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Helpers‐at‐the‐nest in Carrion Crows Corvus corone corone
... Similarly to ravens, carrion crows (Corvus corone) live in flexible social systems, characterised by seasonal variation and fission-fusion dynamics (Braun et al. 2012;Richner 1990) and also exhibit advanced cognitive abilities (Emery & Clayton 2004;Hoffmann et al. 2011; Marzluff & Angell 2005). Both species leave their parents at the end of their first summer and become part of non-breeder groups that forage, roost, and socialize together. ...
... Here, we address this question by investigating the use of post-conflict behaviours in a newly formed group of captive juvenile carrion crows (Corvus corone corone), with relationships still changing and developing. Similar to ravens, crows live in flexible social systems, characterised by seasonal variation and fission-fusion dynamics (Braun et al. 2012;Richner 1990). Crows leave their parents at the end of their first summer and become part of non-breeder groups that forage, roost and socialise together. ...
... Nevertheless, evidence for this is lacking. Causes could also be sought in different feeding and/or social behaviour (Cramp, 1993;Richner, 1990). However, Syrov a et al. (2016) provided no support for this either in their study. ...
An integral characteristic of all predators is their size, which affects, among other things, their food preferences, and the ability of their prey to fight them off. Several studies have already found, unsurprisingly, that birds discriminate between and respond differently to predators of different sizes. The red-backed shrike, Lanius collurio, aggressively attacks the Eurasian jay, Garrulus glandarius, a common nest predator, whereas it remains passive towards the carrion crow, Corvus corone, which also commonly plunders passerine nests. A possible explanation may reside in the larger body size of crows. In our experiments, we exposed red-backed shrikes to downsized crow dummies and enlarged jay dummies. The shrikes responded to the largest jays with less aggression, suggesting that aggression towards the largest jays would increase risk of injury to parent shrikes and/or not increase the likelihood of offspring survival. In contrast, aggression increased only slightly towards the crows with reduced size. Thus, there was no general effect of body size on the attack rate of shrikes to the presented dummies. In the case of the crow, an alternative antipredator strategy, guarding and not attacking the predator, might affect the behaviour of some shrike parents. These results suggest that body size is one of the key parameters in the recognition of predators by red-backed shrikes, but it is evaluated differently in nest defence against two distinct predator species.
... Here, we address this question by investigating the use of post-conflict behaviours in a newly formed group of captive juvenile carrion crows (Corvus corone corone), with relationships still changing and developing. Similar to ravens, crows live in flexible social systems, characterised by seasonal variation and fission-fusion dynamics (Braun, Walsdorff, Fraser, & Bugnyar, 2012;Richner, 1990). Crows leave their parents at the end of their first summer and join non-breeder groups that forage, roost and socialise together. ...
Conflicts are costly because they can damage social relationships. To buffer conflicts, various species use post-conflict behaviour, such as reconciliation or third-party affiliation. Both behaviours have predominantly been studied in non-human primates. However, recently, studies revealed post-conflict behaviour in other mammalian and some bird species (e.g., corvids). While third-party affiliation has been reported in several corvid species, reconciliation has only rarely been observed. The social structure of the studied groups has been postulated as a reason for the absence of reconciliation. Here, we investigated whether post-conflict behaviours in corvids indeed mirror the relationship structure. We studied the behaviour of a newly established group of juvenile carrion crows (Corvus corone corone), where pair bonds had not yet been established. We applied a combination of observations and food monopolisation experiments to quantify the use of post-conflict behaviours. Provisioning food in one or two pieces induced different patterns of aggression during feeding and differently affected the affiliation patterns after feeding. Specifically, victims of severe aggression affiliated with third parties after conflicts in the two-piece condition, while aggressors affiliated with victims of mild aggression in the one-piece condition. We thus provide the first evidence that a corvid species, crows, flexibly engage in both third-party affiliation and reconciliation.
... Scrub-jays are semi-territorial and flock in small groups outside of breeding season (Balda, Kamil, & Bednekoff, 1996). Carrion crows live in territorial pairs, similar to Eurasian jays as well as ravens , and breed mostly unassisted (Richner, 1990). ...
Theory of mind refers to the ability to attribute mental states to others and to predict their behaviour based on inferences about their mental states, for example their perception, desires, or beliefs. Forty years ago, research on theory of mind originated from the question of whether or not chimpanzees (Pan troglodytes) have a theory of mind, a question that – after all this time – is still debated. In the present thesis, I investigate theory of mind and its precursors in birds of the crow family, specifically Eurasian jays (Garrulus glandarius), California scrub-jays (Aphelocoma californica), and carrion crows (Corvus corone corone). Corvids have been reported to possess theory of mind-like abilities. This qualification reflects the fact that most research on theory of mind in these birds has revolved around the ability to respond to perceptual and desire states of conspecifics, and so far has not produced evidence for or against an ability to also respond to others’ beliefs. Further, it is unclear which mechanisms could be the basis of corvids’ abilities. Thus, there are two open questions in regard to corvid theory of mind my thesis aims to address. To address these questions, first, I investigated the ability of Eurasian jays to respond to the false belief of a conspecific in a caching paradigm, where the knowledge of a conspecific observer about the accessibility of two caching sites was manipulated (Chapter 2). In Chapter 3 I explore which behavioural cues might present the basis of the jays’ ability to respond to the desire of a conspecific in a caching context. In Chapter 4, I report a study on biological motion perception in scrub-jays, a phenomenon suggested to be crucial for the detection of social agents. In Chapter 5, I assess scrub-jays’ sensitivity to gaze of a human and a conspecific. Finally, in Chapter 6, I report a study investigating the face inversion effect in carrion crows, an effect that is indicative of a ‘special’ relevance of faces. I conclude by discussing how the presented studies could help us inform our understanding of corvid theory of mind-like abilities.
... In Italy, on the contrary, the absence of adult Carrion Crows on the nesting territories in the postbreeding period deprives the young individuals of the incentive to stay there, which, in turn, excludes the possibility of cooperative breeding (Baglione et al., 2005). Yearround territoriality is inherent to the Carrion Crow population in Switzerland (Richner, 1990), for which helpers were found in 6% of the nests (Baglione et al., 2005). ...
The family of corvids differs from most other passerines by the significant number of species (at least 33) in which the feeding of nestlings and fledglings involves not only parents, but also individuals from their already grown broods (one-year-old and older). A review of the currently known data on cooperative breeding (or helping behavior) in corvids is given. This paper discusses factors that can contribute to the manifestation of delayed dispersion of young birds and the appearance of their helping behavior. It emphasizes the importance of long-term social bonds between parent birds and their offspring in delayed dispersion. At the heart of such social relationships is the tolerance of adult birds to their offspring and prolonged care for the young birds. The appearance of irregular helpers near the nests may be a prerequisite for the emergence of the helping behavior in certain family groups and populations.
Cooperative breeding (i.e. when alloparents care for the offspring of other group members) has been studied for nearly a century. Yet, inconsistent definitions of this breeding system still hamper comparative research. Here, we identify two major inconsistencies, discuss their consequences and propose a way forward. First, some researchers restrict the term 'cooperative breeding' to species with non-breeding alloparents. We show that such restrictive definitions lack distinct quantitative criteria to define non-breeding alloparents. This ambiguity, we argue, reflects the reproductive-sharing continuum among cooperatively breeding species. We therefore suggest that cooperative breeding should not be restricted to the few species with extreme reproductive skew and should be defined independent of the reproductive status of alloparents. Second, definitions rarely specify the type, extent and prevalence of alloparental care required to classify species as cooperative breeders. We thus analysed published data to propose qualitative and quantitative criteria for alloparental care. We conclude by proposing the following operational definition: cooperative breeding is a reproductive system where >5% of broods/litters in at least one population receive species-typical parental care and conspecifics provide proactive alloparental care that fulfils >5% of at least one type of the offspring's needs. This operational definition is designed to increase comparability across species and disciplines while allowing to study the intriguing phenomenon of cooperative breeding as a behaviour with multiple dimensions.
As part of a long-term population study, we investigated the social and reproductive behaviour of Jackdaws in a colony with 70 nestboxes and about 180 birds near Jena, Germany. Three kinds of social relationships were recognized between breeding pairs and non-breeding birds: 'Followers' were associated with a breeding pair, functioning as potential replacement mates and behaving either neutrally or cooperatively with resident pairs. They were mostly young birds without breeding experience and of unknown sex. 'Visitors' were birds of either sex that did not complete, or had lost, their own clutch during incubation. They appeared to be of low social rank and interfered little with resident pairs. 'Usurpers' were also failed breeders, but they had lost their nestlings late during rearing. They remained paired and made aggressive attempts to take over nestboxes from resident pairs. A parentage analysis using multilocus DNA fingerprinting was carried out on 15 broods with 39 nestlings, mostly of pairs associated with followers. It revealed one extra-pair offspring and ruled out intraspecific brood parasitism and pseudo-parasitism.
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Trios (1♂-2♀) of Carrion Crows were observed in three territories. They occurred when the alpha female had failed to breed for several years. In two cases, the new individuals were fledglings from neighboring territories. One of them laid eggs when two years old. The second females bred successfully after the alpha females had died or disappeared. Temporary bigamy might be involved during the process of mate change. Techniques normally used when studying primates applied to individual identification of Carrion Crows are effective, provided that unchanging characteristics of the individuals concerned are systematically recorded and detailed long-term observations based on such characteristics are possible.
A large number of bird species live in stable groups, and this sets the scene for complex social behaviours, such as cooperative breeding. The vast majority of groups consist of families which arise when young postpone dispersal and remain with their parents beyond independence. However, the factors selecting for the evolution of families and thus also cooperative breeding among birds, are still a challenging puzzle. The currently accepted key explanation for the evolution of families and cooperative breeding focuses on dispersal constraints. While constraints successfully explain within-population dispersal decisions, they fail as an ultimate explanation because offspring in the majority of species face some sort of dispersal constraint, yet still disperse promptly. Recent alternative explanations focus on the role of philopatry and nepotism, and emphasise a key role of life-history for the evolution of families. Phylogenetic analyses and field studies have indicated that living in family groups is far more widespread among long-lived species than short-lived ones. A long lifespan gives parents the opportunity to invest in their offspring for a prolonged period, while this option is less viable for short-lived species. Thus, living with nepotistic parents provides offspring with direct fitness benefits that can select for the evolution of family living beyond independence. Nevertheless this generalisation is brought into question since many long-lived bird species do not live in family groups. An alternative approach attempts to explain family living through the variation in territory quality. Here the incentive to remain with the parents is created by the availability of resources on the natal territory independent of parental nepotism. However, there is not only cooperation, conflicts are also common place in families. Living with independent, sexually mature offspring can lead to conflicts through a change in resource availability or the death of a parent. Therefore families can be expected to be dynamic societies where both parent and offspring decisions depend on each other, and family maintenance depends upon the current ecological conditions. Based on this background, here we review recent studies that have investigated the processes that facilitate family formation, and which highlight both cooperation and conflict that arises from living in family groups. We examine the strengths of current models and explore ideas for a more coherent framework in which to understand prolonged family association in birds. We argue that two paths lead to family living, depending on the life-history. In medium-short lived species where the postponement of independent reproduction comes at a high cost, offspring can benefit from an association with their parents until the next breeding season. In longer-lived species, offspring actually benefit from postponing the onset of independent reproduction, making family living beyond the first year of life an adaptive strategy, and giving the option for cooperative breeding. These processes are illustrated by 5 species-specific case studies. We then finally suggest a number of key questions to developing a deeper understanding of the evolution of family living in birds.
Two populations of carrion crows were studied, one in an urban and another in an agricultural environment in SW Switzerland. Chicks in the urban habitat gain weight more slowly, take longer to reach fledging weight and are significantly lighter at fledging than chicks in the agricultural habitat. For the weight curves, chicks in the urban habitat show significantly lower values for both parameters a and k of the logistic equation. Tarsus growth is slower for chicks in the urban habitat, but in contrast to weight gain, growth of tarsus is not prolonged. For tarsus growth the parameter k is identical in the 2 habitats, but urban chicks show significantly lower values for the parameter a. Tarsus length is fixed by the age of fledging. Chicks in the urban habitat have shorter tarsi at fledging. Growth of wing is slower in the urban habitat. Tarsus length of territory-holding adults was measured in both habitats and a critical minimum size for territory acquisition empirically established. Of all fledglings raised in the urban habitat, 79% fall below this critical size and will therefore be unable to acquire a territory and thus be excluded from breeding; only 24% of fledglings raised in the agricultural habitat will be excluded. Successful parents in the agricultural habitat fledge, on average, 2.7 chicks per year, parents in the urban habitat 1.5 chicks, 36% of all territory holders in the agricultural habitat fledge young, 39% in the urban habitat. Since a much higher percentage of fledged chicks reach the critical body size in the agricultural habitat, these parents reach a Darwinian fitness 5 times higher than parents in the urban habitat. -from Author
The ecological factors underlying the evolution of helping behavior in birds and mammals are examined. I argue that a necessary first step for the evolution of cooperative breeding is a substructuring of the population into small, stable, social units; in most known cases these are extended-family units. The ecological conditions leading to the development of such units are explored, and a general model is presented that emphasizes ecological constraints that limit the possibility of personal, independent breeding. When severe constraints occur, selection will favor delayed dispersal and continued retention of grown offspring within their natal units. Differing proximate factors can be responsible for limiting the option of personal reproduction. In stable, predictable environments where marginal habitat is scarce, high population density and resulting habitat saturation can lead to a severe shortage of territory openings (Brown 1974; Koenig and Pitelka 1981). This decreases the chance for independent est...
An overview of the extensive and frequently controversial literature on communally breeding birds developed since the early 1960s, when students of evolution began to examine sociality as a product of natural selection. Jerram Brown provides original data from his own theoretical and empirical studies and summarizes the wide array of results and interpretations made by others.Originally published in 1987.The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
The behaviour of helpers at nests of Northwestern Crows was studied on Mandarte Island and Mitlenatch Island, British Columbia. Not all nests had a helper and there was only one helper per nest. Helpers participated in varying degrees in the defence of the territory and nest, feeding of the nestlings and fledglings and they cached food on the territory. Adult males fed helpers, and helpers obtained most of their food on the adults' territory. Adults with helpers laid larger clutches and produced more fledglings per nest than adults without helpers. It is suggested that cooperative breeding in the Northwestern Crow is of recent origin.
Variation in weight, wing length and bill length in a population of grey-crowned babblers is influenced primarily by sex and age, but correlations with size of social unit, with reproductive success, and with vegetation are also detectable (Table 1). The latter correlations vary with sex, age, and status as helper or breeder. Differential wear according to behavioral role, competition for status, incubation, and inheritance are discussed as possible causal mechanisms. Helpers were not detectably smaller in any dimension than breeders of the same age and sex. Male and female non-breeding helpers differ in patterns of morphological correlation, suggesting that they have different behavioral roles. Breeding males have a unique pattern of morphological correlation, suggesting that their foraging behavior differs from breeding females and non-breeders.
Piñon Jays live year round in a social flock that may number from 50 to 300 birds. Young birds form into creches immediately after leaving the nest. Begging calls are important in the formation of creches. In these creches young interact with each other and with their parents. This study was designed to 1. gain an understanding of the parent-young relationships, 2. investigate the operation of the creche, 3. determine the relationship of young jays to other cohorts in the flock.
Young birds begged and were sometimes fed by foster parents in addition to their own parents. Parent-young recognition, however, is shown to be a strong component of the social system. Young removed from the nest at 20 days of age and transported 1.9 km from the nest-site were recognized by their parents 21 hr after removal. Another brood of young learned to beg from these parents, and were eventually fed by them. In a wire enclosure in a field situation foster feeding was also observed. In both cases, males were more prone to feed foster young than females.
Nestlings at 14 days of age are incapable of giving loud begging calls. These young apparently recognize their parents. Parents appear not to recognize young of this age when they are removed from the nest. Location of the nest is sufficient information for locating nestlings, but young, by recognizing their parents' calls can be prepared to receive food rapidly. This may be an important anti-predator devise as food is transferred rapidly and efficiently.
Fledged young concealed in paper bags were recognized by their parents, thus proving that vocalizations are an important component of parent-young recognition and may serve to reduce confusion in the creche by enhancing contact between parent and young.
Social interactions of young birds among themselves and also with other cohorts were systematically recorded at a feeding station. During the summer when creches roamed as units, young birds engaged in a relatively large number of aggressive interactions among themselves and few interactions with other cohorts. No older cohort consistently dominated the young. In fall and early winter when the entire flock had reformed the aggressiveness of the young birds declined dramatically. All cohorts engaged the young less than expected and only adult males clearly dominated them. During courtship and nesting the yearlings acted aggressively at about the same frequency as older females but less than older males. Most cohorts still engaged yearlings less than expected.
Throughout their first year, young birds appear to enjoy a special status in the flock and are deferred to by most older birds. Young birds did not act like subordinate birds in terms of their approach to the feeder or in their temporal pattern of feeding. Evidence suggests that parent-young recognition may remain in affect for longer than one year.
The feeding of young from other nests may occur as a means to keep the creche relatively quiet so as not to attract predators or it may result because males occasionally are successful in stealing copulations from females other than their mates. Under these circumstances kin-selection arguments cannot be applied independent of individual selection. Apparent altruistic acts appear to have a low cost to benefit ratio.
Colonial nesting and the creching of young probably first evolved among non-related individuals. These acts allow members to forage as a flock, mutually defend nests, and divide up the labor of protection of the young. Inclusive fitness will be further enhanced if these acts benefit relatives, thus a premium should be placed on recruiting kin into the group but not to the total exclusion of strangers.
The role of age, sex and body size as determinants of dominance status was studied in a winter flock of individually marked carrion crows, Corvus corone corone, and their importance in gaining access to a clumped food source assessed. Sex, age and body size determined, in decreasing order of importance, the outcome of agonistic encounters between individuals. Males won over females, adults over juveniles, and within the same age-sex classes, the large birds over the small ones. Males had access to clumped food for a higher proportion of time than females, and large individuals for a higher proportion than small individuals. Juvenile males, however, had as much access to the food as adult males, achieving this through shorter and more frequent feeding bouts. Thus the determinants of dominance, as assessed from the dyadic interactions, did not strictly correspond to the determinants of food access. The rank order of age, sex and body size as determinants of dominance is important, since different orders determine which members of a population will be subordinate. If subordination has consequences for survival, access to resources, dispersal and other life-history parameters, this order is important in predicting which individuals will survive, breed, disperse or migrate.