Social learning in common ravens, Corvus corax

We conducted an experiment to investigate whether the presence of a conspecific model can promote the acquisition of a motor task in common ravens. For this purpose, dyads, either of control birds or of model-observer pairings, were allowed to operate together in an arena with a set of identical boxes. Each box consisted of two compartments each containing a reward of three pieces of meat. The compartments were closed by gliding lids with red flaps on their front, opening horizontally in opposite directions. Naive control individuals opened the lids exclusively by levering, that is, jumping on top of the box, inserting the beak at the posterior rim of the lid and pushing it open. Models were trained to demonstrate an alternative opening technique, pulling at the front flap, then jumping on top of the box to get at the reward. In contrast to the control birds, observers initially opened boxes both ways, by pulling and levering. Furthermore, observers approached the boxes more quickly and showed less fearful behaviour than the control birds, which we attribute to the enhancing effect of the model. We discuss both stimulus enhancement and motor imitation as possible learning mechanisms. Even though observers initially obtained a considerable amount of reward produced by the models, scrounging evidently did not inhibit learning. Copyright 1999 The Association for the Study of Animal Behaviour.     

Effect of rearing style on the development of social behaviour in young ravens (Corvus corax)

Early social experiences can affect the development and expression of individual social behaviour throughout life. In particular, early-life social deprivations, notably of parental care, can later have deleterious consequences. We can, therefore, expect rearing procedures such as hand-raising—widely used in ethology and socio-cognitive science—to alter the development of individual social behaviour. We investigated how the rearing style later affected (a) variation in relationship strength among peers and (b) individuals’ patterns of social interactions, in three captive groups of juvenile non-breeders consisting of either parent-raised or hand-raised birds, or a mix of both rearing styles. In the three groups, irrespectively of rearing style: strongest relationships (i.e., higher rates of association and affiliations) primarily emerged among siblings and familiar partners (i.e., non-relatives encountered in early life), and mixed-sex and male–male partners established relationships of similar strength, indicating that the rearing style does not severely affect the quality and structure of relationships in young ravens. However, compared to parent-raised ravens, hand-raised ravens showed higher connectedness, i.e., number of partners with whom they mainly associated and affiliated, but formed on average relationships of lower strength, indicating that social experience in early life is not without consequences on the development of ravens’ patterns of social interaction. The deprivation of parental care associated with the presence of same-age peers during hand-raising seemed to maximize ravens’ propensity to interact with others, indicating that besides parents, interactions with same-age peers matter. Opportunities to interact with, and socially learn from peers, might thus be the key to the acquisition of early social competences in ravens.     

Decision time modulates social foraging success in wild common ravens,Corvus corax

Social foraging provides several benefits for individuals but also bears the potential costs of higher competition. In some species, such competition arises through kleptoparasitism, that is when an animal takes food which was caught or collected by a member of its social group. Except in the context of caching, few studies have investigated how individuals avoid kleptoparasitism, which could be based on physical strength/dominance but also cognitive skills. Here, we investigated the foraging success of wild common ravens, Corvus corax, experiencing high levels of kleptoparasitism from conspecifics when snatching food from the daily feedings of captive wild boars in a game park in the Austrian Alps. Success in keeping the food depended mainly on the individuals’ age class and was positively correlated with the time to make a decision in whether to fly off with food or consume it on site. While the effect of age class suggests that dominant and/or experienced individuals are better in avoiding kleptoparasitism, the effect of decision time indicates that individuals benefit from applying cognition to such decision-making, independently of age class. We discuss our findings in the context of the ecological and social intelligence hypotheses referring to the development of cognitive abilities. We conclude that investigating which factors underline kleptoparasitism avoidance is a promising scenario to test specific predictions derived from these hypotheses.     

Movement coordination and signalling in ravens (Corvus corax): an experimental field study

Vagrant non-breeding ravens frequently attract conspecifics to rich ephemeral food sources. There, grouping may allow them to overcome the defence of territorial breeders. Here, we focus on ravens making use of regular food supplies in a game park, where they divert food from the provision of park animals. We investigated if ravens foraging in the Cumberland game park (Grünau, Austria) are attentive towards one another when they experience some unpredictability in food provisioning. We confronted a group of 30–50 ravens with two different treatments. Ten minutes ahead of the feeding of either wolves or wild boars we showed buckets containing pieces of meat to the ravens flying overhead. In the reliable cue treatment (RCT), the meat was placed next to one of the two enclosures, whereas in the unreliable cue treatment (UCT), the buckets were placed simultaneously in front of both enclosures though only in one of the enclosures were the animals fed 10 min later. Thus, during RCT but not during UCT, ravens could predict where food would become available. Only during UCT, ravens moved in large groups between the two feeding sites. Many ravens moving at the same time in the same direction may indicate some co-ordination in space and time, which is most likely achieved by social attraction among individuals. Furthermore, the number of ravens approaching and leaving, respectively, a feeding site cross-correlated with a temporary increase in the rate of a food-associated call, the yell. This suggests that in addition to watching each other, calling may have contributed to group formation. Possible benefits of group formation during food inspection are discussed. Received: 9 February 2000 / Received in revised form: 30 May 2000 / Accepted: 1 June 2000     

Corticosterone excretion patterns and affiliative behavior over development in ravens (Corvus corax)

Averse effects of social stress may be buffered by the presence of social allies, which mainly has been demonstrated in mammals and recently also in birds. However, effects of socio-positive behavior prior to fledging in relation to corticosterone excretion in altricial birds have not been investigated yet. We here monitored corticosterone excretion patterns in three groups of hand raised juvenile ravens (n=5, 6 and 11) in the nest, post-fledging (May-July) and when ravens would be independent from their parents (September-November). We related these corticosterone excretion patterns to socio-positive behavior. Behavioral data were collected via focal sampling in each developmental period considered. We analyzed amounts of excreted immunoreactive corticosterone metabolites (CM) using enzyme immuno assays. We collected fecal samples in each developmental period considered and evaluated the most appropriate assay via an isolation stress experiment. Basal CM was significantly higher during the nestling period than post-fledging or when birds were independent. The time nestlings spent allopreening correlated negatively with mean CM. Post-fledging, individuals with higher CM levels sat close to (distance <50 cm) conspecifics more frequently and tended to preen them longer. When birds were independent and a stable rank hierarchy was established, dominant individuals were preened significantly longer than subordinates. These patterns observed in ravens parallel those described for primates, which could indicate that animal species living in a complex social environment may deal with social problems in a similar way that is not restricted to mammals or primates.     

Neophobia affects choice of food-item size in group-foraging common ravens (Corvus corax)

Individuals foraging in groups should develop behavioural tactics to optimise their gain. In novel feeding situations, predation risk and pressure of kleptoparasites may be particularly high and hence may constrain optimal foraging. To create a novel feeding situation, we offered common ravens (Corvus corax) equal numbers of either small (40 g) or large (160 g) pieces of meat on successive days, always in combination with the same novel object. During the first weeks, when ravens were still neophobic, small pieces were taken in larger numbers than large pieces. Intraspecific kleptoparasitism was more likely to occur when ravens carried large food items. It seems that initiating foragers were mainly innovative subdominants. Preference for small items might have decreased with increasing habituation because more dominants were then feeding directly at the source and hence were less likely to resort to kleptoparasitism as an alternative foraging tactic. Electronic Publication     

Genetic signatures of intermediate divergence: population history of Old and New World Holarctic ravens (Corvus corax)

Many studies of phylogeography, speciation, and species limits restrict their focus to a narrow issue: gene tree monophyly. However, reciprocal monophyly does not provide an ideal touchstone criterion of any aspect of evolutionary divergence. There is a continuum of divergence stages as isolated populations go from initial allele frequency differences to well-differentiated species. Studying intermediate stages of divergence will increase our understanding of geographical speciation, species limits, and conservation priorities. We develop a conceptual framework and terminology for thinking about the stages of 'intermediate polyphyly'. The Holarctic clade of common ravens (Corvus corax), found throughout much of Eurasia and North America, provides a case study of these stages of intermediate divergence. We used coalescent, phylogenetic, and population genetic methods to investigate the history and current status of this Old World-New World distribution using 107 mitochondrial control region sequences. Phylogenetically, New World and Old World samples are intermixed. However, most samples are grouped into small subclades that are restricted to either the New World or the Old World, and only one haplotype is shared between the hemispheres. Analysis of moleculalr variance (amova) results reflect this low haplotype sharing between hemispheres (Phi(ST) = 0.13, P < 0.01). Isolation with Migration (im) coalescent results suggest a sustained period of divergence between the hemispheres and low levels of maternal gene flow. Although there has not been sufficient time to evolve reciprocal monophyly and some gene flow may occur, New World and Old World ravens are genetically quite distinct. We use this example to demonstrate these early stages of divergence as populations go from sharing only internal haplotypes, to sharing no haplotypes, to having population specific subclades. Studies of phylogeography, speciation and systematics will benefit from increased attention to these stages of intermediate polyphyly.     

Effects of Group Size on Approach to Novel Objects in Ravens (Corvus corax)

Neophobia may constrain explorative behaviour, learning and innovation, while social context may facilitate approach to novel objects and acceptance of novel food. We examined the effects of neophobia on the exploration of novel objects in relation to social context in ravens (Corvus corax). Ravens are suitable subjects for studying effects of social context, as they are highly neophobic scavengers that recruit conspecifics to food. We tested two groups of six and 11 hand‐raised birds in three conditions: single‐bird, in dyadic combinations and sibling sub‐groups of three to six birds. Contrary to expectation, individuals of both groups were quicker to approach novel objects when tested alone than when tested with conspecifics. However, they spent more time close to and manipulating the novel objects in the social conditions (dyadic and group) than when being alone. We discuss the possibility that the higher latencies of dyads and groups to approach novel objects may reflect a ‘negotiation’ process in a ‘war of attrition’ between the individuals over risk‐taking.     

Threats and control of the brown necked ravens (Corvus ruficollis) in Egypt

The Suez Canal region is a small fertile area in Egypt that is placed under enormous pressure of existing resources. In these areas, intensive agricultural practices are performed in combination with high population densities. The described problem is that together with agricultural practices and urbanization, Brown necked ravens (Corvus ruficollis) are in huge amounts attracted. The birds are very aggressive and showed to be a serious pest. They spread germs and diseases for human health and food production. Therefore, the birds need to be controlled. Our research focuses on identifying food preferences of raven and on the way raven control is most effective. Ravens are omnivorous birds. From our laboratory study it was seen that most preferable foods were, in descending order: fresh fishes, cow liver, crustacean, watermelons, tomatoes and yoghurt. Under field conditions where stomach content was dissected, animal matters showed to a more preferred food source than plant matters. Observations on olfactory sensitivity showed that ravens could easily locate their food. Biological observations in the field on reproduction of ravens showed that raven females lay two to six eggs. Average number of babies per nest was between one and four. Average number of raven flock before sun rise was more than 100, while it was less than 100 before sun set. The impact of mechanical, biological and chemical control was investigated. Without control, approximately flock numbers of more than 100 ravens were recorded. The average number of raven flock was 60 before mechanical control operation (nests destroyed and using net), while it was 40 after mechanical control. Results of the biological control showed that kestrel (Falco tinnunculus rupicolaeformes) predated raven babies more effective than barn owls (Tyto alba). Within the chemical control experiments, Brodifacoum (0.0005%) was most effective against ravens, followed by Zink phosphide (19%) and Methomyl (90%, carbamate compound).     

Ravens (Corvus corax corax L.) in the British landscape: a thousand years of ecological biogeography in place-names

Abstract Aim To investigate the information content of place‐names regarding the habits, habitat and biogeography of ravens in Britain over the past millennium. Location England, Scotland and Wales. Methods Linguistic and ecological analysis of over 400 British place‐names that have a putative ‘raven’ derivation. Results Most of the ‘raven’ place‐names are Old English in origin. Some of these (a minority), however, derive from personal names. The derivations of most names reflect landscape rather than man‐made features; the majority relating to high, craggy ground or coastal features, a minority to wooded situations or human habitations. In lowland Scotland and the Scottish borders the colloquial name corbie dominates ‘raven’ place‐names, perhaps reflecting French influence. In the Highlands and the Western Isles the Gaelic fitheach and its derivatives are predominant. Relatively fewer place‐names that have ‘raven’ roots have been educed in other parts of the Celtic West, i.e. Wales and Cornwall (only one traced in the latter). Main conclusions Comparison of the geographical distribution of ‘raven’‐derived place‐names with the present‐day distribution of the species in Britain reveals the extent of the contraction in the raven's range to the West over historical time, most notably during theprevious two centuries, associated with changed land‐management practices in particular.     

As the raven flies: using genetic data to infer the history of invasive common raven (Corvus corax) populations in the Mojave Desert

Common raven (Corvus corax) populations in Mojave Desert regions of southern California and Nevada have increased dramatically over the past five decades. This growth has been attributed to increased human development in the region, as ravens have a commensal relationship with humans and feed extensively at landfills and on road-killed wildlife. Ravens, as a partially subsidized predator, also represent a problem for native desert wildlife, in particular threatened desert tortoises (Gopherus agassizii). However, it is unclear whether the more than 15-fold population increase is due to in situ population growth or to immigration from adjacent regions where ravens have been historically common. Ravens were sampled for genetic analysis at several local sites within five major areas: the West Mojave Desert (California), East Mojave Desert (southern Nevada), southern coastal California, northern coastal California (Bay Area), and northern Nevada (Great Basin). Analyses of mtDNA control region sequences reveal an increased frequency of raven 'Holarctic clade' haplotypes from south to north inland, with 'California clade' haplotypes nearly fixed in the California populations. There was significant structuring among regions for mtDNA, with high F(ST) values among sampling regions, especially between the Nevada and California samples. Analyses of eight microsatellite loci reveal a mostly similar pattern of regional population structure, with considerably smaller, but mostly significant, values. The greater mtDNA divergences may be due to lower female dispersal relative to males, lower N(e), or effects of high mutation rates on maximal values of F(ST). Analyses indicate recent population growth in the West Mojave Desert and a bottleneck in the northern California populations. While we cannot rule out in situ population growth as a factor, patterns of movement inferred from our data suggest that the increase in raven populations in the West Mojave Desert resulted from movements from southern California and the Central Valley. Ravens in the East Mojave Desert are more similar to ones from northern Nevada, indicating movement between those regions. If this interpretation of high gene flow into the Mojave Desert is correct, then efforts to manage raven numbers by local control may not be optimally effective.     

Novel object exploration in mice: not all objects are created equal

Object exploration is an increasingly popular experimental paradigm in behavioral sciences. We have begun a series of studies with mice specifically looking at the parameters that influence behaviors in this test. The aim of the present study was to examine the effect of object type on performance in the object exploration test. More specifically, adult male C57BL/6J mice were trained and tested using objects that could be climbed (CLIMB) or with those that could only be touched (TOUCH). The results show that activity is affected by the presentation of objects, with object type interacting with some of these changes. C57 mice explored objects that can be climbed over significantly longer than objects that can only be touched and a more rapid habituation was observed using objects that could only be touched. Robust recognition memory was observed in both groups of mice, however mice in the CLIMB group exhibited a significantly greater discrimination index compared to mice in the TOUCH group. Taken together, these findings demonstrate that the selection of objects is of critical importance and it is recommended that special attention be given to the functional (affordant) properties of the objects to-be-used in future studies.     

Buzzards Buteo buteo and Ravens Corvus corax in the uplands of Britain: limits to distribution and abundance

The current breeding ranges of Buzzards Buteo buteo and Ravens Corvus corax in Britain are restricted to the west, and both are relics of former widespread but not necessarily even distributions. Moore (1957) attributed the Buzzard's contraction in range to persecution by gamekeepers, his evidence being the complementary nature of the Buzzard's distribution with those of gamekeepers in the lowlands and grouse moors in the uplands; others have attributed the Raven's decline to the same cause. Is Moore correct and, if so, are these species' ranges still limited by persecution? Here we adopt an approach similar to Moore's, whereby we compare the current geographical patterns of abundance of Buzzards and Ravens in the British uplands with that of an index of grouse moor density. Unlike Moore, however, we take into account climate, land cover, topography and sheep stocking density, as well as grouse moor distribution, using multiple logistic regression modelling. We show that in the uplands the distribution of grouse moors strongly limits that of Buzzards and Ravens but are unable to conclude that this is a result of persecution because there are several competing hypotheses (moor management, food and nest-site availability) between which we are unable to distinguish.     

Interinsular variations in the spring and summer diet of the Raven Corvus corax in the Canary Islands

This paper presents the first data on the diet of the Raven Corvus corax in the Canary Islands, based on analysis of 2315 pellets collected from all of the islands and islets in the archipelago. The Ravens on three groups of island showed differences in diet, but in all cases the diet was clearly omnivorous, both in its qualitative and quantitative composition. It is evident that a broadening of the Raven's trophic niche has occurred in comparison with those living in continental areas. While the diet has a strong plant component on the wetter islands (frequency of occurrence > 87%), an appreciable animal component in the diet (principally vertebrates) is more frequent on the drier islands of the archipelago (frequency of occurrence > 96%). The composition of the plant component of the diet varied markedly from one island to another. Remains of refuse are more commonly found in the Raven's diet on the central and western islands. We concluded that while the animal diet is essential from the bioenergetic point of view, the vegetation diet is only a complementary food source. The Raven plays an important role in seed dispersal among the different habitats within each island.     

The social and spatial organization of winter communal roosting in Rooks (Corvus fmgilegus)

The spatial and social organization of a winter communal roost of Rooks ( Corvus frugilegus L.) was examined. The behaviour of rooks in the roost was found to reduce the rate of loss of heat energy for all or some of the population. The saving of energy experienced by young birds by roosting in sheltered positions was important because of the smaller energy reserves available. When the weather became exceptionally severe, dominant individuals, in seeking sheltered positions, forced less dominant birds from more sheltered to far less sheltered positions, thereby increasing their energy loss. The effects of this selectively-acting social hierarchy during the night is exacerbated on the feeding grounds during the day when some rooks starve especially those low in the hierarchy. The daytime feeding situation will also increase the lower critical metabolic temperature of the young rooks by lowering the nutritional plane. Other evidence is presented to show that in winter, mortality of young rooks is higher than that of adult rooks.
It is argued that the change in the spatial organization in the roost induced by weather and determined by a selectively-actingsocial hierarchy operates to reduce the rate of energy loss of the majority of the rooks while the remainder suffer an increasing energy deficit.     

Seasonal observations and machine-learning-based spatial model predictions for the common raven (Corvus corax) in the urban, sub-arctic environment of Fairbanks, Alaska

The common raven (Corvus corax) is an abundant generalist of the northern hemisphere, known to congregate and roost near human-related food sources. Due to a growing human-footprint and associated anthropogenic food subsidies, raven populations have increased dramatically over the past several years throughout the USA. The sub-arctic region has also witnessed increased urbanization and industrialization, and ravens have taken advantage of these changes. During 2004 and 2006, we surveyed parking lots on a bi-weekly basis in the city of Fairbanks in interior Alaska, showing an influx of ravens in winter. Between 2010 and 2012, we documented the presence and absence of ravens at a permanent set of 30 suspected raven locations and 21 randomized locations within the city limits of Fairbanks. We used machine learning (RandomForests) and 12 spatial GIS datasets from the Fairbanks North Star Borough to accurately model-predict the relative occurrence of ravens during winter and summer in Fairbanks. Our research showed a positive correlation between raven occurrence and commercial and residential zones in both winter and summer, as well as an inverse geographic relationship between ravens and the waste transfer station in the study area in winter, and a direct correlation near restaurants in summer. These results emphasize the link that ravens have with commercial, anthropogenic food sources, and how Fairbanks and its subsidized, urban habitat may be shaping part of the wider sub-arctic biodiversity landscape.