Many eyes or many ewes: vigilance tactics in female bighorn sheep Ovis canadensis vary according to reproductive status

In gregarious animals, there is usually a negative relationship between individual vigilance and group size. This effect of group size is generally explained by increasing probability of predator detection (the many-eyes hypothesis) and by the dilution of risk occurring in larger groups. Few studies have attempted to examine the specific implications of either hypothesis on the expected vigilance pattern of an animal. Here we examine whether reproductive status affects vigilance patterns in bighorn sheep Ovis canadensis ewes. We also test whether the observed vigilance patterns are consistent with predictions from dilution or detection models of vigilance. Although vigilance decreased with increasing group size, vigilance tactics differed between barren and lactating females. Lactating ewes relied solely on predator detection. In contrast, barren ewes benefited from both detection and dilution effects when group size increased and adjusted vigilance effort according to the proportion of lactating ewes in their group. It is generally assumed that gregariousness increases safety. Here we further show that reproductive status influenced how animals reduce predation risk and that some individuals take advantage of the vigilance effort provided by others.     

Grazing and vigilance by Soay sheep on Lundy island: influence of group size, terrain and the distribution of vegetation

Animals allocate the time spent on different behaviours according to nutritional requirements, the distribution of food and the risk of predation. When the perceived predation risk is high, animals primarily behave in ways to increase their safety such as regularly scanning their surroundings, forming large groups and feeding in habitats with cover or high visibility. This study investigated which factors Soay sheep (Ovis aries) are most sensitive to in allocating time to different behaviours when the risk of predation is negligible. Continuous focal sampling was used to record the behaviour of the free-ranging Soay sheep on Lundy Island and measures of vegetation, group size and terrain were also recorded. Stepwise multiple regression produced a model of grazing with terrain and range of grass coverage as predictors and a model of vigilance with terrain as a predictor. Sheep grazed for longer on the slopes and as the range of grass cover decreased. They were more vigilant on the slopes. The results support the view that the group size effect largely depends on anti-predatory vigilance and suggest that time-budgets are more sensitive to other factors in the absence of predation.     

Spatial distribution patterns of sheep following manipulation of feeding motivation and food availability

We hypothesised that (i) increased feeding motivation will cause sheep to move further apart as a result of individuals trying to find food and (ii) in conditions of high food availability, sheep will move less and show greater social attraction. The effects of both feeding motivation and food availability on spatial distribution was examined in eight groups of food-deprived (high feeding motivation) and satiated (low feeding motivation) sheep in good or poor food resource plots in a 2 × 2 design. Distance travelled was assessed using Global Positioning System collars, grazing time using scan sampling and social cohesion using proximity collars that record the number and duration of encounters within 4 m. Food-deprived sheep in the good-resource plots grazed the most, whereas satiated sheep in the poor-resource plots grazed the least (P = 0.004). Food deprivation had no significant effect on the number or duration of encounters and feeding motivation appeared to have little effect on spatial distribution. Contrary to expectation, sheep had more encounters (P = 0.04) of a longer total duration (P = 0.02) in poor-resource plots than in good-resource plots, indicating that sheep were showing more social cohesion if food was scarce. Our findings suggest that when food is scarce, animals may come together in an attempt to share information on food availability. However, when a highly preferred food is abundant and well dispersed, they may move apart in order to maximise the intake. It is concluded that the particular details of our experiment, namely the even distribution or absence of a highly preferred food, affected spatial distribution patterns as sheep tried to find this food and maximise the intake.     

Differences in the Spacing Behaviour of Two Breeds of Domestic Sheep (Ovis aries) – Influence of Artificial Selection?

The aim of this experiment was to investigate differences in spacing behaviour, measured by the individual distance when resting and feeding, between two breeds of sheep with a different selection history. Eight groups of four pregnant ewes from the Nor‐X breed (a heavy, composite breed mainly selected for growth and meat quality) and eight groups of four pregnant ewes of the coloured Spæl breed (a light breed, mainly selected for wool quality) were placed in oblong experimental pens for 7 d. The distance between animals was measured from digital video recordings. The heavy Nor‐X ewes kept a significantly larger individual distance to their pen mates both during resting and feeding compared with the lighter Spæl ewes. Spæl ewes also kept a significantly smaller individual distance during resting than during feeding, but this difference was not found in Nor‐X ewes. Our results indicate that selection for growth and meat quality might influence spacing behaviour in sheep. Looking at the selection history of these two breeds, we discovered differences in how long they had coexisted with large carnivores. The possible effects of previous exposure to carnivores and the role of domestication in modifying spacing behaviour are also discussed.     

Social models fail to induce diet and feeding site avoidance in naïve yearling steers

Social learning can be of critical importance to cattle grazing rangeland environments with high variability of food resources across space and time. Experienced individuals can greatly facilitate foraging decisions (what to eat and where to eat) of na?ve peers in such settings. We conducted an experiment with cattle to investigate strength and persistence of socially induced food and feeding site avoidance behaviours. Sixteen na?ve yearling steers were paired with 16 social models that had either not been trained (control) or been trained with an emetic (LiCl), electrical shock or both to avoid: (a) an unsafe high-quality food (LiCl); (b) an unsafe high-quality feeding site (shock); or (c) both the unsafe high-quality food and the unsafe high-quality feeding site (LiCl + shock). Ten-minute trials were conducted in an experimental arena containing three artificial feeding sites each consisting of groups of bowls with either high- (HQ) or moderate-quality (MQ) foods (HQ = barley and oat grain; MQ = Bermuda grass hay). Unsafe high-quality (UHQ, surrounded by traffic cones) and safe moderate-quality (SMQ) feeding sites consisted of nine rubber bowls containing either HQ or MQ foods. The safe high-quality (SHQ) feeding site consisted of two groups of eight bowls containing HQ food, which surrounded the UHQ and SMQ feeding sites. Social models did not induce diet and feeding site avoidance behaviours in na?ve steers; they exerted small and transient changes in the feeding behaviour of their na?ve counterparts. Consequences to the individual outweighed social influences; when na?ve animals experienced the same punishment contingencies as their social models, their behavioural patterns closely resembled those of their social model. Conditioned food and location aversions via LiCl were apparently influenced by prior exposure to target foods and the experimental arena. Conversely, conditioned feeding site avoidance via shock was apparently not influenced by prior exposure to target foods or the experimental arena.     

Sexual,Seasonal and Group Size Differences in the Allocation of Time between Vigilance and Feeding in the Greater Rhea,Rhea americana

We studied the effect of sex and group size on the proportion of time a greater rhea, Rhea americana, allocates to vigilance and feeding during the breeding and the non-breeding seasons. We analysed 175 records of focal animals that were feeding alone or in groups of 2 to 26 birds. In both seasons, males spent more time in vigilance and less time in feeding than females. Both sexes spent more time in vigilance and less time in feeding during the breeding season. Sexual and seasonal differences in vigilance were the result of different mechanisms. Males had shorter feeding bouts than females but there were no sexual differences in the length of the vigilance bouts. On the contrary, seasonal differences were the result of males and females having longer vigilance bouts during the breeding season but there were no seasonal differences in the length of the feeding bouts. During the non-breeding season, individual vigilance was higher in rheas foraging alone than in groups. In this case, solitary birds had longer vigilance and shorter feeding bouts than birds foraging in groups. We discuss the possible effect of intragroup competition and food availability on the allocation of time between feeding and vigilance in this species.     

Effect of Group Size on Individual and Collective Vigilance in Greater Rheas

We studied the effect of group size on the proportion of time that greater rheas, Rhea americana, allocated to vigilance and feeding during the non‐breeding season. We tested whether: (1) the proportion of time that one bird allocates to vigilance (individual vigilance) decreases with group size, and (2) the proportion of time that at least one bird of the group is vigilant (collective vigilance) increases with group size. We analyzed video‐recordings of birds that were foraging alone or in groups from two to 12 birds. The proportion of time allocated to individual vigilance decreased and the proportion of time spent feeding increased with group size. In both cases the main significant difference was between birds foraging alone and in groups. Collective vigilance did not vary with group size and it was lower than expected if vigilance bouts were random or sequential. Our results indicate that rheas foraging in large groups would not receive the benefit of an increase in collective vigilance, although they could still benefit from a reduction of predation risk by the dilution effect.     

Foraging behaviour alters with social environment in a juvenile songbird

Early independence from parents is a critical period where social information acquired vertically may become outdated, or conflict with new information. However, across natural populations, it is unclear if newly independent young persist in using information from parents, or if group-level effects of conformity override previous behaviours. Here, we test if wild juvenile hihi (Notiomystis cincta, a New Zealand passerine) retain a foraging behaviour from parents, or if they change in response to the behaviour of peers. We provided feeding stations to parents during chick-rearing to seed alternative access routes, and then tracked their offspring''s behaviour. Once independent, juveniles formed mixed-treatment social groups, where they did not retain preferences from their time with parents. Instead, juvenile groups converged over time to use one access route­ per group, and juveniles that moved between groups switched to copy the locally favoured option. Juvenile hihi did not copy specific individuals, even if they were more familiar with the preceding bird. Our study shows that early social experiences with parents affect initial foraging decisions, but social environments encountered later on can update transmission of arbitrary behaviours. This suggests that conformity may be widespread in animal groups, with potential cultural, ecological and evolutionary consequences.     

Vigilance and grouping in the southern African ground squirrel (Xerus inauris)

Animals may form groups in response to the foraging–vigilance trade‐off, through enhanced predator detection (collective detection hypothesis) or reduced predation risk to the individual (dilution hypothesis), allowing individuals to decrease vigilance levels. Both hypotheses predict decreasing individual vigilance levels with increasing group size; however, the collective detection hypothesis also predicts increasing overall group vigilance with increasing group size. However, in species in which vigilance and foraging are not mutually exclusive, where vigilance may not be as costly, neither of these hypotheses may apply. Here, we examine the relationship between group size and vigilance in the social Cape ground squirrel (Xerus inauris), a species that can combine foraging and vigilance behaviours. Ten groups were observed using scan sampling, measuring both group and individual vigilance and group size. A negative relationship existed between individual vigilance and group size and a positive relationship between group vigilance and group size. Therefore, in Cape ground squirrels, vigilance seems to be costly even though it can be combined with foraging behaviours. Furthermore, group vigilance behaviour gives support to the collective detection hypothesis, whilst individual vigilance gives support to both hypotheses.     

Vigilance behavior of Pyrenean chamois Rupicapra pyrenaica pyrenaica: Effect of sex and position in the herd

The Pyrenean chamois Rupicapra pyrenaica pyrenaica is a mountain-dwelling ungulate with an extensive presence in open areas. Optimal group size results from the trade off between advantages (a reduction in the risk of predation) and disadvantages (competition between members of the herd) of group living. In addition, advantages and disadvantages of group living may vary depending on the position of each individual within the herd. Our objective was to study the effect of central vs. Peripheral position in the herd on feeding and vigilance behavior in male and female Pyrenean chamois and to ascertain if a group size effect existed. We used focal animal sampling and recorded social interactions when a focal animal was involved. With males, vigilance rate was higher in the central part of the group than at the periphery, probably due to a higher density of animals in the central part of the herd and a higher probability of being disturbed by conspecifics. With females, vigilance rate did not differ according to position in the herd. Females spent more time feeding than males, and males showed a higher frequency of the vigilance behavior than females. We did not observe a clear relationship between group size and vigilance behavior. The differences in vigilance behavior might be due to social interactions.     

相关风险因子对高原鼠兔摄食行为的影响

研究了捕食风险环境中集和洞口距离对高原鼠兔摄食行为的影响。结果表明,集群数量的增加不仅降低了警觉行为,同时也减少了摄食行为,在高风险环境中,集群为1时的取食行为强度最大,低风险环境中,为0时最大,警觉行为主要出现在距洞口2m的范围内,其行为强度与洞口踪影职责负相关,当洞口距离大于3m时,风险处理区的高原鼠兔几乎无警觉行为出现,且该处理区的取食区域几乎压缩的洞口旁,研究结果表明,在捕食风险环境中,高原鼠兔摄食行为与集群和洞口距离之间具有复杂的关系,其行为决策反映了降低风险与摄取食物间的权衡,行为目标是在降低捕食风险的同时尽可能地取食食物。     

How group size affects vigilance dynamics and time allocation patterns: the key role of imitation and tempo

In the context of social foraging, predator detection has been the subject of numerous studies, which acknowledge the adaptive response of the individual to the trade-off between feeding and vigilance. Typically, animals gain energy by increasing their feeding time and decreasing their vigilance effort with increasing group size, without increasing their risk of predation ('group size effect'). Research on the biological utility of vigilance has prevailed over considerations of the mechanistic rules that link individual decisions to group behavior. With sheep as a model species, we identified how the behaviors of conspecifics affect the individual decisions to switch activity. We highlight a simple mechanism whereby the group size effect on collective vigilance dynamics is shaped by two key features: the magnitude of social amplification and intrinsic differences between foraging and scanning bout durations. Our results highlight a positive correlation between the duration of scanning and foraging bouts at the level of the group. This finding reveals the existence of groups with high and low rates of transition between activities, suggesting individual variations in the transition rate, or 'tempo'. We present a mathematical model based on behavioral rules derived from experiments. Our theoretical predictions show that the system is robust in respect to variations in the propensity to imitate scanning and foraging, yet flexible in respect to differences in the duration of activity bouts. The model shows how individual decisions contribute to collective behavior patterns and how the group, in turn, facilitates individual-level adaptive responses.     

Uncertain availability of a preferred food affects choice in a captive group of chimpanzees (Pan troglodytes)

Food-choice was investigated in a social group of 16 chimpanzees (Pan troglodytes) maintained in a large outdoor compound. Three feeding stations located along the periphery of the compound were considered analogous to food patches. Color-coded aluminum panels temporarily covered each feeding apparatus, with one color corresponding to nonpreferred food (commercial biscuits) available at two locations and other colors corresponding to the certain or uncertain availability of preferred food (oranges) available at one location. Only nine chimpanzees met the criterion for learning the color/food associations and thus only those animals were included in the analysis. There was a significant decrease in choosing the station associated with oranges when the probability of availability of oranges was reduced from 0.5 to 0.1 but not from 1.0 to 0.5. In addition, there was a significant increase in the frequency with which the subjects made no choice when the probability of availability of oranges was reduced from 1.0 to 0.1. The data indicate that the uncertain availability of preferred food in a choice situation affects choice behavior in a social group of chimpanzees studied under controlled conditions.     

Consistency of temperament in bighorn ewes and correlates with behaviour and life history

Individual differences in temperament may affect how animals react to novel situations, avoid predation, invest in reproduction and behave in a variety of social contexts. Little information is available, however, about individual differences in temperament for wild animals. For bighorn sheep, Ovis canadensis, ewes captured as part of a long-term study, we compared behaviour during handling to behaviour in the field and reproductive history. We considered 'bold' ewes those that were frequently trapped during the summer, and assigned to each ewe a docility index based on her behaviour during handling. Measurements of temperament for the same individual at different captures were highly consistent. Temperament was not affected by reproductive status or age, nor was it related to body mass. Correlations between behaviour at the trap and in the field were weak and mostly nonsignificant, suggesting that temperament is domain specific rather than domain general. Bold ewes tended to start reproducing earlier and have higher weaning success than shy ewes. Variability in temperamental traits in the study population could be maintained by life-history trade-offs and by yearly changes in selective pressures. Copyright 2000 The Association for the Study of Animal Behaviour.     

Some aspects of social behaviour in domestic sheep

Aspects of social behaviour in domestic sheep were studied by observations of undisturbed flocks. A group identity was found to develop when small flocks are established: when two such groups of similar age and sex are amalgamated, random mixing takes up to 3 weeks to develop. Breed identity was also found to exist: within flocks made up from groups of sheep of different breeds, the sheep had a strong bias for associating with others of their own breed both whilst grazing and whilst camping, and this remains even after 2 years of grazing together. This breed identity remained in the offspring born into a flock of ewes of different breeds.     

Contact calling behaviour in the male ring‐tailed lemur (Lemur catta)

The ring‐tailed lemur (Lemur catta) is a group‐living strepsirhine primate endemic to Madagascar that has a complex vocal repertoire including affiliative moan and hmm calls. Past research has suggested that both vocalisations may be contact calls, and we assessed their usage in addition to examining the effect of individual differences and social factors on male calling behaviour. We tested three hypotheses: the group cohesion, preferred companion and individual differences hypotheses. From March to July 2010, 565 h of focal animal data were collected on 31 males aged ≥1 year at the Beza Mahafaly Special Reserve, Madagascar. Focal males were observed for 30 min, with vocalisations, allogrooming and agonistic interactions noted using one‐zero sampling, and general behaviour, nearest neighbour identity and distance noted using instantaneous point sampling, all at 2.5 min intervals. We found support for the group cohesion hypothesis for both vocalisations, and support for the preferred companion and individual differences hypotheses for the hmm but not the moan vocalisation. Moan and hmm calls maintained the distance between a male and his nearest neighbour, and were made at higher rates during behaviours which may lead to separation from conspecifics, such as travel and vigilance. Males made hmm calls at higher rates when they were low‐ranking, and/or when the nearest neighbour of a male or a preferred companion of either sex. Low‐ranking males may hmm call to maintain proximity to specific individuals within social groups who will show them increased tolerance, with the hmm signalling peaceful intent. Ring‐tailed lemurs are one of the best living models of gregarious primate ancestors, and gaining a better knowledge of the function and range of usage of their contact calls informs our understanding of the evolution of primate cognition.     

Open-field responses of domestic chicks in the presence or absence of familiar cues

Male domestic chicks were reared in groups with distinctive cues (red crosses) placed on the walls of the home boxes from 2 to 7 d of age and their subsequent behaviour in an open field in the presence or absence of the familiar rearing cues was recorded.Ambulation, peeping, pecking, jumping and standing were all significantly higher and the latency to the first step, duration of freezing, sitting time, lying time and time spent with the eyes closed were significantly lower when the familiar rearing cues were present in the test situation. These observations are consistent with the suggestion that the birds are less fearful in the presence of familiar stimuli. The presence of the familiar cues also increased the time spent feeding and drinking. The preference effect was a specific one, for birds exposed to red crosses in early life preferred such stimuli to black circles in a subsequent two-choice situation, whereas chicks reared with black circles preferred them to red crosses. There was no generalisation of attachment from one stimulus to the other. As the chicks spent more time feeding and drinking in the presence of the familiar cues, it is assumed that fear was reduced. Thus, the results tend to confirm that the frequency of certain behaviour patterns is indicative of certain levels of fear.     

An analysis of avoidance generalization and food preference transitivity in goldfish,Carassius auratus

To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.     

Social responses to variation in food supply and nest suitability in ants (Tapinoma erraticum)

The social organization of Tapinoma erraticum colonies has been studied in two environmental contexts: those of mild starvation and of disturbance inducing a complete change of nest site. Trophallactic activity was compared with brood transport behaviour in tests performed repeatedly on the same group of insects. Workers were individually marked enabling interactions to be analysed within the group. An age-dependent difference in behaviour exists during feeding. However, when the colony changed its location, certain workers were found to be transport specialists, whereas others remained inactive: the transport behaviour of T. erraticum workers does not appear to be agedependent, unlike feeding behaviour. A principal components analysis of the results indicated no link between these two types of activities at the individual level. This study indicates the existence of types of social organization which are specific to each of the activities performed.     

The More the Merrier: Swarming as an Antipredator Strategy in the Mysid <Emphasis Type="Italic">Neomysis Integer</Emphasis>

The swarming behaviour of a Baltic littoral mysid shrimp, Neomysis integer, was studied both in the presence and absence of a predator (European perch, Perca fluviatilis L.). I performed two kinds of laboratory experiments. First, the swarming tendency of mysids and the effect of swarm size on swarm choice were studied. Second, the ingestion rate of mysids was measured when feeding alone versus in a swarm. The results indicate that N. integer actively join swarms. The avoidance of the perch by N. integer individuals was stronger when there was a swarm present. Larger swarms were preferred over smaller ones regardless of presence or absence of the predator. The overall feeding rate was similar when feeding alone and in swarm, but predator cues reduced feeding rate only when the mysids were feeding alone. This study demonstrates the capability of N. integer to assess predation risk and social context and alter their behaviour accordingly.