Daily body mass regulation in dominance-structured coal tit (Parus ater) flocks in response to variable food access: a laboratory study

In a dominance-structured flock, social status may determinepriority of access to food. Birds of low social status mayperceive present and future access to food as less predictable,and so have a higher risk of starvation, than birds of highsocial rank. Theoretical models predict that subordinate birdsshould carry larger fat reserves and incur higher mass-dependentcosts than dominants. However, empirical tests of the assumptionsof these models are still scarce and controversial. We investigatedthe effect of dominance rank on daily mass gain under conditionsof fluctuating food availability in a laboratory experimentusing four flocks of four coal tits (Parus ater) each. Thesame amount of food was delivered in two treatments, but inone treatment the food was offered at a constant rate betweendays (fixed treatment), while in the other treatment the dailyfood supply varied in an unpredictable sequence between days(variable treatment). All birds showed greater variance inbody mass in the variable treatment than in the fixed treatment.Body mass within birds showed the same variability at dawn thanat dusk in the fixed treatment, but less variability at dawnthan at dusk in the variable treatment. This may be a mechanismto reduce the immediate risk of starvation at the beginningof the day, when fat reserves are at their lowest and the aggressionbetween flock members when feeding highest. Subordinate birdswere excluded from the feeders by dominants more often in theearly morning than in the rest of the day, and they showedmore variability in daily mass gain and body mass at dawn thandominant birds. These results support the hypothesis that subordinatebirds have a reduced probability of surviving when food availabilitychanges unexpectedly compared to dominants.     

Starling Flock Networks Manage Uncertainty in Consensus at Low Cost

Flocks of starlings exhibit a remarkable ability to maintain cohesion as a group in highly uncertain environments and with limited, noisy information. Recent work demonstrated that individual starlings within large flocks respond to a fixed number of nearest neighbors, but until now it was not understood why this number is seven. We analyze robustness to uncertainty of consensus in empirical data from multiple starling flocks and show that the flock interaction networks with six or seven neighbors optimize the trade-off between group cohesion and individual effort. We can distinguish these numbers of neighbors from fewer or greater numbers using our systems-theoretic approach to measuring robustness of interaction networks as a function of the network structure, i.e., who is sensing whom. The metric quantifies the disagreement within the network due to disturbances and noise during consensus behavior and can be evaluated over a parameterized family of hypothesized sensing strategies (here the parameter is number of neighbors). We use this approach to further show that for the range of flocks studied the optimal number of neighbors does not depend on the number of birds within a flock; rather, it depends on the shape, notably the thickness, of the flock. The results suggest that robustness to uncertainty may have been a factor in the evolution of flocking for starlings. More generally, our results elucidate the role of the interaction network on uncertainty management in collective behavior, and motivate the application of our approach to other biological networks.     

The content and availability of information affects the evolution of social-information gathering strategies

Social animals can gather information by observing the other members of their groups. Strategies for gathering this type of social information have many components. In particular, an animal can vary the number of other animals it observes. European starlings (Sturnus vulgaris) in flight pay attention to a number of neighbors that allows the flock to reach consensus quickly and robustly. The birds may do this because being in such a flock confers benefits on its members, or the birds may use the strategy that is individually beneficial without regard for the flock’s structure. To understand when individual-level optimization results in a group-level optimum, we develop a model of animals gathering social information about environmental cues, where the cue can be about either predators or resources, and we analyze two processes through which the number of neighbors changes over time. We then identify the number of neighbors the birds use when the two dynamics reach equilibrium. First, we find that the equilibrium number of neighbors is much lower when the birds are learning about the presence of resources rather than predators. Second, when the information is about the presence of predators, we find that the equilibrium number of neighbors increases as the information becomes more widespread. Third, we find that an optimization process converges on strategies that allow the flock to reach consensus when the information is about the presence of abundant resources, but not when it is about the presence of scarce resources or predators.     

Diffusion and Topological Neighbours in Flocks of Starlings: Relating a Model to Empirical Data

Moving in a group while avoiding collisions with group members causes internal dynamics in the group. Although these dynamics have recently been measured quantitatively in starling flocks (Sturnus vulgaris), it is unknown what causes them. Computational models have shown that collective motion in groups is likely due to attraction, avoidance and, possibly, alignment among group members. Empirical studies show that starlings adjust their movement to a fixed number of closest neighbours or topological range, namely 6 or 7 and assume that each of the three activities is done with the same number of neighbours (topological range). Here, we start from the hypothesis that escape behavior is more effective at preventing collisions in a flock when avoiding the single closest neighbor than compromising by avoiding 6 or 7 of them. For alignment and attraction, we keep to the empirical topological range. We investigate how avoiding one or several neighbours affects the internal dynamics of flocks of starlings in our computational model StarDisplay. By comparing to empirical data, we confirm that internal dynamics resemble empirical data more closely if flock members avoid merely their single, closest neighbor. Our model shows that considering a different number of interaction partners per activity represents a useful perspective and that changing a single parameter, namely the number of interaction partners that are avoided, has several effects through selforganisation.     

OBSERVATIONS ON THE AUTUMN MIGRATION IN THE AREA BETWEEN THE SEA OF AZOV AND THE CASPIAN

Bird-migration was observed 5 October-14 November 1942 along 150 km. of railway line between Salsk and Stalingrad (between the Sea of Azov and the Lower Volga). The typical steppe-birds of South Russia were recorded—larks, harriers, bustards etc.—and also astonishing numbers of crows, starlings, finches, thrushes, pigeons and others. Magpies, Yellow Buntings (many), sparrows, Crested Larks, Great Tits and Partridges also appeared as migrants.
Most birds were travelling southwest or south but the geese were going west (except for one flock), as were Redwings and part of the Great Bustards and Yellow Buntings. Eastward movement was rare.
The immediate destination of the birds observed can only be presumed, but those flying west would reach the coasts of the Sea of Azov and very likely continue further. Birds flying southwest and south were headed for the eastern half of the Black Sea, or the Caucasus. This range, which forms a very pronounced barrier, is well known to be crossed by migrants.
After the autumn sojourn another period of observation followed, 1–18 January 1943 (mostly between Proletarskaja and Salsk).
In all, 45 species were observed alive, and under telegraph wires birds of 25 species were found dead, including 10 not otherwise recorded.     

Fear and exploration in European starlings (Sturnus vulgaris): a comparison of hand-reared and wild-caught birds

The revision of EU legislation will ban the use of wild-caught animals in scientific procedures. This change is partially predicated on the assumption that captive-rearing produces animals with reduced fearfulness. Previously, we have shown that hand-reared starlings (Sturnus vulgaris) indeed exhibit reduced fear of humans compared to wild-caught conspecifics. Here, we asked whether this reduction in fear in hand-reared birds is limited to fear of humans or extends more generally to fear of novel environments and novel objects. Comparing 6-8 month old birds hand-reared in the lab with age-matched birds caught from the wild as fledged juveniles a minimum of 1 month previously, we examined the birds' initial reactions in a novel environment (a small cage) and found that wild-caught starlings were faster to initiate movement compared to the hand-reared birds. We interpret this difference as evidence for greater escape motivation in the wild-caught birds. In contrast, we found no differences between hand-reared and wild-caught birds when tested in novel object tests assumed to measure neophobia and exploratory behaviour. Moreover, we found no correlations between individual bird's responses in the different tests, supporting the idea that these measure different traits (e.g. fear and exploration). In summary, our data show that developmental origin affects one measure of response to novelty in young starlings, indicative of a difference in either fear or coping style in a stressful situation. Our data contribute to a growing literature demonstrating effects of early-life experience on later behaviour in a range of species. However, since we did not find consistent evidence for reduced fearfulness in hand-reared birds, we remain agnostic about the welfare benefits of hand-rearing as a method for sourcing wild birds for behavioural and physiological research.     

Effects of predictable and unpredictable food restriction on the stress response in molting and non-molting European starlings (Sturnus vulgaris)

This study tested whether an ethologically relevant stressor, a three-week period of food restriction where food was unavailable for four hours a day, caused chronic stress in molting and non-molting captive European starlings. Although all birds increased weight during the Food Restriction period, only non-molting birds increased food intake. Morning baseline heart rates increased during the Food Restriction period and all birds showed a decrease in heart rate when food was absent from the cage. In non-molting birds, there were no differences in either baseline or stress-induced corticosterone (CORT) concentrations, whereas molting birds showed attenuated baseline CORT, stress-induced CORT, and fecal glucocorticoid metabolite levels over the Food Restriction period. Although several parameters, such as increased morning heart rate, are consistent with chronic stress, the majority of these data suggest that restricting food availability is not chronically stressful. Furthermore, making the timing of food removal less predictable by randomizing when food was removed during the day did not enhance any of the above responses, but did alter the frequency of maintenance and feeding behaviors. In conclusion, starlings appear resistant to developing symptoms of chronic stress from repeated food restriction.     

Flock size and habitat-dependent food and energy intake of foraging Goldfinches

Summary During the breeding season Goldfinches (Carduelis carduelis L.) feed on milky ripe seeds of about 20 food plants. Individual Goldfinches joining a flock reduce the time spent vigilant with increasing flock size. Therefore birds feeding in flocks get an increased intake of kernels per time unit. This was measured for five different food plants (Dactylis glomerata (Gramineae), Knautia arvensis (Dipsacaceae), Senecio vulgaris, Taraxacum officinale, Tragopogon pratensis (Compositae)). In large-sized flocks, birds fed up to 2.3 times more kernels, than when feeding solitarily. In addition, visibility in the vegetation leads to a further increase of kernel intake. Thus feeding under good conditions as in recently mown areas, can raise kernel intake to the seven fold per time unit as compared to solitary feeding. The maximum ingestion rate of kernels was 98 per min which implies a head up-and-down movement every 0.6 s. The calculated energy intake of birds per time unit is lowest in Senecio and highest in Tragopogon. Thus the birds, when feeding on Tragopogon in larger flocks, can gain an energy intake 16 times higher than that reached when feeding on Senecio, despite of a higher kernel intake rate. The energy intake individual Goldfinches gain at the particular plant species is markedly increased with flock sizes up to eight birds, with larger flocks the intake increases only slightly.     

The use of a mirror as a 'social substitute' in laboratory birds

A mirror has been shown to reduce stereotypies in horses housed singly, presumably as it may provide some sort of 'social stimulation'. We investigated here whether a mirror may have such a 'quietening effect' on birds kept in a laboratory, such as European starlings. We observed the reactions to a mirror of starlings of different sexes and with different social experiences. Females and pair-raised males seemed calmer, showing less movement and more comfort behaviour than socially and single-raised birds. The results are discussed in the light of the species' social organization and the effect of social experience. We conclude that a mirror might be a good way to reduce isolation-related stress in laboratory birds, but that sex and social experience of an individual have to be taken into account, as otherwise effects opposite to those wished for may be induced.     

Avian influenza A virus susceptibility,infection, transmission,and antibody kinetics in European starlings

Avian influenza A viruses (IAVs) pose risks to public, agricultural, and wildlife health. Bridge hosts are spillover hosts that share habitat with both maintenance hosts (e.g., mallards) and target hosts (e.g., poultry). We conducted a comprehensive assessment of European starlings (Sturnus vulgaris), a common visitor to both urban and agricultural environments, to assess whether this species might act as a potential maintenance or bridge host for IAVs. First, we experimentally inoculated starlings with a wild bird IAV to investigate susceptibility and replication kinetics. Next, we evaluated whether IAV might spill over to starlings from sharing resources with a widespread IAV reservoir host. We accomplished this using a specially designed transmission cage to simulate natural environmental transmission by exposing starlings to water shared with IAV-infected mallards (Anas platyrhynchos). We then conducted a contact study to assess intraspecies transmission between starlings. In the initial experimental infection study, all inoculated starlings shed viral RNA and seroconverted. All starlings in the transmission study became infected and shed RNA at similar levels. All but one of these birds seroconverted, but detectable antibodies were relatively transient, falling to negative levels in a majority of birds by 59 days post contact. None of the contact starlings in the intraspecies transmission experiment became infected. In summary, we demonstrated that starlings may have the potential to act as IAV bridge hosts if they share water with IAV-infected waterfowl. However, starlings are unlikely to act as maintenance hosts due to limited, if any, intraspecies transmission. In addition, starlings have a relatively brief antibody response which should be considered when interpreting serology from field samples. Further study is needed to evaluate the potential for transmission from starlings to poultry, a possibility enhanced by starling’s behavioral trait of forming very large flocks which can descend on poultry facilities when natural resources are scarce.     

Redshank Tringa totanus flocking behaviour, distance from cover and vulnerability to sparrowhawk Accipiter nisus predation

Over 11 winters I examined the interactions between sparrowhawk Accipiter nisus attack behaviour, the gregariousness of redshanks Tringa totanus and local geography to test hypotheses that suggest birds should flock to reduce their risk of predation and that predation risk should decline with the prey's distance from cover. Sparrowhawk attacks on redshanks feeding on beaches around the high tide mark (the strandline zone) were more frequent and more successful than attacks on redshanks feeding seaward of the strandline zone (in the intertidal zone). The results therefore confirmed hypothetical expectations that predation risk should decline with distance from cover. Flocking only appeared to influence the outcome of hawk attacks at shorter distances from cover on the strandline, with attacks on singletons and small flocks being more successful than attacks on larger flocks. Distance from cover had a stronger influence on the likelihood of attack success than did flock size. Mid-range flock sizes (6–45 birds) were attacked more frequently than expected, but singletons and large flocks were attacked less than expected. Despite these differences an individual redshank's likelihood of predation by a sparrowhawk declined with increasing flock size, thereby confirming the 'dilution effect' and 'vigilance' hypotheses for the evolution of flocking in birds. Food intake rates of redshanks declined with increasing flock size, further indicating that redshanks flocked to avoid predation rather than to increase their food intake rates. The strong interaction between two influences on predation risk revealed by the present study suggests other studies should take great care when considering a single influence on predation risk in isolation from others.     

Intraflock variation in the speed of escape-flight response on attack by an avian predator

The benefits of flocking to prey species, whether through collective vigilance,dilution of risk, or predator confusion, depend on flock members respondingin a coordinated way to attack. We videotaped sparrowhawks attackingredshank flocks to determine if there were differences in thetiming of escape flights between flock members and the factorsthat might affect any differences. Sparrowhawks are surpriseshort-chase predators, so variation in the time taken to takeflight on attack is likely to be a good index of predation risk.Most birds in a flock flew within 0.25 s of the first bird flying,and all birds were flying within 0.7 s. Redshanks that werevigilant, that were closest to the approaching raptor, and thatwere close to their neighbors took flight earliest within aflock. Birds in larger flocks took longer, on average, to takeflight, measured from the time that the first bird in the flockflew. Most birds took flight immediately after near neighbors tookoff, but later flying birds were more likely to fly immediatelyafter more distant neighbors took flight. This result, alongwith the result that increased nearest neighbor distance increasedflight delay, suggests that most redshanks flew in responseto conspecifics flying. The results strongly suggest that thereis significant individual variation in predation risk withinflocks so that individuals within a flock will vary in benefitsthat they gain from flocking.     

Influence of habitat and season on foraging flock composition in the European Starling (Sturnus vulgaris)

Summary This study examines the relative importance of habitat and season in determining size and composition of foraging flocks of European Starlings (Sturnus vulgaris). We hypothesized that if season was the principal determinant of flock size, variation across seasons (within habitat) would be greater than variation across habitats (within season). The calendar year was divided into 6 seasons corresponding to major stages in the annual cycle of starlings. After measuring the availibility of 15 foraging habitats occurring within the study area, we drove a 184 km route weekly (over a 17 month period) to census starling flock size, species composition, habitat use, and activity.Although flock size was influenced by both season and habitat, it varied relatively less within seasons (across habitats). Only five of nine seasons showed significant habitat effects, and two (of the five) were significant mainly because of large aggregations in habitats with unusually abundant food (e.g. feedlots, cornfields). In contrast, eight of nine habitats showed significant seasonal effects. The only exception (hay) was little used (<1% of all birds observed). For starlings the activities associated with seasonal events of the annual cycle were a major influence on patterns of social foraging. Habitat factors were less important because of constraints imposed by seasonal factors, but under some conditions (e.g. drought, clumped food supply) they became dominant.     

灰椋鸟身体大小和内脏器官形态的两性差异

鸟类性二态现象广泛存在,比如身体大小、羽色等,性二态很可能是自然选择和性选择共同作用的结果.为了探索和更好地了解雀形目鸟类身体大小性二态的进化,在2019年繁殖季节早期研究了灰椋鸟(Sturnus cineraceus)野外种群身体大小和内脏器官形态的两性差异.结果表明,除嘴宽外,其他身体特征参数均雄性显著大于雌性,表...     

Timing and speed of migration in male, female and juvenile Ospreys Pandion haliaetus between Sweden and Africa as revealed by field observations, radar and satellite tracking

Breeding Ospreys were studied in southern Sweden and 13 birds were tracked by satellite telemetry on autumn migration to the African wintering grounds. This was supplemented with studies of migrating birds at Falsterbo and radar trackings from southern Sweden. Females generally left the nest site 2–3 weeks ahead of males and juveniles. Among males, failed breeders migrated significantly earlier than successful breeders. At Falsterbo, Ospreys passed in the order adult females (median 22 Aug), adult males (26 Aug) and juveniles (30 Aug). Birds tracked by radar achieved cross‐country speeds of 18–47 km/h. Most of our birds wintered in an area from The Gambia to the Ivory Coast, with one juvenile in Cameroon and one female in Mozambique. Ospreys spent on average 45 days travelling an average distance of 6742 km with no significant differences between sex and age categories. Between 0 and 44 days were used for stopovers en route. Females generally made more stopovers at northerly latitudes than males. Average speed on migration was 174 km/d, which is similar to speeds reported for other large raptors followed by satellite. Speed on travelling days was on average 257 km/d with males generally moving fastest. There was a clear tendency for lower speeds and more stopovers in Europe than during the crossing of the Sahara. Migratory activity generally took place between 8 a. m. and 5 p. m. local time and we have no indications of birds flying at night. With 9 hours travelling time the expected cross‐country speed, derived from the theory of thermal soaring flight and assuming thermal climb rates of 1–2 m/s, varies from 251 to 360 km/d, which is similar to the observed mean speed on travelling days. Even so, one male travelled 746 km/d between Sweden and Spain. Some Ospreys need a much larger fraction of travelling days than expected from theory, suggesting that they deposit fuel on the breeding grounds before departure. This is supported by a correlation between the observed fraction of days spent travelling and departure date. In late departing Ospreys, especially males and juveniles, a major part of the energy for migration is probably deposited on the breeding grounds.     

The effects of cage volume and cage shape on the condition and behaviour of captive European starlings (Sturnus vulgaris)

Cage size is widely recognised as an important determinant of captive animal welfare, but in contrast, cage shape has received far less attention. Husbandry recommendations for flying birds state that cages should be long in shape because this allows greater potential for flight. However, so far no studies have investigated the impact of cage shape on the behaviour or welfare of captive flying birds. We measured the effects of cage size and shape on the condition and behaviour of captive wild-caught European starlings (Sturnus vulgaris) using a 2 × 3 factorial design in which birds were individually housed for 1 week in cages of one of two volumes (either medium at 0.3 m³ or large at 1 m³), and one of three shapes (long with an aspect ratio (i.e. length/height) of 3.43), standard with an aspect ratio of 1.72 or tall with an aspect ratio of 0.86). We found effects of cage size and the interaction of cage size and shape on the behaviour and condition of birds. In interpreting the welfare implications of our results we focused on stereotypic behaviour as measured by incidence of somersaulting and a novel statistic that quantifies sequential dependencies in the birds’ locations within the cage. The lowest measures of stereotypic behaviour were recorded in the large cages and the medium long cage. Cage shape was more important in determining the quantity of stereotypic behaviour in the medium cages than the large cages. Our findings support the recommendation that starlings be housed in long-shaped cages.     

Experience with adults shapes multisensory representation of social familiarity in the brain of a songbird

Social animals learn to perceive their social environment, and their social skills and preferences are thought to emerge from greater exposure to and hence familiarity with some social signals rather than others. Familiarity appears to be tightly linked to multisensory integration. The ability to differentiate and categorize familiar and unfamiliar individuals and to build a multisensory representation of known individuals emerges from successive social interactions, in particular with adult, experienced models. In different species, adults have been shown to shape the social behavior of young by promoting selective attention to multisensory cues. The question of what representation of known conspecifics adult-deprived animals may build therefore arises. Here we show that starlings raised with no experience with adults fail to develop a multisensory representation of familiar and unfamiliar starlings. Electrophysiological recordings of neuronal activity throughout the primary auditory area of these birds, while they were exposed to audio-only or audiovisual familiar and unfamiliar cues, showed that visual stimuli did, as in wild-caught starlings, modulate auditory responses but that, unlike what was observed in wild-caught birds, this modulation was not influenced by familiarity. Thus, adult-deprived starlings seem to fail to discriminate between familiar and unfamiliar individuals. This suggests that adults may shape multisensory representation of known individuals in the brain, possibly by focusing the young's attention on relevant, multisensory cues. Multisensory stimulation by experienced, adult models may thus be ubiquitously important for the development of social skills (and of the neural properties underlying such skills) in a variety of species.     

Is the Periodic “Spontaneous” Activity of Animals Determined by a Quasi-Rhythmic Factor of the External Environment?

Doklady Biological Sciences - We have studied the dynamics of the singing of garden bunting (Emberiza hortulana) and the dispersal of a flock of starlings (Sturnus vulgaris) for the night rest. The...     

Relation of group size and daily activity patterns to southern lapwing (Vanellus chilensis) behaviour

Behavioural patterns of birds commonly vary according to flock size and daily activity pattern. Southern lapwing behaviours and their relation with flock size were studied, as well as the relationship between the frequency of behaviours and the period of the day. Results showed that the proportion of time spent in foraging and vigilance was higher during the morning, when small groups were more common, and decreased from midday on, when group size increased. Maintenance and inactivity (sleeping) behaviours presented the opposite pattern. Correlation between flock size and period of the day, and their similar effects on bird behaviour may be evidence that groups of different sizes could have different functions throughout the day. Our results show that southern lapwings seem to form smaller flocks for feeding in the beginning of the day and larger flocks later for different activities (e.g., maintenance and sleeping). In this sense, it is possible that group size variation throughout the day is related to different demands for specific behaviours (functions) of groups, according to the daily activity patterns of the birds.     

Diffusion of individual birds in starling flocks

Flocking is a paradigmatic example of collective animal behaviour, where global order emerges out of self-organization. Each individual has a tendency to align its flight direction with those of neighbours, and such a simple form of interaction produces a state of collective motion of the group. When compared with other cases of collective ordering, a crucial feature of animal groups is that the interaction network is not fixed in time, as each individual moves and continuously changes its neighbours. The possibility to exchange neighbours strongly enhances the stability of global ordering and the way information is propagated through the group. Here, we assess the relevance of this mechanism in large flocks of starlings (Sturnus vulgaris). We find that birds move faster than Brownian walkers both with respect to the centre of mass of the flock, and with respect to each other. Moreover, this behaviour is strongly anisotropic with respect to the direction of motion of the flock. We also measure the amount of neighbours reshuffling and find that neighbours change in time exclusively as a consequence of the random fluctuations in the individual motion, so that no specific mechanism to keep one''s neighbours seems to be enforced. On the contrary, our findings suggest that a more complex dynamical process occurs at the border of the flock.