Linear and Stable Dominance Hierarchies in Cooperative Carrion Crows

Cooperatively breeding birds typically form cohesive and stable groups that live year‐round in all purpose territories where competition for resources is likely to arise. Understanding how group members negotiate over resources is crucial because conflicts may disrupt the stability of the group and may ultimately hinder cooperation. However, social relationships within the group have been largely neglected so far. Here we investigated how cooperatively breeding carrion crows (Corvus corone corone) share a food source, by observing dyadic interactions in 29 territories that contained retained offspring of the breeding pair and/or immigrants. We found that crows formed linear and stable dominance hierarchies, which were stronger for males than females. We suggest that this difference mirrors the level of competition for resources other than food, such as reproduction and territory inheritance, which is higher in males than females. Interestingly, immigrant males dominated male offspring, suggesting that, for the resident breeder, which is the alpha member of the group, the benefits of an association with an immigrant overcome the costs of having his sons pushed down in the hierarchy. Our study uncovered the key factors that determine hierarchical relationships among cooperatively breeding crows and highlighted the need of focussing on social interactions in every context of group living to fully explain the dynamic of cooperation at the nest.     

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.     

Behavioral Responses to Inequity in Reward Distribution and Working Effort in Crows and Ravens

Sensitivity to inequity is considered to be a crucial cognitive tool in the evolution of human cooperation. The ability has recently been shown also in primates and dogs, raising the question of an evolutionary basis of inequity aversion. We present first evidence that two bird species are sensitive to other individuals'' efforts and payoffs. In a token exchange task we tested both behavioral responses to inequity in the quality of reward (preferred versus non-preferred food) and to the absence of reward in the presence of a rewarded partner, in 5 pairs of corvids (6 crows, 4 ravens). Birds decreased their exchange performance when the experimental partner received the reward as a gift, which indicates that they are sensitive to other individuals'' working effort. They also decreased their exchange performance in the inequity compared with the equity condition. Notably, corvids refused to take the reward after a successful exchange more often in the inequity compared with the other conditions. Our findings indicate that awareness to other individuals'' efforts and payoffs may evolve independently of phylogeny in systems with a given degree of social complexity.     

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 roosting sites, but otherwise spend time seemingly solitary or in small subgroups. We here studied how ravens cope with being socially isolated, and investigated the life characteristics that might explain potential individual differences. For this, we individually separated captive subadult ravens (n = 25) and housed them in physical and visual isolation from their group members across 4 d. During the separation period, we collected behavioural data and measured the amount of immunoreactive corticosterone metabolites from bird droppings to assess the ravens’ physiological stress response. We found behavioural indicators of stress at the start of the separation, when ravens showed higher levels of tension than of comfort – a pattern that reversed at the end of the separation. Furthermore, we found that the upbringing of ravens affected their behaviour during separation. Hand‐raised birds produced more vocalisations in the beginning of the separation, and were less active at the end, while the reverse pattern occurred with parent‐raised ravens. Contrary to our predictions, we did not find differences in hormonal responses between the beginning and end of the separation period or any link between hormonal responses and behaviours. Ravens’ behavioural responses to social separation stress seem to be dependent on their arousal states, although possible links with hormonal reactions remain unclear. Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early‐life experiences.     

Movements of Juvenile Common Ravens in an Arid Landscape

ABSTRACT Movement patterns of juvenile birds are poorly understood, yet critically important ecological phenomena, especially for species with a prolonged juvenile period. We evaluated postfledging movements of juvenile common ravens (Corvus corax) in a western Mojave Desert landscape composed of a mosaic of natural and anthropogenic elements. Generally, ravens do not begin breeding until after their fourth year. We marked 2 annual cohorts of juvenile ravens and followed them from dispersal from their natal territory for up to 33 months. Movements of juvenile common ravens were similar for males and females. Conspecifics and confined livestock feeding operations represented important resources for juvenile ravens, and juveniles were rarely located in open desert. However, initial movements from the natal territory to the nearest communal point subsidy rather than the closest anthropogenic resource suggested juvenile dispersal was influenced by the combination of conspecifics and anthropogenic resources, rather than the distribution of those resources. Land managers concerned with growing raven populations should reduce access to concentrated anthropogenic resources such as landfills and dairies, which serve as important resources for juveniles. Because juvenile ravens rarely venture into open desert, reducing their numbers by lethal removal or other means is unlikely to lessen raven predation of desert tortoises (Gopherus agassizii).     

Space use by Common Ravens in Marbled Murrelet nesting habitat in Northern California

Little is known about space use by Common Ravens (Corvus corax) in coastal old‐growth redwood (Sequoia sempervirens) forests in northern California despite their identification as nest predators of federally threatened Marbled Murrelets (Brachyramphus marmoratus). We used radio‐telemetry to examine home range sizes and space use of breeding Common Ravens in Redwood National and State Parks (RNSP), California, in 2009 (N = 3) and 2010 (N = 8). Mean home range size was 182.5 ha and no home ranges were >2 km from roads or human‐use areas. Ravens exhibited high site fidelity between years, and we found little overlap in the home ranges of adjacent ravens. Areas where ranges did overlap were centered on anthropogenic food sources near territory boundaries. Areas most frequently used by ravens were near roads, old‐growth edge, bare ground, and in mixed hardwood and prairie habitats; areas near human‐use areas and in old‐growth habitat were used less by ravens. Mean perch height of ravens (52 m, N = 38) in redwood trees was similar to the mean height of Marbled Murrelet nests in RNSP (48 m). In RNSP, Marbled Murrelet nests that have been located were in old‐growth forest within 2 km of roads. The attraction to anthropogenic resources with frequent use of roads and old‐growth edges and their tendency to perch high in the canopy may increase the likelihood of ravens locating and predating nests of murrelets in RNSP.     

Differential calls by Carrion and Hooded Crows (Corvus corone corone and C. c. cornix) in the Alpine hybrid zone

Spectrograms of calls given by Carrion and Hooded Crows in the Italian Alpine hybrid zone have been tested for differences between the two subspecies by univariate and multivariate techniques. Vocalizations of the two Crows are similar and composed of 2–15 caws, each usually made up of two harmonics, separated by short intervals. However, one-way ANOVA and discriminant analysis showed that they were differentiated with respect both to temporal and frequency parameters. We suggest that differences in vocalizations reflect mostly the phylogenetic divergence between Hooded and Carrion Crows. The results are in keeping with previous ecological, morphological and molecular data and would confirm that the present designation of the two Crows as distinct subspecies is correct. Differences in vocalizations, together with others regarding ecology and behaviour, may result in assortative mating and homotypic flocking and, therefore, may contribute to reinforcement of the reproductive isolation between the Carrion and the Hooded Crow in the Alpine hybrid zone.     

Behavioural Type Affects Space Use in a Wild Population of Crows (Corvus corone)

While personality‐dependent dispersal is well studied, local space use has received surprisingly little attention in this context, despite the multiple consequences on survival and fitness. Regarding the coping style of individuals, recent studies on personality‐dependent space use within a habitat indicate that ‘proactive’ individuals are wider ranging than ‘reactive’ ones. However, such studies are still scarce and cover limited taxonomic diversity, and thus, more research is needed to explore whether this pattern generalises across species. We examined the link between coping style and space use in a population of crows (Corvus corone) freely inhabiting the urban zoo of Vienna, Austria. We used a binary docility rating (struggle during handling vs. no struggle) and a tonic immobility test to quantify individual coping style. Individual space use was quantified as the number of different sites at which each crow was observed, and we controlled for different number of sightings per individual by creating a space use index. Only the binary docility rating showed repeatability over time, and significantly predicted space use. In contrast to previous studies, we found that reactive crows (no struggle during handling) showed wider ranging space use within the study site than proactive individuals (who struggled during handling). The discrepancy from previous results suggests that the relationship between behavioural type and space use may vary between species, potentially reflecting differences in socioecology.     

Socially Adjusted Synchrony in the Activity Profiles of Common Marmosets in Light-Dark Conditions

Synchronized state of activity and rest might be attained by mechanisms of entrainment and masking. Most zeitgebers not only act to entrain but also to mask circadian rhythms. Although the light-dark (LD) cycle is the main zeitgeber of circadian rhythms in marmosets, social cues can act as weaker zeitgebers. Evidence on the effects of social entrainment in marmosets has been collected in isolated animals or in pairs where activity is not individually recorded. To characterize the synchronization between the daily activity profiles of individuals in groups under LD conditions, the motor activity of animals from five groups was continuously monitored using actiwatches for 15 days during the 5th, 8th, and 11th months of life of juveniles. Families consisting of twins (4 ♂♀/1 ♂♂) and their parents were maintained under controlled lighting (LD 12:12?h), temperature, and humidity conditions. Synchronization was evaluated through the synchrony between the circadian activity profiles obtained from the Pearson correlation index between possible pairs of activity profiles in the light and dark phases. We also calculated the phase-angle differences between the activity onset of one animal in relation to the activity onset of each animal in the group (ψ_on). A similar procedure was performed for activity offset (ψ_off). By visual analysis, the correlation between the activity profiles of individuals within each family was stronger than that of individuals from different families. A mixed-model analysis showed that within the group, the correlation was stronger between twins than between twins and their parents in all families, except for the family in which both juveniles were males. Because a twin is an important social partner for juveniles, a sibling is likely to have a stronger influence on its twin’s activity rhythm than other family members. Considering only the light phase, the second strongest correlation was observed between the activity profiles of the individuals in the reproductive pair. Regarding the parameters ψ_on and ψ_off, the juvenile/juvenile dyad had lower values than the other dyads, but these differences did not reach statistical significance in relation to all dyads. Comparing the results of the ψ_on and ψ_off, and correlation indices, we suggest that the latter could detect differences between the animals that were not observed in the results of the phase-angle differences. These differences could be related to changes that occur during the active phase but not only in a particular phase, such as the temporal changes during the activity phase that characterize unimodal or bimodal patterns. Based on the differences in the correlations between individuals subjected to the same LD routine, we suggest that social cues modulate the circadian activity profiles of marmosets as a result of interactions between the animals within each group. Future studies are necessary to characterize the mechanisms of synchronization that are involved in this social modulation. (Author correspondence: carolina@cb.ufrn.br)     

Common Genetic Variants in FOXP2 Are Not Associated with Individual Differences in Language Development

Much of our current knowledge regarding the association of FOXP2 with speech and language development comes from singleton and small family studies where a small number of rare variants have been identified. However, neither genome-wide nor gene-specific studies have provided evidence that common polymorphisms in the gene contribute to individual differences in language development in the general population. One explanation for this inconsistency is that previous studies have been limited to relatively small samples of individuals with low language abilities, using low density gene coverage. The current study examined the association between common variants in FOXP2 and a quantitative measure of language ability in a population-based cohort of European decent (n = 812). No significant associations were found for a panel of 13 SNPs that covered the coding region of FOXP2 and extended into the promoter region. Power analyses indicated we should have been able to detect a QTL variance of 0.02 for an associated allele with MAF of 0.2 or greater with 80% power. This suggests that, if a common variant associated with language ability in this gene does exist, it is likely of small effect. Our findings lead us to conclude that while genetic variants in FOXP2 may be significant for rare forms of language impairment, they do not contribute appreciably to individual variation in the normal range as found in the general population.     

Differentiation in Searching Behavior for Carcasses Based on Flight Height Differences in Carrion Beetles (Coleoptera: Silphidae)

Flight ability allows insects to search for food and locate oviposition sites across a wide range of environments and, thus, allows insects to locate scarce and patchy resources such as carcasses. We examined differentiation in searching for carcasses, based on capture height differences in carrion beetles, and found that capture height differed among species. For Nicrophorus quadripunctatus and Oiceoptoma nigropunctatum, the height of abundance peaks differed among sites and was related to species composition at each site, indicating that shifts in flight height can occur plastically, whereas those for Nicrophorus maculifrons and Nicrophorus investigator did not differ among sites, indicating that the flight heights of these species are largely genetically determined. Thus, the present differentiation in capture height is primarily determined by current plastic shifts and on some genetic basis.     

Injury and paternity loss in cooperatively breeding American Crows

ABSTRACT Although survivable injuries have been documented in several species of birds, little is known about the social and reproductive consequences of such injuries. We examined relationships between injuries and group composition, reproductive output, and paternity of male breeders in 27 family groups of American Crows (Corvus brachyrhynchos) using 96 broods sampled from 2004 to 2009. Injuries and permanent disfigurement of wings or feet were sustained by 25.9% (7/27) of dominant male breeders. Injured male breeders had smaller broods (2.13 vs. 3.38 nestlings per brood for injured vs. uninjured breeders), lost more paternity (48% vs. 13% extrapair young per brood), and had more adult male auxiliaries in their groups (1.63 vs. 0.65 auxiliaries per group) than uninjured birds. Some of the variation in reproductive partitioning, extrapair paternity rates, and group composition among American Crow family groups can therefore be explained by injuries to male breeders. These results suggest that injuries could account for some of the unexplained variation in the rates and distribution of extrapair paternity across populations and taxa, as well as some of the variation in reproductive skew among cooperatively breeding birds.     

Behavioural responses during feather replacement in house sparrows

Birds lose feathers, whether during molt or by accident, and replace them by processes that are energetically demanding. We hypothesized that house sparrows Passer domesticus biblicus use behavioral means to save energy when feathers are lost, and tested the general prediction that house sparrows growing new feathers adjust their behavior to minimize the energy costs of foraging and to increase net energy gain from their food. To test these predictions we divided 18 house sparrows into three groups: 1) plucked – house sparrows from which we plucked 15 flight feathers; 2) cut – house sparrows in which the same 15 feathers were cut off at the calamus below the barbs; and 3) control – unmanipulated house sparrows with plumage intact. We recorded both the quantity of seeds the house sparrows ate and the time they spent foraging from assay food patches. We found that ‘plucked’ sparrows growing new feathers adjust their foraging behavior by reducing their feeding time and the number of visits to a food patch. This allowed them to increase their patch harvest rate while maintaining a steady body mass.     

Behavioural and autonomic thermoregulation in hamsters during microwave-induced heat exposure

1. 1.|Preferred ambient temperature (T_a) and ventilatory frequency were measured in free-moving hamsters exposed to 2450 MHz microwaves. A waveguide exposure system which permits continuous monitoring of the absorbed heat load accrued from microwave exposure was imposed with a longitudinal temperature gradient which allowed hamsters to select their preferred T_a. Ventillatory frequency was monitored remotely by analysing the rhythmic shifts in unabsorbed microwave energy passing down the waveguide.

2. 2.|Without microwave exposure hamsters selected an average T_a of 30.2°C. This preferred T_a did not change until the rate of heat absorption (SAR) from microwave exposure exceeded approx. 2 W kg⁻¹. In a separate experiment, a SAR of 2.0 W kg⁻¹ at a T_a of 30°C was shown to promote an average 0.5°C increase in colonic temperature. Hamsters maintained their ventilatory frequency at baseline levels by selecting a cooler T_a during microwave exposure. In contrast, hamsters maintained at a T_a of 30°C (without a temperature gradient) underwent a sharp increase in ventilatory frequency compared to animals allowed to select their own T_a.

3. 3.|These data support previous studies suggesting that during thermal stress behavioural thermoregulation (i.e. preferred T_a) takes prescedence over autonomic thermoregulation (i.e. ventilatory frequency). It is apparent that selecting a cooler T_a is a more efficient and/or effective than autonomic thermoregulation for dissipating a heat load accrued from microwave exposure.

Colony Expansion of Socially Motile Myxococcus xanthus Cells Is Driven by Growth,Motility, and Exopolysaccharide Production

Myxococcus xanthus, a model organism for studies of multicellular behavior in bacteria, moves exclusively on solid surfaces using two distinct but coordinated motility mechanisms. One of these, social (S) motility is powered by the extension and retraction of type IV pili and requires the presence of exopolysaccharides (EPS) produced by neighboring cells. As a result, S motility requires close cell-to-cell proximity and isolated cells do not translocate. Previous studies measuring S motility by observing the colony expansion of cells deposited on agar have shown that the expansion rate increases with initial cell density, but the biophysical mechanisms involved remain largely unknown. To understand the dynamics of S motility-driven colony expansion, we developed a reaction-diffusion model describing the effects of cell density, EPS deposition and nutrient exposure on the expansion rate. Our results show that at steady state the population expands as a traveling wave with a speed determined by the interplay of cell motility and growth, a well-known characteristic of Fisher’s equation. The model explains the density-dependence of the colony expansion by demonstrating the presence of a lag phase–a transient period of very slow expansion with a duration dependent on the initial cell density. We propose that at a low initial density, more time is required for the cells to accumulate enough EPS to activate S-motility resulting in a longer lag period. Furthermore, our model makes the novel prediction that following the lag phase the population expands at a constant rate independent of the cell density. These predictions were confirmed by S motility experiments capturing long-term expansion dynamics.