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anthropogenic extinction of top carnivores and interspecific animal behaviour: implications of the rapid decoupling of a web involving wolves, bears, moose and ravens.the recent extinction of grizzly bears (ursus arctos) and wolves (canis lupus) by humans from 95-99% of the contiguous usa and mexico in less than 100 years has resulted in dramatically altered and expanded prey communities. such rampant ecological change and putative ecological instability has not occurred in north american northern boreal zones. this geographical variation in the loss of large carnivores as a consequence of anthropogenic disturbance offers opportunities for examining the poten ...199910629976
experimental infection of nontarget species of rodents and birds with brucella abortus strain rb51 vaccine.the brucella abortus vaccine strain rb51 (srb51) is being considered for use in the management of bnucellosis in wild bison (bison bison) and elk (cervus elaphus) populations in the greater yellowstone area (usa). evaluation of the vaccines safety in non-target species was considered necessary prior to field use. between june 1998 and december 1999, ground squirrels (spermophilus richardsonii, n = 21), deer mice (peromyscus maniculatus, n = 14), prairie voles (microtus ochrogaster, n = 21), and ...200111504226
rapid antigen-capture assay to detect west nile virus in dead corvids.the utility of the vectest antigen-capture assay to detect west nile virus (wnv) in field-collected dead corvids was evaluated in manitoba and ontario, canada, in 2001 and 2002. swabs were taken from the oropharynx, cloaca, or both of 109 american crows, 31 blue jays, 6 common ravens, and 4 black-billed magpies from manitoba, and 255 american crows and 28 blue jays from ontario. the sensitivity and specificity of the antigen-capture assay were greatest for samples from american crows; oropharyng ...200314718083
west nile virus in mexico: evidence of widespread circulation since july 2002.west nile virus (wnv) antibodies were detected in horses from five mexican states, and wnv was isolated from a common raven in the state of tabasco. phylogenetic studies indicate that this isolate, the first from mexico, is related to strains from the central united states but has a relatively high degree of sequence divergence.200314720402
managing a subsidized predator population: reducing common raven predation on desert tortoises.human communities often are an inadvertent source of food, water, and other resources to native species of wildlife. because these resources are more stable and predictable than those in a natural environment, animals that subsist on them are able to increase in numbers and expand their range, much to the detriment of their competitors and species they prey upon. in the mojave desert, common ravens (corvus corax) have benefited from human-provided resources to increase in population size precipi ...200314753646
ravens judge competitors through experience with play caching.complex social behavior builds on the mutual judgment of individuals as cooperation partners and competitors [1]. play can be used for assessing the others' dispositions in humans and nonhuman mammals [2], whereas little is known about birds. recently, food-caching corvids have been found to rival primates in their ability to judge the behaviors and intentions of others in competition for hidden food [3]. here, we show that ravens corvus corax quickly learn to assess the competitive strategies o ...200717949980
short-term observational spatial memory in jackdaws (corvus monedula) and ravens (corvus corax).observational spatial memory (osm) refers to the ability of remembering food caches made by other individuals, enabling observers to find and pilfer the others' caches. within birds, osm has only been demonstrated in corvids, with more social species such as mexican jays (aphelocoma ultramarine) showing a higher accuracy of finding conspecific' caches than less social species such as clark's nutcrackers (nucifraga columbiana). however, socially dynamic corvids such as ravens (corvus corax) are c ...200818504626
the bird species of kumasir lake (kahramanmaras-turkey) and a view of environmental ethics on sustainable wetland management.kumasir lake is located next to towns of donuklu and fatih, nine km west of kahramanmaras city center the region of east mediterranean, turkey this lake is of crucial importance from the point of native and immigrant birds. we located 17 birdspecies in this area during our observations carried out in the spring and autumn of 2005-2006. these were ciconia ciconia l., anas platyrhynchos l., accipiter nisus l., accipiter brevipes l., fulica atra l., columba palumbus l., merops apiaster l., upupa ep ...200818972701
high seroprevalence of toxoplasma gondii and neospora caninum in the common raven (corvus corax) in the northeast of spain.in recent years, multiple cases of aggressive behavior of common ravens (corvus corax) have been reported by farmers in catalonia (ne spain), including attacking of newborn animals and consumption of dead foetuses. in the present study, seroprevalence of toxoplasma gondii and neospora caninum was determined from 113 legally trapped and released common ravens. t. gondii antibodies were found in 91 (80.5%; ci 95%:72-87) of 113 sera tested by the modified agglutination test. antibodies to n. caninu ...201121645913
corvids can decide if a future exchange is worth waiting for.evidence for time-dependent calculations about future rewards is scarce in non-human animals. in non-human primates, only great apes are comparable with humans. still, some species wait for several minutes to obtain a better reward in delayed exchange tasks. corvids have been shown to match with non-human primates in some time-related tasks. here, we investigate a delay of gratification in two corvid species, the carrion crow (corvus corone) and the common raven (corvus corax), in an exchange ta ...201121920957
causes of mortality and unintentional poisoning in predatory and scavenging birds in california.we documented causes of mortality in an opportunistic sample of golden eagles, turkey vultures and common ravens, and assessed exposure to several contaminants that have been found in carrion and common prey for these species.201426392875
unforeseen effects of supplementary feeding: ungulate baiting sites as hotspots for ground-nest predation.despite the ubiquity and magnitude of food provision to wildlife, our understanding of its ecological effects and conservation implications is very limited. supplementary feeding of ungulates, still one of the main paradigms of game management in europe, occurs in natural areas on an enormous scale. we investigated the indirect effects of this practice on nest predation risk in the polish eastern carpathians (bieszczady mountains). we hypothesized that the predators attracted to ungulate baiting ...201424599216
mycobacterium avium subsp. avium found in raptors exposed to infected domestic fowl.we report a case of a falcon breeding facility, where raptors (both diurnal and nocturnal) were raised in contact with domestic fowl (gallus gallus f. domesticus) infected by mycobacterium avium subsp. avium. fecal and environmental samples from 20 raptors and four common ravens (corvus corax) were collected. mycobacterium a. avium dna was detected in feces of four raptors (bald eagle [haliaeetus leucocephalus], eagle owl [bubo bubo], barn owl [tyto alba], and little owl [athene noctua]) using t ...201324283140
environmental contaminants in surrogates, foods, and feathers of california condors (gymnogyps californianus).california condor (gymnogyps californianus) foods and feathers, and turkey vultures (cathartes aura), common ravens (corvus corax), and their eggs were collected within the condor range to determine exposure of condors to environmental contaminants. samples were analyzed for organochlorines and trace elements. food items contained low concentrations of organochlorines and generally low concentrations of lead. dde was detected in all vulture carcasses and nearly all raven carcasses at generally m ...198624254546
a decorated raven bone from the zaskalnaya vi (kolosovskaya) neanderthal site, crimea.we analyze a radius bone fragment of a raven (corvus corax) from zaskalnaya vi rock shelter, crimea. the object bears seven notches and comes from an archaeological level attributed to a micoquian industry dated to between 38 and 43 cal kyr bp. our study aims to examine the degree of regularity and intentionality of this set of notches through their technological and morphometric analysis, complemented by comparative experimental work. microscopic analysis of the notches indicate that they were ...201728355292
a capture to remember: monitoring the health of avian scavengers on the pacific coast.because of concern over risks to the health of avian communities on the washington and oregon coasts, the nonprofit coastal raptors and other partners initiated a study where, to date, coastal raptors has live-captured and sampled 27 bald eagles (haliaeetus leucocephalus), 27 turkey vultures (cathartes aura), and 6 common ravens (corvus corax) for contaminants and disease study. in this article, the author highlights the events of one of the nearly 100 days on which trapping has occurred. an adu ...201526378672
craving ravens: individual 'haa' call rates at feeding sites as cues to personality and levels of fission-fusion dynamics?common ravens aggregate in large non-breeder flocks for roosting and foraging until they achieve the status of territorial breeders. when discovering food, they produce far-reaching yells or 'haa' calls, which attract conspecifics. due to the high levels of fission-fusion dynamics in non-breeders' flocks, assemblies of feeding ravens were long thought to represent anonymous aggregations. yet, non-breeders vary in their degree of vagrancy, and 'haa' calls convey individually distinct acoustic fea ...025984563
The use of referential gestures in ravens (Corvus corax) in the wild.Around the age of one year, human children start to use gestures to coordinate attention towards a social partner and an object of mutual interest. These referential gestures have been suggested as the foundation to engage in language, and have so far only been observed in great apes. Virtually nothing is known about comparable skills in non-primate species. Here we record thirty-eight social interactions between seven raven (Corvus corax) dyads in the Northern Alps, Austria during three consecu ...201122127056
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 aga ...200817908216
ravens, corvus corax, differentiate between knowledgeable and ignorant competitors.human social behaviour is influenced by attributing mental states to others. it is debated whether and to what extent such skills might occur in non-human animals. we here test for the possibility of ravens attributing knowledge about the location of food to potential competitors. in our experiments, we capitalize on the mutually antagonistic interactions that occur in these birds between those individuals that store food versus those that try to pilfer these caches. since ravens' pilfer success ...200516087417
ravens, corvus corax, follow gaze direction of humans around obstacles.the ability to follow gaze (i.e. head and eye direction) has recently been shown for social mammals, particularly primates. in most studies, individuals could use gaze direction as a behavioural cue without understanding that the view of others may be different from their own. here, we show that hand-raised ravens not only visually co-orient with the look-ups of a human experimenter but also reposition themselves to follow the experimenter's gaze around a visual barrier. birds were capable of vi ...200415306330
social bonds and rank acquisition in raven nonbreeder aggregations.complex social life has been characterized as cognitively challenging and recently, social relationships such as long-term social bonds and alliances have been identified as key elements for brain evolution. whereas good evidence is available to support the link between social relations and cognition in mammals, it remains unsatisfying for birds. here we investigated the role of avian social bonds in a nonbreeder aggregation of ravens, corvus corax, in the austrian alps. we individually marked 1 ...023264693
behavioural and hormonal stress responses to social separation in ravens, corvus corax.social life is profitable, but it facilitates conflicts over resources and creates interdependence between individuals. separating highly social animals triggers intense reactions aimed at re-establishing lost connections. less is known, however, about behavioural and physiological responses to separation in socially facultative species, where individuals temporarily form groups and may subsequently leave them. non-breeding common ravens (corvus corax) gather in large numbers at feeding and roos ...201728239221
development and characterization of microsatellite loci for common raven (corvus corax) and cross species amplification in other corvidae.a priority for conservation is the identification of endemic populations. we developed microsatellite markers for common raven (corvus corax), a bird species with a holarctic distribution, to identify and assess endemic populations in alaska.201526545581
systemic collyriclum faba (trematoda: collyriclidae) infection in a wild common raven ( corvus corax ).a hatch-year common raven ( corvus corax ) with subcutaneous and internal pseudocysts, filled with fluid, containing a pair of adult trematodes and numerous eggs consistent with collyriclum faba, died near a riverbank in california, us. while c. faba is incidental in many passeriformes, this case was a fatal systemic infection.201727690192
complex biogeographic history of a holarctic passerine.our analysis of the nd2 sequences revealed six clades within winter wrens (troglodytes troglodytes). these clades corresponded to six geographical regions: western nearctic, eastern nearctic, eastern asia, nepal, caucasus and europe, and differed by 3-8.8% of sequence divergence. differences among regions explained 96% of the sequence variation in winter wren. differences among individuals within localities explained 3% of the sequence variation, and differences among localities within regions e ...200415129966
waiting for better, not for more: corvids respond to quality in two delay maintenance tasks.self-control, that is, overcoming impulsivity towards immediate gratification in favour of a greater but delayed reward, is seen as a valuable skill when making future-oriented decisions. experimental studies in nonhuman primates revealed that individuals of some species are willing to tolerate delays of up to several minutes in order to gain food of a higher quantity or quality. recently, birds (carrion crows, corvus corone, common ravens, corvus corax, goffin cockatoos, cacatua goffiniana) per ...201425892738
hawk calls elicit alarm and defensive reactions in captive geoffroy's marmosets (callithrix geoffroyi).most descriptions of callitrichid antipredator behavior have come from observations of visual encounters with predators, but there is also anecdotal evidence suggesting that callitrichids may use auditory cues associated with raptors for the early detection of potential danger. in the present study, geoffroy's marmosets consistently reacted to the tape-recorded calls of a red-tailed hawk (buteo jamaicensis) with high-intensity antipredator behaviors. compared to the taped calls of a raven (corvu ...201412826731
threat-sensitive anti-predator defence in precocial wader, the northern lapwing vanellus vanellus.birds exhibit various forms of anti-predator behaviours to avoid reproductive failure, with mobbing-observation, approach and usually harassment of a predator-being one of the most commonly observed. here, we investigate patterns of temporal variation in the mobbing response exhibited by a precocial species, the northern lapwing (vanellus vanellus). we test whether brood age and self-reliance, or the perceived risk posed by various predators, affect mobbing response of lapwings. we quantified ag ...201627738383
sex determination in 58 bird species and evaluation of chd gene as a universal molecular marker in bird sexing.the aim of this research was to test the chd gene (chromo helicase dna-binding gene) as a universal molecular marker for sexing birds of relatively distant species. the chd gene corresponds to the aim because of its high degree of conservation and different lengths in z and w chromosomes due to different intron sizes. dna was isolated from feathers and the amplification of the chd gene was performed with the following sets of polymerase chain reaction (pcr) primers: 2550f/2718r and p2/p8. sex de ...201522553188
high risk of lead contamination for scavengers in an area with high moose hunting success.top predators and scavengers are vulnerable to pollutants, particularly those accumulated along the food chain. lead accumulation can induce severe disorders and alter survival both in mammals (including humans) and in birds. a potential source of lead poisoning in wild animals, and especially in scavengers, results from the consumption of ammunition residues in the tissues of big game killed by hunters. for two consecutive years we quantified the level lead exposure in individuals of a sentinel ...201425389754
a pelagic outbreak of avian cholera in north american gulls: scavenging as a primary mechanism for transmission?avian cholera, caused by the bacterium pasteurella multocida , is an endemic disease globally, often causing annual epizootics in north american wild bird populations with thousands of mortalities. from december 2006 to march 2007, an avian cholera outbreak caused mortality in marine birds off the coast of atlantic canada, largely centered 300-400 km off the coast of the island of newfoundland. scavenging gulls ( larus spp.) were the primary species detected; however, mortality was also identifi ...201627455197
social cognition in ravens.complex social life has been proposed as one of the main driving forces for the evolution of higher cognitive abilities in humans and non-human animals. until recently, this theory has been tested mainly on mammals/primates, whereas little attention has been paid to birds. indeed, birds provide a challenge to the theory, on one hand because they show high flexibility in group formation and composition, on the other hand because monogamous breeding pairs are the main unit of social structure in m ...201725893030
vancomycin-resistant enterococcus faecium with vana gene isolated for the first time from wildlife in slovakia.corvids have been identified as an important vector of vancomycin-resistant enterococci (vre) in several european countries. the aim of this study was to assess the prevalence of vre in wildlife in slovakia and to characterize vana-carrying vre. at the beginning of 2013, we collected 287 fecal samples of common raven (corvus corax) in petrovce and 99 fecal samples of rooks (corvus frugilegus) in kosice. samples were cultured selectively on slanetz-bartley agar with vancomycin and screened for va ...201626675586
social networks predict selective observation and information spread in ravens.animals are predicted to selectively observe and learn from the conspecifics with whom they share social connections. yet, hardly anything is known about the role of different connections in observation and learning. to address the relationships between social connections, observation and learning, we investigated transmission of information in two raven (corvus corax) groups. first, we quantified social connections in each group by constructing networks on affiliative interactions, aggressive i ...201627493780
with whom to dine? ravens' responses to food-associated calls depend on individual characteristics of the caller.upon discovering food, common ravens, corvus corax, produce far-reaching 'haa' calls or yells, which are individually distinct and signal food availability to conspecifics. here, we investigated whether ravens respond differently to 'haa' calls of known and unknown individuals. in a paired playback design, we tested responses to 'haa' call sequences in a group containing individually marked free-ranging ravens. we simultaneously played call sequences of a male and a female raven in two different ...025598542
socialized sub-groups in a temporary stable raven flock?a complex social life serves as one of the main driving forces behind the evolution of higher cognitive abilities in vertebrates. in birds, however, data are primarily derived from captive animals, which strongly contrast with free-flying birds in terms of the number of interaction partners as well as available space. in captivity, common raven corvus corax, nonbreeder groups show strong social bonds and complex tactical manoeuvring, whereas wild non-breeders are thought to resemble anonymous ag ...025892747
explorative innovators and flexible use of social information in common ravens (corvus corax) and carrion crows (corvus corone).innovation and social information use are influenced by individual characteristics, and are important for the creation and transmission of novel behavioral patterns. here, we investigated which individual factors predict innovation rates and social transmission of information in a comparative study with identically reared common ravens (corvus corax) and carrion crows (corvus corone corone; corvus corone cornix). in the innovation experiment (1), we presented the birds with a novel problem-solvi ...201627359074
haemosporidian infection in captive masked bobwhite quail (colinus virginianus ridgwayi), an endangered subspecies of the northern bobwhite quail.the avian haemosporidian parasites (phylum apicomplexa) are taxonomically diverse and cosmopolitan in distribution; infecting most bird families. sources of concern are reports of clinical haemosporidian infections in birds kept as part of zoo and aviary collections. recently, severe and acute mortality episodes have been reported in masked bobwhite quail (colinus virginianus ridgwayi), an endangered subspecies from the american southwest. two hundred and five eggs of the captive flock held in a ...201121726940
early development of gaze following into distant space in juvenile greylag geese (anser anser).visual co-orientation with another's gaze direction (gaze following) may provide important information about the location of food, social interactions or predators. gaze following has been shown in a variety of mammals, but only in few bird species, and has not been tested in precocial birds at all. it has been suggested that gaze following is an anti-predator behaviour, and in common ravens (corvus corax) and rooks (c. frugilegus), it emerges shortly after fledging, at a time when young birds l ...201121308474
knower-guesser differentiation in ravens: others' viewpoints matter.differentiating between individuals with different knowledge states is an important step in child development and has been considered as a hallmark in human evolution. recently, primates and corvids have been reported to pass knower-guesser tasks, raising the possibility of mental attribution skills in non-human animals. yet, it has been difficult to distinguish 'mind-reading' from behaviour-reading alternatives, specifically the use of behavioural cues and/or the application of associatively le ...201120826480
studies of trichomonad protozoa in free ranging songbirds: prevalence of trichomonas gallinae in house finches (carpodacus mexicanus) and corvids and a novel trichomonad in mockingbirds (mimus polyglottos).this study refutes the accepted dogma that significant pathogenic effects of trichomonas gallinae are limited to columbiformes and raptors in free ranging bird populations in north america. trichomonads were associated with morbidity and mortality amongst free ranging house finches (carpodacus mexicanus), mockingbirds (mimus polyglottos) and corvids (scrub jay: aphelocoma californica; crow: corvus brachyrhynchos; raven: corvus corax) in northern california. prevalence of trichomonad infection wa ...200919278788
effects of anthropogenic developments on common raven nesting biology in the west mojave desert.subsidized predators may affect prey abundance, distribution, and demography. common ravens (corvus corax) are anthropogenically subsidized throughout their range and, in the mojave desert, have increased in number dramatically over the last 3-4 decades. human-provided food resources are thought to be important drivers of raven population growth, but human developments add other features as well, such as nesting platforms. from 1996 to 2000, we examined the nesting ecology of ravens in the mojav ...200717913134
do common ravens (corvus corax) rely on human or conspecific gaze cues to detect hidden food?the ability of non-human animals to use experimenter-given cues in object-choice tasks has recently gained interest. in such experiments, the location of hidden food is indicated by an experimenter, e.g. by gazing, pointing or touching. whereas dogs apparently outperform all other species so far tested, apes and monkeys have problems in using such cues. since only mammalian species have been tested, information is lacking about the evolutionary origin of these abilities. we here present the firs ...200817762942
tuleremia in the raven (corvus corax). 1979492969
tolerance and reward equity predict cooperation in ravens (corvus corax).cooperative decision rules have so far been shown experimentally mainly in mammal species that have variable and complex social networks. however, these traits should not necessarily be restricted to mammals. therefore, we tested cooperative problem solving in ravens. we showed that, without training, nine ravens spontaneously cooperated in a loose-string task. corroborating findings in several species, ravens' cooperative success increased with increasing inter-individual tolerance levels. impo ...201526442633
subadult ravens generally don't transfer valuable tokens to conspecifics when there is nothing to gain for themselves.the extent to which humans help each other is extraordinary in itself, and difficult to explain from an evolutionary perspective. therefore, there has been a recent surge in studies investigating the evolution of prosocial behavior using a comparative approach. nevertheless, most of these studies have focused on primates only, and little is known about other animal orders. in a previous study, common ravens (corvus corax) have been shown to be indifferent to the gains of conspecifics. however, t ...201526175703
differences in exploration behaviour in common ravens and carrion crows during development and across social context.exploration is particularly important for young animals, as it enables them to learn to exploit their surroundings. it is likely to be affected by species ecology and social context, though there are few comparative, longitudinal studies that control for effects of early experience. here, we investigated group level exploration behaviour in two closely related and identically reared, generalist corvid species: common ravens (corvus corax) and carrion crows (c. corone, c. cornix), during developm ...201726097282
ravens intervene in others' bonding attempts.the competition for power in a complex social world is hypothesized to be a driving force in the evolution of intelligence. more specifically, power may be obtained not only by brute force but also by social strategies resembling human politics. most empirical evidence comes from primate studies that report unprovoked aggression by dominants to maintain power by spreading fear and third-party interventions in conflicts. coalitionary support has also been described in other animals and is often l ...201425455033
combinatory actions during object play in psittaciformes (diopsittaca nobilis, pionites melanocephala, cacatua goffini) and corvids (corvus corax, c. monedula, c. moneduloides).the playful (i.e., not overtly functional) combination of objects is considered a potential ontogenetic and phylogenetic precursor of technical problem solving abilities, as it may lead to affordance learning and honing of mechanical skills. we compared such activities in 6 avian species: 3 psittaciforms (black-headed caiques, red-shouldered macaws, and goffin cockatoos) and 3 corvids (new caledonian crows, ravens, and jackdaws). differences in the type and frequency of object combinations were ...201525437492
ecological and scaling analysis of the energy expenditure of rest, activity, flight, and evaporative water loss in passeriformes and non-passeriformes in relation to seasonal migrations and to the occupation of boreal stations in high and moderate latitudes.a unified system of bioenergetic parameters that describe thermal regulation and energy metabolism in many passerine and non-passerine species has been developed. these parameters have been analyzed as functions of ambient temperature, and bioenergetic models for various species have been developed. the level of maximum food energy or maximal existence metabolism (mpe) is 1.3 times higher in passerines than in non-passerines, which is consistent with the ratio of their basal metabolic rates (bmr ...201424984324
familiarity with the experimenter influences the performance of common ravens (corvus corax) and carrion crows (corvus corone corone) in cognitive tasks.when humans and animals interact with one another over an extended time span they familiarise and may develop a relationship, which can exert an influence on both partners. for example, the behaviour of an animal in experiments may be affected by its relationship to the human experimenter. however, few studies have systematically examined the impact of human-animal relationships on experimental results. in the present study we investigated if familiarity with a human experimenter influences the ...201424333226
will food-handling time influence agonistic behaviour in sub-adult common ravens (corvus corax)?discovering a food source may invoke either competition or cooperation, depending on many factors such as divisibility and accessibility. we experimentally investigated the influence of effort to procure food on the tolerance towards others during feeding. nine sub-adult captive ravens were tested in different foraging contexts that differed in foraging effort, namely three string-pulling conditions and two without pulling requirement. we expected that the effort to gain access to food would pos ...201424239503
ravens (corvus corax) are indifferent to the gains of conspecific recipients or human partners in experimental tasks.although cooperative behaviours are common in animals, the cognitive processes underpinning such behaviours are very likely to differ between species. in humans, other-regarding preferences have been proposed to sustain long-term cooperation between individuals. the extent to which such psychological capacities exist in other animals is still under investigation. five hand-reared ravens were first tested in an experiment where they could provide food to a conspecific at no cost to themselves. we ...201322890834
apes (gorilla gorilla, pan paniscus, p. troglodytes, pongo abelii) versus corvids (corvus corax, c. corone) in a support task: the effect of pattern and functionality.apes (gorilla gorilla, pan paniscus, p. troglodytes, pong abelii) and corvids (corvus corax, c. corone) are among the most proficient and flexible tool users in the animal kingdom. although it has been proposed that this is the result of convergent evolution, little is known about whether this is limited to behavior or also includes the underlying cognitive mechanisms. we compared several species of apes (bonobos, chimpanzees, gorillas, and orangutans) and corvids (carrion crows and common raven ...201222545765
loner or socializer? ravens' adrenocortical response to individual separation depends on social integration.non-breeding common ravens (corvus corax) live in complex social groups with a high degree of fission-fusion dynamics. they form valuable relationships and alliances with some conspecifics, while taking coordinated action against others. in ravens, affiliates reconcile their conflicts, console each other after conflicts with a third party, and provide each other with social support - all behaviors that presumably reduce corticosterone levels and alleviate stress. however, how well an individual ...201626631484
territorial raven pairs are sensitive to structural changes in simulated acoustic displays of conspecifics.human language involves combining items into meaningful, syntactically structured wholes. the evolutionary origin of syntactic abilities has been investigated by testing pattern perception capacities in nonhuman animals. new world primates can respond spontaneously to structural changes in acoustic sequences and songbirds can learn to discriminate between various patterns in operant tasks. however, there is no conclusive evidence that songbirds respond spontaneously to structural changes in patt ...201627346889
partner choice in raven (corvus corax) cooperation.although social animals frequently make decisions about when or with whom to cooperate, little is known about the underlying mechanisms of partner choice. most previous studies compared different dyads' performances, though did not allow an actual choice among partners. we tested eleven ravens, corvus corax, in triads, giving them first the choice to cooperate with either a highly familiar or a rather unfamiliar partner and, second, with either a friend or a non-friend using a cooperative string ...201627286247
ravens attribute visual access to unseen competitors.recent studies purported to demonstrate that chimpanzees, monkeys and corvids possess a basic theory of mind, the ability to attribute mental states like seeing to others. however, these studies remain controversial because they share a common confound: the conspecific's line of gaze, which could serve as an associative cue. here, we show that ravens corvus corax take into account the visual access of others, even when they cannot see a conspecific. specifically, we find that ravens guard their ...201626835849
[comparative study of the ability to solve a string-pulling task in corvidae].the ability of hooded crows (corvus cornix l.) and common ravens (corvus corax l.) to pull up a bait suspended from a horizontal perch by a string was tested. it was shown that some birds of both species successfully solved the string-pulling task. considerable inter-individual and inter-species differences in task performance are discussed.201020737894
carrion crows cannot overcome impulsive choice in a quantitative exchange task.the ability to control an immediate impulse in return for a more desirable - though delayed - outcome has long been thought to be a uniquely human feature. however, studies on non-human primates revealed that some species are capable of enduring delays in order to get food of higher quality or quantity. recently two corvid species, common raven (corvus corax) and carrion crow (corvus corone corone), exchanged food for a higher quality reward though seemed less capable of enduring delays when exc ...201222529833
two strings to choose from: do ravens pull the easier one?there are simple co-occurrences as well as functional relationships between events. one may assume that animals detect and use causation rather than mere co-variation. however, understanding causation often requires concepts of hidden forces. in string pulling, obstacles may hamper the access to food. here, i studied whether ravens have an abstract concept of effort. first, in a competitive situation, ravens (corvus corax) could choose one out of two strings. the strings differed in whether they ...201222437450
reciprocity of agonistic support in ravens.cooperative behaviour through reciprocation or interchange of valuable services in primates has received considerable attention, especially regarding the timeframe of reciprocation and its ensuing cognitive implications. much less, however, is known about reciprocity in other animals, particularly birds. we investigated patterns of agonistic support (defined as a third party intervening in an ongoing conflict to attack one of the conflict participants, thus supporting the other) in a group of 13 ...201222298910
influence of competitors on caching behaviour in the common raven, corvus corax.both territorial breeding common ravens and nonbreeding vagrants scatter-hoard carcass meat extensively. we show experimentally with four captive nonbreeders in a large semi-natural enclosure that common ravens alter their caching behaviour in the presence of conspecifics. when four birds were simultaneously given a small amount of food, which any one bird by itself could easily remove in several trips, all four birds decreased the latency to begin caching and increased caching speed. in contras ...19989819322
ontogeny of social relations and coalition formation in common ravens (corvus corax).the social intelligence hypothesis, originally developed for primates to explain their high intelligence and large relative brain size, assumes that challenges posed by social life in complex societies with many group members lead to the evolution of advanced cognitive abilities. in birds, pair-bonded species have larger brains than non-pair bonded species, indicating that the quality of social relationships better predicts social complexity than group size. ravens are a long-term monogamous and ...201725892846
olfactory acuity in the common raven (corvus corax).the efficacy with which ravens can locate concealed carrion and similar foods has been noted from antiquity. this ability has been claimed in folklore to indicate an acute sense of smell. contemporary opinion among ornithologists is that the sense of smell is weak at best in passerines, and particularly so in corvids which lack developed olfactory apparatus. four studies were performed to test whether ravens could find hidden food (fresh ground fish) under conditions where scent was presumed to ...19863960998
[operant vocal conditioning in the raven (corvus corax l.)]. 1979111841
["counting" experiments with ravens using "matching-from-sample" methods. a contribution on problem-solving behavior in higher animals].the research goal is divided into two parts: 1. detailed analysis of behavior in selection in a 6-choice matching-from-sample task. 2. discussion of all observed preferences on the basis of the models of sutherland and mackintosh and of miller, galanter and pribram. the experiments were run with 4 one-year-old ravens (corvus corax); two of them were probably 2 males. the design is similar to koehler's. in the task the correct responses were equally distributed between all stimuli and positions ( ...1976961120
body temperature regulation in the brown-necked raven (corvus corax ruficollis). ii. thermal changes in the plumage of ravens exposed to solar radiation. 19734145438
body temperature regulation in the brown-necked raven (corvus corax ruficollis). i. metabolic rate, evaporative water loss and body temperature of the raven exposed to heat stress. 19734145437
[on several kinetic plays of the common raven (corvus corax l.)]. 19665995353
gross anatomical and scanning electron microscopic studies of the oropharyngeal cavity in the european magpie (pica pica) and the common raven (corvus corax).there is no descriptive information about morphology of the oropharyngeal cavity including tongue, palate, and laryngeal region in corvidae family. this study not only presents the first definitive anatomical description of the structures in the oropharyngeal cavity of magpie and raven but also reviews and compares the scattered information on the morphology of the other avian species available in the literature. in this study, the organs of four birds (two magpies and two ravens) were used. the ...201221898667
random interbreeding between cryptic lineages of the common raven: evidence for speciation in reverse.dna sequence studies frequently reveal evidence of cryptic lineages in morphologically uniform species, many of which turn out to be evolutionarily distinct species. the common raven (corvus corax) includes two deeply divergent mtdna lineages: one lineage seems restricted to western north america and the other is holarctic in distribution. these deep clades hint of the possibility of cryptic species in the western united states. we tested this hypothesis in a population consisting of an equal pr ...201121518060
the first report of knemidocoptes intermedius fain et macfarlane, 1967 (acari: astigmata) in naturally infected european birds.according to the latest taxonomical review, the genus knemidocoptes (epidermoptidae: knemidocoptinae) comprises 15 species of mites responsible for skin lesions on the face, legs, or body of various wild and domestic birds. a number of 54 common ravens, corvus corax (aves: passeriformes: corvidae) were found dead (accidental poisoning) in march 2009, in târgu mureş, romania. one individual presented bilateral symptoms of scaly leg disease. microscopic examination revealed the presence of knemido ...201121503637
ravens reconcile after aggressive conflicts with valuable partners.reconciliation, a post-conflict affiliative interaction between former opponents, is an important mechanism for reducing the costs of aggressive conflict in primates and some other mammals as it may repair the opponents' relationship and reduce post-conflict distress. opponents who share a valuable relationship are expected to be more likely to reconcile as for such partners the benefits of relationship repair should outweigh the risk of renewed aggression. in birds, however, post-conflict behav ...201121464962
on the evolutionary and ontogenetic origins of tool-oriented behaviour in new caledonian crows (corvus moneduloides).new caledonian crows (corvus moneduloides) are prolific tool users in captivity and in the wild, and have an inherited predisposition to express tool-oriented behaviours. to further understand the evolution and development of tool use, we compared the development of object manipulation in new caledonian crows and common ravens (corvus corax), which do not routinely use tools. we found striking qualitative similarities in the ontogeny of tool-oriented behaviour in new caledonian crows and food-ca ...201125892825
stress associated with group living in a long-lived bird.many long-lived avian species adopt life strategies that involve a gregarious way of life at juvenile and sub-adult stages and territoriality during adulthood. however, the potential associated costs of these life styles, such as stress, are poorly understood. we examined the effects of group living, sex and parasite load on the baseline concentration of faecal stress hormone (corticosterone) metabolites in a wild population of common ravens (corvus corax). corticosterone concentrations were sig ...201121307048
[corvidae are able to understand the logical structure in string-pulling tasks].the ability of the corvidae to understand the logical structure in string-pulling tasks was studied in a set of experiments with varied position of strings. it was demonstrated that some hooded crows (corvus cornix l.) and common ravens (corvus corax l.) successfully completed the tasks where the strings were not intersected but placed so that the bait was positioned opposite the forepart of the empty string. hooded crows also solved the task where the baits were attached to both strings, but on ...201121260978
leading a conspecific away from food in ravens (corvus corax)?active misleading of conspecifics has been described as a social strategy mainly for primates. here we report a raven leading a competitor away from food in a social foraging task. four individuals had to search and compete for hidden food at color-marked clusters of artificial food caches. at the beginning of the experiment, a subordinate male found and exploited the majority of the food. as a result, the dominant male displaced him from the already opened boxes. the subordinate male then devel ...200415069605
consumption of big game remains by scavengers: a potential risk as regards disease transmission in central spain.understanding the role that facultative scavenger species may play in spreading infectious pathogens, and even becoming reservoirs for humans, domestic and wild ungulates or, on the contrary, preventing the spread of disease, requires a prior understanding of the pattern of carrion scavenging in specific scenarios. the objectives of this paper are (i) to describe the guild of vertebrate scavengers and (ii) to study the species-specific, habitat, and management-related factors involved in the usa ...201829552564
the quality of social relationships in ravens.the quality of a social relationship represents the history of past social interactions between two individuals, from which the nature and outcome of future interactions can be predicted. current theory predicts that relationship quality comprises three separate components, its value, compatibility and security. this study is the first to investigate the components of relationship quality in a large-brained bird. following methods recently used to obtain quantitative measures of each relationshi ...201025821236
mesopredators constrain a top predator: competitive release of ravens after culling crows.although predator control programmes rarely consider complex competitive interactions among predators, it is becoming clear that removal of larger 'superior' competitors often releases the 'inferior' ones and can precipitate trophic cascades. in contrast, our study indicates that culling hooded crows corvus cornix appears to release a larger competitor, the common raven corvus corax. ravens ranged more widely, and the predation of artificial nests was significantly faster (although total predati ...200919570777
the potential role of scavengers in spreading african swine fever among wild boar.understanding the transmission patterns of african swine fever (asf) among wild boar (sus scrofa) is an issue of major interest, especially in the wake of the current asf epidemic. given the high stability of asf-virus, there is concern about scavengers spreading infectious carcass material in the environment. here, we describe scavenging activities on 32 wild boar carcasses in their natural habitat in germany. using digital cameras, we detected 22 vertebrates at the study sites, thereof two mam ...201931391480
vocal recognition of a nest-predator in black grouse.corvids count among the important predators of bird nests. they are vocal animals and one can expect that birds threatened by their predation, such as black grouse, are sensitive to and recognize their calls. within the framework of field studies, we noticed that adult black grouse were alerted by raven calls during periods outside the breeding season. since black grouse are large, extremely precocial birds, this reaction can hardly be explained by sensitization specifically to the threat of nes ...201930891367
urbanization and cattle density are determinants in the exposure to anticoagulant rodenticides of non-target wildlife.the persistence and toxicity of second generation anticoagulant rodenticides (sgars) in animal tissues make these compounds dangerous by biomagnification in predatory species. here we studied the levels of sgars in non-target species of wildlife and the environmental factors that influence such exposure. liver samples of terrestrial vertebrates (n = 244) found dead between 2007 and 2016 in the region of aragón (ne spain) were analysed. the presence of sgars was statistically analysed with binary ...201930390453
rich pickings near large communal roosts favor 'gang' foraging by juvenile common ravens, corvus corax.ravens (corvus corax) feed primarily on rich but ephemeral carcasses of large animals, which are usually defended by territorial pairs of adults. non-breeding juveniles forage socially and aggregate in communal winter roosts, and these appear to function as 'information centers' regarding the location of the rare food bonanzas: individuals search independently of one another and pool their effort by recruiting each other at roosts. however, at a large raven roost in newborough on anglesey, north ...200919240813
changes in the body temperature during the annual cycle and metabolic rate in the raven corvus corax at winter ambient temperatures. 201619024689
the performance of ravens on simple discrimination tasks: a preliminary study.recent studies suggest the existence of primate-like cognitive abilities in corvids. although the learning abilities of corvids in comparison to other species have been investigated before, little is known on how corvids perform on simple discrimination tasks if tested in experimental settings comparable to those that have been used for studying complex cognitive abilities. in this study, we tested a captive group of 12 ravens (corvus corax) on four discrimination problems and their reversals. i ...200825948877
enhanced social learning between siblings in common ravens, corvus corax.it has been suggested that social dynamics affect social learning but empirical support for this idea is scarce. here we show that affiliate relationships among kin indeed enhance the performance of common ravens, corvus corax, in a social learning task. via daily behavioural protocols we first monitored social dynamics in our group of captive young ravens. siblings spent significantly more time in close proximity to each other than did nonsiblings. we subsequently tested birds on a stimulus enh ...200825948875
when, what, and whom to watch? quantifying attention in ravens (corvus corax) and jackdaws (corvus monedula).complex social life requires monitoring of conspecifics. the amount and focus of attention toward others has been suggested to depend on the social relationships between individuals. yet there are surprisingly few experiments that have tested these assumptions. this study compared attention patterns toward conspecifics in two corvid species, ravens (corvus corax) and jackdaws (corvus monedula). birds were confronted with affiliated and non-affiliated conspecifics engaged in foraging and object m ...200718085921
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 f ...200818022623
phylogeographic patterns in widespread corvid birds.intraspecific genetic diversity and phylogeography of corvus corone was investigated using the mitochondrial (mt) control region as a molecular marker. a split into two distinct mt lineages was observed. one represents individuals from a wide geographic range spanning from england to the russian far east (kamchatka), while the other one was found in the primorye and khabarovsk regions (southern parts of russian far east) as well as japan. for comparison, we investigated several widespread palear ...200717920300
pilfering ravens, corvus corax, adjust their behaviour to social context and identity of competitors.like other corvids, food-storing ravens protect their caches from being pilfered by conspecifics by means of aggression and by re-caching. in the wild and in captivity, potential pilferers rarely approach caches until the storers have left the cache vicinity. when storers are experimentally prevented from leaving, pilferers first search at places other than the cache sites. these behaviours raise the possibility that ravens are capable of withholding intentions and providing false information to ...200616909235
cryptic genetic variation and paraphyly in ravens.widespread species that are morphologically uniform may be likely to harbour cryptic genetic variation. common ravens (corvus corax) have an extensive range covering nearly the entire northern hemisphere, but show little discrete phenotypic variation. we obtained tissue samples from throughout much of this range and collected mitochondrial sequence and nuclear microsatellite data. our study revealed a deep genetic break between ravens from the western united states and ravens from throughout the ...200011197122
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 opposit ...199910202087
solution acceptance by common ravens (corvus corax) given two-bottle preference tests.two-bottle tests of solution acceptance were conducted in an outdoor aviary with eight common ravens (corvus corax). aqueous concentrations of the following chemicals were used: five common sugars, three salts, two acids, quinine hydrochloride, and sodium saccharin. solution acceptance, as recorded for the different ravens on each test, was the percentage of preference shown for a test solution over water (comparison solution). mid-range saccharin concentrations (0.10% to 0.80% [w/w]) were prefe ...19902236395
functional morphology and integration of corvid skulls - a 3d geometric morphometric approach.sympatric corvid species have evolved differences in nesting, habitat choice, diet and foraging. differences in the frequency with which corvid species use their repertoire of feeding techniques is expected to covary with bill-shape and with the frontal binocular field. species that frequently probe are expected to have a relatively longer bill and more sidewise oriented orbits in contrast to species that frequently peck. we tested this prediction by analyzing computed tomography scans of skulls ...200919128499
novel object exploration in ravens (corvus corax): effects of social relationships.social context has been shown to encourage, or to delay object exploration and learning. this ambiguity might be due to factors such as social relationships and personality of the individuals involved. here, we investigated in ravens (corvus corax) individuals' consistency in response to novel objects over development and across contexts: alone versus social. in the social setting we focussed on the effects of social relationships on social facilitation during the approach to novel objects. we t ...200616682154
individual and sex differences in learning abilities of ravens.behavioral and physiological characteristics of individuals within the same species have been found to be stable across time and contexts. in this study, we investigated individual differences in learning abilities and object and social manipulation to test for consistency within individuals across different tasks. individual ravens (corvus corax) were tested in simple color and position discrimination tasks to establish their learning abilities. we found that males were significantly better in ...200616675158
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 lim ...200616499703
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