Spread of false alarms in foraging flocks of house sparrows

In group‐foraging species with no alarm signals, the sudden departure of neighbours can be used to inform the rest of the group about the detection of a threat. However, sudden departures are ambiguous because they can be triggered by factors unrelated to predator detection. We evaluated how animals react to the sudden departure of neighbours in groups of foraging house sparrows (Passer domesticus). We focussed on false alarms that occurred for no apparent reasons to us because predation attempts were not frequent. Three factors can explain how the sudden departure of a neighbour can influence reaction times, namely group size, the distance between neighbours, and predation risk. We predicted reaction times to be longer in larger groups where individual vigilance levels are low, and when group members are further apart and cannot easily monitor each other. In addition, we expected reaction times to be longer when predation risk is lower. Departures that are more temporally clumped are also expected to be less ambiguous and should trigger faster reaction times. Our results show that sparrows reacted faster, not more slowly, to the sudden departures of neighbours in larger groups, and, as predicted, more slowly when neighbours were more distant from each other. Reaction times were longer in one of the two study years in which predation risk was deemed lower. Sparrows reacted more quickly when earlier departures were more temporally clumped. The results thus provided partial support for the predictions, and future work is needed to assess how individuals react to fleeing responses by their neighbours in species with no alarm signals.     

Out of Sight but Not Out of Mind? Behavioral Coordination in Red-Tailed Sportive Lemurs (<Emphasis Type="Italic">Lepilemur ruficaudatus</Emphasis>)

Many animals are organized into social groups and have to synchronize their activities to maintain group cohesion. Although activity budgets, habitat constraints, and group properties may impact on behavioural synchrony, little is known regarding how members of a group reach a consensus on the timing of activities such as foraging bouts. Game theory predicts that pair partners should synchronize their activities when there is an advantage of foraging together. As a result of this synchronization, differences in the energetic reserves of the two players develop spontaneously and the individual with lower reserves emerges as a pacemaker of the synchrony. Here, we studied the behavioral synchrony of pair-living, nocturnal, red-tailed sportive lemurs (Lepilemur ruficaudatus). We observed 8 pairs continuously for ≥1 annual reproductive cycle in Kirindy Forest, Western Madagascar. During focal observations, one observer followed the female of a pair and, simultaneously, another observer followed the male. We recorded the location and behavioral state of the focal individual every 5 min via instantaneous sampling. Although behavioral synchrony of pair partners appeared to be due mainly to endogenous activity patterns, they actively synchronized when they were in visual contact (<10 m). Nevertheless, red-tailed sportive lemurs benefit from synchronizing their activity only for 15% of the time, when they are close together. The lack of an early warning system for predators and weak support for benefits via social information transfer in combination with energetic constraints may explain why red-tailed sportive lemurs do not spend more time together and thus reap the benefits of behavioral synchrony.     

The effect of energy reserves and food availability on optimal immune defence

In order to avoid both starvation and disease, animals must allocate resources between energy reserves and immune defence. We investigate the optimal allocation. We find that animals with low reserves choose to allocate less to defence than animals with higher reserves because when reserves are low it is more important to increase reserves to reduce the risk of starvation in the future. In general, investment in immune defence increases monotonically with energy reserves. An exception is when the animal can reduce its probability of death from disease by reducing its foraging rate. In this case, allocation to immune defence can peak at intermediate reserves. When food changes over time, the optimal response depends on the frequency of changes. If the environment is relatively stable, animals forage most intensively when the food is scarce and invest more in immune defence when the food is abundant than when it is scarce. If the environment changes quickly, animals forage at low intensity when the food is scarce, but at high intensity when the food is abundant. As the rate of environmental change increases, immune defence becomes less dependent on food availability. We show that the strength of selection on reserve-dependent immune defence depends on how foraging intensity and immune defence determine the probability of death from disease.     

Return Customers: Foraging Site Fidelity and the Effect of Environmental Variability in Wide-Ranging Antarctic Fur Seals

Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredictable, as it often is in marine environments, then habitat familiarity may also present ecological benefits to individuals. We examined the winter foraging distribution of female Antarctic fur seals, Arctocephalus gazelle, over four years to assess the degree of foraging site fidelity at two scales; within and between years. On average, between-year fidelity was strong, with most individuals utilising more than half of their annual foraging home range over multiple years. However, fidelity was a bimodal strategy among individuals, with five out of eight animals recording between-year overlap values of greater than 50%, while three animals recorded values of less than 5%. High long-term variance in sea surface temperature, a potential proxy for elevated long-term productivity and prey availability, typified areas of overlap. Within-year foraging site fidelity was weak, indicating that successive trips over the winter target different geographic areas. We suggest that over a season, changes in prey availability are predictable enough for individuals to shift foraging area in response, with limited associated energetic costs. Conversely, over multiple years, the availability of prey resources is less spatially and temporally predictable, increasing the potential costs of shifting foraging area and favouring long-term site fidelity. In a dynamic and patchy environment, multi-year foraging site fidelity may confer a long-term energetic advantage to the individual. Such behaviours that operate at the individual level have evolutionary and ecological implications and are potential drivers of niche specialization and modifiers of intra-specific competition.     

Self-Improvement for Team-Players: The Effects of Individual Effort on Aggregated Group Information

By putting effort into behaviours like foraging or scanning for predators, an animal can improve the correctness of its personal information about the environment. For animals living in groups, the individual can gain further information if it is able to assess public information about the environment from other group members. Earlier work has shown that consensus group decisions based upon the public information available within the group are more likely to be correct than decisions based upon personal information alone, given that each individual in a group has a fixed probability of being correct. This study develops a model where group members are able to improve their personal likelihood of making a correct decision by conducting some level of (costly) effort. I demonstrate that there is an evolutionarily stable level of effort for all the individuals within the group, and the effort made by an individual should decrease with increasing group size. The relevance of these results to social decision making is discussed: in particular, these results are similar to standard theoretical predictions about the amount of vigilance shown by individuals decreasing with increasing group size. However, this model suggests that these results could come about where individuals are coordinating their effort within the group (unlike standard models, which assume that all individual effort is independent of the actions of others). This ties in with experimental findings where individuals have been shown to monitor the efforts of others.     

Tolerance of understory plants subject to herbivory by roe deer

Classical foraging theory states that animals feeding in a patchy environment can maximise their long term prey capture rates by quitting food patches when they have depleted prey to a certain threshold level. Theory suggests that social foragers may be better able to do this if all individuals in a group have access to the prey capture information of all other group members. This will allow all foragers to make a more accurate estimation of the patch quality over time and hence enable them to quit patches closer to the optimal prey threshold level. We develop a model to examine the foraging efficiency of three strategies that could be used by a cohesive foraging group to initiate quitting a patch, where foragers do not use such information, and compare these with a fourth strategy in which foragers use public information of all prey capture events made by the group. We carried out simulations in six different prey environments, in which we varied the mean number of prey per patch and the variance of prey number between patches. Groups sharing public information were able to consistently quit patches close to the optimal prey threshold level, and obtained constant prey capture rates, in groups of all sizes. In contrast all groups not sharing public information quit patches progressively earlier than the optimal prey threshold value, and experienced decreasing prey capture rates, as group size increased. This is more apparent as the variance in prey number between patches increases. Thus in a patchy environment, where uncertainty is high, although public information use does not increase the foraging efficiency of groups over that of a lone forager, it certainly offers benefits over groups which do not, and particularly where group size is large.     

Kin discrimination in salmonids

Summary The data presented here suggest that significant selection pressures towards kin discrimination behaviour patterns result from kin-biased territorial defence behaviour patterns. Salmonids employ a phenotype matching recognition mechanism allowing individuals to discriminate unfamiliar kin. Kin discrimination abilities allow individuals to reduce the levels of aggression associated with territorial defence towards related conspecifics and to defend smaller territories near kin versus non-kin. This kin-biased territorial defence behaviour is observed in at least one species under a wide range of territorial quality conditions. Within kin groups, subordinate individuals obtain a greater number of foraging attempts, resulting in kin-biased foraging within the social group. As a result of this kin-bias, individuals within kin groups show significantly higher mean weight increases (increased direct fitness benefits) and reduced variance in these increases (increased indirect benefits). Since all individuals within the kin groups obtained higher, less variable weight increases, we can argue that individuals are increasing their inclusive fitness as a result of these kin-biased behaviour patterns.Based on these results, and on what is known about the life history of a variety of salmonid and non-salmonid species, we can formulate a number of testable predictions. By testing these predictions, we may be better able to understand both the proximate and ultimate causation of kin discrimination abilities in a variety of fishes.     

Knowing your habitat: linking patch-encounter rate and patch exploitation in parasitoids

According to optimal foraging theory, animals should decidewhether or not to leave a resource patch by comparing the currentprofitability of the patch with the expected profitability ofsearching elsewhere in the habitat. Although there is abundantevidence in the literature that foragers in general are wellable to estimate the value of a single resource patch, theirdecision making has rarely been investigated with respect tohabitat quality. This is especially true for invertebrates.We have conducted experiments to test whether parasitic waspsadjust patch residence time and exploitation in relation tothe abundance of patches within the environment. We used thebraconid Asobara tabida, a parasitoid of Drosophila larvae,as our model species. Our experiments show that these waspsreduce both the residence time and the degree of patch exploitationwhen patches become abundant in their environment, as predictedby optimal foraging models. Based upon a detailed analysis ofwasp foraging behavior, we discuss proximate mechanisms thatmight lead to the observed response. We suggest that parasitoidsuse a mechanism of sensitization and desensitization to chemicalsassociated with hosts and patches, in order to respond adaptivelyto the abundance of patches within their environment.     

Managing uncertainty: information and insurance under the risk of starvation

In an uncertain world, animals face both unexpected opportunities and danger. Such outcomes can select for two potential strategies: collecting information to reduce uncertainty, or insuring against it. We investigate the relative value of information and insurance (energy reserves) under starvation risk by offering model foragers a choice between constant and varying food sources over finite foraging bouts. We show that sampling the variable option (choosing it when it is not expected to be good) should decline both with lower reserves and late in foraging bouts; in order to be able to reap the reduction in uncertainty associated with exploiting a variable resource effectively, foragers must be able to afford and compensate for an initial increase in the risk of an energetic shortfall associated with choosing the option when it is bad. Consequently, expected exploitation of the varying option increases as it becomes less variable, and when the overall risk of energetic shortfall is reduced. In addition, little activity on the variable alternative is expected until reserves are built up early in a foraging bout. This indicates that gathering information is a luxury while insurance is a necessity, at least when foraging on stochastic and variable food under the risk of starvation.     

Spatial structure in foraging groups of wedge-capped capuchin monkeys Cebus nigrivittatus

Individuals in foraging groups of wedge-capped capuchin monkeys, Cebus nigrivittatus, are organized in consistent and predictable configurations. This study examines how an individual's position in space, as characterized by its position relative to other animals and by its proximity to neighbours, influences its (a) capture success when foraging for invertebrates, (b) access to fruiting trees, and (c) time spent in vigilance (a measure of its vulnerability to predators). The dominant male and female and animals tolerated by this female occupy the advantageous centre-front positions. The positions of other animals depend on their respective age-sex classes, and are discussed relative to the risk of predation and foraging requirements of the different age-sex classes.     

When to use social information: the advantage of large group size in individual decision making

Correct decision making is crucial for animals to maximize foraging success and minimize predation risk. Group-living animals can make such decisions by using their own personal information or by pooling information with other group members (i.e. social information). Here, we investigate how individuals might best balance their use of personal and social information. We use a simple modelling approach in which individual decisions based upon social information are more likely to be correct when more individuals are involved and their personal information is more accurate. Our model predicts that when the personal information of group members is poor (accurate less than half the time), individuals should avoid pooling information. In contrast, when personal information is reliable (accurate at least half the time), individuals should use personal information less often and social information more often, and this effect should grow stronger in larger groups. One implication of this pattern is that social information allows less well-informed members of large groups to reach a correct decision with the same probability as more well-informed members of small groups. Thus, animals in larger groups may be able to minimize the costs of collecting personal information without impairing their ability to make correct decisions.     

Spying on your neighbours? Social information affects timing of breeding and stress hormone levels in a colonial seabird

A good overlap between offspring energetic requirements and availability of resources is required for successful reproduction. Accordingly, individuals from numerous species fine-tune their timing of breeding by integrating cues that predict environmental conditions during the offspring period. Besides acquiring information from their direct interaction with the environment (personal information), individuals can integrate information by observing the behaviours or performance of others (social information). The use of social information is often beneficial because the accumulated knowledge of conspecifics may represent a source of information more reliable than the intrinsically more limited personal information. However, although social information constitutes the major source of information in a wide range of contexts, studies investigating its use in the context of timing of breeding are scarce. We investigated whether black-legged kittiwakes (Rissa tridactyla) used social information to adjust the timing of egg-laying. We manipulated social information using a food-supplementation experiment, known to advance kittiwakes' reproductive phenology. We expected food-supplemented and unsupplemented pairs to delay and advance, respectively, their timing of laying when surrounded by a majority of neighbours from the opposite food-treatment. However, both unsupplemented and food-supplemented kittiwakes delayed egg-laying when surrounded by a higher proportion of neighbours from the opposite food-treatment. This result shows that kittiwakes use social information to time egg-laying, but that it is not used to match the seasonal peak of food availability. We suggest that when social and personal cues give contradictory environmental information, individuals may benefit from delaying laying to gather more information to make better decisions about investment into eggs. Further, we explored a potential proximate mechanism for the pattern we report. We show that baseline corticosterone, known to mediate reproductive decisions, was lower in unsupplemented females facing a higher proportion of food-supplemented neighbours. Altogether, our results suggest that to fine-tune their timing of laying, kittiwakes use complex decision-making processes in which social and personal information interplay.

     

Effects of group size on school structure and behaviour in yellow‐eyed mullet Aldrichetta forsteri

Schooling behaviour in yellow‐eyed mullet Aldrichetta forsteri, a common fish species in New Zealand estuarine habitats, was investigated to identify interaction rules associated with group formation. Tank‐based three‐dimensional studies of three group sizes (15, 75 and 150 individuals) were carried out to measure the effects of these different group sizes on school structure during control, predation risk and foraging behavioural states. Increased group size positively correlated with nearest‐neighbour distance in control and foraging states. Swimming speed was the lowest in all three behavioural states in groups of 15 fish compared with 75 or 150. Immediate behavioural response following visual exposure to a simulated avian predator differed between groups resulting in loss of structure in larger groups. School shape was an oblong–oblate spheroid with a length, breadth and height ratio of 5:2:1 and the area of free space surrounding individual fish was spherical in shape with a high degree of spatial isotropy present in all size groups. These findings challenge traditional theories based on either local or global properties as key drivers of group structure. Instead, our results suggest that a more collaborative approach involving both group size and rules pertaining to nearest‐neighbour interactions affects collective behaviours in this species.     

Effects of habitat complexity,dominance and personality on habitat selection: Ideal despotic cichlids

Habitat structure can impede visibility and movement, resulting in lower resource monopolization and aggression. Consequently, dominant individuals may prefer open habitats to maximize resource gain, or complex habitats to minimize predation risk. We explored the role of dominance on foraging, aggression and habitat choice using convict cichlids (Amatitlania nigrofasciata) in a two‐patch ideal free distribution experiment. Groups of six fish of four distinct sizes first competed for shrimp in one‐patch trials in both an open and complex habitat; half the groups experienced each habitat type first. Following these one‐patch trials, each group then chose between habitat types in a two‐patch trial while competing for food. Finally, each fish underwent an individual behavioural assessment using a battery of “personality” tests to determine if behaviour when alone accurately reflected behaviour within a social context. In the one‐patch trials, dominant fish showed similar food consumption between habitats, but chased more in the complex habitat. In the two‐patch choice trials, dominants preferred and defended the complex habitat, forming an ideal despotic distribution with more than half the fish and competitive weight in the open habitat. Within the groups, individual fish differed in foraging and chasing, with repeatabilities of 0.45 and 0.23 across all treatments. Although a higher foraging rate during the individual assessment predicted foraging rate and use of the complex habitat during the group trials, aggression and boldness tests were not reflective of group behaviour. Across groups, heavier dominants and those with higher foraging rate in the open habitat used the open habitat more, suggesting that both risk and energetic state affect habitat preference in dominant convict cichlids.     

Approximating Optimal Behavioural Strategies Down to Rules-of-Thumb: Energy Reserve Changes in Pairs of Social Foragers

Functional explanations of behaviour often propose optimal strategies for organisms to follow. These ‘best’ strategies could be difficult to perform given biological constraints such as neural architecture and physiological constraints. Instead, simple heuristics or ‘rules-of-thumb’ that approximate these optimal strategies may instead be performed. From a modelling perspective, rules-of-thumb are also useful tools for considering how group behaviour is shaped by the behaviours of individuals. Using simple rules-of-thumb reduces the complexity of these models, but care needs to be taken to use rules that are biologically relevant. Here, we investigate the similarity between the outputs of a two-player dynamic foraging game (which generated optimal but complex solutions) and a computational simulation of the behaviours of the two members of a foraging pair, who instead followed a rule-of-thumb approximation of the game''s output. The original game generated complex results, and we demonstrate here that the simulations following the much-simplified rules-of-thumb also generate complex results, suggesting that the rule-of-thumb was sufficient to make some of the model outcomes unpredictable. There was some agreement between both modelling techniques, but some differences arose – particularly when pair members were not identical in how they gained and lost energy. We argue that exploring how rules-of-thumb perform in comparison to their optimal counterparts is an important exercise for biologically validating the output of agent-based models of group behaviour.     

The influence of diet on foraging habitat models: a case study using nursing Antarctic fur seals

Predictable sources of food underpin lifetime reproductive output in long lived animals. The most important foraging areas of top marine predators are therefore likely to be related to environmental features that enhance productivity in predictable spatial and temporal patterns. Even so, although productive areas within the marine environment are distributed patchily in space and time, most studies assess the relationships between feeding activity and proximate, not long term, environmental characteristics. In addition, individuals within a population may exploit different prey types, and these are often associated with different hydrographic features. Until now, models attempting to associate core foraging areas (CFAs) of marine predators with the environmental characteristics of those areas have not considered the diet of individual animals, despite the influence this could have on these relationships. We used bathymetry and multi‐year (n=24) mean sea surface temperature and variability as predictors of CFAs of lactating Antarctic fur seals Arctocephalus gazella at Heard Island. The effect of prey types on the predictability of these models was explored by matching diet and foraging trip data of individual seals (n=40 seals, n=1 trip each). Differences in diet between seals were mirrored by their spatial behaviour. Foraging strategies differed both between and within groups of seals consuming different diets. Long‐term environmental parameters were useful for predicting the foraging activity of seals that consumed a single prey type with relatively specific habitat preferences, but not for those that consumed single or multiple prey types associated with more varied habitats. Ignoring individual variation in predator diet probably contributes to the poor performance of foraging habitat models. These findings highlight the importance of incorporating individual specialization in foraging behaviour into ecological models and management of predator populations.     

Feeding and metabolic compensations in response to different foraging costs

How energetic cost of locomotion affects foraging decisions, and its metabolic consequences are poorly understood. In several groups of animals, including hermit crabs, exploratory walking enhances the efficiency of foraging by increasing the probability of finding more and better food items; however, the net gain of energy will only be enhanced if the costs of walking are lower than the benefits of enhanced food acquisition. In hermit crabs, the cost of walking increases with the mass of the shell type occupied. Thus, we expected that hermit crabs should adjust their foraging strategy to the cost of movement in different shells. We assessed the foraging, the quantity and quality of food intake, and the energetic cost of maintenance of hermit crabs paying different costs of foraging in the wild. The exploratory walking negatively correlated with shell mass, showing that hermit crabs use different foraging strategies in response to the expenditure required to move. Hermit crabs deal with high energetic costs of foraging in heavy shells by reduces their exploratory walking and overall metabolic rate, as a strategy to maximize the net energy intake. This study integrates behavioral and metabolic compensations as a response to foraging at different costs in natural conditions.     

Urbanization and the temporal patterns of social networks and group foraging behaviors

Urbanization causes dramatic and rapid changes to natural environments, which can lead the animals inhabiting these habitats to adjust their behavioral responses. For social animals, urbanized environments may alter group social dynamics through modification of the external environment (e.g., resource distribution). This might lead to changes in how individuals associate or engage in group behaviors, which could alter the stability and characteristics of social groups. However, the potential impacts of urban habitat use, and of habitat characteristics in general, on the nature and stability of social associations remain poorly understood. Here, we quantify social networks and dynamics of group foraging behaviors of black‐capped chickadees (N = 82, Poecile atricapillus), at four urban and four rural sites weekly throughout the nonbreeding season using feeders with radio frequency identification of individual birds. Because anthropogenic food sources in urban habitats (e.g., bird feeders) provide abundant and reliable resources, we predicted that social foraging associations may be of less value in urban groups, and thus would be less consistent than in rural groups. Additionally, decreased variability of food resources in urban habitats could lead to more predictable foraging patterns (group size, foraging duration, and the distribution of foraging events) in contrast to rural habitats. Networks were found to be highly consistent through time in both urban and rural habitats. No significant difference was found in the temporal clumping of foraging events between habitats. However, as predicted, the repeatability of the clumping of foraging events in time was significantly higher in urban than rural habitats. Our results suggest that individuals living in urban areas have more consistent foraging behaviors throughout the nonbreeding season, whereas rural individuals adjust their tactics due to less predictable foraging conditions. This first examination of habitat‐related differences in the characteristics and consistency of social networks along an urbanization gradient suggests that anthropic habitat use results in subtle modifications in social foraging patterns. Future studies should examine potential implications of these differences for variation in predation risk, energy intake, and information flow.     

The effect of ambient humidity on the foraging behavior of the hawkmoth Manduca sexta

The foraging decisions of flower-visiting animals are contingent upon the need of an individual to meet both energetic and osmotic demands. Insects can alter their food preferences to prioritize one need over the other, depending on environmental conditions. In this study, preferences in nectar sugar concentrations (0, 12, 24 %) were tested in the hawkmoth Manduca sexta, in response to different levels of ambient humidity (20, 40, 60, and 80 % RH). Moths altered their foraging behavior when placed in low humidity environments by increasing the volume of nectar imbibed and by consuming more dilute nectar. When placed in high humidity environments the total volume imbibed decreased, because moths consumed less from dilute nectars (water and 12 % sucrose). Survivorship was higher with higher humidity. Daily foraging patterns changed with relative humidity (RH): moths maximized their nectar consumption earlier, at lower humidities. Although ambient humidity had an impact on foraging activity, activity levels and nectar preferences, total energy intake was not affected. These results show that foraging decisions made by M. sexta kept under different ambient RH levels allow individuals to meet their osmotic demands while maintaining a constant energy input.     

Distinguishing Energy Maximizers from Time Minimizers: A Comparative Study of Two Hummingbird Species

SYNOPSIS. The potential reproductive success of a food energymaximizer increases with foraging time, while that of a foragingtime minimizer increases with time spent in nonforaging activitiesgiven a set energy requirement has been met. How can these foraging"goals" be distinguished for nonbreeding animals in the field?If individuals of two species occupying the same habitat consumethe same foods, face similar foraging constraints, and havesimilar meal sizes (food intake per foraging bout), then relativeto a time minimizer, an energy maximizer should: (1) spend moretime foraging, with greater foragingbout frequency, but no differencein foraging-bout duration; (2) spend less time sitting, withlower sitting-bout duration yet greater sitting-bout frequency;(3) gain mass more rapidly, if net energy intake results inmass accumulation; and (4) exhibit no other differences in timebudgeting. These assumptions and predictions were verified bypopulation- and individual-level comparisons of immature malesof two species of nectar-feeding hummingbirds studied over threefield seasons. The results suggest that, relative to each other,migrant Rufous Hummingbirds are energy maximizers and nonmigrantCosta Hummingbirds are time minimizers. Despite significantdifferences in time budgeting, by far the most striking differencebetween the species was that the Rufous gained mass four toeight times as rapidly as the Costa. This was due to the Rufousentering torpor at night, resulting in relatively little overnightloss in body mass. These patterns underscore the importanceof measuring net energy intake as directly as possible (in thiscase by fat accumulation) in testing foraging theory. Indirectmeasures (such as time budgets) may not always provide the resolutionnecessary to detect important energetic differences betweendifferent foragers.