Flock Members Research Articles

Nepotistic vigilance behavior in Siberian jay parents

Many Siberian jay offspring (up to 50%) postpone independence and stay with their parents for up to 3 years. Parents offer such nondispersers a benefit in that they increase their vigilance while feeding together with retained offspring. In contrast, parents reduce their vigilance while in company of nonrelated flock members according to the “many eyes” principle. The preferential treatment offered by the parents provides an incentive for offspring to forego dispersal. Given evidence for mortality via surprise attacks by predators (goshawks), such nepotistic vigilance by parents could have a bearing on offspring survival and thereby promote delayed dispersal.

Strained energy budget of winter floaters in the Willow Tit as indicated by ptilochronology

Most Willow Tits Parus montanus live within flock territories during the non‐breeding season, but many juveniles roam around or switch between several flocks. Such floaters behave submissively and spend time watching other flock members in addition to scanning for predators. During September–December 1989–2000, I studied individually colour‐ringed Willow Tits living in a subalpine forest area in central Norway. When among flock members, the floaters foraged less in favourable parts of trees and were more vigilant than the lowest‐ranked juvenile flock members. The nutritional condition of the birds was assessed by examining the growth bar widths of their tail feathers. Birds in better condition have wider growth bars than those in poorer condition. The daily growth bars of induced feathers of male and female floaters, laid down under winter conditions, were significantly narrower than those of the lowest ranked flock members. These results suggest that juvenile floater Willow Tits maintain a poorer nutritional status than low‐ranking juvenile flock members during winter.

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 determine priority of access to food. Birds of low social status may perceive present and future access to food as less predictable, and so have a higher risk of starvation, than birds of high social rank. Theoretical models predict that subordinate birds should carry larger fat reserves and incur higher mass-dependent costs than dominants. However, empirical tests of the assumptions of these models are still scarce and controversial. We investigated the effect of dominance rank on daily mass gain under conditions of fluctuating food availability in a laboratory experiment using four flocks of four coal tits (Parus ater) each. The same amount of food was delivered in two treatments, but in one treatment the food was offered at a constant rate between days (fixed treatment), while in the other treatment the daily food supply varied in an unpredictable sequence between days (variable treatment). All birds showed greater variance in body mass in the variable treatment than in the fixed treatment. Body mass within birds showed the same variability at dawn than at dusk in the fixed treatment, but less variability at dawn than at dusk in the variable treatment. This may be a mechanism to reduce the immediate risk of starvation at the beginning of the day, when fat reserves are at their lowest and the aggression between flock members when feeding highest. Subordinate birds were excluded from the feeders by dominants more often in the early morning than in the rest of the day, and they showed more variability in daily mass gain and body mass at dawn than dominant birds. These results support the hypothesis that subordinate birds have a reduced probability of surviving when food availability changes unexpectedly compared to dominants.

Receivers respond differently to chick-a-dee calls varying in note composition in Carolina chickadees, Poecile carolinensis

The chick-a-dee call of the avian genus Poecile is a structurally complex vocal system because it possesses a set of simple rules that governs how the notes of the call are ordered, and variable numbers of each of the note types strung together can generate an extraordinary number of unique calls. Whereas it has been hypothesized that chick-a-dee calls with different notes may convey different information, no experimental evidence has been offered in support of the hypothesis. Previously published studies suggested that flock members use chick-a-dee calls in the context of moving to or from a feeding site. Here, we tested Carolina chickadees' responses to playbacks of chick-a-dee calls that differed in note composition. Playbacks were conducted in the field in the context of a novel food source. Our pilot data had indicated that chick-a-dee calls with relatively large numbers of ‘C’ notes were given by birds on their first contact with a novel seed stand. In the present study, we found that chickadees flew in close to the playback speaker and subsequently took seed from a seed stand more often during playbacks of chick-a-dee calls containing C notes than chick-a-dee calls not containing C notes or than control playbacks. Vocal responses of chickadees to the playbacks also differed in relation to the particular vocal signal being played back. These results indicate that receivers respond differently to chick-a-dee calls containing different compositions of note types and represent a first step to link variation in note composition and ordering in these calls to possible meanings.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .

Factors causing variation in flock size: Decision making to join a foraging flock

In order to clarify the temporal variation of flock size, we examined factors that cause the temporal variation of foraging flock size in a wintering population of the Yellow‐throated bunting (Emberiza elegans). We conducted field observations to examine whether the flock size varies greatly and whether non‐random associations between individuals exist. We confirmed that flock size varied greatly and some individuals showed non‐random associations with other flock members. Then, we carried out computer simulations that assume stochastic risky situation, the condition of hunger level and non‐random associations between individuals. In the simulation, the condition of hunger level caused the variation of flock size. However, the distribution of flock size differed from observed ones. When the condition of non‐random association was added to the simulation, the variation of flock size became large and the distribution of flock size was similar to that of the observed one. In wintering flocks of Yellow‐throated bunting, each individual attempts to forage in an optimal flock size. However, if they are extremely starved, it is suggested that they adopt a conditional strategy to join a flock independently of the flock size to acquire the energy necessary for survival. Simultaneously, they may decide to forage under the effect of non‐random association between individuals.

Mass-dependent take-off ability in wintering great tits ( Parus major ): comparison of top-ranked adult males and subordinate juvenile females

When birds are attacked by predators, initial take-off is crucial for survival. Theoretical studies have predicted that predation risk in terms of impaired flight ability increases with body weight. However, studies in which attacks were simulated, and within-individual daily changes in body weight were used to test mass-dependent take-off outside migration period, have so far failed to show an effect of mass on velocity. In this field study I compared the mass/velocity relationships of alarmed adult male and juvenile female great tits, Parus major. Fattening strategies differ among members of the dominance-structured basic flocks of wintering great tits, and dominant individuals often carry significantly less amount of fat reserves than subordinates. Since the range of body weight gain/loss is the least among dominant males, it was expected that impaired flight ability is more likely in lower-ranked female great tits. The results show that the birds differed significantly in their daily increase of relative body weight. Average daily weight increase of adult males was 6.2%, while it was 12.2% in juvenile females. Males were faster than females at take-off both at dawn and at dusk. Flight velocity of males did not differ significantly between dawn and dusk, whereas females took off at a significantly lower speed at dusk than at dawn. The results suggest that the larger fat reserves of subordinate females needed to increase their chances of overwinter survival probably place them at increased risk of predation.

Breeding bird community and mixed-species flocking in a deciduous broad-leaved forest in western Madagascar

The breeding bird population of a deciduous broadleaved forest in west- ern Madagascar was censused by means of territory mapping. Despite the foliage structure being simpler, neither species richness nor density was less than those in mature temperate forests. Species diversity was higher in the western Madagascan forest owing to the higher species evenness. Tree-cavity nesters and bark foragers were few because woodpeckers, nuthatches, and tits have not colonized Madagascar. The scarcity of birds nesting on or near the forest floor may be attributable to abun- dance of nest-predators such as large lizards and snakes in these areas. The bird com- munity was dominated in abundance by the members of mixed-species flocks, almost all of which forage in the canopy. Mixed-flocking can be beneficial for these birds to avoid predation by raptors, which were frequently observed in the canopy. Since most of the flock members had relatively similar territory sizes resulting in similar densi- ties, the high species evenness in this community may have resulted from mixed- flocking by canopy-foraging species.

Mixed‐species bird flocks in dipterocarp forest of north‐central Burma (Myanmar)

We studied the bird community in deciduous, dipterocarp forest of north‐central Burma (Myanmar) during December 1994, March 1996, and January 1997 and 1999. Most members of this community participated in mixed‐species flocks. Seventy‐three flocks were encountered during our study, containing 52 species. Of these, 25 species occurred in more than 10% of flocks, and were included in our analyses. There were 26 significant correlations among species pairs, 25 of which were positive. Cluster analysis indicated that there were three principal types of flocks: one consisting mostly of small passerines and picids, commonly including Common Wood‐Shrike, Small Minivet and White‐browed Fantail, among others; a second type consisting mainly of sylviids, e.g. Arctic, Dusky and Radde's Warblers; and a third type which generally centred around Greater and Lesser Necklaced Laughingthrushes. Bird‐eating hawks were numerous at these sites, and we witnessed several attacks on flocks during the study. Thus we infer that enhanced protection from predation is an important benefit conferred by flock membership. In contrast, there was little overlap in foraging behaviour among species, suggesting that foraging facilitation is a relatively minor benefit enjoyed by flock members, although we did observe White‐browed Fantails and Greater Racket‐tailed Drongos kleptoparasitizing other species on occasion.

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.

THE SURVIVAL VALUE OF FLOCKING IN NEOTROPICAL BIRDS: REALITY OR FICTION?

Greater foraging efficiency and/or better predator avoidance have long been assumed and used as explanations for the evolution of flocking behavior in birds. Even if the debate between the validity of these two hypotheses remains open, one prediction is that living in flocks can favor increased survival rates. We gathered published and unpublished data from various tropical forests where bird species forage (1) exclusively alone or in pairs (2) in heterospecific flocks some of the time (facultative flock members), or (3) exclusively in heterospecific year-long associations (obligate flock members). We controlled statistically for effects of body size, nest type, clutch size, and phylogeny, and tested whether survival rates differed among these three groups. The survival rates of the obligate flock members (mean survival rate 68.7%, range 48.0–87.0%) were significantly higher than estimates for the species feeding alone or in pairs (mean survival rate 58.3%, range 33.0–79.0%). However, survival rates of the facultative flock members (mean survival rate 60.4%, range 40.0–79.0%) did not differ from those of the nonflocking species. Nevertheless, causes of such differences in survival can be explained by an alternative hypothesis. Life history theory predicts that higher survival for the obligate flocking species may be a response to low fecundity and productivity. Yet, the pattern “high survivorship, strikingly low fecundity” documented in obligate flocking species has never been observed among their solitary or facultative flocking counterparts. This result suggests that permanent obligate flocking can be an alternative ecological factor that may drive the evolution of life histories in tropical birds.

Winter Flocking of Insectivorous Birds in Montane Pine-Oak Forests in Middle America

Abstract We studied mixed-species insectivorous bird flocks in pine-oak forests in Middle America during three winter seasons to determine whether patterns of flock structure and dynamics were similar to those reported from other tropical sites. We also analyzed patterns of association among bird species, as well as their foraging behavior and the vegetation characteristics associated with birds in flocks. We encountered 333 flocks containing 144 species, of which 26 species had adequate sample sizes for analyses. The size and rate of movement of the flocks were similar to those reported from other Neotropical sites, however, the species richness of our flocks was lower than reported in most other studies, perhaps due to simpler vegetation structure or higher latitude. Only 3 of 50 significant correlations between species pairs were negative, indicating that species generally were not restricted in their participation in mixed-species flocks by other species. In only one instance did we observe correspondence between the association of species-pairs in flocks and their foraging behavior. For most species there was no relationship between association between species-pairs in flocks and vegetation parameters with which they were associated. Thus, additional factors besides foraging facilitation and mutual association with particular vegetation characteristics must be responsible for many of the positive correlations among species pairs. We suggest that non-random association among species within flocks may result in part from enhanced vigilance for predator detection afforded by flock members using similar parts of the environment at the same time.

Rearing Conditions for Lambs May Increase Tansy Ragwort Grazing

Grazing by sheep is an accepted method of controlling tansy ragwort (Senecio jacobaea L.), but some flock members seldom eat it. Our objectives were to determine if pre-weaning exposure to tansy ragwort increases later consumption of the plant by lambs, and if confinement with ragwort-eating ewes after weaning facilitates ragwort eating. The sampling periods were Weeks 1, 3, and 12 following weaning. During each period grazing behavior was observed for 1-hour each day and the 24-hour reduction in ragwort volume measured on each of 4 or 5 consecutive days. Lambs exposed to ragwort before weaning removed more ragwort than ragwort-naive lambs during the first 2 sampling periods (P < 0.05). Lambs that grazed with ewes for 11 weeks following weaning ate ragwort more frequently during direct observation, than lambs without ewes during Weeks 3 and 12 (P < 0.05). The ragwort-eating of all lamb groups increased markedly between Weeks 1 and 12 (P < 0.05). This may indicate an increased ability of lambs to consume ragwort with increasing age or an acclimation period during which most lambs come to accept ragwort. Behavioral interventions aimed at increasing the consumption of weeds by lambs may need to take into account age-related differences in toxin tolerances. Exposing lambs to ragwort before weaning and grazing newly-weaned lambs with older ragwort-eating sheep after weaning may increase later ragwort-eating by lambs. DOI:10.2458/azu_jrm_v53i4_sutherland

FLOCKING AND FORAGING BEHAVIOR OF WINTERING PROTHONOTARY WARBLERS

We quantified flocking behavior and examined the impact of social context (solitary, single-species flocks, and mixed-species flocks) on the foraging behavior of Prothonotary Warblers (Protonotaria citrea) wintering in a Costa Rican mangrove forest and surrounding habitats. Based on observations collected over two winters during 70 visits to four sites, 87% (483) of the 555 Prothonotary Warblers encountered moved in flocks and over 48% (271) of these individuals were in single-species flocks. Although the propensity to join flocks was 6% higher for Prothonotary Warblers in the second winter of the study, neither the average size of single-species flocks nor the average number of individuals or species in mixed-species flocks differed between years. Twenty-seven different species were identified in mixed-species flocks that had at least one Prothonotary Warbler, but Nearctic migrants dominated these flocks. Analyses of focal observations on 57 females and 93 males indicated that Prothonotary Warbler foraging behavior was largely independent of flock type and size. Foraging maneuver, substrate, and location did not differ significantly for individuals of either sex foraging alone, in single-species, or mixed-species flocks. The species is almost strictly insectivorous, gleaning made up 70% of 150 prey capture attempts observed and about half of all attempts (76 of 150) were directed towards leaf surfaces. Foraging generally occurred in the outer third of the tree, on branches less than 1 cm in diameter, in the bottom half of the canopy. Agonistic interactions among flock members that involved Prothonotary Warblers were uncommon and neither flock type nor size were useful predictors for rates of foraging, movement, preening, or vigilance.

VIGILANCE IN BRONZE MANNIKIN GROUPS: THE CONTRIBUTIONS OF PREDATION RISK AND INTRA-GROUP COMPETITION

Abstract We describe foraging behaviour and time budgets of the gregarious bronze mannikin, Lonchura cucullata. In addition to being the first such study of a southern African granivore, this was the first study of a group-forager to differentiate between vigilance for other flock members (conspecifics) and vigilance for predators. We verified a perception of predation risk by placing five feeders at increasing distances from cover. The mean number of birds at a feeder decreased significantly with increasing distance from cover. We manipulated levels of aggression by restricting access to random numbers of feeding holes at various distances. The treatments succeeded in forcing birds to feed further from cover, and by inference, increased levels of aggression. We measured time budgets with focal samples on marked individuals. There was no influence of group size on time budgets. There was a non-significant (p &lt; 0.06) trend for vigilance to increase with increasing distance from cover (predation risk). There was no pattern in the relative vigilance for predators as opposed to vigilance for other flock members (conspecifics), either with group size, distance from cover, or manipulated levels of aggression. Despite our inability to detect patterns of vigilance for other flock members, we emphasize the importance of studies to elucidate such a process.

Resemblance within flocks and individual differences in feather mite abundance on long-tailed tits, Aegithalos caudatus (L.)

Even though feather mites are arthropod ectosymbionts widely distributed on almost all orders of birds, the nature and functional relationship of the interaction between feather mites and birds remain unclear. In this paper, we analyzed factors determining the distribution of feather mites at the individual as well as at the flock level, searching for correlates with bird characteristics such as body size and fat accumulation during winter. Long-tailed tits, Aegithalos caudatus (L.), live in family flocks during winter. Foraging, roosting and territory defence are done in groups. Communal roosting facilitates direct body contact among flock members, which may enhance the transmission of feather mites. Feather mite abundance was more similar within than among flocks. Within flocks, those individuals with longer wings and better body condition as determined by fat scores had larger numbers of feather mites. At the flock level, no relationship was found between mean mite intensity and any of the considered variables. We show that the distribution of feather mites among long-tailed tits is not random, but is shaped by individual features and flock ownership.

Individual Distances among Greater Flamingos as Indicators of Tourism Pressure

-One of the greatest challenges facing ecologists and conservationists is to ensure the continued coexistence of wildlife with the increasing pressure of human recreation. In birds, the use of flock members to reduce individual levels of vigilance has been the focus of many studies that have tried to explain the relationship among vigilance, group size, and distance to cover by using foraging or preening as indicators of disturbance. To avoid the confounding variables associated with foraging and preening, in this study I observed the effects of increasing levels of human disturbance on vigilance by measuring distances among individuals in flocks of Greater Flamingos (Phoenicopterus ruber roseus). Reactions to 112 disturbances were recorded during 61 hr of observation. Undisturbed flamingos exhibited no relationship between individual distance and flock size. When joggers appeared, birds became alert but continued to feed. Individual distance was not influenced by flock size when motor vehicles (jeeps) drove past, but was different in value from that in undisturbed flocks. However, when tour groups stopped and the occupants got out of vehicles, individual distance was significantly reduced and flock size positively influenced flock cohesiveness (i.e., smaller flocks had smaller individual distance values than large flocks). Flamingos appeared to be especially disturbed by all-terrain vehicles (ATVs), and in 82% of the encounters they flew away. In these cases, flock cohesiveness was extremely dense, but flock size did not influence flock reaction. This study demonstrated that flocking species seek protection in numbers, but they leave an area when insufficient conspecifics are present and when serious disturbance occurs. LAS DISTANCIAS INDIVIDUALES ENTRE FLAMENCOS COMUNES COMO INDICADORES DE LA

Rearing conditions for lambs may increase tansy ragwort grazing

Grazing by sheep is an accepted method of controlling tansy ragwort (Senecio jacobaea L.), but some flock members seldom eat it. Our objectives were to determine if pre-weaning exposure to tansy ragwort increases later consumption of the plant by lambs, and if confinement with ragwort-eating ewes after weaning facilitates ragwort eating. The sampling periods were Weeks 1, 3, and 12 following weaning. During each period grazing behavior was observed for 1-hour each day and the 24-hour reduction in ragwort volume measured on each of 4 or 5 consecutive days. Lambs exposed to ragwort before weaning removed more ragwort than ragwort-naive lambs during the first 2 sampling periods (P &lt; 0.05). Lambs that grazed with ewes for 11 weeks following weaning ate ragwort more frequently during direct observation, than lambs without ewes during Weeks 3 and 12 (P &lt; 0.05). The ragwort-eating of all lamb groups increased markedly between Weeks 1 and 12 (P &lt; 0.05). This may indicate an increased ability of lambs to consume ragwort with increasing age or an acclimation period during which most lambs come to accept ragwort. Behavioral interventions aimed at increasing the consumption of weeds by lambs may need to take into account age-related differences in toxin tolerances. Exposing lambs to ragwort before weaning and grazing newly-weaned lambs with older ragwort-eating sheep after weaning may increase later ragwort-eating by lambs.

Patch Size and Composition of Social Groups in Wintering Tufted Titmice

Formation of small, non-kin flocks in winter is typical of many resident passerines of the temperate zone (e.g. Ekman 1989). The adaptive significance of such aggregations is usually explained in terms of better predator detection and improved foraging success for flock members (Thorpe 1963, Pulliam 1973). If kin-based aggregations in winter are formed by means of delayed dispersal of young, additional benefits may arise for both adult and first-year group members (Emlen 1997). Ekman and Rosander (1992) suggested that parental control of natal dispersal could be the main factor determining the size and composition of winter groups. According to their model, in the face of limited resources, a territorial mated pair will increase their level of aggression toward non-kin flock members, forcing them to leave. By contrast, subordinate kin (e.g. offspring) will be tolerated to a greater extent by the territorial pair as long as resources are sufficient. When adults cannot afford to share food even with their own offspring, they will exclude such offspring from the flock as well (see Ekman et al. 1994). This model has been supported by studies of Siberian Jays (Perisoreus infaustus; Ekman et al. 1994, 1996) and Gray Jays (Perisoreus canadensis; Waite and Strickland 1997). The Tufted Titmouse (Baeolophus bicolor) is one of few non-corvid, permanent-resident, temperatezone passerines in which offspring are known to spend the winter with their parents (Grubb and Pravosudov 1994). Because cohesive winter units of titmice may include up to eight members (Nice 1930), which may or may not be related, it remains unclear how often offspring are retained in this species and what factors determine the size and composition of winter groups. In our study sites within the agricultural landscape of central Ohio, titmice are permanent residents of forest fragments and often form small wintering groups of three or four birds. We predicted from Ekman and Rosander's (1992) model for offspring retention that under conditions of low resources, a wintering pair of adult titmice would be more likely to tolerate an offspring than a non-offspring flock member. When a pair of titmice is the only territorial pair in a very small woodlot, which presumably affords low levels of food resources, we expected that any juvenile in the same woodlot

Frequency of Mixed Species Flocking in Tropical Forest Birds and Correlates of Predation Risk: An Intertropical Comparison

The composition and frequency of occurrence of mixed flocks among foraging insectivorous birds were compared between several tropical forests from South America to the Indian Ocean and Southeast Asia, and related to forest structure, foraging behaviour and abundance of predators (diurnal raptors), to investigate relationships between flocking behaviour and antipredator defence. Foliage gleaners, the most conspicuous and least vigilant foragers, were usually the most abundant flock members and the birds with the highest flocking propensity. In contrast, species foraging low above ground or in dense vegetation were the least likely to join flocks. Flocking propensity of all insectivores pooled, or of gleaners alone, generally declined from primary lowland forest to open (semi-deciduous), disturbed (logging gaps), managed or montane forest (broken canopy), i.e. when predator detectability was likely to increase. There was also a significant positive correlation between bird-hunting raptor diversity or abundance and flocking rates of foliage gleaners or all insectivores. The results supported the hypothesis that foraging birds most vulnerable to predators were most likely to form mixed species flocks and that flocking tendency decreased when vegetation structure became more protective and/or when predator pressure became lower.

Methods of detection of Chlamydia psittaci in domesticated and wild birds.

To study the occurrence of Chlamydia psittaci in domesticated and wild birds and compare the sensitivity of molecular detection with cell culture isolation. Study of cell culture isolation and PCR detection of C psittaci in avian samples. Samples were obtained from 485 birds. Domesticated birds were selected at random from pet shops, private aviaries and zoos, while wild birds were captured locally, sampled, and immediately released. Swabs were collected from choanal slit, conjunctiva and cloaca of each bird and pooled. Samples were divided into equal portions for use in PCR dot-blot and cell culture detection. PCR and dot-blot detection was based on the ompB gene. Prevalence of infection varied markedly between flocks of captive birds. It was highest where there were frequent changes in the flock members or where there were many birds confined in small areas. C psittaci was not detected in wild birds or water birds. The sensitivity of cell culture compared to PCR dot-blot detection was 68%. All samples positive by cell culture were also positive by PCR. PCR-dot blot detection of C psittaci in birds appears to be more sensitive than cell culture isolation in this study. C psittaci infection of birds may occur in clinically normal captive birds.