How rhesus monkey mothers and infants keep in touch when infants are at risk from social companions

Ten-to 17-week-old rhesus monkey infants that received hits from companions other than their mother at high rates (relative to their rates of involvement in playful social encounters with those companions) tended to be members of mother-infant dyads that were vigilant. Criteria of vigilance were frequent contacts between mother and infant during the first 5 sec of the infants’ social encounters and/or a bias of mother-infant contacts toward that time. Infants that received few hits per encounter came from both vigilant and nonvigilant dyads. When analyzed alone, mothers’ rates showed the same trends. High levels of vigilance tended to reduce infants’rates of making social contacts. Maternal social rank and other measures of the infants’ social involvement were not correlated with vigilance. There is no evidence that mothers and infants were in conflict with each other about interrupting the infants’ encounters. Understanding vigilance becomes important whenever vigilant activity conflicts with other activities. Special problems arise because decisions about vigilance levels require judgments of risk based on the kinds of events that occur only rarely if vigilance is effective. A model providing a framework for studies of vigilance against the risks of infants’ social activities was developed. It recognizes that (1) risk-reducing vigilant behavior can conflict with acquiring information about risk; (2) in social situations where reliable estimates of risk are impossible, individuals might follow rules of thumb (e.g., be restrictive) rather than modify behavior moment by moment according to the current situation;and (3) at the dyad’s optimum balance between vigilance for the current infant and investment in subsequent off-spring, the infant will not be totally protected, so that while dyads at higher risks are more vigilant, the risks are also realized to a greater extent (e.g., itin terms of the number of hits received per encounter).     

Effects of Passive Social Support in Juvenile Greylag Geese (Anser anser): A Study from Fledging to Adulthood

In general, support by social allies may reduce stress, increase an individual's status and facilitate access to resources. In Greylag geese (Anser anser), offspring stay with their parents for an entire year or even longer and thereby enjoy social support in encounters with other flock members. We investigated the influence of spatial distance to one's allies on the outcome of agonistic encounters in a natural flock situation for a total of 12 sibling groups after fledging. In addition, we tested two groups of hand‐raised juvenile geese over a time span of 11/2 yr. Passive (i.e. not interfering) human supporters of different familiarity were placed at a standard distance during food provisionings, which produced a tight flock situation. Success in agonistic interactions increased with decreasing distance to members of their social unit. The hand‐raised juveniles were more successful in agonistic interactions and showed increased feeding rates when accompanied by a familiar human than when alone or with a non‐familiar human. The effect of the presence of familiar humans on success in agonistic encounters significantly decreased with increasing age, while feeding rates remained elevated. The positive effects of social support were particularly evident in females. We conclude that social support has similar effects and functions in the highly social greylag geese as reported for social mammals.     

On dominance relations and the structure of animal societies: II. Some effects of possible social factors

In a previous paper (Landau, 1951) it was shown that a society with a dominance relation would rarely tend to be close to the hierarchy in structure if dominance is determined solely by the inherent characteristics of the members. Here we consider the effects of other factors, due to social rank or to the outcome of previous encounters which affected dominance. The following results are obtained. A uniform bias against reversal of dominance will have no effect on the stationary distribution of the structure of the society. If the probability of dominance is a linear function of the previously established score (number of members dominated), there will be a small tendency for the society to move toward the hierarchy; but this is negligible for large societies. If a member never challenges another whose score exceeds his own by two or more, or if he can never dominate if he should challenge, then the hierarchy is the only stable structure. From the last result it is concluded that social factors which restrict challenges or the probability of dominance could easily account for societies close to the hierarchy, such as are observed in flocks of domestic hens. The effectiveness of social bias in establishing hierarchies is much greater in small societies than in large ones.     

Intergroup encounters in wild white-faced capuchins (Cebus capucinus)

Wrangham (1980) hypothesized that knowledge of the nature of intergroup encounters is crucial to understanding primate social relationships and social organization. I studied a single social group of wild white-faced capuchins over a period of 26 months and observed 44 encounters between social groups during 3703 hr of observation. All intergroup encounters consisted of predominantly hostile social interactions. However, nonaggressive interactions between males of different social groups occurred in a few cases. Adult males were the sole participants in 39 encounters and the primary participants in all 44 encounters. The alpha male was the most frequent participant. High-ranking females participated aggressively in five encounters, and low-ranking females never participated. There was no stable intergroup dominance hierarchy. I hypothesize that the need for male-male cooperation in intergroup aggression is an important factor influencing the quality of intragroup male-male relationships. Behavior during intergroup encounters is consistent with the idea that intergroup behavior is related to male reproductive strategies, but inconsistent with the idea that intergroup aggression is related to female defense of resources. The possibility that males are “hired guns” (Wrangham, 1980) cannot be ruled out.     

Edge effect and structure of mixed-species bird flocks in an Afrotropical lowland forest

Avian mixed-species flocks are a dominant feature of tropical moist forests, yet their cost–benefit balance and habitat dependence in Africa are not fully documented. We recorded the composition of mixed-species bird flocks in a pristine Afrotropical lowland forest site in Salonga NP, DRC. Our data showed that at least four types of flock existed, one of which specialized on edge habitats. We used multivariate analyses to further characterize edge effect on the most documented mixed-species flock type and found a significant effect on flock composition. While neither species guild nor preferential foraging stratum played an important role in flock participation, the nucleus role was played by a different species at the edge and in the interior, and both species abundance and associations were habitat-dependant, suggesting “domino effects” on the structure of mixed-species flocks.     

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.     

On dominance relations and the structure of animal societies: I. Effect of inherent characteristics

Societies are considered in which a non-transitive dominance relation exists between every pair of members, such as the peck-right in a flock of hens. A one-dimensional measure of the structure of such a society,h, is defined, withh=0 for equality andh=1 for the hierarchy. It is assumed that each member of the society is characterized by an ability vector whose components depend on individual characteristics such as size, concentration of sex hormone, etc., but not on social factors such as social rank. The distribution of abilities among members of the society is assumed to be given by a distribution function which is the same for all members, and the probability that one member dominates another is given by a function of the ability vectors of the two. On these assumptions formulas for the expected (mean) value and variance ofh are determined in terms of the distribution and dominance probability functions. Some special cases are calculated, especially that for normany distributed abilities and dominance probability given by the normal probability integral. Several conclusions are derived. If all members are of equal ability, so that dominance probability is 1/2, then any sizable society is much more likely to be near the equality than the hierarchy; and, as the size of the society increases, the probability that it will be near the hierarchy becomes vanishingly small. If the dominance probability is a weighted sum of several independent components, which make up the ability vector, then the society is less likely to be close to the hierarchy as the number of these components increases. The hierarchy is the prevalent structure only if unreasonably small differences in ability are decisive for dominance. From this it appears that the social factors, or psychological factors such as the previous history of dominance, which are not included in the present treatment, may be of great importance in explaining the observed prevalence of structures very close to the hierarchy in flocks of domestic hens.     

Variation in aggressiveness in house mouse populations

Clearly the ability of 'house mice' to vary their social structures is an important feature contributing to their success in a wide range of habitats. Social structure is strongly influenced by aggressiveness and other behaviours in male and female mice. Material is presented illustrating how genotype, intrauterine location and social experiences influence dyadic encounters in this 'species'.     

Aggression in shorebirds in relation to flock density and composition

The aggressive interactions of Turnstones and Purple Sandpipers feeding in wintering mixed-species wader flocks could be classified into those involving food and those involving space. All observed interspecific encounters were of short duration and were initiated and won by the larger species; the majority did not involve food and were resolved by low-intensity displays. Intraspecific interactions (a greater proportion of which involved food) were also resolved quickly and were usually won by the initiator. Space-related encounters between conspecifics were more likely to be resolved than food-related encounters just by threat displays. Aggression rates increased with flock densities. However, the increase in aggression with density was dependent on the species composition of the flock: both Turnstones and Purple Sandpipers were more likely to be involved in fights (both over food and over space) with conspecifics than with other species, indicating that the aggression costs of flocking were less in mixed-species flocks.     

Modeling the flocking propensity of passerine birds in two Neotropical habitats

We examined the importance of mixed-species flock abundance, individual bird home range size, foraging height, and foraging patch characteristics in predicting the propensity for five Neotropical passerine bird species (Slaty Antwren, Myrmotherula schisticolor; Golden-crowned Warbler, Basileuterus culicivorus; Slate-throated Redstart, Myioborus miniatus; Wilson’s Warbler, Wilsonia pusilla; and Black-and-white Warbler, Mniotilta varia) to forage within flocks, rather than solitarily. We used study plots in primary mid-elevation forest and in shade coffee fields in western Panama. We expected that all species would spend as much time as possible flocking, but that the social and environmental factors listed above would limit compatibility between flock movements and individual bird movements, explaining variability in flocking propensity both within and among species. Flocking propensity was well predicted by home range size and flock abundance together, for four of the five species. While flock abundance was uniform across plots, home range sizes varied among species and plots, so that home range size appeared to be the principle factor limiting flocking propensity. Estimates of flock abundance were still required, however, for calculating flocking propensity values. Foraging height and patch characteristics slightly improved predictive ability for the remaining species, M. miniatus. In general, individual birds tended to join flocks whenever one was available inside their home range, regardless of a flock’s specific location within the home range. Flocking propensities of individual species were lower in shade coffee fields than in forests, and probably vary across landscapes with variations in habitat. This variability affects the stability and species composition of flocks, and may affect survival rates of individual species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A note on the dominance hierarchy index

The realized (observed) value of Landau’s dominance hierarchy index is examined. Under a model of constant pairwise dominance probabilities, the observed index is shown to be a strongly consistent estimator of the underlying (true) index. However, a large number of encounters between animals is shown to be required in order to reduce bias and variance to practical levels except when the pairwise dominance probabilities are near one.     

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Background

Adjustment of body weights for systematic environmental effects such as dam age and litter size is essential for accurate prediction of breeding values in meat sheep and often accomplished by pre-adjusting records using simple multiplicative adjustment factors, which are derived as ratios of least-squares means of weights of lambs in target and reference classes. However, increasing use of multibreed genetic evaluations that incorporate data from both purebred and commercial flocks has generated concerns regarding the ability of simple additive or multiplicative adjustment factors to properly correct for environmental effects in flocks that differ widely in mean performance. Thus, consistency of adjustment factors across flocks and systematic effects of the level of flock performance on these factors were evaluated using data from the US National Sheep Improvement Program.

Methods

We used birth and weaning weights of lambs from 29 flocks that had at least 500 records per flock and represented several terminal-sire sheep breeds. Effects of lamb sex, dam age class and litter size on birth weights, and of dam age class and combined effects of type of birth and rearing on weaning weights were evaluated. Interactions between these effects and flock were assessed. Bias associated with different adjustment protocols was evaluated for high- and low-performance flocks.

Results

Effects of litter size and differences between yearling and adult dams varied (P < 0.001) among flocks. For weaning weights, additive adjustment factors were not associated with the level of flock performance, but multiplicative adjustment factors were strongly and inversely related to flock means for weaning weights (W). Flock-specific adjustment factors (F = αW^β) reduced bias in adjusted weaning weights associated with differences in flock performance. By contrast, simple multiplicative adjustment factors were appropriate to adjust birth weights.

Conclusions

Differences in weaning weights among single, twin, and triplet lambs were inversely related to the level of flock performance. Use of simple multiplicative adjustment factors led to adjustment bias when applied across flocks with large differences in mean performance. This bias was reduced by using additive adjustment factors or multiplicative factors that were derived as simple exponential functions of flock means for weaning weight.     

Factors affecting escape behaviour in moulting Greylag Geese Anser anser

The escape behaviour of flightless greylag geese Anser anser has been studied at a Danish moult site. In more than 40% of escapes, a stimulus could not be discerned, suggesting some importance of inaccurate risk assessment among the geese. Quasi-predator stimuli, for example gull alarms and helicopters, were also important and caused 31–43 and 5–13% of escapes, respectively. Geese were, however, displaced in less than 5% of encounters with these stimuli. Each escape prevented geese from feeding for 19 min on average, and hence, the cost of escapes was high. This, the low in-situ predation risk, and the partly distant and not directly threatening nature of the stimuli may have weakened the response of the geese. During the main moult period the geese were, nevertheless, more susceptible to quasi-predator stimuli than before moult—the probability of escape per 15 min period was 0.16–0.22 during moult and 0 before moult. The probability of escapes among moulting geese, which formed large cohesive flocks, was, furthermore, significantly enhanced with increasing flock size. It is possible large flocks were better at detecting quasi-predator stimuli, or simply that there was a greater risk of signals from flock members being misinterpreted. Thus in terms of maintaining uninterrupted foraging it was concluded that an individual would incur extra cost by joining large flocks during the moult period.     

Winter territoriality and flock cohesion in the black-capped chickadee Parus atricapillus

In northwest Massachusetts, black-capped chickadees shifted foraging groups repeatedly each day during the winter. As a result, there was no clear distinction between flock members and floaters, but instead a continuous gradation from birds that formed relatively stable associations to those that shifted groups more frequently. Group territories were absent and individual territories were at most poorly defended, if present at all. This picture differs from other recently studied populations, where flock membership is stable and flock territories are clear. Comparison with other populations indicates that winter social structure in the black-capped chickadee may be sensitive to both winter food levels and the proportion of year-round residents. This indicates that cost-benefit analyses of winter social organization should consider factors acting throughout the year as well as the residence status of the wintering birds. The data suggest that flock size, population density and home range size are sensitive to winter food on the study area, whereas territoriality and flock cohesion may respond more clearly to the local availability of breeding resources or the proportion of year-round residents.     

Contribution to the theory of random and biased nets

The probabilistic theory of random and biased nets is further developed by the “tracing” method treated previously. A number of biases expected to be operating in nets, particularly in sociograms, is described. Distribution of closed chain lengths is derived for random nets and for nets with a simple “reflexive” bias. The “island model” bias is treated for the case of two islands and a single axon tracing, resulting in a pair of linear difference equations with two indices. The reflexive bias is extended to multiple-axon tracing by an approximate method resulting in a modification of the random net recursion formula. Results previously obtained are compared with empirical findings and attempts are made to account for observed discrepancies.     

Does Innovation Success Influence Social Interactions? An Experimental Test in House Sparrows

In group‐living animals, individuals may benefit from the presence of an innovative group‐mate because new resources made available by innovators can be exploited, for example by scrounging or social learning. As a consequence, it may pay off to take the group‐mates' problem‐solving abilities into account in social interactions such as aggression or spatial association, for example because dominance over an innovative group‐mate can increase scrounging success, while spatial proximity may increase the chance of both direct exploitation and social learning. In this study, we tested whether the individuals' innovation success influences their social interactions with group‐mates in small captive flocks of house sparrows (Passer domesticus). First, we measured the birds' actual problem‐solving success in individual food‐extracting tasks. Then, we manipulated their apparent problem‐solving success in one task (by allowing or not allowing them to open a feeder repeatedly) while a new, unfamiliar group‐member (focal individual) had the opportunity to witness their performance. After this manipulation, we observed the frequency and intensity of aggression and the frequency of spatial associations between the focal individuals and their manipulated flock‐mates. Although flock‐mates behaved according to their treatments during manipulations, their apparent problem‐solving success did not affect significantly the focal individuals' agonistic behaviour or spatial associations. These results do not support that sparrows take flock‐mates' problem‐solving abilities into account during social interactions. However, focal individuals attacked those flock‐mates more frequently that had higher actual problem‐solving success (not witnessed directly by the focal individuals), although aggression intensity and spatial association by the focal birds were unrelated to the flock‐mates' actual success. If this association between flock‐mates' actual innovativeness and focal individuals' aggression is not due to confounding effects, it may imply that house sparrows can use more subtle cues to assess the group‐mates' problem‐solving ability than direct observation of their performance in simple foraging tasks.     

Aggression and dominance in the weaver bird, Quelea quelea.

Previous work on agonistic behaviour in Quelea has been concerned primarily with hormonal variables. In the present series of experiments, a number of behavioural correlates of aggression and dominance are examined in male and bisexual groups. These include the effects of group arousal level on rates of agonistic encounters, the relationship between an individual's habitual level of activity and its relative dominance, aggressiveness and position on the perch in a resting "flock". The temporal patterning of encounters is analysed and the reasons why encounters tend to clump in time determined. The relationship between dominance in encounters over individual-distance infringements and dominance in encounters over access to a restricted food source is investigated and the effects of this on loss of weight in males and females determined. The results are discussed in relation to Ward's (1965) finging that in the wild females suffer higher mortality than males during the dry season and in relation to the general determinants of aggression in Quelea.     

Social electric signals in freely moving dyads of <Emphasis Type="Italic">Brachyhypopomus pinnicaudatus</Emphasis>

Brachyhypopomus pinnicaudatus (pulse-type weakly electric fish) is a gregarious species that displays reproductive behavior and agonistic encounters between males only during the breeding season. During social interactions, in addition to its basal electric organ discharge (EOD), fish emit social electric signals (SESs) in the contexts of reproduction and intrasexual aggression. We reproduced natural behavior in laboratory settings: SESs recorded in the field are indistinguishable from those observed in our experimental setup. SESs are nocturnal, change seasonally and exhibit sexual dimorphism. This study provides an exhaustive characterization and classification of SESs produced by males and females during the breeding season. In male–female dyads, males produce accelerations and chirps while females interrupt their EODs. The same SESs are observed in male–male dyads. We present a novel, thorough classification of male chirps into four independent types (A, B, C, and M) based on their duration and internal structure. The type M chirp is only observed in male–male dyads. Chirps and interruptions, both in male–female and male–male dyads, are emitted in bouts, which are also grouped throughout the night. Our data suggest the existence of a sophisticated electric dialog during reproductive and aggressive interaction whose precise timing and behavioral significance are being investigated.     

Movement patterns, social dynamics, and the evolution of cooperation

The structure of social interactions influences many aspects of social life, including the spread of information and behavior, and the evolution of social phenotypes. After dispersal, organisms move around throughout their lives, and the patterns of their movement influence their social encounters over the course of their lifespan. Though both space and mobility are known to influence social evolution, there is little analysis of the influence of specific movement patterns on evolutionary dynamics. We explored the effects of random movement strategies on the evolution of cooperation using an agent-based prisoner’s dilemma model with mobile agents. This is the first systematic analysis of a model in which cooperators and defectors can use different random movement strategies, which we chose to fall on a spectrum between highly exploratory and highly restricted in their search tendencies. Because limited dispersal and restrictions to local neighborhood size are known to influence the ability of cooperators to effectively assort, we also assessed the robustness of our findings with respect to dispersal and local capacity constraints. We show that differences in patterns of movement can dramatically influence the likelihood of cooperator success, and that the effects of different movement patterns are sensitive to environmental assumptions about offspring dispersal and local space constraints. Since local interactions implicitly generate dynamic social interaction networks, we also measured the average number of unique and total interactions over a lifetime and considered how these emergent network dynamics helped explain the results. This work extends what is known about mobility and the evolution of cooperation, and also has general implications for social models with randomly moving agents.     

Individual recognition in crayfish (Cherax dispar): the roles of strength and experience in deciding aggressive encounters

The outcomes of agonistic interactions modulate access to resources and thereby affect fitness. Success in agonistic encounters may depend on intrinsic physical and physiological performance, and on social experience. Here we test the hypothesis that previous experience will override physical strength in determining the outcome of fights in the freshwater crayfish Cherax dispar. Between unfamiliar opponents, greater chelae closing force significantly increases the chances of winning. However, even when the chelae of the original winners were disabled, the winners kept on winning against the same opponents after 30min and 24h. This winner effect disappeared when previous winners encountered unfamiliar individuals. Similarly, a previous loss did not affect the outcomes of subsequent encounters with unknown crayfish. We suggest that this prolonged recognition of individuals and their relative fighting ability is a mechanism that can reduce the number of agonistic encounters experienced by individuals.