Evidence for cumulative cultural evolution in bird song

Sex differences in the impact of social relationships on individual vocal signatures in grey mouse lemurs (Microcebus murinus)

Vocalizations coordinate social interactions between conspecifics by conveying information concerning the individual or group identity of the sender. Social accommodation is a form of vocal learning where social affinity is signalled by converging or diverging vocalizations with those of conspecifics. To investigate whether social accommodation is linked to the social lifestyle of the sender, we investigated sex-specific differences in social accommodation in a dispersed living primate, the grey mouse lemur (Microcebus murinus), where females form stable sleeping groups whereas males live solitarily. We used 482 trill calls of 36 individuals from our captive breeding colony to compare acoustic dissimilarity between individuals with genetic relatedness, social contact time and body weight. Our results showed that female trills become more similar the more time females spend with each other, independent of genetic relationship, suggesting vocal convergence. In contrast, male trills were affected more by genetic than social factors. However, focusing only on socialized males, increasing time as cage partners caused greater divergence in males' trills. Thus, grey mouse lemurs show the capacity for social accommodation, with females converging their trills to signal social closeness to sleeping group partners, whereas males do not adapt or diverge their trills to signal individual distinctiveness. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Vocal convergence and social proximity shape the calls of the most basal Passeriformes, New Zealand Wrens

Despite extensive research on avian vocal learning, we still lack a general understanding of how and when this ability evolved in birds. As the closest living relatives of the earliest Passeriformes, the New Zealand wrens (Acanthisitti) hold a key phylogenetic position for furthering our understanding of the evolution of vocal learning because they share a common ancestor with two vocal learners: oscines and parrots. However, the vocal learning abilities of New Zealand wrens remain unexplored. Here, we test for the presence of prerequisite behaviors for vocal learning in one of the two extant species of New Zealand wrens, the rifleman (Acanthisitta chloris). We detect the presence of unique individual vocal signatures and show how these signatures are shaped by social proximity, as demonstrated by group vocal signatures and strong acoustic similarities among distantly related individuals in close social proximity. Further, we reveal that rifleman calls share similar phenotypic variance ratios to those previously reported in the learned vocalizations of the zebra finch, Taeniopygia guttata. Together these findings provide strong evidence that riflemen vocally converge, and though the mechanism still remains to be determined, they may also suggest that this vocal convergence is the result of rudimentary vocal learning abilities.

Population turnover, behavioral conservatism, and rates of cultural evolution

Cultural evolution facilitates behavioral adaptation in many species. The pace of cultural evolution can be accelerated by population turnover, where newcomers (immigrants or juvenile recruits) introduce adaptive cultural traits into their new group. However, where newcomers are naïve to the challenges of their new group, population turnover could potentially slow the rate of cultural evolution. Here, we model cultural evolution with population turnover and show that even if turnover results in the replacement of experienced individuals with naïve ones, turnover can still accelerate cultural evolution if (1) the rate of social learning is more than twice as fast as the turnover rate and (b) newcomers are more likely to learn socially than behaviorally conservative existing group members. Although population turnover is a relatively simple factor, it is common to all animal societies, and variation in the turnover rate may potentially play an important role in explaining variation in the occurrence and rates of adaptive cultural evolution across species.

Multilevel Bayesian analysis of monk parakeet contact calls shows dialects between European cities

Geographic differences in vocalizations provide strong evidence for animal culture, with patterns likely arising from generations of social learning and transmission. Most studies on the evolution of avian vocal variation have predominantly focused on fixed repertoire, territorial song in passerine birds. The study of vocal communication in open-ended learners and in contexts where vocalizations serve other functions is therefore necessary for a more comprehensive understanding of vocal dialect evolution. Parrots are open-ended vocal production learners that use vocalizations for social contact and coordination. Geographic variation in parrot vocalizations typically take the form of either distinct regional variations known as dialects or graded variation based on geographic distance known as clinal variation. In this study, we recorded monk parakeets (Myiopsitta monachus) across multiple spatial scales (i.e., parks and cities) in their European invasive range. We then compared calls using a multilevel Bayesian model and sensitivity analysis, with this novel approach allowing us to explicitly compare vocalizations at multiple spatial scales. We found support for founder effects and/or cultural drift at the city level, consistent with passive cultural processes leading to large-scale dialect differences. We did not find a strong signal for dialect or clinal differences between parks within cities, suggesting that birds did not actively converge on a group level signal, as expected under the group membership hypothesis. We demonstrate the robustness of our findings and offer an explanation that unifies the results of prior monk parakeet vocalization studies.

What made us "hunter-gatherers of words"

This paper makes three interconnected claims: (i) the "human condition" cannot be captured by evolutionary narratives that reduce it to a recent 'cognitive modernity', nor by narratives that eliminates all cognitive differences between us and out closest extinct relatives, (ii) signals from paleogenomics, especially coming from deserts of introgression but also from signatures of positive selection, point to the importance of mutations that impact neurodevelopment, plausibly leading to temperamental differences, which may impact cultural evolutionary trajectories in specific ways, and (iii) these trajectories are expected to affect the language phenotypes, modifying what is being learned and how it is put to use. In particular, I hypothesize that these different trajectories influence the development of symbolic systems, the flexible ways in which symbols combine, and the size and configurations of the communities in which these systems are put to use.

Does learning matter? Birdsong-learning program determines coping strategies for living in urban noisy environments

Abstract

Urban noise limits perception by masking acoustic signals, with negative consequences for communication. Although animals relying on acoustic communication are affected, they have developed different strategies to reduce the masking effect of urban noise. Theoretically, birdsong vocal learning confers behavioral plasticity, which may be important for adapting to life in urban environments. To understand the role of vocal learning for adjusting to noisy places, we performed a field study combined with a phylogenetic comparative analysis, comparing passerine species that typically exhibit song learning (oscines) and those that do not (suboscines). Under the premise that vocal learning confers behavioral plasticity, we hypothesized that (1) while oscine species would vary song traits (acoustic parameters), under noisy conditions, suboscines would remain consistent; (2) suboscines may vary birdsong activity in relation to noise; and (3) song learning functions as an exaptation for inhabiting noisy urban environments. We found that oscines only shifted the minimum frequency of their song and did not vary song activity in noisy areas. In contrast, suboscines shifted their complete song upwards and decreased song activity in cities. Our phylogenetic analysis indicated that foraging stratum and song frequency, not learning, best explain adaptation to cities in an evolutionary context. If city noise functions as an ecological filter, frequency traits may serve as an exaptation for colonizing noisy environments. We provided clear evidence that passerine species, depending on their song-learning ability, use different strategies to cope with noise, suggesting that vocal learning determines how birds cope with the masking effect of urban noise.

Significance statement

Since birdsong learning may confer behavioral flexibility, we studied its role for adapting to urban noisy environments. We studied passerines that vary in vocal learning ability combining field data with a phylogenetic comparative analysis. Our methodology may provide information on both the response and the evolutionary advantages of vocal learning for living in noisy urban environments. Although both learner and non-learner birds varied their responses, they displayed different strategies for coping with urban noise. Moreover, differences in vocal learning might not limit colonization of noisy environments, and ecological and acoustic traits may explain adaptation to urbanization. Frequency parameters are conserved evolutionary traits among birds living in cities and may function as a preadaptation that facilitates the colonization of urban environments. Our study suggests that the birdsong-learning program does not help birds colonize cities but determines how they cope with the masking effect of urban noise.

The social role of song in wild zebra finches

Male songbirds sing to establish territories and to attract mates.^1,2 However, increasing reports of singing in non-reproductive contexts³ and by females^4,5 show that song use is more diverse than previously considered. Therefore, alternative functions of song, such as social cohesion³ and synchronization of breeding, by and large, were overlooked even in such well-studied species such as the zebra finch (Taeniopygia guttata). In these social songbirds, only the males sing, and pairs breed synchronously in loose colonies,^6,7 following aseasonal rain events in their arid habitat.^8,9 As males are not territorial, and pairs form long-term monogamous bonds early in life, conventional theory predicts that zebra finches should not sing much at all; however, they do and their song is the focus of hundreds of lab-based studies.^{10,11,12,13,14,15,16,17,18,19,20,21,22} We hypothesize that zebra finch song functions to maintain social cohesion and to synchronize breeding. Here, we test this idea using data from 5 years of field studies, including observational transects, focal and year-round audio recordings, and a large-scale playback experiment. We show that zebra finches frequently sing while in groups, that breeding status influences song output at the nest and at aggregations, that they sing year round, and that they predominantly sing when with their partner, suggesting that the song remains important after pair formation. Our playback reveals that song actively features in social aggregations as it attracts conspecifics. Together, these results demonstrate that birdsong has important functions beyond territoriality and mate choice, illustrating its importance in coordination and cohesion of social units within larger societies.

Blind alleys and fruitful pathways in the comparative study of cultural cognition

A mere few decades ago, culture was thought a unique human attribute. Evidence to the contrary accumulated through the latter part of the twentieth century and has exploded in the present one, demonstrating the transmission of traditions through social learning across all principal vertebrate taxa and even invertebrates, notably insects. The scope of human culture is nevertheless highly distinctive. What makes our cultural capacities and their cognitive underpinnings so different? In this article I argue that in behavioural scientists' endeavours to answer this question, fruitful research pathways and their ensuing discoveries have come to exist alongside popular, yet in the light of current empirical evidence, highly questionable scenarios and even scientific blind alleys. I particularly re-evaluate theories that rely on the centrality of a supposed uniquely human capacity for imitative copying in explaining the distinctive capacity for massive cumulative cultural evolution (CCE) in our species. The most extreme versions of this perspective suffer logical incoherence and severe limits on scientific testability. By contrast the field has generated a range of rigorous observational and experimental methodologies that have revealed both long-term cultural fidelity and limited forms of CCE in non-human species. Attention now turns to directly investigating the scope, limits and underlying cognition of non-human versus human CCE, with a broader approach to factors additional to cultural transmission, notably the role of invention, innovation and evolved motivational biases underlying the scope of CCE in the species studied.

Humpback whale song revolutions continue to spread from the central into the eastern South Pacific

Cultural transmission of behaviour is an important aspect of many animal communities ranging from humans to birds. Male humpback whales (Megaptera novaeangliae) sing a repetitive, stereotyped, socially learnt and culturally transmitted song display that slowly evolves each year. Most males within a population sing the same, slow-evolving song type; but in the South Pacific, song 'revolutions' have led to rapid and complete replacement of one song type by another introduced from a neighbouring population. Songs spread eastwards, from eastern Australia to French Polynesia, but the easterly extent of this transmission was unknown. Here, we investigated whether song revolutions continue to spread from the central (French Polynesia) into the eastern (Ecuador) South Pacific region. Similarity analyses using three consecutive years of song data (2016-2018) revealed that song themes recorded in 2016-2018 French Polynesian song matched song themes sung in 2018 Ecuadorian song, suggesting continued easterly transmission of song to Ecuador, and vocal connectivity across the entire South Pacific Ocean basin. This study demonstrates songs first identified in western populations can be transmitted across the entire South Pacific, supporting the potential for a circumpolar Southern Hemisphere cultural transmission of song and a vocal culture rivalled in its extent only by our own.

Humpback whale song revolutions continue to spread from the central into the eastern South Pacific

Cultural transmission of behaviour is an important aspect of many animal communities ranging from humans to birds. Male humpback whales (Megaptera novaeangliae) sing a repetitive, stereotyped, socially learnt and culturally transmitted song display that slowly evolves each year. Most males within a population sing the same, slow-evolving song type; but in the South Pacific, song 'revolutions' have led to rapid and complete replacement of one song type by another introduced from a neighbouring population. Songs spread eastwards, from eastern Australia to French Polynesia, but the easterly extent of this transmission was unknown. Here, we investigated whether song revolutions continue to spread from the central (French Polynesia) into the eastern (Ecuador) South Pacific region. Similarity analyses using three consecutive years of song data (2016-2018) revealed that song themes recorded in 2016-2018 French Polynesian song matched song themes sung in 2018 Ecuadorian song, suggesting continued easterly transmission of song to Ecuador, and vocal connectivity across the entire South Pacific Ocean basin. This study demonstrates songs first identified in western populations can be transmitted across the entire South Pacific, supporting the potential for a circumpolar Southern Hemisphere cultural transmission of song and a vocal culture rivalled in its extent only by our own.

The Neurobiology of Behavior and Its Applicability for Animal Welfare: A Review

Simple Summary

Animal welfare is the result of physical and psychological well-being and is expected to occur if animals are free: (1) from hunger, thirst and malnutrition, (2) from discomfort, (3) from pain, (4) to express normal behavior, and (5) from fear and distress. Nevertheless, well-being is not a constant state but rather the result of certain brain dynamics underlying innate motivated behaviors and learned responses. Thus, by understanding the foundations of the neurobiology of behavior we fathom how emotions and well-being occur in the brain. Herein, we discuss the potential applicability of this approach for animal welfare. First, we provide a general view of the basic responses coordinated by the central nervous system from the processing of internal and external stimuli. Then, we discuss how those stimuli mediate activity in seven neurobiological systems that evoke innate emotional and behavioral responses that directly influence well-being and biological fitness. Finally, we discuss the basic mechanisms of learning and how it affects motivated responses and welfare.

Abstract

Understanding the foundations of the neurobiology of behavior and well-being can help us better achieve animal welfare. Behavior is the expression of several physiological, endocrine, motor and emotional responses that are coordinated by the central nervous system from the processing of internal and external stimuli. In mammals, seven basic emotional systems have been described that when activated by the right stimuli evoke positive or negative innate responses that evolved to facilitate biological fitness. This review describes the process of how those neurobiological systems can directly influence animal welfare. We also describe examples of the interaction between primary (innate) and secondary (learned) processes that influence behavior.

Technical reasoning bolsters cumulative technological culture through convergent transformations

Understanding the evolution of human technology is key to solving the mystery of our origins. Current theories propose that technology evolved through the accumulation of modifications that were mostly transmitted between individuals by blind copying and the selective retention of advantageous variations. An alternative account is that high-fidelity transmission in the context of cumulative technological culture is supported by technical reasoning, which is a reconstruction mechanism that allows individuals to converge to optimal solutions. We tested these two competing hypotheses with a microsociety experiment, in which participants had to optimize a physical system in partial- and degraded-information transmission conditions. Our results indicated an improvement of the system over generations, which was accompanied by an increased understanding of it. The solutions produced tended to progressively converge over generations. These findings show that technical reasoning can bolster high-fidelity transmission through convergent transformations, which highlights its role in the cultural evolution of technology.

When does cultural evolution become cumulative culture? A case study of humpback whale song

Culture presents a second inheritance system by which innovations can be transmitted between generations and among individuals. Some vocal behaviours present compelling examples of cultural evolution. Where modifications accumulate over time, such a process can become cumulative cultural evolution. The existence of cumulative cultural evolution in non-human animals is controversial. When physical products of such a process do not exist, modifications may not be clearly visible over time. Here, we investigate whether the constantly evolving songs of humpback whales (Megaptera novaeangliae) are indicative of cumulative cultural evolution. Using nine years of song data recorded from the New Caledonian humpback whale population, we quantified song evolution and complexity, and formally evaluated this process in light of criteria for cumulative cultural evolution. Song accumulates changes shown by an increase in complexity, but this process is punctuated by rapid loss of song material. While such changes tentatively satisfy the core criteria for cumulative cultural evolution, this claim hinges on the assumption that novel songs are preferred by females. While parsimonious, until such time as studies can link fitness benefits (reproductive success) to individual singers, any claims that humpback whale song evolution represents a form of cumulative cultural evolution may remain open to interpretation. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.

Collective minds: social network topology shapes collective cognition

Human cognition is not solitary, it is shaped by collective learning and memory. Unlike swarms or herds, human social networks have diverse topologies, serving diverse modes of collective cognition and behaviour. Here, we review research that combines network structure with psychological and neural experiments and modelling to understand how the topology of social networks shapes collective cognition. First, we review graph-theoretical approaches to behavioural experiments on collective memory, belief propagation and problem solving. These results show that different topologies of communication networks synchronize or integrate knowledge differently, serving diverse collective goals. Second, we discuss neuroimaging studies showing that human brains encode the topology of one's larger social network and show similar neural patterns to neural patterns of our friends and community ties (e.g. when watching movies). Third, we discuss cognitive similarities between learning social and non-social topologies, e.g. in spatial and associative learning, as well as common brain regions involved in processing social and non-social topologies. Finally, we discuss recent machine learning approaches to collective communication and cooperation in multi-agent artificial networks. Combining network science with cognitive, neural and computational approaches empowers investigating how social structures shape collective cognition, which can in turn help design goal-directed social network topologies. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.

Complex foraging behaviours in wild birds emerge from social learning and recombination of components

Recent well-documented cases of cultural evolution towards increasing efficiency in non-human animals have led some authors to propose that other animals are also capable of cumulative cultural evolution, where traits become more refined and/or complex over time. Yet few comparative examples exist of traits increasing in complexity, and experimental tests remain scarce. In a previous study, we introduced a foraging innovation into replicate subpopulations of great tits, the 'sliding-door puzzle'. Here, we track diffusion of a second 'dial puzzle', before introducing a two-step puzzle that combines both actions. We mapped social networks across two generations to ask if individuals could: (1) recombine socially-learned traits and (2) socially transmit a two-step trait. Our results show birds could recombine skills into more complex foraging behaviours, and naïve birds across both generations could learn the two-step trait. However, closer interrogation revealed that acquisition was not achieved entirely through social learning-rather, birds socially learned components before reconstructing full solutions asocially. As a consequence, singular cultural traditions failed to emerge, although subpopulations of birds shared preferences for a subset of behavioural variants. Our results show that while tits can socially learn complex foraging behaviours, these may need to be scaffolded by rewarding each component. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.