Since responding to a single, active perch during stimulus conditions could simply indicate activity, rather than a reinforcing effect, responding to two perches was recorded . Because there were only two perches in a cage, the birds usually hopped from one to the other. Hence two `dead' perches were added near the centre of the cage and at such a height that the birds could not easily fly directly between the two end perches. Observation through wide-angle lenses in the front of the sound-proof boxes confirmed that they seldom if ever did so. Lastly, if every response produced a reinforcement, then birds with very high rates of perching kept the song playing almost continuously without responding above their control levels . The perch with fewer responses before testing therefore became the active perch, and a ratio schedule of reinforcement was used . Results Measures over the Whole Experiment The arrangement of blocks of `no stimulus, stimulus, no stimulus' raises the question whether a particular measure was greater during the stimulus condition than during the no stimulus conditions . By assigning a `plus' if the measure was greater during the stimulus than no stimulus conditions and a `minus' if it was less, a Sign test can then be applied to a total of 72 signs (+, -, or =) . Although this reduction to signs disregards the size of differences between stimulus and no stimulus conditions, it does not necessitate any assumptions or corrections to allow for differences in absolute frequency of responses between or within days . We shall look first at signs derived from a relative response measure, namely the number of responses to the active perch divided by total responses to both perches, during each 10 min of the 40-min blocks . A `±' would not have been obtained if responding in general increased during the stimulus condition, but only if responding to the active perch increased relative to total responding . Figure 2 shows the number of +'s divided by the number of +'s and -'s for each bird, with equals (a maximum of five for any bird) eliminated, A filled circle indicates

that the absolute number of +'s was significantly different from the absolute number of -'s (Sign Test, P<0 . 05 two-tailed) . No bird of the noise group gave significantly more +'s than -'s, and one showed significantly less . By contrast, five birds of the song group gave significantly more +'s, indicating more perching on the active perch relative to total perching during song than no song, and no bird gave significantly fewer. As Fig. 2 suggests, this measure was significantly higher for the song group than for the noise group (Mann-Whitney U test, onetailed, P<0 . 025) . 80

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Fig. 2 . Percentage of blocks of no stimulus, stimulus, no stimulus, in which the number of responses to the active perch, divided by responses to both perches, was greater when the active perch turned on the stimulus than when it did not .

In Fig. 2 we have considered a single measure which gives an indication of whether or not each bird's perching was differentially affected, and in what direction, by its producing either noise or song . Yet with significantly fewer +'s than -'s, as in the case of one bird in the noise group, absolute responding could have increased during the noise conditions . This did happen, as shown in Fig . 3 (where the + and - on the x-axis refer to active and inactive perches) . On

STEVENSON : REINFORCING EFFECTS OF CHAFFINCH SONG

PLATE VIII

Fig . I . Sound spectrograph and averaged amplitude of white noise (top) and adult song (bottom) .

Stevenson .

Anim . Behav„ 15, 4

STEVENSON : REINFORCING EFFECTS OF CHAFFINCH SONG

the y-axis, a block was assigned a + for either perch if the total of responses to that perch was greater during stimulus than no stimulus conditions, and the number of +'s expressed as a percentage of the total blocks, with blocks assigned ='s neglected . The arrows represent birds which showed a significant difference in Fig. 2 . Thus the bird in the noise group which gave significantly fewer + blocks in Fig . 2 actually gave more blocks in which total responses to both active and inactive perches were greater during noise than no noise . One other bird showed a significant increase to the inactive perch, and another bird a significant decrease to the active perch, indicating a negative effect of noise . The pattern in the song group was quite different, with every bird's point for the active perch higher than that for the inactive . Four birds showed a significant increase to the active perch during song, and three of these showed a significant decrease to the inactive perch during song . Although the song group has higher points



for the active perch than does the noise group, the difference between groups is not significant . However, the song group does show significantly lower points for the inactive perch than does the noise group (Mann-Whitney U test, onetailed, P<0 . 04) . Thus we have shown reinforcing effects of song with both differential and absolute responding between song and no song conditions, and Fig . 4 shows absolute frequency of responding to the active perch (solid lines) during stimulus conditions (filled circles) and during no stimulus conditions (open circles), and to the inactive perch (dashed lines) during stimulus (filled circles) and no stimulus (open circles) conditions . For each group, the median frequency of the eight birds is plotted against successive sets of six blocks . Since each block contains 20 min of either the stimulus or the no stimulus conditions, each point represents the median for 2 hr of responding. In the song group, responding to the inactive and initially preferred perch remained higher than responding to the

Autumn-caught, noise

Autumn- caught, song

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Fig. 3 . Percentage of blocks in which the absolute number of responses either to the active perch (+) or to the inactive perch (-) was greater when the active perch turned on the stimulus than when it did not .

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ANIMAL BEHAVIOUR, 15, 4 Autumn-caught, noise

Autumn-caught, song

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Fig. 4 . Median number of responses over sets of six blocks : to the active perch when it turned on the stimulus (-•-) ; to the active perch when it did not turn on the stimulus (-o-) ; to the inactive perch when the active perch turned on the stimulus (-- •- -) ; and to the inactive perch when the active perch did not turn on the stimulus (--0 --)active perch . In the noise group, there was no consistent difference in median responding between perches . In the noise group, responding to the active perch (solid lines) was higher only 3 times out of 12, when it produced noise (filled circles) than when it did not (open circles) . In the song group, responding to the active perch was higher when it produced song than when it did not for all twelve sets of blocks . There was no consistent tendency for the noise group to go less to the inactive perch during noise than no noise, but the song group went to the inactive perch less during song than no song on nine out of twelve sets . However, this was better represented in Figs . 2 and 3, where each block was considered separately, rather than in groups of six . Thus, although a reinforcing effect of song has been demonstrated, it was not so strong as to reverse the initial perch preference . Although the four median curves for the song group are higher than those for the noise group, response-totals of all sets for each bird in each condition did not differ between groups when a Mann-Whitney U test was used to compare any two conditions . For example, total frequency of responding to the active perch when it produced song did not differ from total responding when the active perch produced noise . Since reinforcement was programmed on a ratio schedule, this implies that the number of song presentations did not differ from the number of noise presentations, so that although we have

found differences in response control, between groups the song group did not turn on more song than the noise group turned on noise . Measures over the First and the Second Half of the Experiment Although in Fig. 4 the points for the song group's responding to the inactive perch during either condition seem to decrease over time, this was not the case when points for all eight individuals rather than medians were considered . That is, there was no significant change in total responding between the first and the second half using a Wilcoxon Matched-Pairs test . This was true for any of the eight sets of points in Fig . 4 . A significant change between halves did occur with the song group in the measure used in Fig . 3 . The number of times that the absolute frequency of responding to the active perch was greater during song than during no song increased from the first to the second half for seven out of eight birds (Sign test, one-tailed, P<0 . 035) . However, an increase over halves in +/+&- with respect to relative frequency to the active perch occurred in only five of the eight birds . With noise, -}-/±& - with respect to relative frequency to the active perch increased in only two of the eight birds . Thus, considering measures in Figs . 2 to 4, the only_ significant change over halves occurred in the song group, with birds going more to the active perch during song than no song in the last thirty-six blocks than in the first thirty-six blocks .

STEVENSON : REINFORCING EFFECTS OF CHAFFINCH SONG Relations between Measures Since the relative measure of responding to the active perch increased more during song as compared with no song than it did during noise as compared with no noise (Fig . 2), and since the song group showed higher total absolute responding, though not significantly so, than the noise group (Fig . 4), the possibility of a correlation between these measures arises . However, the total number of responses over the whole experiment for each bird was not significantly correlated with the number of +/+&- derived from relative frequencies to the active perch (Spearman rank correlation coefficient = 0 .09 for the noise group and + 0 . 17 for the song group). On the chance that responding before any stimulus was presented was correlated with +/+&-, the correlations between responding during the first 10 min of the very first block and /+ &- were calculated . Again, these correlations were not significant (- 0 . 17 for the noise group and - 0 . 26 for the song group) . Thus total responding, either before any stimulus presentations or over the whole experiment, was not correlated with the effect of the stimulus presentations on relative responding to the active perch . Discussion We have seen that for five out of eight birds in the song group, responding to the active perch divided by responding to both perches was significantly higher when the active perch did produce song than when it did not ; and this did not occur with any birds in the noise group (Fig . 2) . Furthermore, absolute responding during song as compared with no song increased to the active perch and decreased to the inactive perch (Fig . 3) . Yet no high steady rate of responding to the active perch when it occurred produced song, as with `typical' fixed-ratio responding . Thus although control of this operant by song has been established, this control differs from that usually found on a ratio schedule with either `primary reinforcement' (e .g . Ferster & Skinner, 1957) or `conditioned reinforcement' (e .g . Stevenson & Reese, 1962) . With other 'species-specific' reinforcers, Thompson (1963, 1964) has found an increase in a fighting fish's response of swimming through a loop for an image of himself or of a model fish, followed by a decrease during extinction, and an increase in a fighting cock's pecking a key on fixed ratio schedules for an image of himself or another rooster, followed by a decrease during

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extinction . Thompson did mention that the key pecking `occurred in irregularly-spaced short bursts, interspersed with periods of more characteristic ratio behaviour' (p . 47, 1964) ; thus, irregular responding occurred here, although not as much as in the present study . Another difference from Thompson's studies is that no responses were observed to be elicited by the stimulus . The birds occasionally sang immediately after a song presentation, usually sat on the perch during the song and did not show any agonistic responses such as crest-raising or crouching . The difference between the control of the operant in this situation and the others could be due to differences in subject, procedure or reinforcer. The perching response has a high operant level, and this is one reason why it was chosen . But if a high response rate were associated with decreased control, there should have been a negative correlation between total responding and the measure of control used in Fig . 2, and this was not found . Of course the subject and procedure cannot be ruled out as the reason for differences until one asks how response is controlled when the birds work for a more conventional reinforcer, such as food, in the same situation . Other questions about the nature of this effect involve asking what aspects of the song are responsible for the reinforcing effect, how important early experience of the song is, and, if testosterone should be important, in what way it would act . Summary When young chaffinches turned on either white noise or song in an operant situation, a reinforcing effect of song, but not noise, was found . For one out of eight birds in the noise group, responding to an active perch, divided by responding to both the active and an inactive perch, was significantly lower when the active perch did produce noise than when it did not . By contrast, for five out of eight birds in the song group this ratio was significantly higher when the active perch did produce song than when it did not . However, the effects of song on responding to the active perch did not overcome initial perch preferences and did not produce a high steady rate of responding. Acknowledgments I would like to thank Professor W . H . Thorpe, FRS, who initiated the experiments on the development of chaffinch song, for the privilege

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of working with him in his laboratory . I am especially grateful to Professor R . A . Hinde, who not only suggested this problem but also made invaluable suggestions throughout the course of research. I would also like to thank Professor D . S . Blough for his comments on the manuscript. This research was conducted during the author's tenure as a U .S . Public Health Service Postdoctoral Research Fellow, N.I .M.H. REFERENCES Ferster, C . B . & Skinner, B . F . (1957) . Schedules of Reinforcement. New York : Appleton-Century-Crofts . Hinde, R . A. (1958). Alternative motor patterns in chaffinch song . Anim . Behav ., 6, 211-218.

Lowe, H . L . & Stevenson, J. G . (1966) . A responsecontrolled tape loop. Anim . Behav., 14,184-186. Marler, P . (1956) . Territory and individual distance in the chaffinch Fringilla coelebs. Ibis, 98, 496-501 . Stevenson, J . G . & Reese, T. W. (1962). The effect of two schedules of primary and conditioned reinforcement . J. exp . Analysis Behav ., 5, 505-5 10 . Thompson, T. 1 . (1963). Visual reinforcement in Siamese fighting fish . Science, 141, 55-57 . Thompson, T . I . (1964) . Visual reinforcement in fighting cocks. J. exp. Analysis Behav., 7, 45-49. Thorpe, W. H . (1958) . The learning of song patterns by birds, with especial reference to the song of the chaffinch Fringilla coelebs. Ibis, 100, 535-570 . (Received 12 January 1967 ; Ms . number : 716)