Social Corvid Research Articles

Anthropogenic disturbance affects calling and collective behaviour in corvid roosts.

Acoustic communication plays an important role in coordinating group dynamics and collective movements across a range of taxa. However, anthropogenic disturbance can inhibit the production or reception of acoustic signals. Here, we investigate the effects of noise and light pollution on the calling and collective behaviour of wild jackdaws (Corvus monedula), a highly social corvid species that uses vocalizations to coordinate collective movements at winter roosting sites. Using audio and video monitoring of roosts in areas with differing degrees of urbanization, we evaluate the influence of anthropogenic disturbance on vocalizations and collective movements. We found that when levels of background noise were higher, jackdaws took longer to settle following arrival at the roost in the evening and also called more during the night, suggesting that human disturbance may cause sleep disruption. High levels of overnight calling were, in turn, linked to disruption of vocal consensus decision-making and less cohesive group departures in the morning. These results raise the possibility that, by affecting cognitive and perceptual processes, human activities may interfere with animals' ability to coordinate collective behaviour. Understanding links between anthropogenic disturbance, communication, cognition and collective behaviour must be an important research priority in our increasingly urbanized world. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Rookognise: Acoustic detection and identification of individual rooks in field recordings using multi-task neural networks

Individual-level monitoring is essential in many behavioural and bioacoustics studies. Collecting and annotating those data is costly in terms of human effort, but necessary prior to conducting analysis. In particular, many studies on bird vocalisations also involve manipulating the animals or human presence during observations, which may bias vocal production. Autonomous recording units can be used to collect large amounts of data without human supervision, largely removing those sources of bias. Deep learning can further facilitate the annotation of large amounts of data, for instance to detect vocalisations, identify the species, or recognise the vocalisation types in recordings. Acoustic individual identification, however, has so far largely remained limited to a single vocalisation type for a given species. This has limited the use of those techniques for automated data collection on raw recordings, where many individuals can produce vocalisations of varying complexity, potentially overlapping one another, with the additional presence of unknown and varying background noise. This paper aims at bridging this gap by developing a system to identify individual animals in those difficult conditions. Our system leverages a combination of multi-scale information integration, multi-channel audio and multi-task learning. The multi-task learning paradigm is based the overall task into four sub-tasks, three of which are auxiliary tasks: the detection and segmentation of vocalisations against other noises, the classification of individuals vocalising at any point during a sample, and the sexing of detected vocalisations. The fourth task is the overall identification of individuals. To test our approach, we recorded a captive group of rooks, a Eurasian social corvid with a diverse vocal repertoire. We used a multi-microphone array and collected a large scale dataset of time-stamped and identified vocalisations recorded, and found the system to work reliably for the defined tasks. To our knowledge, the system is the first to acoustically identify individuals regardless of the vocalisation produced. Our system can readily assist data collection and individual monitoring of groups of animals in both outdoor and indoor settings, even across long periods of time, and regardless of a species’ vocal complexity. All data and code used in this article is available online.

Clark's nutcrackers (Nucifraga columbiana) use a visual barrier for cache protection.

Previous work with corvids such as scrub jays (Aphelocoma californica) and ravens (Corvus corax) suggests that many social corvids alter their caching behavior when observed by conspecifics to protect their caches. We examined whether the Clark's nutcracker (Nucifraga columbiana), an asocial corvid, can utilize a barrier to conceal its caching activities from a conspecific observer. Nutcrackers were allowed to cache nuts in a visible or concealed location in either the presence or absence of an observer. Nutcrackers were also given experience of having their caches pilfered. The nutcrackers cached significantly more nuts in the concealed compared to a visible location when observed. Importantly, nutcrackers also recovered a larger percentage of their nuts 24 hr later from a visible cache location but when the observer was no longer present. The results extend recent work suggesting that relatively nonsocial corvids, similar to their more social relatives, also engage in multiple forms of cache protection. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Conspecific presence, but not pilferage, influences pinyon jays' (Gymnorhinus cyanocephalus) caching behavior.

Caching species store food when plentiful to ensure availability when resources are scarce. These stores may be at risk of pilferage by others present at the time of caching. Cachers may reduce the risk of loss by using information from the social environment to engage in behaviors to secure the resource-cache protection strategies. Here, we examined whether pinyon jays, a highly social corvid, use information from the social environment to modify their caching behavior. Pinyon jays were provided with pine seeds to cache in two visually distinct trays. The cacher could be observed by a non-pilfering conspecific, a pilfering conspecific, or an inanimate heterospecific located in an adjoining cage compartment, or the cacher could be alone. After caching, the pilfered tray was placed in the adjoining compartment where caches were either pilfered (pilfering conspecific and inanimate heterospecific conditions) or remained intact (non-pilfering conspecific and alone conditions). The safe tray was placed in a visible, but inaccessible, location. Overall, pinyon jays reduced the number of pine seeds cached in the pilfered tray when observed, compared with caching alone. However, their caching behavior did not differ between the pilfering conspecific and the non-pilfering conspecific conditions. These results suggest that either pinyon jays were unable to discriminate between the pilfering and non-pilfering conspecifics, or they generalized their experience of risk from the pilfering conspecific to the non-pilfering conspecific. Thus, we report evidence that pinyon jays use cache protection strategies to secure their resources when observed, but respond similarly when observed by pilfering and non-pilfering conspecifics.

Task Aspects Triggering Observational Learning in Jackdaws (Corvus monedula)

Complex novel tasks are often used in animal cognition research to allow discrimination between various learning mechanisms. Successful performance relies on the capacity to identify informational cues from features in the environment. Additionally, observational learning is often considered more beneficial for survival than individual learning. Despite the importance of controlling task complexity, it can often be challenging to operationalize. This study investigated whether jackdaws, a highly social corvid species, can learn to drop stones inside a tube to release a reward after observing a trained conspecific. Additionally, it aimed to identify the underlying learning mechanisms and to detect the informational cues triggering learning. A research design was developed to highlight different aspects of the required action sequence. Experimental conditions included a conspecific model demonstrating the full sequence, parts of the sequence, consuming the reward without solving the task, and consuming the reward after the solution was demonstrated without a visible model. None of the 12 naïve jackdaws solved the task in pretests. Two subjects started solving in test sessions and they developed modified versions of the demonstrated action. Observing the full action sequence performed by a conspecific seemed to trigger learning. The majority of the subjects exhibited changes in their stone-oriented behavior, most likely due to stimulus and/or local enhancement. As predicted, jackdaws were influenced by conspecific model demonstrations when manipulating a complex novel foraging task. Factors contributing to the apparent task difficulty and directions for future studies are discussed within a tri-dimensional framework including the task, setup, and individuals.

Individual signature in the most common and context-independent call of the Rook (Corvus frugilegus)

The ability to recognize other individuals (e.g., mates, neighbors, and offspring) is crucial to process relationships between group members in social species. For bird species with limited use of visual information, like species living in colonies or dense environments, the acoustic channel provides a long-distance and fast means to effectively convey identity-related information. The Rook (Corvus frugilegus) is a monogamous species, and one of the most social corvids, living in highly cohesive groups within colonies of hundreds to thousands of individuals. However, despite being a highly vocal species, only a few studies have focused on its acoustic communication skills, investigating mostly its vocal repertoire and kin recognition in fledglings. Among the vocal repertoire of the Rook, the “caw” is the most common sound type. It is emitted independently in various contexts and is often considered as a “presenting” vocalization, serving to introduce the identity of the emitter bird to the assembly. In this study, we investigated the potential individual signature of the caw. To do so, we recorded the caws of 5 semi-captive male Rooks and conducted acoustic analyses on both the frequency and time domains. A discriminant function and a potential for individuality coding analyses revealed the existence of a clear individual signature (mean of 75% correct classification, SD 10), which was mainly supported by the caw duration and distribution of energy in the low-frequency part of the spectrum. We discuss the potential variability of individuality coding across behavioral contexts and social affinities that needs further work.

Heterospecific information supports a foraging mutualism between corvids and raptors

Although animal social information is most commonly utilized by conspecifics, some conditions may favour heterospecific transmission. Generalists living in social groups are thought to produce information that is conspicuous and broadly useful to other species. Information may be signalled intentionally to other species when the sender benefits. We examined these predictions in a scavenger guild comprising two generalist social corvids (ravens, Corvus corax; magpies, Pica hudsonia), four raptor species and coyotes, Canis latrans. We used game cameras to monitor scavenging at 89 mule deer, Odocoileus hemionus, carcasses in Oregon and Washington, U.S.A. Corvid appearance times explained variation in golden eagle, Aquila chrysaetos, bald eagle, Haliaeetus leucocephalus, hawk (Buteo jamaicensis and Buteo lagopus) and coyote arrivals, indicating that raptors and canids use corvids to locate food. Larger numbers of magpies, but not ravens, were associated with shorter raptor appearance times, providing partial support for the importance of group size in broadcasting information to heterospecifics. We also directly observed simulated carcasses composed of a deer hide and antler. Seventy one corvids and 13 raptors appeared among 16 treatments accompanied by raven decoys and playbacks, whereas only one corvid and no raptors appeared at paired controls. The time that ravens first flew in circles above a simulated carcass explained 98% of the variation in subsequent raptor arrival time, indicating that a specific raven behaviour provides a cue of carrion. After hide-cutting raptors opened a carcass, corvids benefited by switching from feeding at the eyes and the anus to feeding on flesh. However, raptors did not arrive sooner after corvids at closed carcasses than experimentally pre-opened carcasses, suggesting that corvids do not intentionally transmit more information to raptors when a carcass requires opening, at least under these conditions. A scavenging mutualism with corvids built on carrion discovery and access, but not intentional recruitment, may facilitate winter survival of raptors.

Mesotocin influences pinyon jay prosociality.

Many species exhibit prosocial behaviour, in which one individual's actions benefit another individual, often without an immediate benefit to itself. The neuropeptide oxytocin is an important hormonal mechanism influencing prosociality in mammals, but it is unclear whether the avian homologue mesotocin plays a similar functional role in birds. Here, we experimentally tested prosociality in pinyon jays (Gymnorhinus cyanocephalus), a highly social corvid species that spontaneously shares food with others. First, we measured prosocial preferences in a prosocial choice task with two different pay-off distributions: Prosocial trials delivered food to both the subject and either an empty cage or a partner bird, whereas Altruism trials delivered food only to an empty cage or a partner bird (none to subject). In a second experiment, we examined whether administering mesotocin influenced prosocial preferences. Compared to choices in a control condition, we show that subjects voluntarily delivered food rewards to partners, but only when also receiving food for themselves (Prosocial trials), and administration of high levels of mesotocin increased these behaviours. Thus, in birds, mesotocin seems to play a similar functional role in facilitating prosocial behaviours as oxytocin does in mammals, suggesting an evolutionarily conserved hormonal mechanism for prosociality.

Eurasian jays do not copy the choices of conspecifics, but they do show evidence of stimulus enhancement.

Corvids (birds in the crow family) are hypothesised to have a general cognitive tool-kit because they show a wide range of transferrable skills across social, physical and temporal tasks, despite differences in socioecology. However, it is unknown whether relatively asocial corvids differ from social corvids in their use of social information in the context of copying the choices of others, because only one such test has been conducted in a relatively asocial corvid. We investigated whether relatively asocial Eurasian jays (Garrulus glandarius) use social information (i.e., information made available by others). Previous studies have indicated that jays attend to social context in their caching and mate provisioning behaviour; however, it is unknown whether jays copy the choices of others. We tested the jays in two different tasks varying in difficulty, where social corvid species have demonstrated social information use in both tasks. Firstly, an object-dropping task was conducted requiring objects to be dropped down a tube to release a food reward from a collapsible platform, which corvids can learn through explicit training. Only one rook and one New Caledonian crow have learned the task using social information from a demonstrator. Secondly, we tested the birds on a simple colour discrimination task, which should be easy to solve, because it has been shown that corvids can make colour discriminations. Using the same colour discrimination task in a previous study, all common ravens and carrion crows copied the demonstrator. After observing a conspecific demonstrator, none of the jays solved the object-dropping task, though all jays were subsequently able to learn to solve the task in a non-social situation through explicit training, and jays chose the demonstrated colour at chance levels. Our results suggest that social and relatively asocial corvids differ in social information use, indicating that relatively asocial species may have secondarily lost this ability due to lack of selection pressure from an asocial environment.

Observational learning in the large-billed crow (Corvus macrorhynchos)

Exploiting the skills of others enables individuals to reduce the risks and costs of resource innovation. Social corvids are known to possess sophisticated social and physical cognitive abilities. However, their capacity for imitative learning and its inter-individual transmission pattern remains mostly unexamined. Here we demonstrate the large-billed crows' ability to learn problem-solving techniques by observation and the dominance-dependent pattern in which this technique is transmitted. Crows were allowed to observe one of two box-opening behaviours performed by a dominant or subordinate demonstrator and then tested regarding action and technique. The observers successfully opened the box on their first attempts by using non-matching actions but matching techniques to those observed, suggesting emulation. In the subsequent test sessions, dominant observers (i.e. those dominant to the bird acting as demonstrator) consistently used the learned technique, whereas subordinates (i.e. those subordinate to the bird acting as demonstrator) learned alternative techniques by explorative trial and error. Our findings demonstrate crows' capacity to learn by observing behaviours and the effect of dominance on transmission patterns of behavioural skills. Keywords: social learning; imitation; emulation; affordance; culture; innovation

Cache protection strategies of a non-social food-caching corvid, Clark’s nutcracker (Nucifraga columbiana)

Clark's nutcrackers (Nucifraga columbiana), a non-social corvid, cache much of their food in order to survive periods of resource uncertainty. These caches are at risk as they are subject to pilferage from other animals including conspecifics. Potentially, nutcrackers can ensure the safety of these caches by keeping track of whether they have been observed making a cache and subsequently engage in cache protection strategies-strategies that have been shown by other members of the corvid family (e.g., scrub-jays and ravens). Behaviors including creating more caches, eating a higher proportion of seeds, and re-caching existing compromised sites have been shown in laboratory settings with social corvids and have provided preliminary evidence of the complex cognitive abilities of corvids. In the present study, Clark's nutcrackers are shown to engage in similar cache protection behaviors when observed by a conspecific. Furthermore, we show that these behaviors are a result of social, rather than associative, cues.

The social structure of New Caledonian crows

New Caledonian (NC) crows, Corvus moneduloides, have impressive tool-manufacturing and tool-using skills in the wild, and captive birds have displayed exceptional cognitive abilities in experimental situations. However, their social system is largely unknown. In this study we investigated whether the social structure of NC crows might have had a role in the development of their cognitive skills. We observed crows in their natural habitat on the island of Mare, New Caledonia, and estimated their social network size based on tolerance to family and nonfamily crows at feeding tables. Our ! ndings suggest that NC crows are not a highly social corvid species. Their core unit was the immediate family consisting of a pair and juveniles from up to two consecutive breeding years. Pairs stayed together year round, and were closely accompanied by juveniles during their ! rst year of life. Parents were highly tolerant of juveniles and sometimes continued to feed them well into their second year. NC crows predominantly shared feeding tables with immediate family. Of the nonfamily crows tolerated, juveniles were overrepresented. The main mechanism for any social transmission of foraging skills is likely to be vertical (from parents to offspring), with only limited opportunity for horizontal transmission. The social organization we found on Mare is consistent with the idea that NC crows’ multiple pandanus tool designs on mainland Grande Terre are an example of cumulative technological evolution.

Jackdaws Respond to Human Attentional States and Communicative Cues in Different Contexts

Humans communicate their intentions and disposition using their eyes, whereas the communicative function of eyes in animals is less clear. Many species show aversive reactions to eyes, and several species gain information from conspecifics' gaze direction by automatically co-orienting with them. However, most species show little sensitivity to more subtle indicators of attention than head orientation and have difficulties using such cues in a cooperative context. Recently, some species have been found responsive to gaze direction in competitive situations. We investigated the sensitivity of jackdaws, pair-bonded social corvids that exhibit an analogous eye morphology to humans, to subtle attentional and communicative cues in two contexts and paradigms. In a conflict paradigm, we measured the birds' latency to retrieve food in front of an unfamiliar or familiar human, depending on the state and orientation of their eyes toward food. In a cooperative paradigm, we tested whether the jackdaws used familiar human's attentional or communicative cues to locate hidden food. Jackdaws were sensitive to human attentional states in the conflict situation but only responded to communicative cues in the cooperative situation. These findings may be the result of a natural tendency to attend to conspecifics' eyes or the effect of intense human contact during socialization.

Using video playback to investigate the social preferences of rooks, Corvus frugilegus

It is important for social animals to be able to discriminate between group members. Much is known about vocal social communication through auditory playback techniques; however, visual information may also be important for conspecific recognition in the absence of auditory cues. Within the visual channel both static and dynamic features may play important roles in individual recognition. Rooks are a social corvid and they live in large colonies and form long-term pair bonds, both requiring the ability to recognize individuals. In this study we investigated whether rooks ‘see’ a digital image as a representation of a real animal, using visual playback techniques and a new paradigm for assessing social preferences that uses stimuli differing in features such as whether they are live animals, static or video images, or stuffed models. We presented the rooks with two different stimuli of the same category and recorded the amount of time they observed each stimulus. Rooks preferred to look at a live bird, static or video image of a bird, and a stuffed model over an empty compartment. Rooks also showed a clear preference for a strongly affiliated conspecific (e.g. their partner) over a nonaffiliated conspecific. This preference was not apparent when we presented subjects with static images; however, the preference was seen with video, indicating that rooks can recognize individuals in video. We conclude that video playback is a useful technique for investigating rook social behaviour.

The social life of corvids

The social life of corvids

Male‐biased dispersal, female philopatry, and routes to fitness in a social corvid

1 Dispersal in many species is sex-biased. Greenwood (1980, Animal Behaviour, 28, 1140–1162) hypothesized that the direction of sex bias was dependent on the mating system, and suggested that female-biased dispersal in birds is associated with monogamy and resource defence by males, while mammalian male-biased dispersal is associated with polygyny and male defence of mates. 2 Cooperatively breeding brown jays Cyanocorax morio live in large territorial groups and are one of the few bird species known to exhibit male-biased dispersal. Survivorship of adults is high, and both males and females delay breeding for many years. 3 In this study, dispersers almost always moved to neighbouring social groups, rarely in response to a known breeding vacancy, and both sexes dispersed into groups with fewer members of the same sex than their origin group. 4 Dispersal and extra-group forays were strongly male biased. Forays were more common during nest building and egg laying, suggesting that males were monitoring mating opportunities, and many males later dispersed into the groups they visited. Genetic parentage analyses indicated that males mainly obtain paternity outside their natal groups through extra-group forays and dispersal. 5 The major routes to breeding status for females are inheritance of breeding positions on their natal territories and/or breeding there concurrently with an established breeder. Females usually dispersed on their own into groups where reproductive success had previously been poor. 6 Kin facilitation appears to affect male dispersal options: related males formed coalitions and tended to disperse to groups where male relatives were already established. 7 Male dispersal, female philopatry, and a matrilineal society correspond to three of Greenwood's seven predictions for a ‘mate-defence’ system, but overt mate defence itself is absent, territorial defence is communal, and genetic polyandry is common. Social behaviour appears to affect a reversal in sex-specific costs and benefits of dispersal, so that females benefit from philopatry and matrilineal inheritance, while males benefit from expanded dispersal options in part through kin facilitation, but without effective mate defence or clear cut sex-specific resource defence.

Female control of reproductive skew in cooperatively breeding brown jays ( Cyanocorax morio )

Brown jays (Cyanocorax morio) are long-lived, social corvids that live in large, stable, territorial groups (mean = 10 individuals). In this study, I determined the distribution of reproductive success within groups using multi-locus DNA fingerprinting. Breeding females produced virtually all (99%) of the young within their own nests. Reproduction within groups was highly skewed towards a single primary female, although long term data indicate that secondary females (female breeders that were usually younger and subordinate to the primary female) were sometimes successful. The high reproductive skew observed for females was associated with primary female aggression. Successful reproduction by secondary females may have been due to parental facilitation or the inability of primary females to completely suppress secondary females. Multiple paternity occurred in 31–43% of broods and extra-group paternity occurred in a minimum of 22% of broods. Patterns of paternity also varied between years, since females often switched or included new genetic mates. Although male consorts of nesting females fathered relatively few offspring (20%), they still had a higher chance of fathering offspring than any other single group male. Reproduction was less skewed for males than females as a result of female mating patterns. Female reproductive patterns are consistent with some of the predictions and assumptions from optimal skew models, while male reproductive patterns are not. The factors affecting skew in species with complex social systems such as incomplete control by breeders over subordinate reproduction, female control of paternity, and resource inheritance have not been well incorporated into reproductive skew models.

Sexual Size Dimorphism and Positive Assortative Mating in Alpine Choughs (Pyrrhocorax graculus)

AbstractThe degree of sexual size dimorphism in a number of different morphological characters was examined in a social corvid, the Alpine Chough, using measurements taken on 178 males and 144 females. A small amount of size dimorphism appeared in all morphological characters, and weight was the most dimorphic character. To identify if Alpine Choughs mate assortatively, measurements of mates were compared in 76 pairs. A positive assortative mating was found on tarsus length, and a small positive trend is suggested between body condition of partners, but that needs to be confirmed with a larger sample size.

Sexual Size Dimorphism and Positive Assortative Mating in Alpine Choughs (Pyrrhocorax graculus)

Abstract The degree of sexual size dimorphism in a number of different morphological characters was examined in a social corvid, the Alpine Chough, using measurements taken on 178 males and 144 females. A small amount of size dimorphism appeared in all morphological characters, and weight was the most dimorphic character. To identify if Alpine Choughs mate assortatively, measurements of mates were compared in 76 pairs. A positive assortative mating was found on tarsus length, and a small positive trend is suggested between body condition of partners, but that needs to be confirmed with a larger sample size.

Foraging strategy in a social bird, the alpine chough: effect of variation in quantity and distribution of food

I conducted feeding experiments to determine the effect of variations in food availability on individual flocking behaviour and foraging efficiency in a social corvid, the alpine choughPyrrhocorax graculus,which lives in large flocks all year round. In 37 trials I varied both food quantity and the number of food patches. A decrease in the amount of available food reduced the mean flock size, the proportion of birds that had access to food, and their mean pecking rate. A decrease in the number of patches, on the other hand, reduced only the proportion of birds that had access to food. The number of choughs foraging was not influenced by food competition but depended only on the number visiting the site. Females competed less well than males: when food was made scarce, they frequented the site in the same proportion as did males, but had less access to food. I suggest that in this social corvid, long-term advantages to flocking related to social bonds, such as the maintenance of pair bonds, may compensate for short-term costs such as a reduction in foraging efficiency.