Learning to forage in a regenerating patchy environment: Can it fail to be optimal?

The behaviour of animals foraging along closed traplines of regenerating patches of food has been simulated using a learning rule that determines when an animal should leave the patch at which it is currently feeding to search for another one. The rule causes the animal to stay at the patch as long as it is feeding faster than it remembers doing. The foraging behaviour of one animal, and of two or more animals together, feeding in traplines containing patches of the same and of differing types has been simulated, and in all cases the foraging behaviour generated by the rule allowed the animals to exploit the food very efficiently. The learning model is also responsible for indirect social interactions among animals sharing the same trapline because the feeding of each animal reduces the availability of food for the others. This causes a population of animals to disperse themselves, on average, among patches of food according to the ideal free distribution. The relationship between the learning model and conventional optimal foraging models is examined and it is shown that it is pointless to try to account for learned behaviour in the context of optimal foraging theory.     

Diurnal foraging routines in a tropical bird,the rock finch Lagonosticta sanguinodorsalis: how important is predation risk?

An animal's foraging decisions are the outcome of the relative importance of the risk of starvation and predation. Fat deposition insures against periods of food shortage but it also carries a cost in terms of mass dependent predation risk due to reduced escape probability and extended exposure time. Accordingly, birds have been observed to show a unimodal foraging pattern with foraging concentrated at the end of the day under conditions of predictable food resources and high predation risk. We tested this hypothesis in a tropical granivorous finch, the rock firefinch Lagonosticta sanguinodorsalis , in an outdoor aviary experiment during which food was provided ad lib and the risk of predation was varied by providing food either adjacent to, or 5 m away from cover. Rock firefinches showed a bimodal foraging pattern regardless of the risk of predation at which they fed. The results suggest that predation is relatively unimportant in shaping their daily feeding pattern despite mass gain during the day being similar to temperate birds. Foraging patterns closely follow diurnal temperature variation and this is suggested to be the main determinant of the observed bimodal pattern.     

How social relationships influence a monkey's choice of feeding sites in the troop of Japanese macaques (Macaca fuscata fuscata) on Koshima islet

When the individual Japanese macaques of the Koshima troop feed on natural food, they usually feed alone. In situations where animals usually feed without other animals, there is a possibility that subordinate animals may avoid feeding sites at which dominant animals are feeding. This paper examines whether social relationships such as kinship or dominance exert any influence on an animal's choice of feeding sites, by analyzing episodes in which an animal approached and climbed into a tree where other animals were. As a result, it was found that social relationships did not influence whether an animal climbed into a tree where other animals were feeding, and that no particular age-sex pair co-fed. Agonistic interactions frequently occurred when the inter-individual distance was less than 1 m. From these findings, the feeding sites were divided into two spaces: (1) a tolerance feeding space, and (2) an intolerance feeding space. It is presumed that animals can feed without entering others' intolerance feeding spaces when food is abundant, as it was in the present study period. Thus social relationships do not influence an animal's choice of feeding sites in such a situation.     

Orientation behavior of butterflyfishes (family Chaetodontidae) on coral reefs: spatial learning of route specific landmarks and cognitive maps

Synopsis Foraging butterflyfishes follow predictable paths as they swim from one food patch to another within their territories and home ranges. The pattern is repeated throughout the day. The behavior is described in species belonging to the coral feeding guild. Habit formation and spatial learning are implicated. Foraging paths are based on learned locations of route specific landmarks. When a coral head is removed the fish look for it in its former location. If pairs of foraging fish are deflected from the path, they resume their routine pattern at the first landmark they encounter. Periodically, fish make excursions of 30 m or more to distant parts of the reef. Usually they follow different paths on the outbound and homeward legs of these excursions. The critical question is: Are the paths novel? If they are, it is evidence for the use of cognitive maps. Certainly fishes living in the highly structured coral reef environment are prime candidates to use cognitive maps in their orientation behavior.     

Dominance and feeding interference in small groups of blackbirds

Dominance and/or interference parameters play a pivotal rolein most ideal free distribution models, but there has beenscant empirical study of the exact manner in which they jointlyoperate. We investigate how foraging effort and success variedamongst individuals of different dominance rankings in groupsof 1-3 wild blackbirds (Turdus merula) attracted to patchesof hidden food. Foraging effort (number of feeding movementsper unit time), as opposed to vigilance tradeoffs, was greaterwhen an individual fed with a subordinate conspecific thanwhen it fed alone, but tended to be less when it fed with adominant individual. Within dyads, changes in foraging effortwere associated with the direction of the dominance relationship,but not the relative difference in dominance rank between thetwo individuals. Similarly, amongst threesomes, top-rankedbirds (but not the lowest-ranked individual) showed higherforaging effort compared to when foraging alone. Top-ranked birds also profited from a greater increase in foraging success(food items per unit effort) than bottom-ranked birds whenfeeding in threesomes than when feeding alone. Dominant birdsshowed increased foraging success, but not effort, after displacinga subordinate. Our results suggest that an individual's foragingeffort is determined by the interplay of group vigilance benefitsand interference costs, the latter being more expensive for subordinate individuals. The foraging success of dominant birdsmay further increase if they use subordinates as food-finders.We discuss the implications of our findings for interferenceparameters in current Ideal Free Distribution models.     

栗喉蜂虎捕食差异

2010年4～5月和2011年4～6月,用焦点动物取样法对云南省保山市潞江镇怒江河谷栗喉蜂虎捕食差异进行了观察。对栗喉蜂虎雌性成年鸟、雄性成年鸟、青年鸟捕食种类、数量、成功率、食物组成、食物资源量、处理食物成功率及处理时间进行了统计。结果表明,栗喉蜂虎捕食种类包括7类昆虫,以膜翅目Hymenoptera、蜻蜓目Odonate、鳞翅目Lepidoptera昆虫为主;成年雄鸟捕食频次高于成年雌鸟和青年鸟;成年鸟与青年鸟处理食物成功率无显著差异,但二者捕食成功率和处理食物时间差异显著。     

Variation in foraging behavior facilitates resource partitioning in a polymorphic cichlid, Herichthys minckleyi

We examined foraging behavior (microhabitat use and feeding behavior) in a trophically polymorphic cichlid fish, Herichthys minckleyi, to address several questions regarding resource partitioning in this threatened species. These include: (1) do morphotypes demonstrate different foraging behaviors? (2) do individuals within a morphotype vary in their foraging behavior (e.g. are some individuals specialists, only using a subset of available resources, while other are generalists)? (3) do foraging behaviors vary between isolated pools? (4) do foraging behaviors vary across seasons? We quantified microhabitat use and feeding behavior for over 100 individuals (of two morphotypes) feeding freely in two isolated pools (populations) and across two seasons (winter and summer). We found differences in foraging behavior between morphotypes and individual specializations within morphotypes; i.e. some individuals specialize on certain food resources by using a few feeding behaviors within a subset of microhabitats, whereas others employ a range feeding behaviors across many microhabitats. Foraging behavior also varied between pools and across seasons. This spatial and temporal variation in foraging behavior and resource use may serve to maintain this polymorphism, as the relative fitness of the each morph may vary over space and time.     

First evidence for relocation of stationary food resources during foraging in a strepsirhine primate (Microcebus murinus)

Field observations suggest that the diet of the Malagasy gray mouse lemur consists not only of non-stationary animal prey (invertebrates or small vertebrates), but also of stationary food resources such as gum or homopteran larvae secretions (HLS). We studied the foraging behavior of five mouse lemurs radiotelemetrically, each during six consecutive nights in the dry season, to explore to which extent they use these food resources and whether there is evidence for their relocation. We found that animals used all three different food categories. Mouse lemurs fed on gums and spent 68.5% (range 20.1-99.7%) of their feeding time eating this item. They were observed eating HLS in 8.4% (range 0-71.5%) of the feeding time and consuming small animals in 8.4% (range 0.3-26%) of their feeding time. The animals relocated stationary feeding sites significantly more frequently than non-stationary ones. They revisited the relocated stationary food sites about five times over the six nights. Furthermore, departure directions when leaving the sleeping site at dusk were not randomly distributed but showed a preferred orientation. Altogether, we provided first evidence for the relocation of stationary food resources in nature and thereby for the potential significance of spatial memory during foraging in a strepsirhine primate.     

A fine-scale time budget of Cape gannets provides insights into the foraging strategies of coastal seabirds

Central-place foragers organize their feeding trips both to feed themselves and to provide their offspring with food. In seabirds, several long-range foragers have been shown to alternate long and short trips to balance these dual needs. However, the strategies of short-range foragers remain poorly understood. We used a precise, miniaturized motion sensor to examine the time budget of 20 breeding Cape gannets, Morus capensis, foraging off the coast of South Africa. Birds stayed at sea for 5.5-25.3 h, occasionally spending the night at sea. The large number of isolated dives and extended flight time observed during these overnight trips suggested that birds either experienced poor foraging conditions or exploited more distant, yet more profitable prey patches. Conversely, birds that stayed at sea for less than 1 day had relatively consistent activity patterns. Most of these birds (88%) foraged actively at the beginning and at the end of the foraging trip. These feeding bouts were separated by protracted periods of sitting on the sea surface. Such resting periods probably allow birds to digest the food ingested during the first part of the foraging trip, so they initially feed themselves, and then obtain food for their chick on the way back to the breeding site.     

Path integration controls nest-plume following in desert ants

The desert ant Cataglyphis fortis is equipped with sophisticated navigational skills for returning to its nest after foraging. The ant's primary means for long-distance navigation is path integration, which provides a continuous readout of the ant's approximate distance and direction from the nest. The nest is pinpointed with the aid of visual and olfactory landmarks. Similar landmark cues help ants locate familiar food sites. Ants on their outward trip will position themselves so that they can move upwind using odor cues to find food. Here we show that homing ants also move upwind along nest-derived odor plumes to approach their nest. The ants only respond to odor plumes if the state of their path integrator tells them that they are near the nest. This influence of path integration is important because we could experimentally provoke ants to follow odor plumes from a foreign, conspecific nest and enter that nest. We identified CO(2) as one nest-plume component that can by itself induce plume following in homing ants. Taken together, the results suggest that path-integration information enables ants to avoid entering the wrong nest, where they would inevitably be killed by resident ants.     

Movements and Conflicts in a Flock of Foraging Black‐Tailed Godwits (Limosa limosa): The Influence of Feeding Rates on Behavioural Decisions

We studied movements and conflicts within a small flock of free‐living black‐tailed godwits foraging on benthic invertebrates in a brackish lagoon. To interpret our results in the framework of foraging theory, we studied the influence of individual feeding rate on the decisions to move and to attack flock companions. Birds changed their position within the flock more often when their intake rate was low and sometimes attacked conspecifics to supplant them from their feeding place. Aggressors significantly avoided front attacks and were almost always successful. They attacked individuals having higher feeding rates than themselves and their own feeding rate significantly increased after the attack, although victims were not chased off to particularly poor sites. Our results suggest that aggressors could obtain reliable information about the quality of the foraging site they coveted by observing their victim’s feeding activity before attacking. Although aggression seemed to be caused by a low intake rate, we show that displacing another bird was more time‐consuming than independent foraging. We conclude that it was not the most profitable behaviour in terms of energy intake. Foraging site displacement probably also had social functions, such as reinforcement of social status in a flock of birds preparing for pre‐breeding migration.     

A lifetime perspective on foraging and mortality

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.     

Foraging behaviour and habitat use of the serotine bat (Eptesicus serotinus) in southern England

Radio-tracking was useed to dertermine the foraging behaviour and habitat use of the serotine bat, Eptesicus serotinus , at two roosts in southren England. The basts communted an average of 6.5 km to and from distinct foraging sites and used up ot five sites per night. Serotine foraged in a wide range of habitats and were able to locate and exploit temporary feeding site such as recently mown grass. They foraged regulary arround white streelamps and in alte summer over cattle pasture on which fresh dung was present. Reproductively active females were strongly philopatric to their day-roost. In contrast, reproductively inactive females, from the same roosts. moved to new day-roosts up to 10 km from the site of capture. Serotines used thre distinct foraging strategies, short filight, ground feeding, and, predominantly, aerial hawking. Foraging bouts were interpresed with resting phases, with individuals roosting alone on walls of houses or in trees close to foraging sites. It is concluded that serotines are well adapted to an anthropogenic envioronment. They are strongly philopartric to roosts in human habitations, in close proximity to a range of feeding sites wehre they can take advantage of favourarble land amangement practices.     

The choice of foraging methods of the Brown Dipper,Cinclus pallasii (Aves: Cinclidae)

The Brown Dipper,Cinclus pallasii, forages for large prey by diving deeply among submerged rocks, and for small prey in shallow water by wading and pecking on the bottom. Foraging by diving entailed a higher energy cost but resulted in taking larger prey than foraging by wading-and-pecking. Foraging by diving was seldom observed from May to October, but increased from December to April, when the dippers came into breeding condition and the proportion of large prey in the benthic fauna increased. During the breeding season, adult dippers fed themselves mainly by foraging by wading-and-pecking, whereas those feeding nestlings and fledglings foraged by diving. The foraging methods employed was determined by the individuals being fed and the abundance of the large prey. Foraging by diving may be advantageous for individuals provisioning their young because of the high gross intake rate, but may be less advantageous for the foragers themselves because of the high energy cost.     

Fitness consequences of foraging success in water striders (Gerris remigis; Heteroptera: Gerridae)

Foraging theory's central premise assumes that behavioral actionsthat affect the acquisition of food also ultimately affect fitness.However, very few investigations in behavioral ecology actuallydemonstrate ultimate fitness consequences of any particularbehavior. Many studies focus on short-term estimates of fitnessin animals with considerable life spans. I investigated whetherdifferences in foraging performance, as related to patch choiceand behavioral dominance, show consistent patterns over extendedperiods of an animal's life such that they translate into differencesin reproductive success. In one experiment, I focused on theability of single female water strider (Gerris remigis) to discriminatebetween foraging patches of differing prey abundances in laboratorystreams simulating natural conditions. In another experiment,I focused on competitive interactions within groups of threefemale water striders foraging in laboratory streams where resourceavailability varied with position in a patch. The first experimentshowed that, overall, the individuals detected and preferredto forage in the richer patch, which directly increased theirforaging success and their lifetime fecundity. However, therewas marked variability among individuals in their ability torespond to the differences in food availability, ranging fromno tracking to fast tracking when the patch qualities were switched.In the second experiment, both the foraging position of individualsin the stream and their dominance rank were reasonably consistentover their entire reproductive life. Foraging position and dominancerank were significant predictors of lifetime fecundity, theformer being the better predictor due to an imperfect correlationbetween the two variables. In both experiments, the increasein fecundity was achieved by higher oviposition rates ratherthan by extending the oviposition period or by inducing firstreproduction at an earlier age. [Behav Ecol 1991; 2: 46-55)     

食物大小对棕果蝠和犬蝠取食行为的影响

按照最优化觅食理论,动物在取食时需在能量获取与捕食风险之间权衡。本文通过室内行为实验,研究两种旧大陆果蝠棕果蝠和犬蝠对食物大小的选择规律与取食策略。按体积由小到大将苹果分为Ⅰ型、Ⅱ型、Ⅲ型、Ⅳ型4 种类型的食物块,通过红外相机观察果蝠对不同大小食块的取食情况,并就其对各类型食块的取食率、取食次数和停留时间进行统计分析。结果表明:这两种果蝠对Ⅱ型和Ⅲ型食块的取食率显著高于Ⅰ型和Ⅳ型;对Ⅰ型食块的取食次数显著高于Ⅱ型和Ⅳ型;对Ⅳ型食块的停留时间显著高于Ⅰ型和Ⅱ型。它们在摄取体积较小的食块时,以取走后进食为主要取食方式,但摄取大体积食块时则主要在原地进食。取食过程中,果蝠优先选择大小适于搬运的食块,是捕食风险与能量收益权衡的结果。     

Hazardous duty pay and the foraging cost of predation

We review the concepts and research associated with measuring fear and its consequences for foraging. When foraging, animals should and do demand hazardous duty pay. They assess a foraging cost of predation to compensate for the risk of predation or the risk of catastrophic injury. Similarly, in weighing foraging options, animals tradeoff food and safety. The foraging cost of predation can be modelled, and it can be quantitatively and qualitatively measured using risk titrations. Giving‐up densities (GUDs) in depletable food patches and the distribution of foragers across safe and risky feeding opportunities are two frequent experimental tools for titrating food and safety. A growing body of literature shows that: (i) the cost of predation can be big and comprise the forager's largest foraging cost, (ii) seemingly small changes in habitat or microhabitat characteristics can lead to large changes in the cost of predation, and (iii) a forager's cost of predation rises with risk of mortality, the forager's energy state and a decrease in its marginal value of energy. In titrating for the cost of predation, researchers have investigated spatial and temporal variation in risk, scale‐dependent variation in risk, and the role of predation risk in a forager's ecology. A risk titration from a feeding animal often provides a more accurate behavioural indicator of predation risk than direct observations of predator‐inflicted mortality. Titrating for fear responses in foragers has some well‐established applications and holds promise for novel methodologies, concepts and applications. Future directions for expanding conceptual and empirical tools include: what are the consequences of foraging costs arising from interference behaviours and other sources of catastrophic loss? Are there alternative routes by which organisms can respond to tradeoffs of food and safety? What does an animal's landscape of fear look like as a spatially explicit map, and how do various environmental factors affect it? Behavioural titrations will help to illuminate these issues and more.     

FREQUENCY-DEPENDENT SUCCESS OF CHEATERS DURING FORAGING BOUTS MIGHT LIMIT THEIR SPREAD WITHIN COLONIES OF A SOCIALLY POLYMORPHIC SPIDER

Although several studies have demonstrated that frequency-dependent effects can promote the maintenance of cooperative behavior in microbes, experimental evidence of frequency-dependent effects in cooperative animal societies is rare. We staged mixed phenotype feeding bouts in the spider Anelosimus studiosus , which shows a within-population social polymorphism, to determine how phenotype frequency affects the foraging success of the social (cooperative) and asocial (cheater) phenotypes. Foraging performance was inferred from average change in percent mass for the respective phenotypes after staged group foraging events. We then performed a field census of multifemale colonies of A. studiosus to determine the phenotypic composition of naturally occurring colonies. Our data indicate that asocial (i.e., cheater) individuals experience negative frequency-dependent foraging success in staged foraging contests. Asocial individuals outperform social individuals when their representation is low, but lose this competitive advantage as their relative numbers increase. Naturally occurring colonies, on average, contained 58.33% social and 41.67% asocial individuals.     

How does hunger affect convergence on prey patches in a social forager?

Internal state, in this case hunger, is known to influence both the organisation of animal groups and the social foraging interactions that occur within them. In this study, we investigated the effects of hunger upon the time taken to locate and converge upon hidden simulated prey patches in a socially foraging fish, the threespine stickleback (Gasterosteus aculeatus). We predicted that groups of food‐deprived fish would find and recruit to prey patches faster than recently fed groups, reasoning that they might search more rapidly and be more attentive to inadvertent social information produced by other foragers. Instead we saw no difference between the two groups in the time taken to find the patches and found that in fact, once prey patches had been discovered, it was the recently fed fish that converged on them most rapidly. This finding is likely due to the fact that recently fed fish tend to organise themselves into fewer but larger subgroups, which arrived at the food patch together. Hunger has a significant impact upon the social organisation of the fish shoals, and it appears that this has a stronger effect upon the rate at which they converged upon the food patches than does internal state itself.     

Solving post-prandial reduction in performance by adaptive regurgitation in a freshwater fish

Foraging animals must balance benefits of food acquisition with costs induced by a post-prandial reduction in performance. Eating to satiation can lead to a reduction in locomotor and escape performance, which increases risk should a threat subsequently arises, but limiting feeding behaviour may be maladaptive if food intake is unnecessarily reduced in the prediction of threats that do not arise. The efficacy of the trade-off between continued and interrupted feeding therefore relies on information about the future risk, which is imperfect. Here, we find that black carp (Mylopharyngodon piceus) can balance this trade-off using an a posteriori strategy; by eating to satiation but regurgitating already ingested food when a threat arises. While degrees of satiation (DS) equal to or greater than 60% reduce elements of escape performance (turning angle, angular velocity, distance moved, linear velocity), at 40% DS or lower, performance in these tasks approaches levels comparable to that at 0% satiation. After experiencing a chasing event, we find that fish are able to regurgitate already ingested food, thereby changing the amount of food in their gastrointestinal tract to consistent levels that maintain high escape performance. Remarkably, regurgitation results in degrees of satiation between 40 and 60% DS, regardless of whether they had previously fed to 40, 60 or 100% DS. Using this response, fish are able to maximize food intake, but regurgitate extra food to maintain escape performance when they encounter a threat. This novel strategy may be effective for continual grazers and species with imperfect information about the level of threat in their environment.