Dialects as cultural traits

The communication behaviour of animals can change because of genetic differences, maturational effects, or learning. Communicative traditions in animals are expected to be socially learned. Recently many authors consider dialects as a part of animals’ culture. Dialects are specific communication traditions of sympatric living or neighbouring groups of subpopulations. Potentially, dialects could arise from communications whose functional structure is determined by genetic templates. Recently a growing body of literature includes examinations of dialects in many species. Some of variations of communications are likely to be based on genetic and not social influences. Such are variations in dance dialects in honey bees (Rinderer and Beaman, 1995; Johnson et al., 2002) and possibly in alarm calls in ground squirrels (Randall et al., 2005). Even in chimpanzees, differences in species-typical male call (“pant hoot”) which serves for communication with conspecifics over long distances have been interpreted in terms of ecological rather than social factors (Mitani et al., 1999). Nevertheless, many studies have been concentrated on cultural constituents of dialects. Among cultural communication systems in animals, song dialects in two very different groups of animals, birds and whales, are perhaps the most intensively studied.

Birds, especially song birds and parrots, are well known for their ability to learn complex communication signals. Vocal dialects have been documented in a range of bird species (Thorpe, 1958; Baptista, 1975; Marler, 1984; Slater, 1989). Many birds, such as the white crowned sparrow chaffinch, or parrot, can develop local song dialects. For example, the song of male white-crowned sparrow Zonotrichia leucophrys pugetensis forms about 12 dialects along the Pacific Northwest coast (Nelson et al., 2004).

It was a long standing hypothesis that avian dialects contribute to reproductive isolation between populations (Mayr, 1942, 2001; Marler, Tamura, 1962; Nottenbohm, 1993). Behavioural studies have shown that in many bird species variation in songs results from learning, and that cultural transmission of song is the rule for most oscine birds – nearly half of the worlds’ avian species (Kroodsma and Baylis, 1982; Baker and Thompson, 1985). Recent genetic examinations also revealed low degree of correspondence between population genetic structure and dialect boundaries in many songbird species (see: Wright et al., 2001 for a review). Interestingly, studies in humans have repeatedly found a correspondence between geographical variations, genes and languages (Sokal et al., 1988; Cavalli-Sforza, 1997). This enables researchers to speculate about “real differences between humans and birds in the degree of co-evolution of genetic and cultural traits” (Wright and Wilkinson, 2001).

A good example of recent examining the relationship between genes and culture in birds is the study of Wright et al. (2005) on the yellow-naped Amazon Amazona auropalliata. In this species dialects are comprised to communal roots of 50-200 parrots. Playback experiments have shown that most birds attending a roost within a dialect only use calls specific to that dialect; the rare exceptions are some birds at roosts bordering two dialects that produce the calls of both neighbouring dialects. To test the correspondence between dialects and genetic population structures, Wright et al. (2005) have compared geographic variations in microsatellite allele frequencies at nine sites in Costa Rica. There was no relationship between the genetic distances between individuals and their dialect membership, and high rates of gene flow were estimated between vocal dialects based on genetic differentiation. The results suggest that the observed mosaic pattern of geographic variation in vocalisations is maintained by learning of local call types by immigrated birds after dispersal. The lack of concordance between vocal dialects and population genetic structure in the yellow-naped Amazon mirrors that found in a range of songbird species with vocal dialects (see Wright et al., 2005 for a review).

Now we pass on to dialects in Cetaceans. Dialects have been documented in several species of whales and dolphins. Among them, the vocal dialects of killer whales, Orcinus orca, have been studied most extensively (Ford and Fisher, 1983; Yurk et al., 2002; Tarasyan et al., 2005). The north-eastern Pacific Ocean is home to two distinct forms of killer whales. Resident killer whales live in large stable groups and feed exclusively on fishes. Transient killer whales live in smaller social groups and prey only on marine mammals. The two different forms do not interbreed and rarely interact. They show striking differences in their vocal behaviour. Residents frequently emit a variety of vocalisations whereas transients are usually silent. Vocalisations of residents include echolocation clicks, tonal whistles and pulse calls. The most common pulsed vocalisations of resident killer whales are “discrete calls”, which can be divided into distinct call types. Long term studies have shown that resident killer whales have a complex system of vocal dialects: different social groups have repertoires of 7-17 structurally distinct call types. Comparison of two call types made by two matrilineal social groups of resident killer whales have suggested that vocal learning is not limited to vertical transmission from mother to offspring, and that distinct acoustic repertoires persist in the northern resident community in the form of acoustic clans. Frequent prolonged acoustic contacts between members of different clans occur, however, clan boundaries rather than boundaries between matrilines are the barriers to vocal matching and horizontal transmission (Deecke et al., 2000).

It is interesting that existence of a “hearth of culture” reflected in dialect clans of killer whales possibly has generated a “mirror culture” in populations of harbour seals that learned to distinguish between characteristics of communications of those acoustic clans of killer whales which are dangerous or harmless for marine mammals. Playback experiments have shown that harbour seals (Phoca vitulina) responded by panic diving strongly to the calls of mammal-eating killer whales (transient populations) and unfamiliar fish-eating killer whales that migrate with salmon shoals and use vocal dialects unfamiliar to local populations of seals. Harbour seals learn vocal repertoire of resident fish eating killer whales and do not react to their signals thus saving much energy due to their capacity of complex acoustic discrimination (Deecke et al, 2002).

To what extend dialects can be considered a part of language behaviour, is one of intriguing questions of the large topic of intelligent communication in animals which will be considered in Part IX.

CONCLUDING COMMENTS

Social learning plays an important role in the processes of “tuning” behaviour in group living species and in those which live solitary but at least have contacts with relatives at early stages of ontogenesis. Readiness to gain information from conspecifics reflects both the conformity prevailing in animals’ society and the flexibility that enables animals to improve their individual behaviour in changeable environment.

Capabilities of learning from others and about others allow members of species to decrease the cost of being equipped by inherited suite of a great number of behavioural characteristics. Being extra guided by means of social learning, animals can increase their fitness and make relationships with their environment more flexible and thus more adequate. It is possible that social learning has more fundamental importance as a part of evolutionary strategies of many species than we thought before. In principle, it could be more adaptive for populations to have dormant “sketches” of complex behavioural patterns being implemented on several carriers and then spread by means of social learning under suitable circumstances. Integration of behaviour thus takes place not only at an individual level but at the population level as well. Behavioural strategies of carriers of such “sketches” of behavioural patterns can be evolutionary stable. Following these strategies does not require feats of intelligence from animals, being based on relatively simple forms of social learning. Moreover, in these cases social learning underlies species’ predisposition to learn certain behavioural patterns. Several examples can be adduced by experimental studies on ants, crows, apes and some others.

Animals’ ability to develop completely new behaviour by observing innovations invented by a single or a few advanced individuals should be based on intelligence rather than automatic population processes. Effectiveness of new behaviours performed by “wild prodigies” may be evident for conspecifics but this does not mean that many imitators will subscribe to the same activity. Usually animals observe innovators and try to stand aside. Innovations are most often extinguished within a viscous environment of wild minds. One can say that non-humans badly teach and poorly learn, and that preparedness is the best teacher for animals.

It is very likely that, as D. Premack and A.J. Premack (1996) give this, humans possess unique “pedagogic disposition” to exploit the learners’ “predisposition to culture”, for teachers to demonstrate correct performance for the benefit of the learner.

In general, social learning is based on difference between members of animal communities, that is, on behavioural specialisation in populations, and in some situations, on cognitive specialisation of individuals.

With the exception of rare cases of “true teaching”, social learning is based on “public information” rather than on deliberate exchange of messages. Animals definitely have something to communicate to each others. The question of and to what extent intelligence is involved in their communication will be considered further in Part IX. We also passed over such an original form of social learning as “social learning from information centre”. This feature is typical first of all for eusocial organisms and will also be considered in Part X.