The social organization of non-breeding Magpies Pica pica

The social behaviour of non-breeding individuals in a colour-marked population of Magpies was studied. In early autumn most non-breeders began to forage in a common area, the 'Non-breeding Flock Area'. A few individuals remained on their natal territories away from the flock area as solitary non-breeders. Most non-breeders were first-year birds, but some were second years or adults which no longer held a territory. Birds foraged in groups, their food intake rate differing with both group size and location. It appeared that the area in which birds foraged had a significant effect on food intake rate; foraging groups tended to form at sites rich in food. There was a dominance hierarchy amongst non-breeders; an individual's foraging behaviour, survivorship and chances of breeding were status dependent, with subordinates feeding less in groups and being less likely to survive and breed. Solitary individuals' chances of breeding were similar to those of high status birds, although their survivorship to breeding age may have been lower. Non-breeding Magpies are compared with non-breeders of other species and the factors which may influence their social behaviour are discussed. It is suggested that remaining as a solitary non-breeder is a viable alternative to becoming a low-status flock member for some birds.     

Mallards Feed Longer to Maintain Intake Rate under Competition on a Natural Food Distribution

Animals foraging in groups may benefit from a faster detection of food and predators, but competition by conspecifics may reduce intake rate. Competition may also alter the foraging behaviour of individuals, which can be influenced by dominance status and the way food is distributed over the environment. Many studies measuring the effects of competition and dominance status have been conducted on a uniform or highly clumped food distribution, while in reality prey distributions are often in‐between these two extremes. The few studies that used a more natural food distribution only detected subtle effects of interference and dominance. We therefore conducted an experiment on a natural food distribution with focal mallards Anas platyrhynchos foraging alone and in a group of three, having a dominant, intermediate or subordinate dominance status. In this way, the foraging behaviour of the same individual in different treatments could be compared, and the effect of dominance was tested independently of individual identity. The experiment was balanced using a 4 × 4 Latin square design, with four focal and six non‐focal birds. Individuals in a group achieved a similar intake rate (i.e. number of consumed seeds divided by trial length) as when foraging alone, because of an increase in the proportion of time feeding (albeit not significant for subordinate birds). Patch residence time and the number of different patches visited did not differ when birds were foraging alone or in a group. Besides some agonistic interactions, no differences in foraging behaviour between dominant, intermediate and subordinate birds were measured in group trials. Possibly group‐foraging birds increased their feeding time because there was less need for vigilance or because they increased foraging intensity to compensate for competition. This study underlines that a higher competitor density does not necessarily lead to a lower intake rate, irrespective of dominance status.     

Patterns of group movements in juvenile domestic geese

We investigated collective movements in a flock of domestic geese (Anser domesticus) to test the consistency of group orders and the influence of individual traits and social relationships on movement patterns. The subjects were 20 juvenile females kept in an herbaceous enclosure. Two observers continuously videotaped their movements. Although the positions of individuals might change during moves, the geese tended to hold predictable positions in different movements. We found that geese more reactive to unexpected noises more often held front positions. Moreover, the higher the associativity of a bird as measured by number of neighbors at rest, the more frequent the bird acted as first mover. The analysis did not evidence any influence of dominance status on the positions of geese during progression. In contrast, geese linked by close bonds clustered during progression. The structuring influence of social bonds in collective movements might be a general feature of animals gifted with individual recognition abilities.     

Expensive Traditions: Energy Expenditure of Aleutian Geese in Traditional and Recently Colonized Habitats

ABSTRACT In an effort to reduce goose depredation at a traditional spring migratory stopover site, private landowners implemented a coordinated hazing plan to scare Aleutian cackling geese (Branta hutchinsii leucopareia) from private lands to adjacent public pastures that were cultivated and set aside specifically for geese. Coincidentally, some Aleutian geese began using a new stopover site 150 km farther south in their spring migratory range; numbers at the new site continue to increase. We tested the idea that when their ability to acquire resources deteriorates geese are likely to seek improved foraging conditions, especially during spring migration when individuals strive to maximize nutrient stores and minimize energy expenditure. We quantified measures of goose foraging performance in traditional and new spring staging sites by calculating foraging opportunity, foraging effort, body condition, and daily energy expenditure. Geese staging at the site with higher levels of human disturbance had less foraging opportunity and, despite increased foraging effort and more nutritious food-plants at the site, birds there experienced an elevated energy expenditure and poorer body condition than birds at the new stopover site. Reduced foraging time and increased energy expenditure at the traditional spring staging site may have triggered the colonization process. Suitability assessment of habitat for migratory geese should include measures of foraging opportunity, disturbance risks, and daily energy expenditure in addition to quantity and quality of foods.     

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

Variation in foraging success in relation to spatial position in a group is little known in species that feed on mobile prey that can hide or flee upon disturbance by foragers. I examined the foraging success of individuals located either at the edge or at the centre of flocks of semipalmated sandpipers (Calidris pusilla) feeding on a burrowing amphipod (Corophium volutator) during migration stopover in the Bay of Fundy, Canada. The rates of pecking, prey capture and success were lower for individuals foraging at the edge than at the centre of flocks. Edge birds spent more time running and more time flying than centre birds. Edge birds moved away from the centre of the flock and made frequent short flights towards the centre. In contrast, centre birds rarely moved in a specific direction and flew mostly to relocate elsewhere with the whole flock. Sandpiper flocks foraged over a large area in a relatively short amount of time. In addition, amphipod density is high in this habitat. It thus appears unlikely that prey depletion or low food availability at the edges of groups could explain the spatial variation in foraging success. Low foraging success at the edges of flocks thus arose mainly because of time costs related to flock expansion and retraction. The effect of mutual interference among foragers and of predation risk by falcons is discussed with respect to flock expansion and retraction.     

The Effect of Within-Flock Spatial Position on the Use of Social Foraging Tactics in Free-Living Tree Sparrows

The benefit of producer (searches for own food) or scrounger (exploits the others’ food discoveries) foraging tactic in a group of socially feeding animals may depend on where the individual searches for food within the group. Scrounging may be more advantageous in the centre of the group, having more individuals around to join, while producing may be more beneficial at the edges, where more unexplored food patches may be found. This study shows within‐flock position correlates with foraging tactic use of feeding birds in socially foraging tree sparrows, Passer montanus. Sparrows staying closer to the centre of the flock found their food patches more frequently by joining (i.e. use more frequently the scrounging tactic) than those staying toward the edges. To our knowledge this is the first field study demonstrating the relationship between spatial position and foraging tactic use. We investigated this relationship under different perceived predation hazard, and found that under elevated risk of predation, central individuals may increase their use of joining more than individuals on the periphery of the flock. Moreover, we show that extremely specialized use of searching tactics may be very infrequent in tree sparrows. As both within‐flock position and search tactic use can be altered very quickly and without leaving the flock, individuals may easily alter them in order to adjust their behaviour.     

Dominance and feeding interference in small groups of blackbirds

Dominance and/or interference parameters play a pivotal rolein most ideal free distribution models, but there has beenscant empirical study of the exact manner in which they jointlyoperate. We investigate how foraging effort and success variedamongst individuals of different dominance rankings in groupsof 1-3 wild blackbirds (Turdus merula) attracted to patchesof hidden food. Foraging effort (number of feeding movementsper unit time), as opposed to vigilance tradeoffs, was greaterwhen an individual fed with a subordinate conspecific thanwhen it fed alone, but tended to be less when it fed with adominant individual. Within dyads, changes in foraging effortwere associated with the direction of the dominance relationship,but not the relative difference in dominance rank between thetwo individuals. Similarly, amongst threesomes, top-rankedbirds (but not the lowest-ranked individual) showed higherforaging effort compared to when foraging alone. Top-ranked birds also profited from a greater increase in foraging success(food items per unit effort) than bottom-ranked birds whenfeeding in threesomes than when feeding alone. Dominant birdsshowed increased foraging success, but not effort, after displacinga subordinate. Our results suggest that an individual's foragingeffort is determined by the interplay of group vigilance benefitsand interference costs, the latter being more expensive for subordinate individuals. The foraging success of dominant birdsmay further increase if they use subordinates as food-finders.We discuss the implications of our findings for interferenceparameters in current Ideal Free Distribution models.     

Age bias in the bag of pink-footed geese <Emphasis Type="Italic">Anser brachyrhynchus</Emphasis>: influence of flocking behaviour on vulnerability

In pink-footed goose (Anser brachyrhynchus) wintering in Denmark, The Netherlands and Belgium, the proportion of juveniles in the hunting bag is consistently higher than that observed in the autumn population. Such juvenile bias in the bag is usually ascribed to young geese lacking experience with hunting or disruption of juveniles from families. An alternative explanation may be that flocking behaviour of families make juveniles more vulnerable. Observations of morning flights of pink-footed geese to the feeding grounds from two of the major autumn-staging areas showed that geese were distributed in many small flocks (median flock size = 9). This was not significantly different from the flock size distribution shot at by hunters (median = 8), suggesting that hunters targeted goose flock size in proportion to the general probability of encounter. The rate at which hunters downed geese was independent of flock size. The ratio between juveniles and adults in flocks decreased with flock size and flocks of <60 individuals primarily comprised family groups. The likelihood of being shot at was 2.4 times higher for juveniles and 3.4 times higher for older birds in small flocks (<10 individuals) compared to larger flocks. The observations suggest that both juveniles as well as successful adult breeding birds were more vulnerable than non-breeding/failed breeding birds as a result of flocking behaviour.     

Movements and Conflicts in a Flock of Foraging Black‐Tailed Godwits (Limosa limosa): The Influence of Feeding Rates on Behavioural Decisions

We studied movements and conflicts within a small flock of free‐living black‐tailed godwits foraging on benthic invertebrates in a brackish lagoon. To interpret our results in the framework of foraging theory, we studied the influence of individual feeding rate on the decisions to move and to attack flock companions. Birds changed their position within the flock more often when their intake rate was low and sometimes attacked conspecifics to supplant them from their feeding place. Aggressors significantly avoided front attacks and were almost always successful. They attacked individuals having higher feeding rates than themselves and their own feeding rate significantly increased after the attack, although victims were not chased off to particularly poor sites. Our results suggest that aggressors could obtain reliable information about the quality of the foraging site they coveted by observing their victim’s feeding activity before attacking. Although aggression seemed to be caused by a low intake rate, we show that displacing another bird was more time‐consuming than independent foraging. We conclude that it was not the most profitable behaviour in terms of energy intake. Foraging site displacement probably also had social functions, such as reinforcement of social status in a flock of birds preparing for pre‐breeding migration.     

Bird mixed‐species flock formation is driven by low temperatures between and within seasons in a Subtropical Andean‐foothill forest

According to both the predation avoidance and foraging efficiency hypotheses, birds within mixed flocks increase their foraging efficiency and/or can spend more time feeding and less time looking out for predators. These hypotheses predict that birds in mixed flocks obtain benefits. Thus, mixed flock formation could serve as a strategy to cope with difficult conditions imposed on birds such as climatic conditions that ultimately result in a change in predation pressure or food resources. We evaluate the hypotheses that forming part of a flock confers benefits to its members and the associated prediction that birds will take advantage of these benefits and flock more often under cold and dry weather conditions between and within seasons to cope with such conditions. We surveyed the presence of mixed flocks, flocking propensity, number of species and individuals in mixed flocks in the Subtropical Yungas foothill of Argentina, to examine seasonality, flocking behavior of birds and their responses to two climatic variables: temperature and humidity. Bird species presented a higher flocking propensity and mixed flocks occurred more frequently during the dry and cold seasons than during the more benign seasons, and lower values of temperature within seasons triggered the flocking behavior. Although effects between seasons were expected, birds also showed a short‐term response to small changes in temperature within seasons. These results strengthen the ideas proposed by the foraging hypothesis. Although benefits derived from flocking have yet to be determined, whatever they are should be understood in the context of seasonal variation in life‐history traits.     

安徽沿江浅水湖泊越冬水鸟群落的集团结构

长江中下游湖泊是越冬水鸟的重要栖息地,随着湖泊渔业养殖强度的不断加大,湖泊湿地严重退化,水鸟的越冬生态受到影响。为揭示长江中下游浅水湖泊越冬水鸟对湿地资源的利用特征,2008年12月至2009年3月,通过扫描取样法采集安徽省长江沿江升金湖、菜子湖和武昌湖3个浅水湖泊30种越冬水鸟的取食行为百分比数据,利用聚类分析法对越冬水鸟进行集团划分,并采用无倾向对应法(DCA)分析越冬水鸟的取食特征。聚类分析结果表明,安庆沿江湖泊越冬水鸟群落可分为4个集团,即深水取食集团G1、挖掘和啄取集团G2、浅水取食集团G3和泥滩拾取集团G4。G2集团的鸟种最多,共有13种,优势种为鸿雁(Anser cygnoides)、豆雁(Anser fabalis);G3集团次之,共6种,优势种为小天鹅(Cygnus columbianus)、白琵鹭(Platalea leucorodia);G4集团共5种,优势种为黑腹滨鹬(Calidris alpina)、鹤鹬(Tringa erythropus)和红脚鹬(Tringa totanus);G1集团水鸟种类有6种。这些水鸟的觅食生境主要在湖泊滩涂和浅水区域,其食物资源的可利用性和觅食对策共同决定群落组成结构。DCA分析表明,取食方式及取食时运动方式组成的觅食对策决定了集团食物资源的分割,草滩中取食鸟类主要采用静止取食和啄取方式,泥滩取食集团主要采取拾取及奔-停取食,深水区取食集团则主要采用潜水方式取食,因此,维持湖泊不同区域的丰富食物资源对于保护湖泊丰富的水鸟资源具有重要意义。     

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.     

Seeing without being seen: a removal experiment with mixed flocks of Willow and Crested Tits Parus montanus and cristatus

This paper tests the hypothesis that foraging site selection reflects a trade-off between the various needs for concealment from predators, to find food, and for the individual to maintain some view of its surroundings. After removal of Crested Tits Parus cristatus (the dominant species in mixed flocks), Willow Tits P. montanus did not decrease their foraging heights as expected but remained in the most exposed parts of young pines. In contrast, after removal of Willow Tits, Crested Tits increased their foraging height from the sheltered lower canopy to sites previously occupied by Willow Tits. When flock size was reduced, the birds maintained the same high levels of vigilance without concealing themselves in dense vegetation. I suggest that flock members may benefit from foraging in sites that afford good anti-predator vigilance.     

Social environment and immunity in male red jungle fowl

We examined the relationship between social dominance, immuneresponse, and ornamentation in captive red jungle fowl by comparingthese variables in males housed individually with a singlefemale to those in the same males after they were placed inflocks with an unfamiliar male and three unfamiliar females. Males with larger combs before being placed in the flocks weremore likely to become dominant, and dominant males' combs grewafter flock formation, whereas subordinate males' combs shrank.Immune response as reflected in hematocrit, immunoglobulinlevels, and wing web swelling (a measure of cell-mediated immunity)was stronger in males that later became dominant, both beforeand after flock formation, although the difference betweendominant and subordinate birds was more pronounced after maleswere housed in the multi-male groups. Dominant and subordinatemales also differed in the relationship between comb lengthand wing web swelling. Among dominant males, individuals withlarger combs had significantly larger swellings after flock formation, whereas within the subordinate males, those withrelatively larger combs had worse cell-mediated immunity thanthose with smaller combs. These results suggest that malesof different quality pay different costs to maintain both ornamentationand immune defense.     

Predation by Australian magpies (Gymnorhina tibicen) on pasture invertebrates: Are non-territorial birds less successful?

Diet composition and prey intake rates of Australian magpies in a New Zealand population were investigated to determine whether flocking, non-territorial birds were less successful predators of pasture invertebrates than territorial birds. Time-activity budgets showed that flock magpies foraged throughout the day during February and March, indicative of a prey shortage at that time. Prey abundance was therefore measured in the autumn months but there was no evidence of a large quantitative difference in the food supply of flock and territorial magpies. Significantly fewer invertebrates were collected from pitfall traps in the flock foraging area, but these were counterbalanced by significantly more scarab beetle larvae and more flying insects, obtained by sweep-netting. When compared with territorial magpies, flock birds exhibited similar peck rates, prey intake rates, and earthworm intake rates. While there were qualitative differences in the diets of flock and territorial magpies, determined by faecal analysis, five of seven prey items analysed were captured in the same relative proportions by the flock and territorial birds. Earthworms exceeded their relative availability in the diets of flock birds, and more scarab larvae were found in the diets of territorial magpies. Non-territorial magpies were therefore no less successful than territorial birds during the autumn, and it is suggested that the function of flocking behaviour may eventually be discovered through consideration of why non-territorial birds never occur as solitary individuals, rather than emphasizing comparisons with territorial magpies.     

Mortality of geese as a result of collision with the ground

Two incidents are reported in which groups of migrating wild geese were found dead in agricultural fields in southern Manitoba during spring. In each case, the birds died overnight and poisoning was suspected; however, the birds had lesions of severe traumatic injury. The first incident, in 1985, involved about 150 lesser snow geese (Anser caerulescens caerulescens); the second, in 2003, involved 62 Canada geese (Branta canadensis). Both incidents occurred on dark, moonless nights. One possible explanation is that the birds became disoriented in a manner analogous to spatial disorientation described in aircraft pilots and flew as a flock directly into the earth. In the first incident, geese might have been frightened by sonic booms from aircraft; in the second, there was a thunderstorm with strong gusty winds in the area.     

Costs and benefits of flocking in foraging white-fronted geese (Anser albifrons): effects of resource depletion

This study investigated the costs and benefits of flocking in white-fronted geese Anser albifrons foraging on rice grains in Japan. The time budgets of focal geese were recorded, and the effects of flock size on the proportions of time spent in vigilant and agonistic behaviour were tested. The results showed that the decline in vigilance level and consequent increase in foraging time were beneficial results of flocking whereas agonistic interactions, a potential cost of flocking, did not increase with increasing flock size. However, seasonal variation in flock size suggested that exploitative competition could be a cost of flocking; the sizes of flocks in spring, when resource depletion had progressed, were significantly reduced compared with those in autumn. An experimental increase in rice density resulted in a significant increase in flock size. We conclude that the flock size of foraging white-fronted geese is a result of compromise between a constant benefit of flocking (i.e. decline in vigilance level) and a cost of flocking varying with food abundance (i.e. exploitative competition).     

Familiarity Breeds Tolerance: the Development of Social Stability in Flocking Siskins (Carduelis spinus)

Behavioural integration associated with the fusion of two flocks is analyzed in captive siskins (Carduelis spinus) by quantifying changes in social behaviour with time since joining. In general there was an increase in the incidence of tolerant behaviour, supplanting attacks and hopping withdrawals with time since fusion of the flocks. However, the number of displays and flights showed the opposite, negative, trend. Taking dominance status into account, the greatest change in behaviour with time since joining is an increase in tolerance by dominants of new flock companions. Factorial analysis of correspondences was used to study how different birds changed their behaviour with time since joining a flock. This analysis showed that the introduction of new birds did not disrupt relationships with familiar birds, and that residents are dominant in interactions with the incoming new flock companions. The analysis also demonstrated that relationships within the new flock had stabilized 20 days after the flocks had joined. The characteristics of the socially integrated group of siskins are quite similar to those described by Rohwer & Ewald (1981) in their shepherds hypothesis: dominants tolerate their subordinates feeding in close proximity, offering them a profitable feeding area, but also supplant them to obtain food; both dominants and subordinates benefit from being in a flock. As a consequence, constant changes of membership in flocks is costly not only because birds lose dominance status, but also the advantages of clear dominant and subordinate roles.     

Travel schedules to the high arctic: barnacle geese trade-off the timing of migration with accumulation of fat deposits

On their way from the wintering area to the breeding grounds in Spitsbergen, barnacle geese Branta leucopsis stage on islands off the coast of Norway. The aim of this study was to describe when the geese migrate in relation to the body stores deposited and explore questions related to the concept of optimal migration schedules and on the possible mechanisms involved. We estimated fat stores by repeated assessments of the abdominal profile index of individually marked females throughout staging. Reproductive success was derived from observations of the same individuals later in the annual cycle. Females arriving late, or with low fat stores at arrival, achieved higher fat deposition rates, probably by spending more time foraging. But they were unable to match final fat scores of birds that arrived earlier or with larger fat stores. Reproductive success was correlated with the timing of migration and individuals departing at intermediate dates achieved highest success. The exact date of peak reproductive success depended on the size of fat stores accumulated, such that low-quality birds (depositing less fat) benefited most from an early departure to the breeding grounds. Observations in the breeding colonies showed that these birds did not initiate a nest earlier but they spent a longer time in Spitsbergen before settling. The length of stay in Norway was close to the prediction derived from an optimisation model relating spring events to eventual breeding success. Poorest performing birds stayed longer than expected, perhaps depositing more fat to avoid the risk of starvation. Two possible mechanisms of the timing of migration were contrasted and it seemed that the geese departed for migration as soon as they were unable to accumulate any more fat stores.     

The effects of demonstrator social status and prior foraging success on social learning in laying hens

Opportunities for social learning within a group of animals are likely to be influenced by the social dynamics of that group. Some individuals may be more influential demonstrators than others even when there are no differences in their skill level or performance. In this study of domestic hens, Gallus gallus domesticus, differences in demonstrator salience were examined. From 24 separate flocks we selected as demonstrators a dominant cockerel, a dominant hen, a mid-ranking hen or a subordinate hen. Demonstrators were pretrained to perform an operant discrimination task to obtain food. Six observers from each flock individually watched the demonstrator perform the task for four 5-min sessions held on consecutive days. On the fifth day observers were tested individually in the operant chamber. We analysed data from 19 flocks, where there were no quantitative differences in demonstrator performance. Observer hens of relatively high social status performed more correct operant pecks than observer hens of relatively low social status. Demonstrator category also had a significant effect on subsequent observer behaviour. Hens that had observed cockerels performed very few general pecks or operant pecks. Hens that had observed dominant hens performed more operant pecks, but hens that had observed sub-ordinate hens performed more general pecks in the chamber. The results suggested either that there was an interaction between dominance and gender in demonstrator salience or that dominant hens might have been influential because of some factor imperfectly associated with their dominance status. A possible candidate was the foraging ability of the dominant hens. In a second experiment using the same protocol, we manipulated the prior foraging success of dominant hens from four additional flocks but this had no significant effect on their subsequent influence as demonstrators. Copyright 1999 The Association for the Study of Animal Behaviour.