Estimating vocal repertoire size is like collecting coupons: a theoretical framework with heterogeneity in signal abundance.

Vocal repertoire size is an important behavioural measure in songbirds and mammals with complex vocal communication systems, and has traditionally been used as an indicator of individual fitness, cognitive ability, and social structure. Estimates of asymptotic repertoire size have typically been made using curve fitting techniques. However, the exponential model usually applied in these techniques has never been provided with a theoretical justification based on probability theory, and the model has led to inaccurate estimates. We derived the precise expression for the expected number of distinct signal types observed for a fixed sampling effort: a variation of what is known in the statistical literature as the "Coupon Collector׳s problem". We used empirical data from three species (northern mockingbird, Carolina chickadee, and rock hyrax) to assess the performance of the Coupon Collector model compared to commonly used techniques, such as exponential fitting and repertoire enumeration, and also tested the different models against simulated artificial data sets with the statistical properties of the empirical data. We found that when signal probabilities are dissimilar, the Coupon Collector model provides far more accurate estimates of repertoire size than traditional techniques. Enumeration and exponential curve fitting greatly underestimated repertoire size, despite appearing to have reached saturation. Application of the Coupon Collector model can generate more accurate estimates of repertoire size than the commonly used exponential model of repertoire discovery, and could go a long way towards re-establishing repertoire size as a useful indicator in animal communication research.

Titmouse calling and foraging are affected by head and body orientation of cat predator models and possible experience with real cats.

Although anti-predator behavior systems have been studied in diverse taxa, less is known about how prey species detect and assess the immediate threat posed by a predator based on its behavior. In this study, we evaluated a potential cue that some species may utilize when assessing predation threat-the predator's body and head orientation. We tested the effect of this orientation cue on signaling and predation-risk-sensitive foraging of a prey species, tufted titmice (Baeolophus bicolor). Earlier work revealed sensitivity of titmice and related species to the presence of predator stimuli. Here, we manipulated cat models to face either toward or away from a food source preferred by titmice and then measured titmouse calling and seed-taking behavior. Titmice showed greater feeder avoidance when the cat predator models faced the feeder, compared to when the models faced away from the feeder or when titmice were exposed to control stimuli. Titmouse calling was also sensitive to predator head/body orientation, depending upon whether titmice were from sites where real cats had been observed or not. This study experimentally demonstrated that both calling and foraging of prey species can be affected by the head and body orientation of an important terrestrial predator. Prey species may therefore signal in strategic ways to conspecifics not just about predator presence, but also urgency of threat related to the more subtle cue of the head and body orientation of the predator. These findings hold potential implications for understanding animal cognition and learning processes.

Animal vocal sequences: not the Markov chains we thought they were.

Many animals produce vocal sequences that appear complex. Most researchers assume that these sequences are well characterized as Markov chains (i.e. that the probability of a particular vocal element can be calculated from the history of only a finite number of preceding elements). However, this assumption has never been explicitly tested. Furthermore, it is unclear how language could evolve in a single step from a Markovian origin, as is frequently assumed, as no intermediate forms have been found between animal communication and human language. Here, we assess whether animal taxa produce vocal sequences that are better described by Markov chains, or by non-Markovian dynamics such as the 'renewal process' (RP), characterized by a strong tendency to repeat elements. We examined vocal sequences of seven taxa: Bengalese finches Lonchura striata domestica, Carolina chickadees Poecile carolinensis, free-tailed bats Tadarida brasiliensis, rock hyraxes Procavia capensis, pilot whales Globicephala macrorhynchus, killer whales Orcinus orca and orangutans Pongo spp. The vocal systems of most of these species are more consistent with a non-Markovian RP than with the Markovian models traditionally assumed. Our data suggest that non-Markovian vocal sequences may be more common than Markov sequences, which must be taken into account when evaluating alternative hypotheses for the evolution of signalling complexity, and perhaps human language origins.

Tufted titmouse (Baeolophus bicolor) calling and risk-sensitive foraging in the face of threat.

Individuals often produce alarm or mobbing calls when they detect a threat such as a predator. Little is known about whether such calling is affected by the facial orientation of a potential threat, however. We tested for an effect of facial orientation of a potential threat on tufted titmice, Baeolophus bicolor, a songbird that uses chick-a-dee calls in a variety of social contexts. In two studies, a human observer wore an animal mask that either faced or faced away from the focal bird(s). In Study 1, focal birds were individual titmice captured in a walk-in trap, and the observer stood near the trapped bird. In Study 2, focal birds were titmouse flocks utilizing a feeding station and the observer stood near the station. In both studies, calling behavior was affected by mask orientation. In Study 2, foraging and agonistic behavior were also affected. Titmice can therefore perceive the facial orientation of a potential threat, and this perception affects different behavioral systems, including calling. Our results indicate sensitivity of titmice to the facial orientation of a potential predator in two quite different motivational contexts. This work suggests the possibility of strategic signaling by prey species depending upon the perceptual space of a detected predator.

Mixed-species flock sizes and compositions influence flock members' success in three field experiments with novel feeders.

Mixed-species groups and aggregations are quite common and may provide substantial fitness-related benefits to group members. Individuals may benefit from the overall size of the mixed-species group or from the diversity of species present, or both. Here we exposed mixed-species flocks of songbirds (Carolina chickadees, Poecile carolinensis, tufted titmice, Baeolophus bicolor, and the satellite species attracted to these two species) to three different novel feeder experiments to assess the influence of mixed-species flock size and composition on ability to solve the feeder tasks. We also assessed the potential role of habitat density and traffic noise on birds' ability to solve these tasks. We found that likelihood of solving a novel feeder task was associated with mixed-species flock size and composition, though the specific social factor involved depended on the particular species and on the novel feeder. We did not find an influence of habitat density or background traffic noise on likelihood of solving novel feeder tasks. Overall, our results reveal the importance of variation in mixed-species group size and diversity on foraging success in these songbirds.

Conspecific and heterospecific cueing in shelter choices of Blaptica dubia cockroaches.

Background: Like many cockroaches, Argentinian wood roaches, Blaptica dubia, prefer darker shelters over lighter shelters. In three experiments, we asked whether chemical cues from other roaches might influence shelter choice, a process known as conspecific or heterospecific cueing, depending on whether the cues come from an individual of the same or a different species, respectively. Methods: Each experiment involved trials with focal B. dubia cockroaches in testing arenas containing plastic shelters of varying levels of darkness, with filter paper under each shelter acting as a carrier for chemical cues. In Experiment 1, we tested female and male B. dubia cockroaches with two shelters matched for darkness but differing in cues (conspecific vs. none). The shelter with no cue contained a blank filter paper as a control. In Experiment 2 (conspecific cueing) and Experiment 3 (heterospecific cueing), we tested B. dubia cockroach choices for lighter or darker shelters with filter papers containing chemical cues of other roaches or no chemical cues. For the conspecific cueing study of Experiment 2, we used chemical cues from other B. dubia cockroaches. In contrast, for the heterospecific cueing study of Experiment 3, we used chemical cues from a different species, the death's head cockroach, Blaberus craniifer. Results: In Experiment 1, B. dubia cockroaches overwhelmingly preferred shelters with conspecific chemical cues over darkness-matched shelters without cues. In Experiments 2 and 3, they strongly preferred darker shelters, especially when chemical cues were present. Additionally, they were more likely to be under the lighter shelter when chemical cues were present there. These results reveal that the public information B. dubia cockroaches gain from chemical cues-including those from other species-can drive shelter choices in this species.

The power of sound: unravelling how acoustic communication shapes group dynamics.

Acoustic signalling is a key mode of communication owing to its instantaneousness and rapid turnover, its saliency and flexibility and its ability to function strategically in both short- and long-range contexts. Acoustic communication is closely intertwined with both collective behaviour and social network structure, as it can facilitate the coordination of collective decisions and behaviour, and play an important role in establishing, maintaining and modifying social relationships. These research topics have each been studied separately and represent three well-established research areas. Yet, despite the close connection of acoustic communication with collective behaviour and social networks in natural systems, only few studies have focused on their interaction. The aim of this theme issue is therefore to build a foundation for understanding how acoustic communication is linked to collective behaviour, on the one hand, and social network structure on the other, in non-human animals. Through the building of such a foundation, our hope is that new questions in new avenues of research will arise. Understanding the links between acoustic communication and social behaviour seems crucial for gaining a comprehensive understanding of sociality and social evolution. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Influence of group size on shelter choice in Blaptica dubia cockroaches.

Individuals in social groups can gain benefits from being in those groups, including an increased ability to find food and avoid predators. We tested for potential group benefits in shelter choice in the Argentinian wood roach, Blaptica dubia. Roaches were tested in arenas with two shelters available in which one shelter was significantly darker than the other. Female and male roaches, housed separately, were tested as solitary individuals, or in same-sex groups of 5, 10, or 15. The roaches were tested under two light regimes (lights on vs. lights off) and two shelter distances (shelters near vs. shelters far) to provide variation in shelter search conditions. Solitary individuals chose the darker shelter at chance levels, but the roaches in groups chose the darker shelter significantly more often than chance. Furthermore, the two largest groups chose the darker shelter more often than the group of five roaches. We detected effects related to light variation that indicated roaches were more likely to be under either shelter in the lights-on conditions, and more likely to be out in the arena and under no shelter in the lights-off condition. Shelter distances had negligible effects on shelter choice and sex had no effect. Taken together, our results indicate individuals can make more optimal choices regarding shelter darkness if they are in a group, and that decision-making related to shelter is sensitive to variation in social context. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Mixed-species flock composition matters: interspecific influences on finding novel food in North American parids.

Individuals of a wide range of species are sensitive to the presence of other species, and can often benefit from associations with other species in mixed-species groups (MSGs) through food-finding or avoiding predation. In an earlier field study, we found that both Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolphus bicolor, were better able to solve a novel feeder task when their MSGs were more diverse in terms of species composition. Like most studies of MSGs, however, that earlier study did not experimentally manipulate MSG size and composition. We did that manipulation here, providing experimental flocks of chickadees and titmice with three novel feeder tasks in semi-natural aviary environments. We found that successful titmouse flocks generally had a higher proportion of titmice in them, going against the findings of our earlier field study. Conversely, successful chickadee flocks solved one of the novel feeder tasks more quickly with a higher proportion of titmice in them, corroborating the findings of our earlier field study. We now need to assess socio-ecological influences on MSG size and composition, and how those relate to individual behaviour. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes.

Mixed-species groups of birds, fishes and mammals have traditionally been described in taxa-specific journals. However, mixed-species systems are actually more widely found when one includes aggregative (non-moving) systems, such as those common in amphibians and invertebrates. The objective of this special issue is to dispel the idea that mixed-species phenomena are a 'niche topic' to ecology and instead explore how taking a mixed-species perspective can change our conception of important ecological patterns and processes. A mixed-species perspective starts by understanding the relative abundance and positioning of individuals of different species and their behavioural synchrony; it is enriched by understanding differences between species in their vulnerability/attractiveness to predators, their potential for competing with other group participants and their use as a source of public information. Contributions to the special issue show how the mixed-species perspective can change our ideas about invasion ecology, island biogeography, keystone species, mimicry, predator eavesdropping and more. Rather than seeking synthesis, the special issue celebrates the taxonomic and conceptual breadth of the field of mixed-species groups, with detailed descriptions of many distinctive systems. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Influence of social and physical environmental variation on antipredator behavior in mixed-species parid flocks.

Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) regularly form flocks with multiple species through the winter months, including white-breasted nuthatches (Sitta carolinensis). Earlier studies found that behavior of both chickadees and titmice was sensitive to mixed-species flock composition. Little is known about the influence of background noise level and vegetation density on the antipredator behaviors of individuals within these flocks, however. We tested for the effects of vegetation density, traffic noise, and flock composition (conspecific number, flock diversity, and flock size) on antipredator behavioral responses following an alarm call playback (Study 1) and an owl model presentation (Study 2) at feeders. We recorded background traffic noise and performed lidar scans to quantify vegetation density at each site. After a feeder had been stocked with seed and a flock was present, we recorded calls produced, and we identified flock composition metrics. We coded seed-taking latency, call latency, mob latency, and mob duration following the respective stimulus presentation and tested for effects of flock composition metrics, vegetation density, and background noise on these responses. For the alarm call playback study, flock composition drove behaviors in chickadees and titmice, and vegetation density drove behaviors in chickadees and nuthatches. For the owl model study, conspecific number predicted behavior in chickadees, and mob duration was predicted by nuthatch number. The results reveal individual sensitivity to group composition in anti-predatory and foraging behavior in simulated risky contexts. Additionally, our data suggest that the modality of perceived simulated risk (acoustic vs. visual) and the density of vegetation influence behavior in these groups.

Simplicity and complexity in human and nonhuman communication.

Comments on an article by Limor Raviv et al. (see record 2023-07345-001). Raviv et al. argue that the conflicting findings from human language and from studies of communication in nonhuman animals boil down to different levels of analysis used by researchers studying non-humans compared with those studying humans. Researchers studying nonhuman animal communication typically focus on the size of signal repertoires or the structural variation within and among signals within a repertoire. Researchers studying human language, conversely, largely focus on the question of grammatical rules that govern the way units (words and phrases) are put together in speech streams. Rules of composition that govern the way units are put together are considered more complex in nonhuman signaling systems, but simpler in human language systems. The discrepancy here, according to Raviv et al., stems from two sources. According to the commenting authors, the take home message of Raviv et al. is one that will be helpful to future studies of the evolution of communication systems. Raviv et al. recommend that we work harder to avoid terms such as "complex" and "simple" with regard to communication and instead focus on the specifics of what we are analyzing. Phrases such as "larger repertoire size" or "stronger compositional structure" represent cleaner and more neutral phrases for discussions of communication and would better allow findings from non-humans and from humans to be compared. Finally, Raviv et al. advocate for greater collaborative work across nonhuman and human communication systems, and interdisciplinary work has a long history of fundamental discoveries. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Testing the role of macaque social tolerance in ability to follow human eye gaze.

Comments on an article by R. Bettle and A. G. Rosati (see record 2022-45647-001). The testing of subjects' abilities to follow human eye gaze has been particularly well studied in nonhuman primates, and this is the question addressed by the Featured Article for this issue by Bettle and Rosati. As described in Bettle and Rosati, he competition hypothesis, stemming from the Machiavellian Intelligence Hypothesis, predicts that species that are more competitive and aggressive will exhibit greater ability to use cues like eye gaze. The tolerance hypothesis, conversely, predicts that species that are more tolerant and affiliative will exhibit greater ability to use these cues. Bettle and Rosati tested Barbary macaques with identical methods. Compared to rhesus macaques, Barbary macaques are relatively tolerant and highly affiliative. Importantly, the authors coded the video-recorded data blind and with high interobserver reliability. The authors found that Barbary macaques were also able to follow human eye gaze: Although roughly half the individuals looked up and followed human's eye gaze in the no barrier condition, only a third looked up in the barrier condition where they could not see what the human was looking at by doing so. These results were quite comparable to the earlier study conducted with rhesus macaques, suggesting that tolerant and less competitive species actually show similar skills. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Social dynamics of core members in mixed-species bird flocks change across a gradient of foraging habitat quality.

Social associations within mixed-species bird flocks can promote information flow about food availability and provide predator avoidance benefits. The relationship between flocking propensity, foraging habitat quality, and interspecific competition can be altered by human-induced habitat degradation. Here we take a close look at sociality within two ecologically important flock-leader (core) species, the Carolina chickadee (Poecile carolinensis) and tufted titmouse (Baeolophus bicolor), to better understand how degradation of foraging habitat quality affects mixed-species flocking dynamics. We compared interactions of free ranging wild birds across a gradient of foraging habitat quality in three managed forest remnants. Specifically, we examined aspects of the social network at each site, including network density, modularity, and species assortativity. Differences in the social networks between each end of our habitat gradient suggest that elevated levels of interspecific association are more valuable in the habitat with low quality foraging conditions. This conclusion is supported by two additional findings: First, foraging height for the subordinate Carolina chickadee relative to the tufted titmouse decreased with an increase in the number of satellite species in the most disturbed site but not in the other two sites. Second, the chickadee gargle call rate, an acoustic signal emitted during agonistic encounters between conspecifics, was relatively higher at the high-quality site. Collectively, these results suggest an increase in heterospecific associations increases the value of cross-species information flow in degraded habitats.

Zing-Yang Kuo and "Giving up instincts in psychology", 100 years later.

A hundred years ago, the Journal of Comparative Psychology began being published and currently stands as the longest-running science journal devoted to the study of animal behavior. In that same year, 1921, a paper was published in the Journal of Philosophy that was foundational to our field of study-"Giving up Instincts in Psychology" by Zing-Yang Kuo. This brief essay discusses some of the main arguments of Kuo's article and how they have extended into today's thinking and empirical work on behavioral development. The essay emphasizes his ideas about the need to study neophenotypes to understand the range of behavioral possibilities and to assess nonobvious sources of experience in the development of species-typical behavior. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Clark's nutcrackers (Nucifraga columbiana) modify caching behavior when observed.

The featured article of this issue focused on a species with relatively simple sociality-Clark's nutcrackers (Nucifraga columbiana; Tornick & Gibson, 2021; Figure 1), a species that regularly (and readily in experimental conditions) caches food items. The question at hand was whether individual nutcrackers cached food items-and then later retrieved them-differently depending upon whether they were being observed by a conspecific or not at the time of caching. Tornick and Gibson (2021) found that individual nutcrackers were highly sensitive to whether they were being observed by a conspecific. When they were being observed, nutcrackers cached more food items behind the barrier than in the visible area of their cage. However, in the "private" condition when they were not being observed, nutcrackers cached food items roughly equally in the two areas. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Factors in forgetting in spider monkeys, Ateles geoffroyi.

This essay discusses current problems and factors with memory testing in spider monkeys. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A community context for aggression? Multi-species audience effects on territorial aggression in two species of Paridae.

Territorial aggression in birds is widely observed and is commonly linked to sex, age, body size, physiology, seasonal cues, food resource, urbanization, and a variety of social contexts including conspecific audience effects. However, little is known about the heterospecific audience effects on territorial aggression.Here, we address an emerging idea that heterospecific audience effects may be pervasive influences in the social lives of free-living birds. We tested the hypothesis that the composition, number, and relative body size of heterospecific audiences observing an aggressive contest will influence the response probability and intensity of aggression displayed.We subjected two Paridae species, tufted titmouse (TUTI, Baeolophus bicolor) and Carolina chickadee (CACH, Poecile carolinensis), to playbacks of aggressive calls during a breeding season in north-central Florida. At widely spaced playback sites (N = 134) in woodland habitats, we characterized the makeup of heterospecific audiences, aggression type (intra vs. interspecific territoriality), local population density, and various environmental factors (tree density, wind speed, and noise level) that are likely to influence territorial aggression.We found that the presence of heterospecific audiences increased TUTI aggression levels and that both parids were more likely to respond to playback stimuli when their audiences had higher heterospecific diversity (more heterospecific individuals and species). We also found TUTI were more likely to respond when CACH were present but not vice versa.In conclusion, we found evidence that heterospecific audiences significantly influenced the metrics of territorial aggression of free-living animals and we suggest that the definition of audience effects on the behavior of free-living animals be expanded to incorporate heterospecific audiences.

Familiarity-The bridge from social interactions to relationships?

One approach that is starting to reveal interesting variation in social interactions assesses how familiarity of individuals affects their behavior toward one another. This was studied by Prior, Smith, Dooling, and Ball (2020) with a model songbird species, zebra finches (Taeniopygia guttata). This work is important in that it reveals how fundamental simple familiarity-repeated social experience with another individual-is to communication and interaction in social species. More work is now needed, and in a wide range of species exhibiting a wide range of variation in social behavior, to assess the extent to which variation in familiarity is the bridge that links social interactions to social relationships in groups of animals. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

From simple rules of individual proximity, complex and coordinated collective movement.

In this brief article, the author notes that the empirical study of coordinated collective motion (CCM) has often been built upon the theoretical foundation of mathematical models and computer simulation of behavior. One key assumption of CCM models is that individuals' movement behavior is influenced by rules of proximity-a balance of attraction and repulsion tendencies depending on how close an immediate neighbor is. When individuals are moving in groups, these rules therefore have a bearing on the alignment of individuals in space and time, and so also on the orientation and speed of movement of individuals. As Quera et al. (this issue) point out in a study, however, we have relatively little empirical evidence to support these key assumptions about orientation and speed of movement. Taken together, their study is significant in that it provides the movement detail to support key assumptions made by CCM models. (PsycINFO Database Record (c) 2019 APA, all rights reserved).