Social dominance in captive jackdaws (Corvus monedula)

Social hierarchy was studied in two flocks (14 and 10 individuals, respectively) of captive jackdaws. Parent birds acquired high-ranking positions during the nesting period. Outside the breeding season the hierarchy seemed to be stable. Males generally dominated females. When the top-ranking male arrived at the feeding place it tended to supplant one of the feeding birds rather than choose an unoccupied site.     

Recipients affect prosocial and altruistic choices in jackdaws, Corvus monedula

Other-regarding preferences are a critical feature of human cooperation but to what extent non-human animals exhibit these preferences is a matter of intense discussion. We tested whether jackdaws show prosocial behaviour (providing benefits to others at no cost to themselves) and altruism (providing benefits to others while incurring costs) with both sibling and non-sibling recipients. In the prosocial condition, a box was baited on both the actor's and the recipient's side (1/1 option), whereas another box provided food only for the actor (1/0 option). In the altruistic condition, the boxes contained food for either the actor (1/0 option) or the recipient (0/1 option). The proportion of selfish (1/0 option) and cooperative (1/1 and 0/1 option, respectively) actors' choices was significantly affected by the recipients' behaviour. If recipients approached the boxes first and positioned themselves next to the box baited on their side, trying to access the food reward (recipient-first trials), actors were significantly more cooperative than when the actors approached the boxes first and made their choice prior to the recipients' arrival (actor-first trials). Further, in recipient-first trials actors were more cooperative towards recipients of the opposite sex, an effect that was even more pronounced in the altruistic condition. Hence, at no cost to the actors, all recipients could significantly influence the actors' behaviour, whereas at high costs this could be achieved even more so by recipients of different sex. Local/stimulus enhancement is discussed as the most likely cognitive mechanism to account for these effects.     

Daily distribution of sleep states in the jackdaw, Corvus monedula

Polygraphic and behavioral studies of the jackdaws Corvus monedula have revealed a strong influence of the natural day-night cycle on their daily wakefulness-sleep activity. The jackdaws were behaviorally active during the light part of the photoperiod. The daily distribution of slow wave sleep (SWS) was symmetric and that of paradoxical sleep (PS) was asymmetric. The amount of PS was greater in the second half of the night than in the first. Short and intermediate length episodes occurred almost homogeneously throughout the night. The longest sleep episodes clustered toward the middle part of the night and did not occur in the periods following onset of sleep and before the end of sleep.     

Preferential learning from non-affiliated individuals in jackdaws (Corvus monedula)

It has been suggested that affiliated social relations may facilitate information transfer between individuals. We here tested this rarely examined hypothesis with juvenile and adult jackdaws (Corvus monedula) in three stimulus enhancement tasks, both in a non-food context (experiment 1) and in a food context (experiments 2 and 3). We first show that siblings and pair partners maintain stronger bonded social relations than do non-siblings and non-pair partners. We therefore tested individuals in sibling and non-sibling dyads and, later in ontogeny, in pair and non-pair dyads. Jackdaws either did not learn from any other conspecific (experiment 1), or they learned from non-affiliated individuals (non-siblings, non-pair partners in experiments 2 and 3). This may be related to two main characteristics of jackdaws' affiliated relationships. First, affiliates share food at a high rate and may rely on their knowledgeable partners to secure food rather than learning from them. Second, affiliates spend most time in close spatial proximity to each other which increases the probability that they simultaneously experience occurrences in their environment. Hence, spatially more distant individuals, which are more likely to be non-affiliated, face different foraging situations and may therefore provide more relevant information which may lead to selective social learning.     

Strict monogamy in a semi-colonial passerine: the Jackdaw Corvus monedula

In this study we used DNA fingerprinting to provide an accurate measure of paternity in a nest-box colony of Jackdaws. The species is a semi-colonial, socially monogamous passerine which establishes long-term pair bonds. Parents raise a single annual brood in which 50% brood reduction is commonplace. However, nest sites are a limited resource, non-breeding adults are also common around colonies and males are frequently separated from their incubating females during the fertile egg-laying period so that opportunities arise for extra-pair copulation. The parentage analysis, however, revealed no cases of extra-pair fertilisation (EPF) or intra-specific brood parasitism. Therefore fledgling output or survival is likely to be a good measure of individual reproductive success in this species. The lack of EPFs is not explained by nesting synchrony and we discuss the relative costs and benefits to females of seeking EPFs; the likelihood that paternal care and a life-history strategy similar to many long-lived non-passerines may also constrain the species to monogamy.     

Sex-specific hatching order, growth rates and fledging success in jackdaws Corvus monedula

In the jackdaw Corvus monedula , eggs hatch asynchronously with the youngest chicks in the brood often starving to death. So far, it is unknown whether there are sex differences in vulnerability to starvation. Adult females are smaller than males suggesting that daughters should be cheaper to produce than sons and so, less likely to starve when nest conditions are poor. Here, we determine whether sex, laying order and season interact to influence growth and fledging success. In a nestbox population of jackdaws, we found a non-significant female bias at both hatching (112:120) and fledging (37:52). Generalised linear models revealed that parents seemed to be investing differently in sons and daughters depending on their chances of success. Broods produced late in the season were significantly female biased, particularly those from small clutches. Females hatched towards the end of the season, when conditions were poor, were more likely to fledge than males. Nestlings that were relatively large at hatching were more likely to fledge. This effect was particularly important for last hatched individuals. Overall, males had a higher mortality rate than females. The most likely cause was starvation due to higher energetic requirements, because males were larger than females at fledging. We suggest that in species with brood reduction, sex-biased mortality may be at least as important as primary sex ratio manipulation in determining avian sex ratios.     

Salient eyes deter conspecific nest intruders in wild jackdaws (Corvus monedula)

Animals often respond fearfully when encountering eyes or eye-like shapes. Although gaze aversion has been documented in mammals when avoiding group-member conflict, the importance of eye coloration during interactions between conspecifics has yet to be examined in non-primate species. Jackdaws (Corvus monedula) have near-white irides, which are conspicuous against their dark feathers and visible when seen from outside the cavities where they nest. Because jackdaws compete for nest sites, their conspicuous eyes may act as a warning signal to indicate that a nest is occupied and deter intrusions by conspecifics. We tested whether jackdaws’ pale irides serve as a deterrent to prospecting conspecifics by comparing prospectors’ behaviour towards nest-boxes displaying images with bright eyes (BEs) only, a jackdaw face with natural BEs, or a jackdaw face with dark eyes. The jackdaw face with BEs was most effective in deterring birds from making contact with nest-boxes, whereas both BE conditions reduced the amount of time jackdaws spent in proximity to the image. We suggest BEs in jackdaws may function to prevent conspecific competitors from approaching occupied nest sites.     

Effects of experimental food provisioning on reproduction in the Jackdaw Corvus monedula, a semi-colonial species

Two Jackdaw Corvus monedula colonies were given supplementary food before and during breeding in 1983. Breeding density and cavity use were compared with those of the same colonies in previous years, when no food was provided. Predation rate and reproductive parameters were compared with those in the same colonies in previous years and with those of two control colonies, without experimental food. Jackdaws preferred safe cavities with small minimum nest-entrance dimensions and avoided those with a high risk of nest predation. In experimental (fed) colonies, however, there was a tendency to use all cavities, which resulted in an increased breeding density. No nests were preyed upon by Ravens Corvus corax in the experimental colonies because supplemental food favoured group defence by increasing colony size and by increasing the time the Jackdaws spent in the colony. Additional food advanced laying date, increased clutch size independently of laying date and increased fledging success. Supplementary food significantly increased fledging success in less than half of all experimental studies on birds. We suggest that the key to this problem is the species' breeding strategy, and we show that supplementary food significantly increased fledging success in brood-reduction strategist species but not in species which directly adjusted their clutch size.     

Colonial breeding and nest predation in the Jackdaw Corvus monedula using old Black Woodpecker Dryocopus martius holes

Jackdaws Corvus monedula breeding in old holes of the Black Woodpecker Dryocopus martius were studied during 6 years in central Sweden. Of 131 breeding attempts, only 56% were successful. Nest predation caused 74% of the breeding failures. The most common predator was probably the Pine Marten Mattes mattes , as fresh hair was found in 42% of the nests whose contents had been predated. Predation risk of nest contents was not related to the height above ground, but it was significantly reduced with increasing colony size. Since Jackdaws are known to communally defend their nests, a likely explanation is that the Jackdaw benefits from group defence against predators. During the study, the number of breeding Jackdaw pairs in Black Woodpecker holes declined, probably linked with a recent increase in the numbers of Pine Martens in the area.     

No sexual differences in embryonic period in jackdaws Corvus monedula and black‐headed gulls Larus ridibundus

Offspring survival probability usually decreases with hatching order, especially in species with brood reduction. Brood reduction in combination with a sex difference in embryonic period (the time between laying and hatching of an egg) can potentially have a profound effect on sex allocation, with higher investment in chicks of the early hatching sex because they are more likely to survive to fledge. Two recent studies reported sex differences in the embryonic period, but compared embryonic period between, rather than within, clutches, which does not control for possible environmental effects on both clutch sex ratio and embryonic period. We compared the embryonic period of sons and daughters within clutches in jackdaws Corvus monedula and black‐headed gulls Larus ridibundus, two species with frequent brood reduction, and found no sexual difference in embryonic period. This suggests that sex allocation is not affected by sex differences in embryonic period in these species, but more studies are required to verify whether this is a general pattern.     

Fitness increases with partner and neighbour allopreening

Altruism and selfishness are fundamental characteristics of human and animal societies. Among colonial biparental species, breeding outcome depends on interactions between mates and neighbours. However, the relationships between cooperation within and among partnerships and fitness have not been fully investigated. We show that in the highly colonial common guillemot (Uria aalge), altruistic behaviour (allopreening) towards a mate was positively related to long-term fitness, whereas allopreening a neighbour was related to current fitness. Turnover is much lower within than between pairs, so our results suggest that allopreening within pairs generates fitness returns at longer timescales than between pairs. Allopreening not only removes ectoparasites and maintains plumage condition, but may also have important social functions. We found a negative relationship between fight rate and allopreen rate between breeding neighbours, with nests exhibiting low breeding success having a higher frequency of fights with neighbours. We also found evidence for reciprocity in allopreening. Thus, allopreening may function as a reciprocal stress reducer, to decrease the likelihood of fights and associated breeding failure. We suggest that altruistic behaviour has long-term benefits for the survival of the offspring when living in a crowded neighbourhood.     

Formation of linear dominance relationship in captive jungle crows (Corvus macrorhynchos): implications for individual recognition

Jungle crows (Corvus macrorhynchos) flexibly change their social forms depending on their age, time of the day, and the season. In the daytime, paired adults behave territorially and unpaired subadults form small flocks of ten birds, whereas at night hundreds of birds roost together. In the breeding season, pairings remain in their nest all day. This fission-fusion raises questions about the underlying social structure and the cognitive capability of jungle crows. In this study, dyadic encounters were used to investigate dominance relationships (linear or non-linear) and the underlying mechanisms in captive jungle crows. Fourteen crows were tested in 455 encounters (i.e., 5 encounters per dyad), and a stable linear dominance relationship emerged. Sex and aggressiveness were determinants as individual characteristics for dominance formation. Males dominated females, and more aggressive individuals dominated less aggressive ones. Aggressive interactions in dyads occurred primarily during the first encounter and drastically declined during subsequent encounters without any signs of a confidence effect. These results suggest that, in captive jungle crow, a linear form of dominance is intrinsically determined by sex and aggressiveness and maintained extrinsically by memories of past outcomes associated with specific individuals, implying individual recognition.     

Ontogeny of heart rate in embryonic and nestling crows (Corvus corone and Corvus macrorhynchos)

The developmental patterns of mean heart rate (MHR) and instantaneous heart rate (IHR) were investigated in embryos and chicks of altricial Corvuscorone and Corvus macrorhynchos. The MHR of embryos increased linearly with time from 250 beats · min⁻¹ at mid-incubation to 290 beats · min⁻¹ in hatchlings. MHR during the pipping period was maximal, but only marginally higher than in hatchlings. MHR was stable at about 290–300 beats · min⁻¹ during the 1st week after hatching. Spontaneous heart rate (HR) decelerations and accelerations were found in embryos and chicks, disturbing the baseline HR with increasing frequency during development. However, the IHR accelerations developed later and were less frequent than in precocial species. IHR and body temperature decreased during mild cold exposure (23–25 °C) and IHR accelerations were reduced in nestlings during the 1st week. We suggest that the development of parasympathetic control of HR in crows occurs at 60% of incubation, similar to precocial embryos, but sympathetic control may be delayed and suppressed in contrast to precocial embryos. Accepted: 3 March 1999     

Comparative phylogeography of two crow species: jungle crow Corvus macrorhynchos and carrion crow Corvus corone

The jungle crow Corvus macrorhynchos Wagler, 1827, and the carrion crow Corvus corone L., 1758, are two closely related species with similar ecological requirements that occupy wide distribution ranges in the Palearctic. We studied patterns of their genetic variation by using sequences of the mitochondrial cytochrome b gene. Corvus macrorhynchos demonstrates a low level of variation and differentiation throughout its range, except for a highly diverged population of Cheju Island (Korea). The haplotype network shows two haplogroups. The island group comprises populations of Sakhalin, Hokkaido, Honshu, and Kyushu, while the haplotypes of Taiwan and Ryukyu Islands proved to be closer to the mainland group, which also includes populations from the Primorye, Khabarovsk, Amur, and Magadan regions in the Russian Far East. This pattern allowed us to develop a phylogeographic hypothesis regarding the two modes of settling of the island populations. Concerning C. corone, the presence of two distinct haplogroups was confirmed within the range of C. c. orientalis. Both haplogroups are found within the same populations in Kamchatka and North Sakhalin, which implies secondary contacts there. Populations of C. corone are found to be rather stable in the western parts of its range, while in the Far East populations experienced recent growth, as was observed for C. macrorhynchos in general. The two species appear to have passed through different evolutionary scenarios.     

Winter Fighting in Feeding Flocks of Rooks,Jackdaws and Carrion Crows

The great majority of Oystercatchers sport a white collar outside the nesting season. The authors discuss the incidence of this plumage character and its significance to Oystercatcher breeding behaviour.