Comments on a kin association model of bird song dialects

Anita. Behav., 1980, 28, 310-314

SHORT COMMUNICATIONS S uch a test is to compare the response of males to songs of their own dialect with their response to songs of a different dialect. To eliminate the effects of habituation, the songs of the same dialect should not belong to neighbours. Such observations have been made of three territorial species that have local dialects: white-crowned sparrow (Milligan & Verner 1971), cardinal (Lemon 1967), and song sparrow (Harris & Lemon 1974). In each experiment the males responded more intensely to the playback of the same dialect than to the playback of a different dialect. These results contradict the predictions of Treisman's kin association model. Possibly the songs of the familiar dialect act as a more effective releaser of territorial responses than songs of an unfamiliar dialect. This would be expected in a situation discussed by Nottebohm (1969) where most behavioural interactions such as territorial disputes and mate selection occur between individuals that learned the same dialect. Nottebohm proposed that dialects might function to restrict gene flow between dialect populations genetically adapted to the local environment. Presumably, low dispersal of males from their natal dialect area and female selection of mates singing the familiar dialect would allow individuals to preserve local adaptations in their offspring. This model is consistent with the observation of greater response to the familiar dialect. A more complete evaluation of this model's assumptions has been presented by Payne (in press). The most direct method of testing a model of kin association is to determine whether or not neighbours are kin. Observations of juvenile dispersal in two species exhibiting dialects suggest that young cardinals may settle near kin while saddlebacks probably do not (Lemon 1975; Jenkins 1977). Knowledge of relatedness between birds and comparison of interactions between kin and non-kin before habituation to songs has occurred would illuminate the interesting possibility of kin associations in songbirds. I thank Peter R. Grant, Tom C. Will, and F. Stephen Dobson for their criticisms of this manuscript. JILL M. TRAINER

Comments on a Kin Association Model of Bird Song Dialects Treisman (1978) proposed a new model to explain the role of song dialects in the social life of songbirds. He tested the major prediction of his model by citing certain field studies; however, other studies in the literature provide a more appropriate test of the model. As discussed below, the results of the latter test correspond more closely to the predictions of the dialect model described by Nottebohm 0969) than to the predictions of Treisman's model. Using game theory analysis, Treisman showed that male songbirds able to distinguish kin from non-kin gain a selective advantage by choosing territories near those of kin: the evolutionarily stable strategy employed by related individuals is less aggressive, and the expected return is higher in conflicts between kin. Treisman speculated that individuals recognize relatives by the structure of their songs, with kin singing songs of similar structure. Song repertoires perhaps contain sufficient information for identification of kin. The degree of relatedness between birds might be conveyed in a system of dialects, a form of geographic variation in song exhibiting lower variation within locations than between locations (Lemon 1967). Because recognition of relatives by song requires that song structure reflect relatedness between individuals, Treisman's model applies only to species with the following characteristics: learning of song early in life from nearby relatives, male dispersal within the vicinity of their parents' territory, and dialect variance over short distances. The model is rather restricted since many species with song dialects do not exhibit these requirements (Payne in press). The main prediction of Treisman's model is that aggression between males singing songs of the same dialect should be lower than aggression between males singing songs of different dialects. To test this prediction, Treisman pointed out that male ovenbirds and whitethroated sparrows respond less aggressively to taped playback of songs of neighbours (birds with adjacent territories) than to songs of strangers (Weeden & Falls 1959; Falls & Brooks 1975). Other field studies on yellowthroats (Wunderle 1978), field sparrows (Goldman 1973), and song sparrows (Kroodsma 1976) have yielded similar results. Unfortunately, this type of experiment does not constitute a proper test of the model for two reasons. First, of the species whose responses to neighbours and strangers have been studied, only the song sparrow exhibits local dialects in some populations (Harris & Lemon 1972). According to the model, dialects are necessary to indicate relatedness. Second, the experiments cannot distinguish between lower levels of aggressive response as a consequence of habituation to repeated songs and lower aggression applied in kin associations. Field experiments have shown that white-throated sparrow and yellowthroat males habituate to the songs of neighbours at territorial boundaries, reducing the energy spent disputing previously established boundaries (Falls & Brooks 1975; Wunderle 1978). Because habituation could lower response to both kin and non-kin neighbours, measuring intensity of response to neighbours is a weak test to detect kin associations. A stronger test would examine the prediction that males recognize and behave differently toward relatives and non-relatives.

Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109.

References Falls, J. B. & Brooks, R. J. 1975. Individual recognition by song in white-throated sparrows. II. Effects of location. Can. J. Zool., 53, 1412-1420. Goldman, P. 1973. Song recognition by field sparrows. Auk, 90, 106-113. Harris, M. A. & Lemon, R. E. 1972. Songs of song sparrows (Melospiza melodia): individual variation and dialects. Can. J. Zool., 50, 301-309. Harris, M. A. & Lemon, R. E. 1974. Songs of song sparrows: reactions of males to songs of different localities. Condor, 76, 33--44. Jenkins, P. F. 1977. Cultural transmission of song patterns and dialect development in a free-living bird population. Anim. Behav., 25, 50-78. Kroodsma, D. E. 1976. The effect of large song repertoires on neighbor 'recognition' in male song sparrows. Condor, 78, 97-99. 310

SHORT COMMUNICATIONS Lemon, R. E. 1967. The response of cardinals to songs of different dialects. Anim. Behav., 15, 538-545. Lemon, R. E. 1975. How birds develop song dialects. Condor, 77, 385--406. Milligan, M. M. & Verner, J. 1971. Inter-populational song dialect discrimination in the white-crowned sparrow. Condor, 73, 208-213. Nottebohm, F. 1969. The song of the chingolo, Zonotriehia eapensis, in Argentina: description and evaluation of a system of dialects. Condor, 71, 299-315. Payne, R. B. In press. Population structure and social behavior: models for testing the ecological significance of song dialects in birds. In: Natural Selection

and Social Behavior: Recent Research and New Theory (Ed. by R. D. Alexander & D. W. Tinkle). New York: Chiron Press. Treisman, M. 1978. Bird song dialects, repertoire size, and kin association. Anim. Behav., 26, 814-817. Weeden, J. S. & Falls, J. B. 1959. Differential responses of male ovenbirds to recorded songs of neighboring and more distant individuals. Auk, 76, 343-351. Wunderle, J. M. 1978. Differential response of territorial yellowthroats to the songs of neighbors and nonneighbors. Auk, 95, 389-395.

(Received 22 June 1979; revised 8 August 1979; MS. number: AS-77) Some Difficulties in Testing Explanations for the Occurrence of Bird Song Dialects A possible explanation for the occurrence of distinctive localised dialects in the song of some songbirds put forward by Treisman (1978) was that the evolutionarily stable strategy (Maynard Smith 1974) for conflict between kin would involve less employment of the more destructive types of aggression available to the contestants than conflict between strangers, and thus a higher return to both contestants. Consequently there would be a selective advantage for patterns of behaviour that increased the probability of competing with kin rather than with nonrelatives. Establishing a territory in a region where the songs of competitors sound familiar rather than novel might be such a pattern of behaviour. It would facilitate using song as a guide to the choice of a territory if the birds produced individually and regionally varying songs, so that familiar and unfamiliar dialect areas could readily be distinguished. This would lead to larger repertoires of songs. This is only one possible explanation for the occurrence of bird song dialects; as Treisman (1978) noted, other factors may also contribute in particular cases, and the various explanations are not necessarily mutually exclusive. In support of the kin association explanation, Treisman (1978) noted that in some cases the songs of strangers may elicit a greater response than those of neighbours (Nottebohm 1972). Trainer (1980) objects to this as evidence on the ground that habituation may occur to the songs of neighbours, and suggests that it would be more informative to compare the response of males to their own dialect sung by non-neighbours with their response to foreign dialects. The first point is acceptable, and illustrates the difficulty of deriving unambiguous evidence for complex hypotheses from field observations. But similar difficulties of interpretation arise with Trainer's (1980) suggested alternative. On the one hand, consider Weeden & Falls' (1959) observation that male ovenbirds react faster and more strongly if the songs of birds from non-adjacent territories

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are played to them than they do to the songs of their nearest neighbours. This can be given a straightforward explanation (as, indeed, Weeden & Fails do): late in the breeding season, when the study was done, boundaries with nearest neighbours are well established and there is little basis for conflict. But if a bird from a more distant neighbourhood migrates into a resident's territory it may indeed be seeking to take it over, and this warrants a more vigorous defence. On the other hand, consider a study such as that of Milligan & Verner (1971) which found that male whitecrowned sparrows react more strongly, in terms of numbers of songs and flights, to (non-neighbour) songs played in their own territories in their own dialect, than to songs in foreign dialects. Trainer (1980) considers that this refutes Treisman's (1978) hypothesis. In fact it is easily reconcilable with it. Suppose that the kin association model does indeed apply to white-crowned sparrows, and that the resulting bias to nest in an area in which a familiar dialect is sung is sufficiently well established to make it unlikely that any individual bird would do otherwise. Then the song of a non-neighbour, singing in the familiar dialect, may well represent an immediate threat (as discussed above in relation to the Weeden & Falls study) and warrant a strong response. But a song in a strange dialect will most likely come from a migrant or a transient, and so will justify a lesser response, especially when it has been heard for only a short period. Thus neither type of study contributes strong evidence for or against the hypothesis. Treisman's (1977, 1978) model does not imply that competition will be less between kin; need to establish territories will still exist and confrontations must still take place. What does follow from the model is that animals will employ the more destructive forms of aggression (Attack) less often, and the less destructive forms (Display) more often, in conflict with kin than when competing with strangers. It is of interest in this respect that although Milligan & Verner (1971) found more response in terms of songs and flights (i.e. threat displays) to a song in familiar dialect than to a strange one, they found less response in terms of approach to the loudspeaker. The defending white-crowned sparrows came physically nearer to their heard opponents when the latter sang in a strange dialect than when the song was in their own dialect. This is what the kin association process might lead to. However, this pattern has not been seen in other similar studies such as that of Lemon (1967) with cardinals or Harris & Lemon (1974) with song sparrows. It seems likely that more active experimental intervention would be required to gain stronger evidence for or against the theory. One approach might be to oblige birds of different dialect to occupy adjacent territories, and to examine the quality of their aggressive interactions and how well they thrive and reproduce themselves under these circumstances. Another observation that might be revealing is the behaviour of females of species in which males choose territories in areas of familiar dialect. If the females are out-breeding, as may be the case for blackbirds (Greenwood & Harvey 1976), this would be compatible with the present hypothesis, as a compensatory device to reduce inbreeding depression, but it would be incompatible with an explanation based on an advantage of assortative mating (Nottebohm 1969, 1970). Finally, since Trainer (1980) mistakenly states: 'Treisman speculated that individuals recognize relatives by the structure of their songs' it should be made clear that Treisman did not postulate any process of individual