Todd M. Freeberg

Social complexity as a proximate and ultimate factor in communicative complexity.

The ‘social complexity hypothesis’ for communication posits that groups with complex social systems require more complex communicative systems to regulate interactions and relations among group members. Complex social systems, compared with simple social systems, are those in which individuals frequently interact in many different contexts with many different individuals, and often repeatedly interact with many of the same individuals in networks over time. Complex communicative systems, compared with simple communicative systems, are those that contain a large number of structurally and functionally distinct elements or possess a high amount of bits of information. Here, we describe some of the historical arguments that led to the social complexity hypothesis, and review evidence in support of the hypothesis. We discuss social complexity as a driver of communication and possible causal factor in human language origins. Finally, we discuss some of the key current limitations to the social complexity hypothesis—the lack of tests against alternative hypotheses for communicative complexity and evidence corroborating the hypothesis from modalities other than the vocal signalling channel.

Culture and courtship in vertebrates: a review of social learning and transmission of courtship systems and mating patterns

Female and male animals often choose mates based upon the complementarity of their courtship behaviours and preferences. The importance of this fact on the evolutionary dynamics of populations has long been appreciated. What has not been appreciated is the role that social learning might play in the transmission of systems of courtship behaviour across generations. This paper addresses the social transmission of courtship behavioural traditions in vertebrates. It discusses views of culture in the context of behavioural signals and preferences in courtship. It then reviews empirical evidence for culture-like processes affecting courtship behaviour, focusing on studies of song learning in passerine birds and work on social learning of mating preferences. The paper concludes with potential future directions for research on social traditions in systems of courtship behaviour, including determining mechanisms of transmission, genetic and non-social environmental effects, and selective factors influencing the stability of behavioural traditions over time. By integrating proximate and ultimate questions for the transmission of courtship systems, this work would increase our understanding of the ways individual development, cultural processes, and population evolution influence, and are in turn influenced by, one another.

Receivers respond differently to chick-a-dee calls varying in note composition in Carolina chickadees, Poecile carolinensis

The chick-a-dee call of the avian genus Poecile is a structurally complex vocal system because it possesses a set of simple rules that governs how the notes of the call are ordered, and variable numbers of each of the note types strung together can generate an extraordinary number of unique calls. Whereas it has been hypothesized that chick-a-dee calls with different notes may convey different information, no experimental evidence has been offered in support of the hypothesis. Previously published studies suggested that flock members use chick-a-dee calls in the context of moving to or from a feeding site. Here, we tested Carolina chickadees’ responses to playbacks of chick-a-dee calls that differed in note composition. Playbacks were conducted in the field in the context of a novel food source. Our pilot data had indicated that chick-a-dee calls with relatively large numbers of ‘C’ notes were given by birds on their first contact with a novel seed stand. In the present study, we found that chickadees flew in close to the playback speaker and subsequently took seed from a seed stand more often during playbacks of chick-a-dee calls containing C notes than chick-a-dee calls not containing C notes or than control playbacks. Vocal responses of chickadees to the playbacks also differed in relation to the particular vocal signal being played back. These results indicate that receivers respond differently to chick-a-dee calls containing different compositions of note types and represent a first step to link variation in note composition and ordering in these calls to possible meanings.

A comparative study of avian auditory brainstem responses: correlations with phylogeny and vocal complexity, and seasonal effects

Abstract. We conducted a comparative study of the peripheral auditory system in six avian species (downy woodpeckers, Carolina chickadees, tufted titmice, white-breasted nuthatches, house sparrows, and European starlings). These species differ in the complexity and frequency characteristics of their vocal repertoires. Physiological measures of hearing were collected on anesthetized birds using the auditory brainstem response to broadband click stimuli. If auditory brainstem response patterns are phylogenetically conserved, we predicted woodpeckers, sparrows, and starlings to be outliers relative to the other species, because woodpeckers are in a different Order (Piciformes) and, within the Order Passeriformes, sparrows and starlings are in different Superfamilies than the nuthatches, chickadees, and titmice. However, nuthatches and woodpeckers have the simplest vocal repertoires at the lowest frequencies of these six species. If auditory brainstem responses correlate with vocal complexity, therefore, we would predict nuthatches and woodpeckers to be outliers relative to the other four species. Our results indicate that auditory brainstem responses measures in the spring broadly correlated with both vocal complexity and, in some cases, phylogeny. However, these auditory brainstem response patterns shift from spring to winter due to species-specific seasonal changes. These seasonal changes suggest plasticity at the auditory periphery in adult birds.

Social Complexity Can Drive Vocal Complexity Group Size Influences Vocal Information in Carolina Chickadees

One hypothesis to explain variation in vocal communication in animal species is that the complexity of the social group influences the groups vocal complexity. This social-complexity hypothesis for communication is also central to recent arguments regarding the origins of human language, but experimental tests of the hypothesis are lacking. This study investigated whether group size, a fundamental component of social complexity, influences the complexity of a call functioning in the social organization of Carolina chickadees, Poecile carolinensis. In unmanipulated field settings, calls of individuals in larger groups had greater complexity (more information) than calls of individuals in smaller groups. In aviary settings manipulating group size, individuals in larger groups used calls with greater complexity than individuals in smaller groups. These results indicate that social complexity can influence communicative complexity in this species.

Acoustic sequences in non-human animals: a tutorial review and prospectus

Animal acoustic communication often takes the form of complex sequences, made up of multiple distinct acoustic units. Apart from the well‐known example of birdsong, other animals such as insects, amphibians, and mammals (including bats, rodents, primates, and cetaceans) also generate complex acoustic sequences. Occasionally, such as with birdsong, the adaptive role of these sequences seems clear (e.g. mate attraction and territorial defence). More often however, researchers have only begun to characterise – let alone understand – the significance and meaning of acoustic sequences. Hypotheses abound, but there is little agreement as to how sequences should be defined and analysed. Our review aims to outline suitable methods for testing these hypotheses, and to describe the major limitations to our current and near‐future knowledge on questions of acoustic sequences. This review and prospectus is the result of a collaborative effort between 43 scientists from the fields of animal behaviour, ecology and evolution, signal processing, machine learning, quantitative linguistics, and information theory, who gathered for a 2013 workshop entitled, ‘Analysing vocal sequences in animals’. Our goal is to present not just a review of the state of the art, but to propose a methodological framework that summarises what we suggest are the best practices for research in this field, across taxa and across disciplines. We also provide a tutorial‐style introduction to some of the most promising algorithmic approaches for analysing sequences. We divide our review into three sections: identifying the distinct units of an acoustic sequence, describing the different ways that information can be contained within a sequence, and analysing the structure of that sequence. Each of these sections is further subdivided to address the key questions and approaches in that area. We propose a uniform, systematic, and comprehensive approach to studying sequences, with the goal of clarifying research terms used in different fields, and facilitating collaboration and comparative studies. Allowing greater interdisciplinary collaboration will facilitate the investigation of many important questions in the evolution of communication and sociality.

Seasonal variation in avian auditory evoked responses to tones: a comparative analysis of Carolina chickadees, tufted titmice, and white-breasted nuthatches

We tested for seasonal plasticity of the peripheral auditory system of three North American members of the Sylvioidea: Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). We measured three classes of auditory evoked responses (AER) to tone stimuli: sustained receptor/neural responses to pure-tone condensation waveforms, the frequency-following response (FFR), and the earliest peak of the AER to stimulus onset (tone onset response). Seasonal changes were detected in all classes of AERs in chickadees and nuthatches. Seasonal changes in titmice were restricted to the tone onset response. Interestingly, changes detected in chickadees (and to a lesser extent in titmice) were generally in an opposite direction to changes seen in nuthatches, with chickadees exhibiting greater amplitude AER responses in the spring than in winter, and nuthatches exhibiting greater amplitude AER responses in winter than in spring. In addition, the seasonal differences in the sustained responses tended to be broad-band in the chickadees but restricted to a narrower frequency range in nuthatches. In contrast, seasonal differences in the onset response were over a broader frequency range in titmice than in chickadees and nuthatches. We discuss some possible mechanistic and functional explanations for these seasonal changes.

Cultural influences on female mate choice: an experimental test in cowbirds,Molothrus ater

Previous studies of brown-headed cowbirds Molothrus ater, have shown that social learning and cultural transmission can influence courtship and mating patterns. These earlier studies did not test whether cultural background influenced mate choice in females and therefore whether culture could potentially play a role in sexual selection in this species, as has been suggested by recent theory. Here, we tested whether culture influences female mate choice in brown-headed cowbirds. Female cowbirds from a South Dakota population were housed with adult cowbirds from the same South Dakota population or with adult cowbirds from a behaviourally distinct population from Indiana. We tested the mating preferences of females of the South Dakota culture and females of the Indiana culture in sequential mate-choice trials with males, controlling for intrasexual interactions. The males were South Dakota cowbirds that had also been housed either in the South Dakota culture or in the Indiana culture. Females showed mating preferences for males from their own culture. These results suggest that mate choice in female cowbirds can be influenced by cultural background. We briefly discuss the effect that culture may have on sexual selection and on the evolution of female mating preferences. Copyright 1999 The Association for the Study of Animal Behaviour.

The cultural transmission of courtship patterns in cowbirds, Molothrus ater

In this study, I tested whether the courtship behaviours that facilitate patterns of assortative pairing and mating could be culturally transmitted across generations of brown-headed cowbirds. In an earlier study, I housed a first generation of young South Dakota cowbirds in one of two cultural backgrounds: (1) with adult social models from the same population; or, (2) with adult social models from a behaviourally distinct Indiana population. During the breeding season, the first cultural generation of South Dakota cowbirds paired and mated assortatively based upon their cultural backgrounds. In the present study, I tested whether these courtship patterns could be culturally transmitted to a second generation of young South Dakota cowbirds. Serving as adult social models for birds of the second cultural generation were the first cultural generation of South Dakota birds from the previous study. During their first breeding season, the birds of the second cultural generation paired assortatively by cultural background at roughly a 3:1 ratio. In addition to the pairing data, the behavioural responses of females to the vocalizations of males indicated the influence of cultural backgrounds. This experimental demonstration of the cultural transmission of courtship patterns points to the importance of social environments as mechanisms whereby behavioural systems are inherited from one generation of animals to the next. Copyright 1998 The Association for the Study of Animal Behaviour.

Linking social complexity and vocal complexity: a parid perspective

The Paridae family (chickadees, tits and titmice) is an interesting avian group in that species vary in important aspects of their social structure and many species have large and complex vocal repertoires. For this reason, parids represent an important set of species for testing the social complexity hypothesis for vocal communication—the notion that as groups increase in social complexity, there is a need for increased vocal complexity. Here, we describe the hypothesis and some of the early evidence that supported the hypothesis. Next, we review literature on social complexity and on vocal complexity in parids, and describe some of the studies that have made explicit tests of the social complexity hypothesis in one parid—Carolina chickadees, Poecile carolinensis. We conclude with a discussion, primarily from a parid perspective, of the benefits and costs of grouping and of physiological factors that might mediate the relationship between social complexity and changes in signalling behaviour.