Patch choice as a function of procurement cost and encounter rate.

The effects of patch encounter rate on patch choice and meal patterns were studied in rats foraging in a laboratory environment offering two patch types that were encountered sequentially and randomly. The cost of procuring access to one patch was greater than the other. Patches were either encountered equally often or the high-cost patch was encountered more frequently. As expected, rats exploited the low-cost patch on almost 100% of encounters and exploited the high-cost patch on a percentage of encounters that was inversely proportional to its cost. Meal size was the same at both patches. Surprisingly, when low-cost patches were rare, the rats did not increase their use of high-cost patches. This resulted in spending more time and energy searching for patches and a higher average cost per meal. The rats responded to this increased cost by reducing the frequency and increasing the size of meals at both patches and thereby limited total daily foraging cost and conserved total intake.     

Carbon dioxide narcosis modifies the patch leaving decision of foraging parasitoids

Gleaning information is a way for foragers to adjust their behavior in order to maximize their fitness. Information decreases the uncertainty about the environment and could help foragers to accurately estimate environmental characteristics. In a patchy resource, information sampled during previous patch visits is efficient only if it is retained in the memory and retrieved upon arrival in a new patch. In this study, we tested whether the braconid Asobara tabida, a parasitoid of Drosophila larvae, retains information gleaned on patch quality in the memory and adjusts its foraging behavior accordingly. Females were anesthetized with CO₂ after leaving a first patch containing a different number of hosts and were allowed to visit a second patch containing only kairomones. CO₂ is known to erase unconsolidated information from the memory. We show that in the absence of a short CO₂ narcosis, females responded according to their previous experience, whereas anesthetized females did not. The anesthetized females stayed a given time in the second patch irrespective of what they encountered before. CO₂ narcosis had no effect on the residence time of the non-experienced females in a patch containing hosts or only kairomones in comparison with the non-anesthetized females that had a previous foraging experience. We conclude that CO₂ narcosis erases the effect of the previous patch quality, perhaps due to a memory disruption. Direct information processing is likely to be involved in parasitoid decision making through retention of the information on the previous patch quality into a CO₂ sensitive memory.     

Dynamic averaging and foraging decisions in horses (Equus callabus)

The variability of most environments taxes foraging decisions by increasing the uncertainty of the information available. One solution to the problem is to use dynamic averaging, as do some granivores and carnivores. Arguably, the same strategy could be useful for grazing herbivores, even though their food renews and is more homogeneously distributed. Horses (Equus callabus) were given choices between variable patches after short or long delays. When patch information was current, horses returned to the patch that was recently best, whereas those without current information matched choices to the long-term average values of the patches. These results demonstrate that a grazing species uses dynamic averaging and indicate that, like granivores and carnivores, they can use temporal weighting to optimize foraging decisions.     

Colour cues or spatial cues? Context-dependent preferences in the European greenfinch (<Emphasis Type="Italic">Carduelis chloris</Emphasis>)

Using featural cues such as colour to identify ephemeral food can increase foraging efficiency. Featural cues may change over time however; therefore, animals should use spatial cues to relocate food that occurs in a temporally stable position. We tested this hypothesis by measuring the cue preferences of captive greenfinches Carduelis chloris when relocating food hidden in a foraging tray. In these standardised associative learning trials, greenfinches favoured colour cues when returning to a foraging context that they had encountered before only once (“one-trial test”) but switched to spatial cues when they had encountered that scenario on ten previous occasions (“repeated-trial test”). We suggest that repeated encounters generated a context in which individuals had a prior expectation of temporal stability, and hence context-dependent cue selection. Next, we trained birds to find food in the absence of colour cues but tested them in the presence of visual distracters. Birds were able to learn spatial cues after one encounter, but only when visual distracters were identical in colouration. When a colourful distracter was present in the test phase, cue selection was random. Unlike the first one-trial test, birds were not biased towards this colourful visual distracter. Together, these results suggest that greenfinches are able to learn both cue types, colour cue biases represent learning, not simply distraction, and spatial cues are favoured over colour cues only in temporally stable contexts.     

Honeybee methodology, cognition, and theory: recording local directional decisions in interpatch foraging and interpreting their theoretical relevance

Investigations made into the cognitive decision making of honeybees (Apis mellifera) traveling from one flower patch to another flower patch (interpatch foraging) are few. To facilitate such research, we present methods to artificially emulate interpatch foraging and quantify the immediate decision making of honeybees (within 50 cm) choosing to fly an interpatch path. These “Interpatch Methods” are validated, applied, and shown to produce novel information for the field of honeybee spatial cognition. Generally, we demonstrate that a single foraging cohort of honeybees is shown to be capable of making decisions based upon different sets of learned cues, in the exact same context. Specifically, both terminal beacon orientation cues and compass navigation cues can guide the cognitive decision making of interpatch foraging honeybees; our bees chose both cues equally. Finally, the theoretical importance of decision making for interpatch paths is compared with the other foraging paths (outward and homing) with respect to the information available to recruited foragers and scout foragers. We conclude that the ability to analyze interpatch foraging is critical for a more complete understanding of honeybee foraging cognition and that our methods are capable of providing that understanding.     

GROUP FORAGING SENSITIVITY TO PREDICTABLE AND UNPREDICTABLE CHANGES IN FOOD DISTRIBUTION: PAST EXPERIENCE OR PRESENT CIRCUMSTANCES?

The ideal free distribution theory (Fretwell & Lucas, 1970) predicts that the ratio of foragers at two patches will equal the ratio of food resources obtained at the two patches. The theory assumes that foragers have "perfect knowledge" of patch profitability and that patch choice maximizes fitness. How foragers assess patch profitability has been debated extensively. One assessment strategy may be the use of past experience with a patch. Under stable environmental conditions, this strategy enhances fitness. However, in a highly unpredictable environment, past experience may provide inaccurate information about current conditions. Thus, in a nonstable environment, a strategy that allows rapid adjustment to present circumstances may be more beneficial. Evidence for this type of strategy has been found in individual choice. In the present experiments, a flock of pigeons foraged at two patches for food items and demonstrated results similar to those found in individual choice. Experiment 1 utilized predictable and unpredictable sequences of resource ratios presented across days or within a single session. Current foraging decisions depended on past experience, but that dependence diminished when the current foraging environment became more unpredictable. Experiment 2 repeated Experiment I with a different flock of pigeons under more controlled circumstances in an indoor coop and produced similar results.     

Residence time in concurrent foraging with fixed times to prey arrival

Five pigeons were trained in a concurrent foraging procedure in which reinforcers were occasionally available after fixed times in two discriminated patches. In Part 1 of the experiment, the fixed times summed to 10 s, and were individually varied between 1 and 9 s over five conditions, with the probability of a reinforcer being delivered at the fixed times always .5. In Part 2, both fixed times were 5 s, and the probabilities of food delivery were varied over conditions, always summing to 1.0. In Parts 3 and 4, one fixed time was kept constant (Part 3, 3 s; Part 4, 7 s) while the other fixed time was varied from 1 s to 15 s. Median residence times in both patches increased with increases in the food-arrival times in either patch, but increased considerably more strongly in the patch in which the arrival time was increased. However, when arrival times were very different in the two patches, residence time in the longer arrival-time patch often decreased. Patch residence also increased with increasing probability of reinforcement, but again tended to fall when one probability was much larger than the other. A detailed analysis of residence times showed that these comprised two distributions, one around a shorter mode that remained constant with changes in arrival times, and one around a longer mode that monotonically increased with increasing arrival time. The frequency of shorter residence times appeared to be controlled by the probability of, and arrival time of, reinforcers in the alternative patch. The frequency of longer residence times was controlled directly by the arrival time of reinforcers in a patch, but not by the probability of reinforcers in a patch. The environmental variables that control both staying in a patch and exiting from a patch need to be understood in the study both of timing processes and of foraging.     

Time horizons in rats foraging for food in temporally separated patches

An important tenet of optimal foraging theory is that foragers compare prey densities in alternative patches to determine an optimal distribution of foraging behavior over time. A critical question is over what time period (time horizon) this integration of information and behavior occurs. Recent research has indicated that rats do not compare food density in a depleting patch with that in a rich patch delayed by an hour or more (Timberlake, 1984). In the present research we attempted to specify over what time period a future rich patch would affect current foraging. The effect of future food was measured by early entry into the rich patch (anticipation) and by a decrease in food obtained in the depleting patch (suppression). The rats showed anticipation of a rich patch up to an hour distant, but suppressed current feeding only if the rich patch was 16 min distant or less. The suppression effect appeared mediated by competition for expression between anticipatory entries into the rich patch and continued foraging in the depleting patch. These results suggest that optimal foraging is based on a variety of specific mechanisms rather than a general optimizing algorithm with a single time horizon.     

Testing a stochastic foraging model in an operant simulation: Agreement with qualitative but not quantitative predictions

An operant simulation of foraging through baited and empty patches was studied with 4 pigeons. On a three-key panel, side keys were designated as patches, and successive opportunities to complete 16 fixed-ratio 10 schedules on side keys were defined as encounters with feeders. In a random half of the patches in any session, some of the fixed-ratio 10 schedules yielded reinforcement (baited feeders) and the other schedules yielded nonreinforcement (empty feeders). In the other half of the patches, all feeders were empty. Pigeons could travel between patches at any time by completing a fixed-ratio schedule on the center key. An optimal foraging model was tested in Experiments 1 and 2 by varying center-key travel time and number of baited feeders in baited patches. The ordinal predictions that number of feeders visited in empty patches would increase with travel time and decrease as number of baited feeders increased were supported, but pigeons visited far more feeders in empty patches than the optimal number predicted by the model to maximize energy/time. In Experiment 3, evidence was found to suggest that the number of empty feeders encountered before the first baited feeder in baited patches is an important factor controlling leaving empty patches.     

Decision ecology: Foraging and the ecology of animal decision making

In this article, I review the approach taken by behavioral ecologists to the study of animal foraging behavior and explore connections with general analyses of decision making. I use the example of patch exploitation decisions in this article in order to develop several key points about the properties of naturally occurring foraging decisions. First, I argue that experimental preparations based on binary, mutually exclusive choice are not good models of foraging decisions. Instead, foraging choices have a sequential foreground-background structure, in which one option is in the background of all other options. Second, behavioral ecologists view foraging as a hierarchy of decisions that range from habitat selection to food choice. Finally, data suggest that foraging animals are sensitive to several important trade-offs. These trade-offs include the effects of competitors and group mates, as well as the problem of predator avoidance.     

Common marmosets (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>) do not utilize social information in three simultaneous social foraging tasks

Social foraging is suggested to increase foraging efficiency, as individuals might benefit from public information acquired by monitoring the foraging activities of other group members. We conducted a series experiments with captive common marmosets (Callithrix jacchus) to investigate to what extent marmosets utilize social information about food location when foraging simultaneously with conspecifics. Subjects were confronted with dominant and subordinate demonstrators in three experiments which differed in the amount of information about food location available to the demonstrators. In all three experiments, the focal subjects’ performance in the social condition was not enhanced in comparison to a non-social control condition. Because we could rule out kleptoparasitism and aggressive displacements as explanations, we argue that the subjects’ tendency for scramble competition by avoiding others and dispersing over the foraging area seems to inhibit or mask the acquisition of social information about the location of rewarded patches.     

Fishing for the right words: decision rules for human foraging behavior in internal search tasks

Animals depleting one patch of resources must decide when to leave and switch to a fresh patch. Foraging theory has predicted various decision mechanisms; which is best depends on environmental variation in patch quality. Previously we tested whether these mechanisms underlie human decision making when foraging for external resources; here we test whether humans behave similarly in a cognitive task seeking internally generated solutions. Subjects searched for meaningful words made from random letter sequences, and as their success rate declined, they could opt to switch to a fresh sequence. As in the external foraging context, time since the previous success and the interval preceding it had a major influence on when subjects switched. Subjects also used the commonness of sequence letters as a proximal cue to patch quality that influenced when to switch. Contrary to optimality predictions, switching decisions were independent of whether sequences differed little or widely in quality.     

Timing and Foraging: Gibbon's Scalar Expectancy Theory and Optimal Patch Exploitation

We present a study that links optimal foraging theory (OFT) to behavioral timing. OFT's distinguishing feature is the use of models that compute the most advantageous behavior for a particular foraging problem and compare the optimal solution to empirical data with little reference to psychological processes. The study of behavioral timing, in contrast, emphasizes performance in relation to time, most often without strategic or functional considerations. In three experiments, reinforcer-maximizing behavior and timing performance are identified and related to each other. In all three experiments starlings work in a setting that simulates food patches separated by a flying distance between the two perches. The patches contain a variable and unpredictable number of reinforcers and deplete suddenly without signal. Before depletion, patches deliver food at fixed intervals (FI). Our main dependent variables are the times of occurrence of three behaviors: the “peak” in pecking rate (Peak), the time of the last peck before “giving in” (GIT), and the time for “moving on” to a new patch (MOT). We manipulate travel requirement (Experiment 1), level of deprivation and FI (Experiment 2), and size of reinforcers (Experiment 3). For OFT, Peak should equal the FI in all conditions while GIT and MOT should just exceed it. Behavioral timing and Scalar Expectancy Theory (SET) in particular predict a Peak at around the FI and a longer (unspecified) GIT, and make no prediction for MOT. We found that Peak was close to the FI and GIT was approximately 1.5 times longer, neither being affected by travel, hunger, or reinforcer size manipulations. MOT varied between 1.5 and just over 3 times the FI, was responsive to both travel time and the FI, and did not change when the reinforcer rate was manipulated. These results support the practice of producing models that explicitly separate information available to the subject from strategic use of this information.     

What wild primates know about resources: opening up the black box

We present the theoretical and practical difficulties of inferring the cognitive processes involved in spatial movement decisions of primates and other animals based on studies of their foraging behavior in the wild. Because the possible cognitive processes involved in foraging are not known a priori for a given species, some observed spatial movements could be consistent with a large number of processes ranging from simple undirected search processes to strategic goal-oriented travel. Two basic approaches can help to reveal the cognitive processes: (1) experiments designed to test specific mechanisms; (2) comparison of observed movements with predicted ones based on models of hypothesized foraging modes (ideally, quantitative ones). We describe how these two approaches have been applied to evidence for spatial knowledge of resources in primates, and for various hypothesized goals of spatial decisions in primates, reviewing what is now established. We conclude with a synthesis emphasizing what kinds of spatial movement data on unmanipulated primate populations in the wild are most useful in deciphering goal-oriented processes from random processes. Basic to all of these is an estimate of the animal’s ability to detect resources during search. Given knowledge of the animal’s detection ability, there are several observable patterns of resource use incompatible with a pure search process. These patterns include increasing movement speed when approaching versus leaving a resource, increasingly directed movement toward more valuable resources, and directed travel to distant resources from many starting locations. Thus, it should be possible to assess and compare spatial cognition across a variety of primate species and thus trace its ecological and evolutionary correlates. This contribution is part of the special issue “A Socioecological Perspective on Primate Cognition” (Cunningham and Janson 2007b)     

An experimental analysis of optimal foraging behaviour in patchy environments

A series of experiments was designed to explore the cognitive mechanisms involved in optimal foraging models by using the behavioural controls of operant methodology. Rats were trained to press one of two levers to obtain reinforcement on a progressive variable-interval schedule, which modelled food patch depletion; the schedule was reset by pressing the other lever. Thus both duration (residence time in a patch) and rate-related (interval before and after the final reward) measures were obtained. Experiment 1, which manipulated environmental stability and quality, and Experiment 2, which varied travel time between patches, found results that supported the marginal value theorem (Charnov, 1976) and suggested that rats adjust capture rate to the environment average by monitoring the length of the interval between rewards. Experiment 3 modelled the clumping of food items and found that capture rate was now adjusted by adoption of a fixed giving-up time. Finally, Experiments 4a and 4b ruled out a time expectancy hypothesis by manipulating the number of food clumps and the series of inter-reinforcement intervals. Overall the experiments demonstrate the value of modelling foraging strategies in operant apparatus, and suggest that rats adopt rate predictive strategies when deciding to switch patches.     

Drinking in a patchy environment: the effect of the price of water.

Rats in a laboratory foraging paradigm searched for sequential opportunities to drink in two water patches that differed in the bar-press price of each "sip" (20 licks) of water within a bout of drinking (Experiment 1) or the price and size (10, 20, or 40 licks) of each sip (Experiment 2). Total daily water intake was not affected by these variables. The rats responded faster at the patch where water was more costly. However, they accepted fewer opportunities to drink, and thus had fewer drinking bouts, and drinking bouts were smaller at the more costly patch than at the other patch. This resulted in the rats consuming a smaller proportion of their daily water from the more costly patch. The size of the differences in bout frequency and size between the patches appears to be based on the relative cost of water at the patches. The profitability of each patch was calculated in terms of the return (in milliliters) on either effort (bar presses) or time spent there. Although both measures were correlated with the relative total intake, bout size, and acceptance of opportunities at each patch, the time-based profitability was the better predictor of these intake measures. The rats did not minimize bar-press output; however, their choice between the patches and their bout sizes within patches varied in a way that reduced costs compared to what would have been expended drinking randomly. These data accord well with similar findings for choices among patches of food, suggesting that foraging for water and food occurs on the basis of comparable benefit-cost functions: In each case, the amount consumed is related to the time spent consuming.     

Non-transitive looks &; fallibilism

Fallibilists about looks deny that the relation of looking the same as is non-transitive. Regarding familiar examples of coloured patches suggesting that such a relation is non-transitive, they argue that, in fact, indiscriminable adjacent patches may well look different, despite their perceptual indiscriminability: it’s just that we cannot notice the relevant differences in the chromatic appearances of such patches. In this paper, I present an argument that fallibilism about looks requires commitment to an empirically false consequence. To succeed in deflecting putative cases of non-transitivity, fallibilists would have to claim that there can’t be any perceptual limitations of any kind on human chromatic discrimination. But there are good reasons to think such limitations exist.     

Visual discrimination,sequential learning and memory retrieval in the Australian desert ant <Emphasis Type="Italic">Melophorus bagoti</Emphasis>

Bees, wasps and ants—so-called central-place foragers—need potent homing strategies to return to their nest. Path integration and view-based landmark guidance are the key strategies for the ants’ navigation. For instance, they memorise different views in a sequence (sequential memory) but also have a step counter that informs them about the covered distance during each foraging trip (odometer). The sequential memory and the odometer information can act as contextual cues during travel for retrieving the appropriate stored view. When and which cue is used at different stages and lengths of the foraging trips is still unknown. In this study, we examined how the Australian desert ant Melophorus bagoti uses sequential memory and odometric information to retrieve visual memories. Using a set-up made out of channels and two-choice boxes (Y-mazes), we demonstrate first that M. bagoti foragers are able to learn and discriminate a variety of visual stimuli in a sequence of views along the inbound trip back to the nest. We then forced the homing ants to encounter a fixed sequence of two visual patterns during their inbound trips. By manipulating the position and distance of the visual stimuli and decision boxes, we could set the two contextual cues (sequential memory and odometer) into conflict. After the short 4-m outbound distance, a preference for odometric information as a contextual cue was found, but after the long 8-m outbound distance, ants relied primarily on their sequential memory retrieval. Odometer precision deteriorates with increasing travel distance, and accordingly, our findings imply that desert ants may be relying on the most reliable contextual cue for retrieving visual memories.     

Leaving patches: effects of economy, deprivation, and session duration

Three pigeons pecked keys for food reinforcers in a laboratory analogue of foraging in patches. Half the patches contained food (were prey patches). In prey patches, pecks to one key occasionally produced a reinforcer, followed by a fixed travel time and then the start of a new patch. Pecks to another key were exit responses, and immediately produced travel time and then a new patch. Travel time was varied from 0.25 to 16 s at each of three session durations: 1, 4, and 23.5 hr. This part of the experiment arranged a closed economy, in that the only source of food was reinforcers obtained in prey patches. In another part, food deprivation was manipulated by varying postsession feeding so as to maintain the subjects' body weights at percentages ranging from 85% to 95% of their ad lib weights, in 1-hr sessions with a travel time of 12 s. This was an open economy. Patch residence time, defined as the time between the start of a patch and an exit response, increased with increasing travel time, and consistently exceeded times predicted by an optimal foraging model, supporting previously published results. However, residence times also increased with increasing session duration and, in longer sessions, consistently exceeded previously reported residence times in comparable open-economy conditions. Residence times were not systematically affected by deprivation levels. In sum, the results show that the long residence times obtained in long closed-economy sessions should probably be attributed to session duration rather than to economy or deprivation. This conclusion is hard to reconcile with previous interpretations of longer-than-optimal residence times but is consistent with, in economic terms, a predicted shift in consumption towards a preferred commodity when income is increased.     

Optimal foraging in semantic memory

Do humans search in memory using dynamic local-to-global search strategies similar to those that animals use to forage between patches in space? If so, do their dynamic memory search policies correspond to optimal foraging strategies seen for spatial foraging? Results from a number of fields suggest these possibilities, including the shared structure of the search problems-searching in patchy environments-and recent evidence supporting a domain-general cognitive search process. To investigate these questions directly, we asked participants to recover from memory as many animal names as they could in 3 min. Memory search was modeled over a representation of the semantic search space generated from the BEAGLE memory model of Jones and Mewhort (2007), via a search process similar to models of associative memory search (e.g., Raaijmakers & Shiffrin, 1981). We found evidence for local structure (i.e., patches) in memory search and patch depletion preceding dynamic local-to-global transitions between patches. Dynamic models also significantly outperformed nondynamic models. The timing of dynamic local-to-global transitions was consistent with optimal search policies in space, specifically the marginal value theorem (Charnov, 1976), and participants who were more consistent with this policy recalled more items.