Species song discrimination in adult female song and swamp sparrows

Anita. Behav., 1981, 29, 997-1003

SPECIES SONG DISCRIMINATION IN ADULT FEMALE SONG AND SWAMP SPARROWS BY WILLIAM A. SEARCY, PETER MARLER & SUSAN S. PETERS

Rockefeller University Field Research Center for Ecology and Ethology, Tyrrel Road, Millbrook, New York 12545 (Melospiza melodia) and six female swamp sparrows (Melospiza georgiana) were treated with oestradiol, and their response to song measured by frequency and intensity Abstract. Six female song sparrows

of copulation-solicitation display. Test stimuli were synthetic songs composed of either song sparrow or swamp sparrow syllables assembled in either song-sparrow-like or swamp-sparrow-like temporal patterns. Female song sparrows responded preferentially to songs containing their own species' syllables and to songs containing their own species' temporal patterns. Swamp sparrows were also sensitive to both syllable type and temporal pattern, in contrast to male swamp sparrows, which show no preference for swamp sparrow temporal patterns. Swamp sparrows (Melospiza georgiana) and song sparrows (Melospiza melodia) are closely related species that often share breeding habitats in the eastern United States. Individual song and swamp sparrows must be able to distinguish between songs of their own and the other species in a variety of situations: young males must recognize and learn their own species' song for later production, adult males must recognize their own species' song for effective territorial defence, and adult females must recognize their own species' song as a step in mate choice and courtship. Marter & Peters (t977, 1981) have previously investigated song recognition in naive young song and swamp sparrows, and Peters et al. (1980) have investigated song recognition in territorial adult males. In the present paper, we examine the parameters of song used by adult females to discriminate conspecific from other species' song and compare them with those used by adult males and naive young. Though similar in many respects, the songs of swamp and song sparrows differ considerably in temporal organization. Swamp sparrow song is, with rare exceptions, a single-phrase song consisting of a steady-rate trill composed of one repeated multi-note syllable. The multi-phrase song of the song sparrow is composed of several trills of repeated syllables separated by groups of unrepeated syllables called note complexes (Mulligan 1963; Kroodsma 1977). Song sparrow trills, especially introductory ones, may be delivered in an accelerating pattern, with progressively shorter intervals between syllables; other trills are delivered at a steady rate. There are typically two to seven phrases in a single song sparrow song. Song and swamp sparrow

songs also differ in the fine structure of their component syllables. In particular, song sparrow syllables often show rapid frequency modulations lacking in swamp sparrow syllables. Song development is influenced by learning in both song and swamp sparrows (Mulligan 1966; Kroodsma 1977; Marler & Peters 1977). Marler & Peters (1977, 1981) have investigated the basis of selective learning in young song and swamp sparrows. They exposed naive young to artificial songs composed of either song or swamp sparrow syllables assembled in either song-sparrow-like or swamp-sparrow-like temporal patterns. Swamp-sparrow-like temporal patterns consisted of single identical syllables repeated at a steady rate. Song-sparrow-like patterns consisted of two trills, each with a different syllable type and a different tempo (e.g. one accelerating and one steady rate). Swamp sparrows were highly selective with respect to syllable type, learning and later producing copies of only swamp sparrow syllables. Swamp sparrows disregarded temporal pattern, learning syllables equally often from swamp-sparrow-like and song-sparrow-like temporal patterns. In contrast, song sparrows learned both song and swamp sparrow syllables in about equal proportions, though they were more likely to learn swamp sparrow syllables if presented in a songsparrow-like temporal pattern than if presented in a swamp-sparrow-like pattern (Marler & Peters 1981). Song sparrows showed no further tendency to discriminate on the basis of temporal pattern in this experiment, learning song sparrow syllables equally frequently from song-sparrow-like and swamp-sparrow-like patterns. When naive song sparrows were presented 997

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with natural song sparrow and swamp sparrow songs in another experiment, they produced mainly song sparrow syllables, indicating that the added complexities of natural song sparrow temporal patterns allowed improved discrimination (Marler & Peters 1981). Peters et al. (1980) used aggressive reaction toward playback to measure song recognition in territorial male song and swamp sparrows. In a series of experiments, adult males were scored on their approach to two different songs played in quick alternation from separate speakers placed on a territory. Test songs were again composed of either song or swamp sparrow syllables assembled in song- or swamp-sparrowlike temporal patterns. Both song and swamp sparrows were highly selective with respect to syllable type, reacting much more strongly to songs constructed of their own species' syllables than to songs of the other species' syllables. Song sparrows also preferred to approach songs with their own species' temporal patterns, but swamp sparrows showed no such preference. In the present paper, we report on the application of a new technique for testing song recognition in adult female birds, in which recognition is judged by the number of copulation solicitation displays elicited by song in oestradioltreated females. We used this technique to judge recognition by adult female song and swamp sparrows of the same sound patterns employed earlier with adult males and naive young. We believe that this is the first example of comparative data on the parameters used in species recognition by adult females, adult males, and naive young of the same species. Methods

Adult female sparrows were treated with oestradiol and their response to song was measured in terms of copulation solicitation display. This method was suggested by the fact that female white-crowned sparrows (Zonotrichia leucophrys) perform solicitation display following oestrogen treatment (Kern & King 1972). Pilot experiments with hand-reared female swamp sparrows showed that about 5 0 ~ of oestrogen-treated birds responded to song playback with copulation solicitation (Searcy & Marler, unpublished data). Subjects for the present experiments were six female song sparrows and six female swamp sparrows captured as adults in Dutchess County, New York, just prior to the onset of breeding in 1980. Birds were sexed by incipient brood patch

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development and size of cloacal protuberance. Doubtful cases were checked by laparotomy. After a period of habituation to captivity in open cages, subjects were rehoused singly in 45- x -45x-20-cm cages contained within soundproof boxes. By opening one box while the others were closed, it was possible to isolate all but the one subject under observation during a given playback trial. Prior to testing, subjects were given implants of 17 13-oestradiol packed into lengths of Silastic medical grade tubing of 1.96 mm outside diameter, with both ends plugged by adhesive. Tube lengths varied (see below). Implants were placed under the skin of the back where they could be easily seen and removed later. In each playback experiment, three different 3-rain song bouts were presented. The order of presentation of song bouts was determined randomly for each subject on each day of testing. All song bouts consisted of a single song, 2 to 2.5 s in length, repeated with 8 s between songs. The three song bouts were presented one after another to a given subject, with 3 min of silence between bouts. In copulation solicitation display, a female song or swamp sparrow arches her back, bringing her tail forward and her head back. The wings are moved away from the body and vibrated. During playback trials, an observer noted all such displays and scored them on the following scale: 1 for an incomplete display, 2 for a complete display of short duration (approximately 1 s or less), and 3 for a complete, prolonged display. Displays were recorded as separate events if they were separated by more than 1 s of normal posture. Display scores were summed for all displays given during a 3-min song bout. The observer watched from behind a blind in a darkened room, about 1 m from the subject's welMit cage. The observer could hear the test songs. Both song and swamp sparrows were first tested with Normal Song Sparrow, Normal Swamp Sparrow, and Normal Chaffinch (Fringilla coelebs) song (Fig. 1). The song and swamp sparrow songs used in these song bouts were recorded from free-living males in Dutchess County in 1975. Normal Chaffinch song was taken from a commercial recording (North & Simms 1958). Artificial songs combining features of song and swamp sparrow song were also presented. Artificial songs were made by entering natural syllables through the analogue-to-digital converter of a DEC 11/10 minicomputer and

SEARCY ET AL.: SONG DISCRIMINATION IN FEMALES

~_NORMAL SONG SPARROW

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+ NORMAL SWAMP SPARROW

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'~t''" 2FSWAMP SYNTHETIC

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999

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~t'jt vt vt'Jt 'it vl 'it 'Jt'Jt i,i ,l~ i i

I

SWAMP PA'I:TERN SONG SYLLABLE

~SONG PATTERN SWAMP SYLLABLE

ACCELERATED SWAMP SYLLABLE

'it '~i 'A '/! 'Ji 'J! 'Jt'Jt'Jl t

NORMAL CHAFFINCH';~,

Fig. I. Sonagraras of playback songs. then re-editing the syllables into the desired temporal patterns using software routines (see Zoloth et al., in press, and Peters et al. 1980 for more details).

Song SparrowExperiments Silastic tubes containing 15 mm of oestradiol were implanted in six female song sparrows on 16 May. The six were tested with Normal Song Sparrow, Swamp Sparrow, and Chaffinch songs on 26, 28, and 30 May. The three birds that failed to give any solicitation displays were each given a second oestradiol implant of the same size on 30 May and then were tested again with the same three songs on 2, 4, 6, and 8 June. The three song sparrows that displayed during the first three trials were tested on 1, 3, 5, 7, 9, and 11 June with three artificial songs, These

songs were identical to three previously presented to adult territory-owning male song sparrows (Peters et al. 1980). The Song Synthetic song (Fig. 1) is composed of a song sparrow syllable in an accelerated trill followed by a second song sparrow syllable in a steady rate trill. The temporal pattern of this song has two features common in song sparrow songs but typically lacking in swamp sparrow songs: (1) the presence of two phrases, each containing a different syllable, and (2) the presence of an accelerated trill. Though this song is actually simpler in temporal organization than most natural song sparrow songs and lacks a notecomplex between the two trills, it evoked as strong a reaction from male song sparrows as did normal song (Peters et al. 1980). The Swamp Pattern Song Syllable song (Fig. 1) is composed

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of a single song sparrow syllable repeated in the typical swamp sparrow temporal pattern, a steady-rate trill. The Song Pattern Swamp Syllable song (Fig. 1) is composed of one swamp sparrow syllable in an accelerated-rate trill followed by a second swamp sparrow syllable in a steady-rate trill. Swamp Sparrow Experiments On 13 June, six adult female swamp sparrows were given silastic implants containing 8 to 9 mm of oestradiol. On 20, 22, and 24 June, these females were tested with the Normal Chaffinch, Song Sparrow, and Swamp Sparrow songs. On 28 and 30 June and 1 and 4 July, the six swamp sparrows were tested with three artificial songs: Song Pattern Swamp Syllable song, Swamp Pattern Song Syllable song, and Swamp Synthetic song. The first two have already been described. The Swamp Synthetic song (Fig. I) is composed of a single swamp sparrow syllable in a steady-rate trill. This song resembles natural swamp sparrow song very closely and evokes as great a response from adult male swamp sparrows as does Normal Swamp Sparrow song (Peters et al. 1980). On 6, 8, and 10 July, the six swamp sparrows were tested with the Swamp Synthetic song and two new artificial songs. This set of trials was designed to produce more information on the sensitivity of female swamp sparrows to temporal pattern. One of the new artificial songs was the Accelerated Swamp Syllable song (Fig. 1), which is composed of a single swamp sparrow syllable in an accelerated trill. This song is less songsparrow-like than the Song Pattern Swamp Syllable song in having only one phrase but is less swamp-sparrow-like in containing no steady rate trill. The second new song was the Complex Song Pattern Swamp Syllable song, which has a more elaborate temporal pattern than the Song Pattern Swamp Syllable song, one more closely approximating natural song sparrow temporal patterns. The Complex Song Pattern Swamp Syllable song (Fig. 1) contains four phrases, each composed of swamp sparrow syllables, assembled in the following order: (1) an accelerated introductory trill, (2) a phrase containing three different syllables with intersyllable intervals matched to those in a song sparrow note complex, (3) a steady-rate trill, and (4) a terminal, unrepeated syllable resembling a terminal song sparrow note-complex.

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Statistics Responses to different song bouts presented in the same set of playback trials were compared using Wilcoxon matched-pairs signed-ranks tests. In these tests, the basic information used was the difference in response to the two songs under comparison for each bird on each day. The sample sizes given are the number of birdobservation-days for which non-tied response scores were obtained. Since all birds were tested on more than one day and the statistics applied to the total bird observation days, the results of the tests apply to the population of all possible scores of the subjects used rather than the population of all possible individual female song and swamp sparrows. All significance levels are from two-tailed tests. Results Song Sparrows The first set of song presentations (Normal Chaffinch, Normal Song Sparrow, and Normal Swamp Sparrow songs) was designed to test whether adult female song sparrows would discriminate between their own species' song and other species' songs using solicitation display as an assay. In the first three presentations, three of six song sparrows gave solicitation displays one or more times in response to Normal Song Sparrow song, and none gave any displays in response to either Normal Swamp Sparrow or Normal Chaffinch song. In the four further trials with the three doubly implanted birds, one female gave solicitation displays for Normal Song Sparrow song and none gave displays to either Normal Swamp Sparrow or Normal Chaffinch song. Response for Normal Song Sparrow song (mean score = 2.8, range 0-26) was significantly greater than for Normal Swamp Sparrow song (mean score = 0, range 0-0, N = 10, T = 0, P < 0.01) or for Normal Chaffinch song (mean s c o r e - - 0 , range 0-0, N = 10, T = 0, P < 0.01). For all four individuals that responded, mean scores (across days) were greater for Normal Song Sparrow song than for either heterospecific song. The second set of trials (Song Synthetic song, Song Pattern Swamp Syllable song, and Swamp Pattern Song Syllable song) was designed to ascertain tile importance of syllable type and temporal organization in song recognition. This set of trials was performed using only the three females that had responded on the three initial trials. Response was greatest for Song Synthetic song (mean score = 7.2, range 0.25), which has

SEARCY ET AL.: SONG DISCRIMINATION IN FEMALES both the correct species' syllables and correct species' temporal pattern; intermediate for Swamp Pattern Song Syllable song (mean score = 3.9, range 0-19), which has correct species' syllables but wrong species' temporal pattern; and least for Song Pattern Swamp Syllable song (mean score = 1.9, range 0-20), which has correct species' temporal pattern but wrong species' syllables. The difference in response to the Song Synthetic and Swamp Pattern Song Syllable songs was significant (N = 11, T = 4, P < 0.01), and all three subjects gave greater mean responses (across days) for the Song Synthetic song. The difference in response to the Song Synthetic song and the Song Pattern Swamp Syllable song was also significant (N = 12, T = 3, P < 0.01), and again all three subjects gave higher mean responses to Song Synthetic song. The difference in response to the Swamp Pattern Song Syllable song and the Song Pattern Swamp Syllable song was not quite significant (0.10 > P > 0.05). Thus both temporal pattern and syllable type are important in song recognition by female song sparrows.

Swamp Sparrows Swamp sparrows were first presented with Normal Swamp Sparrow, Normal Song Sparrow, and Normal Chaffinch songs. Four of the six birds gave solicitation displays on at least one of the three trials with Normal Swamp Sparrow song, and none ever displayed for Normal Song Sparrow or Normal Chaffinch song. Response was significantly greater for Normal Swamp Sparrow song (mean score = 7.9, range 0-26) than for Normal Song Sparrow song (mean score = 0, range 0-0, N = 10, T = 0, P < 0.01) or for Normal Chaffinch song (mean score = 0, range 0-0, N = 10, T = 0, P < 0.01). Mean response (across days) was greater for Normal Swamp Sparrow song than for either heterospecific song for each of the four subjects that responded. The second set of trials with female swamp sparrows (Swamp Synthetic, Swamp Pattern Song Syllable, and Song Pattern Swamp Syllable songs) was designed to investigate the importance of syllable type and temporal pattern in song recognition by female swamp sparrows. Four of the six subjects displayed during at least one of the four days of trials; three of the four had displayed on the previous trials and one had not. Response to the Swamp Synthetic song (mean score = 7.7, range 0-48) was significantly greater than to the Swamp Pattern Song Syllable

1001

song (mean score -- 0.1, range 0-3, N = 13, T = 0, P < 0.01). All four subjects that responded gave greater mean responses to Swamp Synthetic than to Swamp Pattern Song Syllable song. Response to Song Pattern Swamp Syllable song (mean score = 5.6, range 0-53) was less than to Swamp Synthetic, but the difference was not significant (N = 12, T = 29, P > 0.10). Two birds gave greater mean responses to Swamp Synthetic song, while two others gave greater mean responses to Song Pattern Swamp Syllable song. Thus in this experiment, adult female swamp sparrows showed responsiveness to syllable type but not to temporal pattern (but see below). On the final set of trials, we presented the Swamp Synthetic, Accelerated Swamp Syllable, and Complex Song Pattern Swamp Syllable songs to the six female swamp sparrows in another test for discrimination on the basis of temporal pattern. The Accelerated Swamp Syllable song lacks the song-sparrow-like feature of two-partedness, but at the same time lacks the swamp-sparrow-like feature of a steady-rate trill. Response to the Accelerated Swamp Syllable song (mean score = 0.1, range 0-1) was significantly less than to the Swamp Synthetic song (mean score = 1.8, range 0-13, N = 6, T = 0, P < 0.05). The three females that responded gave greater mean responses for the Swamp Synthetic song. The Complex Song Pattern Swamp Syllable song imitates natural song sparrow temporal patterns more closely than the simpler Song Pattern Swamp Syllable song, and at the same time diverges more radically from natural swamp sparrow temporal patterns. Mean response was significantly less to Complex song (mean score = 0 . 1 , range 0-1) than to the Swamp Synthetic song ( N - 6, T = 0, P < 0.05). Again, the three females that responded gave greater mean responses for the Swamp Synthetic song. Thus the trials with the Accelerated Swamp Syllable and Complex Song Pattern Swamp Syllable songs demonstrated discrimination by adult female swamp sparrows on the basis of temporal pattern.

Discussion This study illustrates a technique that may prove of widespread value in judging response to song in female birds. Copulation solicitation display was used previously to measure response to song in female brown-headed cowbirds (Molothrus ater) (King & West 1977; West et al. 1979).

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Captive female cowbirds without oestrogen treatment give this display in response to song, but this does not appear to be true of other passerines. Captive female song sparrows, for example, do not respond to playback with solicitation until they are treated with oestrogen (Searcy & Marler, unpublished data). The method used here should be valuable in measuring song response in adult females o f other passerine species. In the present study we tested each individual more than once and applied statistics to the total number of bird-observation-days. Therefore the conclusions can be narrowly interpreted to apply only to the population o f possible responses of the particular subjects used rather than to the population of all possible individuals. However, in each case where we report statistical significance, all the subjects that responded gave higher mean responses (across days) to the same stimulus song. We feel that it is unlikely that females within either of these species differ significantly in what features they use in song recognition, and thus we feel justified in applying our conclusions to female song and swamp sparrows in general. Adult females of both song and swamp sparrows readily discriminated between conspecific and heterospecific songs, performing solicitation display only in response to conspecific song. This finding supports the view that song can be an ethological isolating mechanism. However, we still do not know the relative importance of song as an isolating mechanism in these two species, since in natural situations other cues may override song in species identification. Emlen et al. (1975) suggest that visual cues are more important than song in choosing a conspecific mate m indigo buntings (Passerina cyanea) and lazuli buntings (P. amoena). Our results show that adult female song sparrows discriminate between song sparrow and swamp sparrow songs on the same basis as do adult males. Peters et al. (1980) showed that adult male song sparrows are more aggressive toward songs containing song sparrow syllables than toward ones containing swamp sparrow syllables; using the same artificial songs, we have shown a similar sensitivity to syllable type in adult females. Adult male song sparrows also react more strongly to song-sparrow-like temporal patterns than to swamp-sparrow-like ones; again, we have shown a similar sensitivity to temporal pattern in adult females. Syllable type is more Important to song recognition in adult

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male song sparrows than is temporal pattern (Peters et al. 1980); our results show the same trend in adult females, though the preference for syllable type over temporal pattern is not quite significant. In song sparrows, both adult females and adult males show much more sophisticated song recognition abilities than nalve young males, which failed to discriminate between song sparrow and swamp sparrow song using either syllable type or temporal pattern alone, and which show only a limited discrimination ability using both cues together (Marler & Peters 1981). Adult female swamp sparrows resemble adult males of the same species in showing a great sensitivity to syllable type. Males prefer to approach and females prefer to display to songs constructed of swamp sparrow syllables rather than ones constructed of song sparrow syllables (Peters et al. 1980, this study). In fact, response by female swamp sparrows to a song composed of song sparrow syllables in a swamp sparrow temporal pattern is near zero. Adult male swamp sparrows actually preferred to approach the two-parted temporal pattern in the Song Pattern Swamp Syllable song rather than the normal, one-parted swamp sparrow temporal pattern in the Swamp Synthetic song (Peters et al. 1980). Adult females did not discriminate between these two songs. Adult males failed to discriminate between the Accelerated pattern and a normal swamp sparrow pattern (Peters et al. 1980) and also failed to discriminate between the Complex Song pattern and a normal swamp sparrow pattern (Searcy et al., unpublished data). In contrast, adult females showed a significant preference for a normal swamp sparrow pattern over both the Accelerated and the Complex Song Sparrow patterns. Thus we could show no preference by adult males for temporal features of their own species' songs, whereas certain temporal features clearly were important to adult females. It must be borne in mind, however, that responsiveness of males and females to these cues might be different in different contexts. Adult male swamp sparrows seem to base species song recognition on the same song features, at least on a gross level, as do naive young males: syllable type but not temporal pattern. Thus we have no evidence that male swamp sparrows develop greater species song recognition abilities during maturation. Female swamp sparrows are able to discriminate swamp sparrow from song sparrow temporal patterns, while males fail to do so in the context of aggres-

SEARCY ET AL.: SONG DISCRIMINATION 1N FEMALES sive response to a territorial intruder. I f adult males prove to be unresponsive to their own species' temporal patterns in all contexts, then clearly females must be born with more sophisticated song recognition abilities than males or, as seems more likely, they must acquire more sophisticated abilities than males through learning. Our results also bear on the problem of the coevolution of song and song recognition. It is obviously adaptive, at least in most contexts, to have a close match between the features used in song recognition and the features actually present in the species' song. Such a match is exh i n t e d in song sparrows in the contexts of male territory-owners responding aggressively to the song of intruding males and of females responding with courtship to male song. Such a match is not exhibited by male swamp sparrow territory-owners responding to intruder song in that such males do not respond preferentially to correct species' temporal patterns. W h y then does swamp sparrow song adhere to such an extremely narrow range of the infinite array of possible temporal patterns ? One possible answer is that males might respond preferentially to species-typical temporal patterns in another context; for example, songs with swamp sparrow temporal patterns sung by territory-owners might be more effective at keeping potential intruders out of the territory. Another answer, which is in itself sufficient though not exclusive of other explanations, is supported by the results of the present study. Adult female swamp sparrows court preferentially in response to speciestypical temporal patterns. It is selectively advantageous to a male to be able to stimulate females in courtship, thus generating selective pressure on male swamp sparrows to adhere to species-typical temporal patterns in their songs.

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Margaret Hairston Searcy for helping with the figure, and Esther Arruza for typing the manuscript. Financial support was provided by N I M H grant M H 14651 to Peter Marler. William Searcy was supported by N I M H grant PHS MH1525 to the Rockefeller University.

REFERENCES Emlen, S. T., Rising, J.R. & Thompson, W. L. 1975. A behavioral and morphological study of sympatry in the indigo and lazuli buntings of the great plains. Wilson Bull., 87, 145-177. Kern, M. D. & King, J. R. 1972. Testosterone-induced singing in female white-crownedsparrows. Condor, 74, 204-209. King, A. P. & West, M. J. 1977. Species identification in the North American cowbird: Appropriate responses to abnormal song. Science, N.Y., 195, 1002-1004. Kroodsma, D. E. 1977. A re-evaluation of song development in the song sparrow. Anita. Behav., 25, 390399. Marler, P. & Peters, S. 1977. Selective vocal learning in a sparrow. Science, N.Y., 198, 519-521. Marler, P. & Peters, S. 1981. Birdsong and speech: Evidence for special processing. In: Perspectives on the Study of Speech (Ed. by P. Eimas & J. Miller), pp. 75-112. Hillsdale, N. J.: Lawrence Erlbaum Associates. Mulligan, J. A. 1963. A description of song sparrow song based on instrument analysis. Proc. XIIIth Int. Ornith. Congr., 272-285. Mulligan, J. A. 1966. Singing behavior and its development in the song sparrow, Melospiza melodia. Univ. Calif. Publ. Zool., 81, 1-76. North, M. & Simms, E. 1958. Witherby's Sound-Guide to British Birds. London: H. F. & G. Witherby Ltd. Peters, S. S., Searcy, W. A. & Marler, P. 1980. Species song discrimination in choice experiments with territorial male swamp and song sparrows. Anita. Behav., 28, 393-404. West, M. J., King, A. P., Eastzer, D. H. & Staddon, J. E. R. 1979. A bioassay of isolate cowbird song. or. comp. physiol. Psychol., 93, 124-133. Zoloth, S., Dooling, R., Miller, R. & Peters, S. In press. A minicomputer system for the synthesis of animal vocalizations. Z. TierpsychoL

Acknowledgments We thank Carl Whitney for reading and criticizing a draft of the paper, Virginia Sherman and

(Received 12 September 1980; revised 11 December 1980; MS. number: A2540)