Crows "count" the number of self-generated vocalizations.

Producing a specific number of vocalizations with purpose requires a sophisticated combination of numerical abilities and vocal control. Whether this capacity exists in animals other than humans is yet unknown. We show that crows can flexibly produce variable numbers of one to four vocalizations in response to arbitrary cues associated with numerical values. The acoustic features of the first vocalization of a sequence were predictive of the total number of vocalizations, indicating a planning process. Moreover, the acoustic features of vocal units predicted their order in the sequence and could be used to read out counting errors during vocal production.

Observation of female-male mounting in the carrion crow.

In the biological sciences, sexual behaviours in non-human animals are traditionally investigated in the context of reproduction and direct fitness benefits. While the evolutionary functions of non-conceptive sexual behaviours ('socio-sexual behaviours') remain less well explored, these interactions and displays have been suggested to be important for shaping and maintaining social relationships. Here, we report an observation of a captive female carrion crow, Corvus corone corone, mounting her co-housed male partner. We highlight the importance of more systematic research, reporting, and discussions of rarely observed behaviours in social evolution research, including considerations for behaviours that transcend binary or heteronormative frameworks, for a more comprehensive understanding of non-conceptive socio-sexual behaviours.

Nearest neighbour distance does not affect escape behaviour in urban hooded crows.

The nearest-neighbour distance is an important property of a group, as individuals can obtain environmental information more quickly and easily from nearby individuals. We examined whether distance to the nearest neighbour affected two components of escape behaviour - alert distance (AD) and flight initiation distance (FID) - in an urban population of hooded crows Corvus cornix, while controlling for confounding variables. We did not find evidence that AD and FID were influenced by the nearest neighbour distance. However, both AD and FID were negatively affected by feeding activity of individuals - focal crows alerted later and escaped at shorter distance if they were feeding during our approach. In addition, AD and FID were positively related to starting distance and grass coverage. The lack of evidence for the nearest neighbour effect on escape behaviour of crows may be due to: (1) disturbance by close neighbours that may impede antipredator behaviour of focal birds, (2) variable distribution of familiar, dominant or experienced individuals within a flock, and (3) dynamic change in position of the nearest neighbour during the potential predator approach.

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'.

Input and Output Connections of the Crow Nidopallium Caudolaterale.

The avian telencephalic structure nidopallium caudolaterale (NCL) functions as an analog to the mammalian prefrontal cortex. In crows, corvid songbirds, it plays a crucial role in higher cognitive and executive functions. These functions rely on the NCL's extensive telencephalic connections. However, systematic investigations into the brain-wide connectivity of the NCL in crows or other songbirds are lacking. Here, we studied its input and output connections by injecting retrograde and anterograde tracers into the carrion crow NCL. Our results, mapped onto a published carrion crow brain atlas, confirm NCL multisensory connections and extend prior pigeon findings by identifying a novel input from the hippocampal formation. Furthermore, we analyze crow NCL efferent projections to the arcopallium and report newly identified arcopallial neurons projecting bilaterally to the NCL. These findings help to clarify the role of the NCL as central executive hub in the corvid songbird brain.

Spontaneous tempo production in cockatiels (Nymphicus hollandicus) and jungle crows (Corvus macrorhynchos).

Musical and rhythmical abilities are poorly documented in non-human animals. Most of the existing studies focused on synchronisation performances to external rhythms. In humans, studies demonstrated that rhythmical processing (e. g. rhythm discrimination or synchronisation to external rhythm) is dependent of an individual measure: the individual tempo. It is assessed by asking participants to produce an endogenous isochronous rhythm (known as spontaneous motor tempo) without any specific instructions nor temporal cue. In non-human animal literature, studies describing spontaneous and endogenous production of motor tempo without any temporal clue are rare. This exploratory study aims to describe and compare the spontaneous motor tempo of cockatiels and jungle crows. Data were collected on spontaneous beak drumming behaviours of birds housed in laboratory. Inter beak strokes intervals were calculated from sound tracks of videos. The analyses revealed that inter beak strokes intervals are non-randomly distributed intervals and are isochronous. Recorded spontaneous motor tempos are significantly different among some cockatiels. Since we could only conduct statistical analysis with one corvid, we cannot conclude about this species. Our results suggest that cockatiels and jungle crows have individual tempos, thus encouraging further investigations.

Working memory capacity of crows and monkeys arises from similar neuronal computations.

Complex cognition relies on flexible working memory, which is severely limited in its capacity. The neuronal computations underlying these capacity limits have been extensively studied in humans and in monkeys, resulting in competing theoretical models. We probed the working memory capacity of crows (Corvus corone) in a change detection task, developed for monkeys (Macaca mulatta), while we performed extracellular recordings of the prefrontal-like area nidopallium caudolaterale. We found that neuronal encoding and maintenance of information were affected by item load, in a way that is virtually identical to results obtained from monkey prefrontal cortex. Contemporary neurophysiological models of working memory employ divisive normalization as an important mechanism that may result in the capacity limitation. As these models are usually conceptualized and tested in an exclusively mammalian context, it remains unclear if they fully capture a general concept of working memory or if they are restricted to the mammalian neocortex. Here, we report that carrion crows and macaque monkeys share divisive normalization as a neuronal computation that is in line with mammalian models. This indicates that computational models of working memory developed in the mammalian cortex can also apply to non-cortical associative brain regions of birds.

Working memory is the brain's ability to temporarily hold and manipulate information. It is essential for carrying out complex cognitive tasks, such as reasoning, planning, following instructions or solving problems. Unlike long-term memory, information is not stored and recalled, but held in an accessible state for brief periods. However, the capacity of working memory is very limited. Humans, for example, can only hold around four items of information simultaneously. There are various competing theories about how this limitation arises from the network of neurons in the brain. These models are based on studies of humans and other primates. But memory limitations are not exclusive to mammals. Indeed, the working memory of some birds, such as crows, has a similar capacity to humans despite the architecture of their brains being very different to mammals. So, how do brains with such distinct structural differences produce working memories with similar capacities? To investigate, Hahn et al. probed the working memory of carrion crows in a change detection task developed for macaque monkeys. Crows were trained to memorize varying numbers of colored squares and indicate which square had changed after a one second delay when the screen went blank. While the crows performed the task, Hahn et al. measured the activity of neurons in an area of the brain equivalent to the prefrontal cortex, the central hub of cognition in mammals. The experiments showed that neurons in the crow brain responded to the changing colors virtually the same way as neurons in monkeys. Hahn et al. also noticed that increasing the number of items the crows had to remember affected individual neurons in a similar fashion as had previously been observed in monkeys. This suggests that birds and monkeys share the same central mechanisms of, and limits to, working memory despite differences in brain architecture. The similarities across distantly related species also validates core ideas about the limits of working memory developed from studies of mammals.

Mosquito blood-feeding patterns and nesting behavior of American crows, an amplifying host of West Nile virus.

BACKGROUND: Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population. METHODS: Sixty artificial mosquito resting sites were deployed from May to September 2014 in varying proximity to known crow nesting sites, and Culex blood meal hosts were identified by DNA barcoding. Genotypes from crow blood meals and local crows (72 nestlings from 30 broods and 389 local breeders and helpers) were used to match mosquito blood meals to specific local crows. RESULTS: Among the 297 identified Culex blood meals, 20 (6.7%) were attributable to crows. The mean percentage of blood meals of crow origin was 19% in the nesting period (1 May-18 June 2014), but 0% in the weeks after fledging (19 June-1 September 2014), and the likelihood of a crow blood meal increased with proximity to an active nest: the odds that crows hosted a Culex blood meal were 38.07 times greater within 10 m of an active nest than > 10 m from an active nest. Nine of ten crow blood meals that could be matched to a genotype of a specific crow belonged to either nestlings in these nests or their mothers. Six of the seven genotypes that could not be attributed to sampled birds belonged to females, a sex bias likely due to mosquitoes targeting incubating or brooding females. CONCLUSION: Data herein indicate that breeding crows serve as hosts for Culex in the initial stages of the WNV spring enzootic cycle. Given their high viremia, infected crows could thereby contribute to the re-initiation and early amplification of the virus, increasing its availability as mosquitoes shift to other moderately competent later-breeding avian hosts.

Climatic change and extinction risk of two globally threatened Ethiopian endemic bird species.

Climate change is having profound effects on the distributions of species globally. Trait-based assessments predict that specialist and range-restricted species are among those most likely to be at risk of extinction from such changes. Understanding individual species' responses to climate change is therefore critical for informing conservation planning. We use an established Species Distribution Modelling (SDM) protocol to describe the curious range-restriction of the globally threatened White-tailed Swallow (Hirundo megaensis) to a small area in southern Ethiopia. We find that, across a range of modelling approaches, the distribution of this species is well described by two climatic variables, maximum temperature and dry season precipitation. These same two variables have been previously found to limit the distribution of the unrelated but closely sympatric Ethiopian Bush-crow (Zavattariornis stresemanni). We project the future climatic suitability for both species under a range of climate scenarios and modelling approaches. Both species are at severe risk of extinction within the next half century, as the climate in 68-84% (for the swallow) and 90-100% (for the bush-crow) of their current ranges is predicted to become unsuitable. Intensive conservation measures, such as assisted migration and captive-breeding, may be the only options available to safeguard these two species. Their projected disappearance in the wild offers an opportunity to test the reliability of SDMs for predicting the fate of wild species. Monitoring future changes in the distribution and abundance of the bush-crow is particularly tractable because its nests are conspicuous and visible over large distances.

Neural Code of Motor Planning and Execution during Goal-Directed Movements in Crows.

The planning and execution of head-beak movements are vital components of bird behavior. They require integration of sensory input and internal processes with goal-directed motor output. Despite its relevance, the neurophysiological mechanisms underlying action planning and execution outside of the song system are largely unknown. We recorded single-neuron activity from the associative endbrain area nidopallium caudolaterale (NCL) of two male carrion crows (Corvus corone) trained to plan and execute head-beak movements in a spatial delayed response task. The crows were instructed to plan an impending movement toward one of eight possible targets on the left or right side of a touchscreen. In a fraction of trials, the crows were prompted to plan a movement toward a self-chosen target. NCL neurons signaled the impending motion direction in instructed trials. Tuned neuronal activity during motor planning categorically represented the target side, but also specific target locations. As a marker of intentional movement preparation, neuronal activity reliably predicted both target side and specific target location when the crows were free to select a target. In addition, NCL neurons were tuned to specific target locations during movement execution. A subset of neurons was tuned during both planning and execution period; these neurons experienced a sharpening of spatial tuning with the transition from planning to execution. These results show that the avian NCL not only represents high-level sensory and cognitive task components, but also transforms behaviorally-relevant information into dynamic action plans and motor execution during the volitional perception-action cycle of birds.SIGNIFICANCE STATEMENT Corvid songbirds have become exciting new models for understanding complex cognitive behavior. As a key neural underpinning, the endbrain area nidopallium caudolaterale (NCL) represents sensory and memory-related task components. How such representations are converted into goal-directed motor output remained unknown. In crows, we report that NCL neurons are involved in the planning and execution of goal-directed movements. NCL neurons prospectively signaled motion directions in instructed trials, but also when the crows were free to choose a target. NCL neurons showed a target-specific sharpening of tuning with the transition from the planning to the execution period. Thus, the avian NCL not only represents high-level sensory and cognitive task components, but also transforms relevant information into action plans and motor execution.

A histological study of the song system of the carrion crow (Corvus corone).

The song system of songbirds (oscines) is one of the best studied neuroethological model systems. So far, it has been treated as a relatively constrained sensorimotor system. Songbirds such as crows, however, are also known for their capability to cognitively control their audio-vocal system. Yet, the neuroanatomy of the corvid song system has never been explored systematically. We aim to close this scientific gap by presenting a stereotactic investigation of the extended song system of the carrion crow (Corvus corone), an oscine songbird of the corvid family that has become an interesting model system for cognitive neuroscience. In order to identify and delineate the song nuclei, the ascending auditory nuclei, and the descending vocal-motor nuclei, four stains were applied. In addition to the classical Nissl-, myelin-, and a combination of Nissl-and-myelin staining, staining for tyrosine hydroxylase was used to reveal the distribution of catecholaminergic neurons (dopaminergic, noradrenergic, and adrenergic) in the song system. We show that the crow brain contains the important song-related nuclei, including auditory input and motor output structures, and map them throughout the brain. Fiber-stained sections reveal putative connection patterns between the crow's song nuclei comparable to other songbirds.

Gross morphological, histological and scanning electron specifications of the oropharyngeal cavity of the hooded crow (Corvus cornix pallescens).

The present study was carried out on the oropharyngeal cavity of the hooded crow to investigate the gross and microscopic structures via gross anatomy, light microscopy and scanning electron microscopy (SEM). The gross anatomy clarified the elongated triangular shape of the oropharyngeal cavity with a non-protruding tongue with a bifid apex. The lingual body contained median groove rostrally and separated caudally from the root by a transverse papillary crest. The laryngeal mound located posterior to the lingual root, contained midline laryngeal cleft and bounded caudally by a transverse row of pharyngeal papillae. The palate contained choanal cleft rostrally and infundibular slit caudally in addition to five palatine ridges. By light microscopy, the dorsal lingual epithelium was highly keratinised stratified squamous with a lingual nail in the most rostral part of the apex. Then, the thickness of the keratin layer decreased caudally, while in the ventral surface, the lining epithelium became non-keratinised. The entoglossum supported the lingual body and root, but not extended to the apex. The lining epithelium of the palate was also keratinised stratified squamous and became none-keratinised at the oral side of the choanal cleft. There were numerous lobules of polystomatic salivary glands in the lingual root and the palate. SEM revealed the arrangement of different types of papillae covering both the floor and the roof of the oropharynx besides numerous openings of salivary glands in the lingual root, laryngeal mound and the palate. These findings reflect the functional relationship of the oropharyngeal cavity of the hooded crow during feeding.

Ravens parallel great apes in physical and social cognitive skills.

Human children show unique cognitive skills for dealing with the social world but their cognitive performance is paralleled by great apes in many tasks dealing with the physical world. Recent studies suggested that members of a songbird family-corvids-also evolved complex cognitive skills but a detailed understanding of the full scope of their cognition was, until now, not existent. Furthermore, relatively little is known about their cognitive development. Here, we conducted the first systematic, quantitative large-scale assessment of physical and social cognitive performance of common ravens with a special focus on development. To do so, we fine-tuned one of the most comprehensive experimental test-batteries, the Primate Cognition Test Battery (PCTB), to raven features enabling also a direct, quantitative comparison with the cognitive performance of two great ape species. Full-blown cognitive skills were already present at the age of four months with subadult ravens' cognitive performance appearing very similar to that of adult apes in tasks of physical (quantities, and causality) and social cognition (social learning, communication, and theory of mind). These unprecedented findings strengthen recent assessments of ravens' general intelligence, and aid to the growing evidence that the lack of a specific cortical architecture does not hinder advanced cognitive skills. Difficulties in certain cognitive scales further emphasize the quest to develop comparative test batteries that tap into true species rather than human specific cognitive skills, and suggest that socialization of test individuals may play a crucial role. We conclude to pay more attention to the impact of personality on cognitive output, and a currently neglected topic in Animal Cognition-the linkage between ontogeny and cognitive performance.

A neural correlate of sensory consciousness in a corvid bird.

Subjective experiences that can be consciously accessed and reported are associated with the cerebral cortex. Whether sensory consciousness can also arise from differently organized brains that lack a layered cerebral cortex, such as the bird brain, remains unknown. We show that single-neuron responses in the pallial endbrain of crows performing a visual detection task correlate with the birds' perception about stimulus presence or absence and argue that this is an empirical marker of avian consciousness. Neuronal activity follows a temporal two-stage process in which the first activity component mainly reflects physical stimulus intensity, whereas the later component predicts the crows' perceptual reports. These results suggest that the neural foundations that allow sensory consciousness arose either before the emergence of mammals or independently in at least the avian lineage and do not necessarily require a cerebral cortex.

Decision-making flexibility in New Caledonian crows, young children and adult humans in a multi-dimensional tool-use task.

The ability to make profitable decisions in natural foraging contexts may be influenced by an additional requirement of tool-use, due to increased levels of relational complexity and additional work-effort imposed by tool-use, compared with simply choosing between an immediate and delayed food item. We examined the flexibility for making the most profitable decisions in a multi-dimensional tool-use task, involving different apparatuses, tools and rewards of varying quality, in 3-5-year-old children, adult humans and tool-making New Caledonian crows (Corvus moneduloides). We also compared our results to previous studies on habitually tool-making orangutans (Pongo abelii) and non-tool-making Goffin's cockatoos (Cacatua goffiniana). Adult humans, cockatoos and crows, but not children and orangutans, did not select a tool when it was not necessary, which was the more profitable choice in this situation. Adult humans, orangutans and cockatoos, but not crows and children, were able to refrain from selecting non-functional tools. By contrast, the birds, but not the primates tested, struggled to attend to multiple variables-where two apparatuses, two tools and two reward qualities were presented simultaneously-without extended experience. These findings indicate: (1) in a similar manner to humans and orangutans, New Caledonian crows and Goffin's cockatoos can flexibly make profitable decisions in some decision-making tool-use tasks, though the birds may struggle when tasks become more complex; (2) children and orangutans may have a bias to use tools in situations where adults and other tool-making species do not.

Crows control working memory before and after stimulus encoding.

The capacity of working memory is limited and this limit is comparable in crows and primates. To maximize this resource, humans use attention to select only relevant information for maintenance. Interestingly, attention-cues are effective not only before but also after the presentation of to-be-remembered stimuli, highlighting control mechanisms beyond sensory selection. Here we explore if crows are also capable of these forms of control over working memory. Two crows (Corvus corone) were trained to memorize two, four or six visual stimuli. Comparable to our previous results, the crows showed a decrease in performance with increasing working memory load. Using attention cues, we indicated the critical stimulus on a given trial. These cues were either presented before (pre-cue) or after sample-presentation (retro-cue). On other trials no cue was given as to which stimulus was critical. We found that both pre- and retro-cues enhance the performance of the birds. These results show that crows, like humans, can utilize attention to select relevant stimuli for maintenance in working memory. Importantly, crows can also utilize cues to make the most of their working memory capacity even after the stimuli are already held in working memory. This strongly implies that crows can engage in efficient control over working memory.

Predation of young tortoises by ravens: the effect of habitat structure on tortoise detectability and abundance.

The predation of young tortoise is considered a major cause of mortality for many tortoise species. The predation by common ravens has been identified as being responsible for significant decreases in tortoise populations. Mediterranean spur-thighed tortoise hatchlings and juveniles in Maamora forest (Morocco) were studied in order to describe the size/age class predation of common ravens on young tortoises and infer the drivers of predation risk and population abundance. The results showed a high level of predation on young tortoises (<75 mm carapace length) attributed to ravens in areas with low vegetation cover, representing 100% of the cases of mortality (n = 147), but it was moderate in covered areas (n = 19), representing 12-27%. The population structure of living juveniles differed significantly between covered and uncovered areas, thus suggesting that raven predation might modify juvenile population structure. Finally, N-mixture models showed a positive relationship between (i) bare cover and tortoise detectability that is only evidenced when the plot is far from a perch and (ii) population abundance and shrub species-richness, being higher in uncovered areas. Our results improve the knowledge on predation and survival on this critical stage in life, which is crucial for the conservation of the Mediterranean spur-thighed tortoise.

Format-dependent and format-independent representation of sequential and simultaneous numerosity in the crow endbrain.

Humans' symbolic counting skills are built on a primordial ability to approximately estimate the number of items, or numerosity. To date it is debated whether numerosities presented in categorically different formats, that is as temporal sequences versus spatial arrays, are represented abstractly in the brain. To address this issue, we identified the behavioral characteristics and neuronal codes for sequential and simultaneous number formats in crows. We find a format-dependent representation by distinct groups of selective neurons during the sensory encoding stage. However, an abstract and format-independent numerosity code emerges once the encoding phase is completed and numerosities needed to be memorized. These results suggest a successive two-stage code for categorically different number formats and help to reconcile conflicting findings observed in psychophysics and brain imaging.

Corvids exhibit dynamic risk assessment during escape.

It is widely accepted that stationary prey are able to carefully assess the risk levels associated with an approaching predator to make informative decisions on when to escape. However, little is known about subsequent decision-making process. We set out to compare whether escape durations of three species of corvids differ depending on how a human observer (in the role of a predator) behaves after the escape has begun. When birds were being followed during escape, escape durations were the longest, escape trajectory was modified the most during escape, and a larger proportion of individuals changed from terrestrial to aerial escape strategy compared to observations where birds were not followed. Mean horizontal escape angle of ca 120° was also a potential indication that monitoring the threat is taken into account when deciding on the escape trajectory. While there were some differences between the behaviour of these three closely related species, the general patterns supported the notion that birds dynamically assess risk during escape to find an optimal balance between getting caught and spending too much time and energy on escaping. Further research using different predator-prey combinations or making comparisons between habitats could help understand the generality of our results.

Behavioural plasticity and the transition to order in jackdaw flocks.

Collective behaviour is typically thought to arise from individuals following fixed interaction rules. The possibility that interaction rules may change under different circumstances has thus only rarely been investigated. Here we show that local interactions in flocks of wild jackdaws (Corvus monedula) vary drastically in different contexts, leading to distinct group-level properties. Jackdaws interact with a fixed number of neighbours (topological interactions) when traveling to roosts, but coordinate with neighbours based on spatial distance (metric interactions) during collective anti-predator mobbing events. Consequently, mobbing flocks exhibit a dramatic transition from disordered aggregations to ordered motion as group density increases, unlike transit flocks where order is independent of density. The relationship between group density and group order during this transition agrees well with a generic self-propelled particle model. Our results demonstrate plasticity in local interaction rules and have implications for both natural and artificial collective systems.