1. Animals produce sounds for diverse biological functions such as defending territories, attracting mates, deterring predators, navigation, finding food and maintaining contact with members of their ...social group. Biologists can take advantage of these acoustic behaviours to gain valuable insights into the spatial and temporal scales over which individuals and populations interact. Advances in bioacoustic technology, including the development of autonomous cabled and wireless recording arrays, permit data collection at multiple locations over time. These systems are transforming the way we study individuals and populations of animals and are leading to significant advances in our understandings of the complex interactions between animals and their habitats. 2. Here, we review questions that can be addressed using bioacoustic approaches, by providing a primer on technologies and approaches used to study animals at multiple organizational levels by ecologists, behaviourists and conservation biologists. 3. Spatially dispersed groups of microphones (arrays) enable users to study signal directionality on a small scale or to locate animals and track their movements on a larger scale. 4. Advances in algorithm development can allow users to discriminate among species, sexes, age groups and individuals. 5. With such technology, users can remotely and non-invasively survey populations, describe the soundscape, quantify anthropogenic noise, study species interactions, gain new insights into the social dynamics of sound-producing animals and track the effects of factors such as climate change and habitat fragmentation on phenology and biodiversity. 6. There remain many challenges in the use of acoustic monitoring, including the difficulties in performing signal recognition across taxa. The bioacoustics community should focus on developing a common framework for signal recognition that allows for various species' data to be analysed by any recognition system supporting a set of common standards. 7. Synthesis and applications. Microphone arrays are increasingly used to remotely monitor acoustically active animals. We provide examples from a variety of taxa where acoustic arrays have been used for ecological, behavioural and conservation studies. We discuss the technologies used, the methodologies for automating signal recognition and some of the remaining challenges. We also make recommendations for using this technology to aid in wildlife management.
Animals that migrate in mixed-species groups may communicate with both conspecific and heterospecific individuals, providing a low-cost mechanism for navigation whenever individuals share similar ...migratory routes or destinations. Many migratory birds produce calls while flying, but the function of these calls, and the forces contributing to their evolution, are poorly known. We studied flight calls in mixed-species groups of wood warblers (Parulidae), a biodiverse group of migratory songbirds. We used a spatial approach to examine whether acoustic similarity of flight calls varies with group composition, recording flight calls of mixed-species flocks with a wireless microphone array and triangulating the positions of birds in three dimensions. We found that the acoustic similarity of flight calls was correlated with spatial proximity: birds with similar calls fly closer together during migration. We also found relationships between acoustic similarity, flock size and mixed-species flock diversity: birds with similar calls fly in smaller flocks and in flocks with lower species diversity. Our results support the idea that migrating birds use flight calls to maintain contact with acoustically similar individuals in mixed-species flocks, with communication transcending species boundaries. These results suggest that acoustically similar flight calls are used as cues of group assembly for migratory animals. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
In many tropical animals, male and female breeding partners combine their songs to produce vocal duets
1–5. Duets are often so highly coordinated that human listeners mistake them for the songs of a ...single animal
6. Behavioral ecologists rank duets among the most complex vocal performances in the animal kingdom
7, 8. Despite much research, the evolutionary significance of duets remains elusive
9, in part because many duetting animals live in tropical habitats where dense vegetation makes behavioral observation difficult or impossible. Here, we evaluate the duetting behavior of rufous-and-white wrens (
Thryothorus rufalbus) in the humid forests of Costa Rica. We employ two innovative technical approaches to study duetting behavior: an eight-microphone acoustic location system capable of triangulating animals' positions on the basis of recordings of their vocalizations
10 and dual-speaker playback capable of simulating duets in a spatially realistic manner
11. Our analyses provide the first detailed spatial information on duetting in both a natural context and during confrontations with rivals. We demonstrate that birds perform duets across highly variable distances, that birds approach their partner after performing duets, and that duets of rivals induce aggressive, sex-specific responses. We conclude that duets serve distinct functions in aggressive and nonaggressive contexts.
Many territorial animals are less aggressive towards neighbours than they are towards strangers. This phenomenon is known as the ‘dear enemy’ effect and it occurs because strangers represent a ...considerably higher threat to territory take-over compared to neighbours. Some evidence has suggested that large repertoires may constrain neighbour–stranger discrimination. We tested whether songbirds with large repertoires exhibit neighbour–stranger discrimination, conducting a playback study on a songbird with a large vocal repertoire, and a comparative analysis of the dear enemy effect across all published studies of songbirds. In our playback study, we broadcast neighbour and stranger songs within the breeding territories of red-eyed vireos, Vireo olivaceus, a songbird species with a large song repertoire (ca. 50 songs per individual). Vireos responded significantly more aggressively to playback of stranger versus neighbour songs; subjects approached closer to the loudspeaker, had a lower latency to approach the loudspeaker, spent more time near the loudspeaker and sang more soft songs during stranger trials than during neighbour trials. We examined song sharing between red-eyed vireos and found low levels of song sharing between neighbours, suggesting that red-eyed vireos may discriminate among conspecifics based on individually distinctive song types. We then conducted a comparative analysis of neighbour–stranger discrimination across the published literature on songbirds, using a phylogenetically controlled analysis to explore whether species with large repertoires are less likely to discriminate between neighbours and strangers. Across 34 species, we found no evidence that songbirds with large repertoires are constrained in their ability to distinguish between neighbours and strangers. We conclude that large song repertoires do not inhibit neighbour–stranger discrimination in red-eyed vireos specifically, or songbirds generally.
•In theory, large repertoires may constrain neighbour–stranger discrimination.•We used playback to test discrimination in a songbird with a large repertoire.•Playback subjects capably discriminated, showing a stronger response to strangers.•We then used a comparative analysis to explore this idea across 34 songbirds.•We found no effect of repertoire size on neighbour–stranger discrimination ability.
Diverse animal species engage in long-distance migrations. Many migrants travel in groups, and communication within these groups may be important to survival and successful migration. We examined ...migration and communication in 36 species of wood warblers (Parulidae), songbirds that breed in North America and migrate in mixed-species flocks to their wintering grounds. During migration, wood warblers produce short vocalizations called “flight calls.” The function of flight calls and the patterns of acoustic similarity between species are poorly understood. We investigated whether acoustic similarity of flight calls of different species of warbler reflects the similarity in their migratory journeys or their phylogenetic relatedness. We found that phylogeny, similarity in breeding latitude, and overlap in the timing of migration predict acoustic flight call similarity across warbler species. Further, we found that phylogeny, similarity in migration distance, and overlap in wintering range predict acoustic flight call similarity in a subset of 12 species with highly similar calls, although this analysis has a small sample size. We conclude that migratory similarity may be an important force driving the evolution of acoustically similar calls in wood warblers, in addition to phylogenetic relatedness. Acoustic convergence in these species may facilitate communication between individuals with similar migrations.
Abstract
Cumulative cultural evolution, the accumulation of sequential changes within a single socially learned behaviour that results in improved function, is prominent in humans and has been ...documented in experimental studies of captive animals and managed wild populations. Here, we provide evidence that cumulative cultural evolution has occurred in the learned songs of Savannah sparrows. In a first step, “click trains” replaced “high note clusters” over a period of three decades. We use mathematical modelling to show that this replacement is consistent with the action of selection, rather than drift or frequency-dependent bias. Generations later, young birds elaborated the “click train” song form by adding more clicks. We show that the new songs with more clicks elicit stronger behavioural responses from both males and females. Therefore, we suggest that a combination of social learning, innovation, and sexual selection favoring a specific discrete trait was followed by directional sexual selection that resulted in naturally occurring cumulative cultural evolution in the songs of this wild animal population.
In eight groups of animals, including humans and songbirds, juveniles are understood to learn vocalizations by listening to adults 1–4. Experimental studies of laboratory-reared animals support this ...hypothesis for vocal learning 5–7, yet we lack experimental evidence of vocal learning in wild animals. We developed an innovative playback technology involving automated loudspeakers that broadcast songs with distinctive acoustic signatures. We used this technology to simulate vocal tutors in the wild and conducted year-long tutoring sessions to five cohorts of free-living migratory Savannah Sparrows in eastern Canada. We confirm that wild birds learn songs by listening to adult conspecific animals, and we show that they pass these songs on to subsequent generations. Further, we provide the first experimental evidence in the wild that the timing of exposure to tutor song influences vocal learning: wild Savannah Sparrows preferentially learn songs heard during both their natal summer and at the outset of their first breeding season. This research provides direct experimental evidence of song learning by wild animals and shows that wild birds learn songs during two critical stages of development early in life.
Display omitted
Display omitted
•Wild Savannah Sparrows learn songs from playback-simulated vocal tutors•Birds preferentially learn songs heard in both their natal summer and first spring•Birds pass experimentally introduced songs on to subsequent generations
Using playback to broadcast novel songs, Mennill et al. show that wild Savannah Sparrows learn songs by listening to adult tutors. Birds preferentially learn songs heard during both their natal summer and the outset of their first breeding season. Birds that learn from simulated vocal tutors also pass these songs on to subsequent generations.
In many tropical birds, both sexes use conspicuous vocal signals during territorial interactions. Although a growing number of studies examine male and female signals in the context of coordinated ...vocal duets, the use of vocal signals by both sexes in non-duetting species is poorly documented, even though these species are more numerous than duetting species. Furthermore, few studies of tropical non-duetting species test for seasonal variation in signaling behavior. We studied season-specific and sex-specific variation in signaling behavior of a tropical resident songbird, the Rufous-capped Warbler (Basileuterus rufifrons), by conducting a playback experiment where we simulated conspecific territorial intruders producing three types of vocalizations (male songs, female calls, or a "pair" with simultaneous male songs and female calls) and a heterospecific control. We repeated playback during the pre-breeding and breeding seasons. Response intensity to playback varied with season and sex of the focal birds. During the pre-breeding season, both sexes showed strong physical approach responses and vocal responses to all conspecific intrusions, especially paired intrusions. During the breeding season, males responded strongly to all conspecific treatments, whereas females showed little response. Although females primarily used calls in response to conspecific playback, many females also sang, especially during the non-breeding season. Our results therefore suggest that both male and female signals are used for shared territory defense, but that the contributions of each sex to territory defense vary seasonally. Our results also contribute to our understanding of the evolution of combined male and female signaling during territory defense.
Abstract
When animals vocalize under the threat of predation, variation in the structure of calls can play a vital role in survival. The chick-a-dee calls of chickadees and titmice provide a model ...system for studying communication in such contexts. In previous studies, birds’ responses to chick-a-dee calls covaried with call structure, but also with unmeasured and correlated parameters of the calling sequence, including duty cycle (the proportion of the calling sequence when a signal was present). In this study, we exposed flocks of Black-capped Chickadees (Poecile atricapillus) and heterospecific birds to playback of chick-a-dee calls and taxidermic models of predators. We quantified birds’ responses to variation in number of D notes and duty cycle of the signalling sequence. Chickadees and heterospecific birds responded more intensely to high-duty-cycle treatments, and equally to treatments where duty cycle was held constant and the number of D notes varied. Although our study does not disentangle the effects of call rate and duty cycle, it is the first to investigate independently the behavioural responses of birds to variation in structural and sequence-level parameters of the chick-a-dee call during a predator confrontation. Critically, our results confirm that the pattern previously observed in a feeding context holds true in a mobbing context: variation in calling sequences, not in call structure, is the salient acoustic feature of chick-a-dee calls. These results call into question the idea that chick-a-dee call structure carries allometric information about predator size, suggesting instead that sequence-level parameters play a central role in communication in a mobbing context.
Lay Summary
Many animals use vocalizations when mobbing predators. Vocal behavior may communicate information about the threat posed by the predator. Using playback of chick-a-dee calls during a simulated predator confrontation, we show that birds respond more intensely to treatments with greater vocal output, but do not respond differently to calls that differ in the number of dee notes. Our results reveal that variation in calling sequences plays a central role in communication in a mobbing context.
PDF
