Shape of,and body direction in,huddles of Japanese macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>) in Arashiyama,Japan

We studied huddles of Japanese macaques (Macaca fuscata) in the Arashiyama E troop at the “Arashiyama Monkey Park, Iwatayama” of Kyoto, central Japan. The macaques made physical contact with other individuals and formed huddles when the air was cold. The 99–101 adult females and 26–36 adult males in the study troop formed 345 huddles during 42 scan samples in the winter of 2001 and 376 huddles during 52 scan samples in the winter of 2002. The average size of huddles was 2.3 (range 2–7) individuals. Males huddled less frequently than females. Maternal kin-related dyads formed 2-female huddles more frequently than unrelated dyads. Choice of huddling partners might restrict the size of huddles. The most frequently observed 3 and 4-member huddles were triangular and diamond-shaped. Macaques usually huddled ventro–ventrally, ventro–laterally, and ventro–dorsally. A third individual frequently placed the ventral part of its body against the first individual and simultaneously put the lateral part of its body against the second individual, so that the 3 individuals formed a triangular huddle. This behaviour indicates that Japanese macaques choose their position and body direction in the huddle to reduce the area of body surface exposed to the air, thereby conserving body heat.     

Social rank in winter flocks of Willow Tits Parus montanus

The social hierarchies in winter of ten flocks of Willow Tits Parus montanus were studied when the birds were foraging naturally and when visiting feeders. All the flocks consisted of one adult mated pair together with two juvenile males and two juvenile females (probably pairs). All flocks studied had a stable composition and the hierarchies remained constant throughout the study period. The hierarchies were linear and unilateral. The adults of each sex dominated the respective juveniles and within each age group the male dominated the female. The dominance relationships between the age and sex groups were not consistent. Although the males dominated all the females in six flocks, in one flock the adult female dominated both the juvenile males, but only one of them in three other flocks. The degree of aggression between flock-members was 0.8 encounters per hour, and males initiated 94% of all attacks. Body-weight explained 77% of the variation in dominance rank. It is suggested that the dominance rank of a male is also a function of his seniority, while the rank of a juvenile female is correlated with the rank of her mate.     

Social Dominance Hierarchies and Phenotypic Correlates of Dominance in Captive Groups of the Grey‐cheeked Fulvetta Alcippe morrisonia in Taiwan

Dominance hierarchies usually form quickly among avian foraging groups because they are beneficial to most individuals by reducing conflict. Several characteristics that correlate with dominance rank have been identified in birds, but most of these conclusions rely on studies of temperate species. Hence, we studied whether captive group members of a subtropical species, grey‐cheeked fulvetta Alcippe morrisonia, form social dominance hierarchies when competing for food during the non‐breeding season. We also investigated whether sex, age, body condition and fat score were related to an individual's dominance rank which was established by counting aggressive interactions in six captive groups of nine individuals each. In all groups, linear dominance hierarchies were formed whereby yearlings dominated over adult birds, and individuals with a better body condition were also more dominant, while sex and fat score had no discernable effect. Male yearlings had significantly higher body masses and body condition indices than male adults, while female yearlings had significantly higher body masses, body condition indices and fat scores than female adults. However, there were no significant differences between male and female yearlings or adults for any of these variables. We suggest possible reasons for the dominance of yearlings, such as captive conditions or the higher body weight of yearlings.     

Territory acquisition during winter by juvenile Willow Tits Parus montanus

Willow Tits Parus montanus live within exclusive territories in non-kin winter flocks with a dominance hierarchy in which males dominate females and adults dominate juveniles. Because they live in habitats that are saturated with dominant territory owners, the options of subordinate juveniles surviving the winter are: (1) to become a dominant owner of a vacated territory, (2) to stay in an occupied territory and hope for ownership or (3) to leave the area and hope for territory acquisition elsewhere. Removal experiments during December to February revealed that particularly the most dominant of the juvenile pairs left their own flock territory and replaced birds experimentally removed from a neighbouring flock, if by doing so they increased their own dominance position. It is suggested that juvenile Willow Tits updated their information about the composition and dominance structure of adjacent winter flocks by regularly visiting these territories and attempted to become dominant owners during winter, thereby increasing their chances of breeding.     

The Maintenance of Stable Dominance Hierarchies and the Pattern of Aggression: Support for the Suppression Hypothesis

Three hypotheses have been proposed to explain the development and maintenance of dominance hierarchies. According to the first hypothesis the dominance hierarchy is a result of the animals fighting once at their first encounter and then using the outcome of that fight to determine the rank order. The second hypothesis proposes that a dominance hierarchy reflects the fighting ability of the individuals in the group at each moment and is therefore relatively fluid with individuals continuously fighting for position. A third hypothesis, the suppression hypothesis, states that the dominance hierarchy is based to a large extent on the outcome of the first fight between the individuals but the dominant animal in each pair continuously attacks the subdominant individuals to condition them to lose in future encounters. We studied six well‐established flocks containing six adult hens each (Gallus gallus domesticus). Five of the flocks had linear hierarchies. The aggression was significantly more often directed towards the next low‐ranking individual. There was a good correlation between rank and comb size (height × width), but no significant correlation between rank and weight, or rank and level of fluctuating asymmetry. There was no significant correlation between levels of aggression and similarity of comb size for individuals of neighboring ranks. Our results tentatively support the suppression hypothesis for the maintenance of dominance hierarchies in the domestic hen.     

Social dominance in free-living Willow Tits Parus montanus: determinants and some implications of hierarchy

Several features of social dominance among Willow Tit Parus montanus winter flocks were examined during a four-winter study. Birds of both sexes were evenly distributed over the 33 flocks studied. In nearly half of the flocks there was an adult pair accompanied by yearlings, but one-third of the flocks consisted of more than two adults with yearlings. Males were found to be dominant over and larger than females. Within a sex, yearlings were usually subordinate to adults. The effect of size on dominance, after controlled for sex and age, remained obscure in our field data. The hierarchical status of an individual was found to rise or at least stay the same in different years, which supports the "hopeful dominants" hypothesis, i.e. birds stay in flocks hoping to achieve a higher status in the future. The ranks of mates correlated highly significantly, implying that high-ranking birds were paired with other high-ranking birds and low-ranking birds with other low-ranking birds. Birds of different age and sex did not show any differences in the proportion of initiated aggressive encounters directed at other individuals. However, males were more aggressive to other males than to females and also tended to behave less aggressively towards their own mates than towards other individuals in the flock. This could be a male strategy to strengthen the pair-bond and to enhance mate protection described earlier in     

Within-brood social status and consequences for winter hierarchies amongst Mallard Anas platyrhynchos ducklings

Juveniles of many birds establish dominance hierarchies within family social units, only to leave and compete to acquire dominance status in new social groups. Little is known about the role of sex, body mass, size or experience during the duckling period on subsequent dominance rank and adult social relationships. We used captive Mallard Anas platyrhynchos ducklings to test for the role of individual characteristics and growth parameters in establishing within-brood hierarchies, the maintenance of within-brood hierarchies in the subsequent wintering group and differences in social ranks between broods. Strong stable linear hierarchies were present within each brood and, later, within each phase of the winter. There was a reorganisation of the hierarchical order between the duckling period and early winter, but only few modifications afterwards during the winter. None of the tested “hatching”, “duckling” and “adult” traits explained either the within-brood or the winter hierarchies, but winter rank was related to brood of origin with ducklings from the same brood having similar social ranks. These differences between broods were maintained through the whole winter in most cases, though one brood drastically progressed in the hierarchy during late-winter. These results suggest that the factors affecting the establishment of social relationships within broods differ from those in winter groups, and that brood-related mechanisms influence social relationships during winter. We discuss our results in the light of direct and indirect maternal influence.     

Dominance and anti-predator behaviour in blue tits (Parus caeruleus)

Evidence from captive flocks of blue tits (Parus caeruleus) suggests that following the appearance of a predator, socially dominant individuals are likely to wait until subordinate members of their flock resume feeding before doing so themselves. After a model sparrowhawk (Accipiter nisus) was flown over captive flocks of blue tits at a feeder, there was a significant negative correlation between sequence of return to the feeder and status within a linear dominance hierarchy. During this period, birds increased the proportion of their time budgets devoted to scanning for predators. These results suggest that during periods of danger, high-ranking individuals are able to be more cautious than are low-ranking individuals, possibly because their ability to control food resources reduces the energetic costs of their extra caution.     

Triadic Positions of Tibetan Macaques Huddling at a Sleeping Site

We studied huddling of Tibetan macaques (Macaca thibetana) at a sleeping site in Huangshan, China, during the mating and birth seasons. Tibetan macaques in a free-ranging group made physical contact with each other and formed huddling groups on the ledge of a steep cliff at night. We analyzed the size and composition of huddling groups and the frequencies of dyadic huddles—two individuals in physical contact—in the huddling group to determine the social influences on huddling behavior. Affiliated dyads that frequently groomed in the daytime frequently formed dyadic huddles in night-time huddling groups. Female–male dyads formed dyadic huddles less frequently than expected. In addition, Tibetan macaques chose 2 partners with which they initiated contact when they approached a huddling group. The frequencies with which some combinations of 3 individuals contacted each other and formed triangular huddles are not consistent with the expected frequencies. For example, female–male–male triads frequently formed triangular huddles in the birth season but did so infrequently in the mating season because of male competition for estrous females. When all 3 dyads within a certain triad formed dyadic huddles frequently, the triad was more likely to form a triangular huddle. The choices of approaching individuals might make a systematic, rather than random, positioning of individuals in huddling groups at their sleeping site.     

Genetic relatedness in wintering groups of house sparrows (Passer domesticus)

Social behaviour of group-living animals is often influenced by the relatedness of individuals, thus understanding the genetic structure of groups is important for the interpretation of costs and benefits of social interactions. In this study, we investigated genetic relatedness in feeding aggregations of free-living house sparrows ( Passer domesticus ) during the nonbreeding season. This species is a frequent model system for studies of social behaviour (e.g. aggression, social foraging), but we lack adequate information on the kin structure of sparrow flocks. During two winters, we ringed and observed sparrows at feeding stations, and used resightings to identify stable flock-members and to calculate association indices between birds. We genotyped the birds using seven highly polymorphic microsatellite loci, and estimated pairwise relatedness coefficients and relatedness categories (close kin vs. unrelated) by maximum likelihood method. We found that most birds were unrelated to each other in the flocks (mean ± SE relatedness coefficient: 0.06 ± 0.002), although most individuals had at least a few close relatives in their home flock (14.3 ± 0.6% of flock-mates). Pairwise association between individuals was not significantly related to their genetic relatedness. Furthermore, there was no difference between within-flock vs. between-flock relatedness, and birds had similar proportions of close kin within and outside their home flock. Finally, relatedness among members of different flocks was unrelated to the distance between their flocks. Thus, sparrow flocks were not characterized by association of relatives, nevertheless the presence of some close kin may provide opportunity for kin-biased behaviours to evolve.     

Preservation of winter social dominance status in Brent Geese Branta bernicla bernicla within and across winters

Dominant and subordinate individuals in a group may benefit from the stability of the social dominance organisation, avoiding excessive waste of time and energy in aggressive interactions and reducing injury risks. Nevertheless, the likely evolutionary incentive for individuals to become, and furthermore to stay, dominant may destabilise such dominance hierarchies. In this context, the relative importance of fixed (e.g. sex, morphological size) and fluctuating (e.g. body condition, mating status, reproductive success, social unit size) traits influencing the establishment and preservation of dominance relationships could play a key role in group structure. We investigated the relative role of fixed and fluctuating traits on social status in Dark-bellied Brent Geese Branta bernicla bernicla which form large fairly unstable groups both within and across winters. We compared individual dominance scores of ringed Brent Geese during four consecutive winters. Brent Geese conserved their dominance score within a given winter irrespective of their age but were generally unable to conserve it across consecutive winters. As winter dominance scores correlated best with social unit size, dominance status thus appeared to be mostly a by-product of a fluctuating trait: breeding success in the previous summer. When we considered only adults that had the same social unit size during two consecutive winters, we observed a significant preservation of dominance scores. This result suggests that a fixed trait such as sex or morphological size may still play a role in setting dominance status.     

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.     

Linear social dominance hierarchy and corticosterone responses in male mallards and pintails

In winter, dabbling ducks gather in large flocks and males compete not only for food resources but also for mates. Setting up a social hierarchy is one way to reduce the costs of conflicts, but the position in the hierarchy has implications for individuals, for instance their susceptibility to conflict and interference, hence to social stress. We investigated relationships between linear social dominance and corticosterone levels, baseline levels and induced-stress response, in captive male mallards Anas platyrhynchos and pintails Anas acuta during the winter period. We hypothesised that corticosterone responses would reflect the costs associated with social stress. From previous work on dominance and corticosterone in wintering birds, we expected that, where the social hierarchy is linear, there would be (1) no relationship between social ranks and baseline corticosterone levels and (2) a significant positive relationship between dominance ranks and responses to acute stress. Our results demonstrated the existence of a linear hierarchy in both species (h' = 0.95 for mallards and h' = 0.97 for pintails), and we found that pintails had on average more corticosterone than mallards. The relationship between dominance and corticosterone responses followed the predictions, with no differences for baseline levels and an attenuated response to induced-stress for subordinates. We discuss these results in the perspective of the cost-benefits of dominance and wintering strategies of waterbirds.     

DHEA levels and social dominance relationships in wintering brent geese (Branta bernicla bernicla)

After testosterone, dehydroepiandrosterone (DHEA) is the main hormone involved in aggressive behaviour in birds. While the role of DHEA has been verified for wintering territorial passerines, it has not been shown for gregarious species. In wintering geese species, both sexes present very low testosterone levels and aggression in a non-sexual context is not testosterone-related. Therefore, testosterone does not seem to be responsible for aggressive behaviour by geese during winter and the role of DHEA must be explored. We used brent geese (Branta bernicla bernicla) to examine the roles of testosterone and DHEA in dominance relationships. For the first time, we highlighted the presence of plasma DHEA in free-living geese. As the level of DHEA was lower than that of testosterone, and there was no obvious impact of DHEA level on dominance status, our results failed to confirm the role of plasma DHEA in the social hierarchies of this species during winter. Nevertheless, because DHEA levels were greater in singletons than in paired birds, we discuss the need to explore hormonal and/or behavioural mechanisms implicated within dominance status acquisition and maintenance within each reproductive status class, to underline the role of the presence of relatives as a signal of dominance abilities. We also acknowledge and discuss the possibility that the long handling time may have affected DHEA levels and masked subtle differences between individuals.     

Is ‘nocturnal hypothermia’ a valid physiological concept in small birds?: a study on Bronze Mannikins Spermestes cucullatus

The thermoregulatory capacity and metabolic responses to light–dark cycles under various mild food-deprivation treatments were measured in Bronze Mannikins Spermestes cucullatus (10–11 g). We measured the response of minimum oxygen consumption to ambient temperature in order to determine the basal metabolic rate (BMR), thermal conductance and limits of thermoneutrality of the Mannikins. In addition, we measured oxygen consumption in response to light–dark cycles and three mild food-deprivation treatments. Bronze Mannikins have a low BMR (1.67 mlO₂/g/h) that is c. 50–60% of that predicted from phylogenetically independent allometric curves for all birds. A low BMR resulted in amplitudes of metabolism between the active and rest phases that were double those predicted allometrically from body mass. The reduced nocturnal metabolic rate did not represent torpor. Typically, Mannikins would need to reduce their metabolic rate during the rest phase to c. 17% of BMR to attain the average torpor metabolic rate of other birds. The data are, however, consistent with those of other group-living Afrotropical birds that benefit energetically from group huddling in environments in which moderate seasonality is accompanied by unpredictable climates – and thus unpredictable energy inputs in time and space. When food-deprived and placed under moderate cold stress (20 °C), Mannikins decreased their rest-phase metabolic rates to the same magnitude as several small Holarctic birds. We suggest that, in the context of the progress made to quantify and define proximate heterothermic responses in endotherms, such as torpor and hibernation, the term nocturnal hypothermia often applied to moderate nocturnal reductions in metabolic rate is vague, misleading and inappropriate.     

Cold tolerance,and not earlier arrival on breeding grounds,explains why males winter further north in an Arctic‐breeding songbird

Sex biases in distributions of migratory birds during the non‐breeding season are widespread; however, the proximate mechanisms contributing to broad‐scale sex‐ratio variation are not well understood. We analyzed a long‐term winter‐banding dataset in combination with spring migration data from individuals tracked by using geolocators to test three hypotheses for observed variation in sex‐ratios in wintering flocks of snow buntings Plectrophenax nivalis. We quantified relevant weather conditions in winter (temperature, snowfall and snow depth) at each banding site each year and measured body size and condition (fat scores) of individual birds (n > 5500). We also directly measured spring migration distance for 17 individuals by using light‐level geolocators. If the distribution pattern of birds in winter is related to interactions between individual body size and thermoregulation, then larger bodied birds (males) should be found in colder sites (body size hypothesis). Males may also winter closer to breeding grounds to reduce migration distance for early arrival at breeding sites (arrival timing hypothesis). Finally, males may be socially dominant over females, and thus exclude females from high‐quality wintering sites (social dominance hypothesis). We found support for the body size hypothesis, in that colder and snowier weather predicted both larger body size and higher proportions of males banded. Direct tracking revealed that males did not winter significantly closer to their breeding site, despite being slightly further north on average than females from the same breeding population. We found some evidence for social dominance, in that females tended to carry more fat than males, potentially indicating lower habitat quality for females. Global climatic warming may reduce temperature constraints on females and smaller‐bodied males, resulting in broad‐scale changes in distributional patterns. Whether this has repercussions for individual fitness, and therefore population demography, is an important area of future research.     

Social Control and Physiological Cost of Cheating in Status Signalling Male House Sparrows (Passer domesticus)

Flock-forming passerines often use plumage characteristics to signal their social dominance. While the benefits to signal dominance seem obvious, costs associated with status signalling are ambiguous. The social control hypothesis predicts that individuals of high social status – with large badges – are involved in more social interactions with individuals of similar badge size. Cheaters are therefore exposed to increased risk of fighting with high quality individuals and the costs associated with enhanced fights with dominant males are supposed to outweigh the benefits of cheating. We tested the social control hypothesis in male house sparrows ( Passer domesticus ), by observing social interactions in captive flocks and determining dominance relationships. Two low status individuals within each flock had the size of their badge experimentally increased and the interactions involving experimental and control birds were recorded. We also assessed the potential physiological cost of cheating in terms of enhanced levels of the stress hormone, corticosterone. Dominance was significantly positively correlated with badge size, but not with other morphological traits. We found little support for the social control hypothesis. Birds did not have significantly more interactions with individuals of similar badge size, before the manipulation. Similarly, after the experimental increase in badge size, experimental birds did not tend to have more encounters with large-badged males. Experimental birds with enlarged badges won more fights compared with prior to the manipulation, suggesting that badge size is used as a signal of social dominance even in small and stable flocks. Finally, corticosterone levels in the blood did not increase significantly after the manipulation of badge size, suggesting that there is no measurable cost, resulting from stress, in cheaters.     

A Novel Method of Assessing Dominance Hierarchies Shows Nuance,Linearity and Stability in the Dinosaur Ant Dinoponera quadriceps

Many social species with relatively simple societies have dominance hierarchies of individuals, with dominant individuals achieving fitness and subordinate individuals either queuing to obtain fitness or achieving only indirect fitness by helping relatives. Assessing the dominance hierarchy in a social group is generally based upon observing dyadic interactions as and when they occur spontaneously within the whole‐group setting. However, this method can be very time‐consuming because many dyads interact only very rarely, necessitating either extremely long observation periods or many dyadic relationships being unresolved. Here, we report an alternative method using the queenless dinosaur ant Dinoponera quadriceps, which lives in colonies containing tens of individuals. We removed all individuals from their nest and observed the dominance behaviours expressed in isolated dyadic interactions for every pairwise combination of individuals. Individuals showed a classic dominance behaviour in this setting, and the rapid nature of the assay allowed us to observe every dyadic relationship on a weekly basis over 4 weeks. The dominance hierarchies based on these isolated dyadic interactions correlated well with those produced by the conventional method of colony observations. They showed the hierarchies to be highly linear and stable, and also revealed that dominance relationships may extend further down the hierarchy than previously thought. Although highly manipulative, the isolated dyadic interaction method works well and will likely make more feasible the study of other social species in which pairs of individuals can be isolated together.     

Feeding ecology of wintering terns in Guinea-Bissau

We studied the feeding ecology of Little Terns Sterna albifrons , Sandwich Terns S. sandvicensis and Royal Terns S. maxima in the Archipélago dos Bijagós (11°40'N, 15°45'W) in Guinea-Bissau (West Africa) during the winter of 1992/1993. More than 95% of all prey taken by these terns were roundfish, ranging in weight from 0.3 to 40 g. Birds usually fed alone, but sometimes they were observed feeding in mixed-species flocks consisting of 15–200 individuals. Capture rate ( n fish per hour foraging) in these flocks was higher than that of solitary birds. However, smaller fish were caught by birds foraging in flocks, so food intake rate (g/h) did not differ between solitary and flock-feeding birds. The relationships between foraging behaviour of the three tern species and abiotic factors, such as time, tide and water clarity, have been investigated. Capture rate of Royal Terns increased with water clarity. For Little Terns and Sandwich Terns, food intake rate was lower in the most turbid waters compared to clearer waters. There was very little foraging activity during high tide. For Little Terns and Royal Terns, food intake rate was about twice as high during receding and low tides as during an incoming tide. Food intake rate averaged 8 g/h in Little Terns, 60 g/h in Sandwich Terns and 45 g/h in Royal Terns. With a rough model, we estimate the maximum rate of daily energy expenditure of terns wintering in the tropics at 3 × BMR (defined as energy expenditure of inactive bird at thermoneutrality in a post-absorptive state during the resting phase of the daily cycle). From an energetic viewpoint, wintering Sandwich Terns in Guinea-Bissau seem to have an easy living.     

WINTER SURVIVAL IN RELATION TO DOMINANCE CLASSES AMONG SILVEREYES ZOSTEROPS LATERALIS CHLOROCEPHALA OF HERON ISLAND, GREAT BARRIER REEF

Winter survival with respect to dominance classes of 932 individually colour-ringed Silvereyes was examined on Heron Island, Great Barrier Reef, between 1965 and 1969. The dominants (winning two-thirds or more of aggressive encounters) had significantly better chances of survival between May and August (southern winter) than other birds. The 1967/68 year group was studied in detail; the young born early in the breeding season contained proportionately more dominants than those born later in the season and dominant birds tended to survive better in winter. Adults in the same period showed no dominance dependent survival. The weight of birds in winter differed between first-year birds and adults in most cases, but winter mortality within each year-group was not related to the weight of individual birds in May. However, the dominant class had a smaller proportion of birds losing weight through the winter than other classes, and the dominant adults and the intermediate class of first-year birds tended to be heavier than others in August. The lengths of wing, tail, tarsus and exposed culmen examined for the 1967/68 year group showed no significant trends in either survival or dominance classes. Better survival of dominant birds is considered to be a consequence of their feeding advantages over others, but the intensity of selection for an ability for dominance may fluctuate from year to year in relation to the population density and distribution and abundance of food supply.