Honeyeater foraging: A test of optimal foraging theory

Honeyeaters (Meliphagidae) were observed foraging for nectar from Lambertia formosa inflorescences, each of which has seven flowers. The frequency distribution of numbers of flowers probed per visit to an inflorescence was found to be bimodal, with one peak at two and the other at seven. It is hypothesized that this frequency distribution results from a rule of departure from inflorescences that maximizes the net rate of energy gain. Patterns of nectar distribution were determined for a large sample of inflorescences. In addition the extent to which the honeyeaters re-probe flowers during a visit to an inflorescence was estimated. From these data and from field measurements of the times required by the honeyeaters to perform the various foraging behaviours, computer simulations of honeyeater foraging were constructed. These simulations led in turn to optimal frequency distributions of numbers of flowers probed per inflorescence that were bimodal but had peaks at 1 and 7 instead of 2 and 7. Although the observed and predicted behaviour were consequently similar, the difference between them was nevertheless significant. This difference could have been due to the birds' transient occupancy of the study area.     

Subject: foraging

Research Notes on Avian Biology 1994: Selected Contributions from the 21st International Ornithological CongressBehavior: Foraging

Subject: foraging     

Downy woodpecker foraging behavior: foraging by expectation and energy intake rate

Summary I describe an artificial patch system that was used to study the foraging behavior of free-roaming downy woodpeckers (Picoides pubescens) in a woodlot in southeastern Michigan. The artificial patches used were thin logs into which were drilled small holes to hold food items (bits of sunflower seed kernels). Downy woodpeckers would systematically search the holes of a patch for food items and thus by manipulating the food distribution within the patches, the birds could be made to experience differing rates of energy intake while foraging.Simple deterministic theories of optimal foraging in patchy environments indicate that an optimal forager, who experiences a decreasing rate of energy intake while foraging in a patch, should leave a patch when its rate of energy intake falls below the average intake rate for the overall environment. In other words, an optimal forager is continually assessing the quality of a patch and makes decisions as to when to leave a patch via its energy intake rate. When the downy woodpeckers studied could encounter any one of several types of patches each with differing, decreasing rates of energy intake, they followed a patch quality assessment strategy similar to that suggested by theory. Upon encountering a single type of patch for a number of consecutive days, however, the birds appeared to forage according to prior expectations of patch quality and not according to a quality assessment strategy based on energy intake rates. The observed expectations were not related to the number of food items per patch but they appeared to be based on expectations of when or where to leave a patch.     

Noise distracts foraging bats

Predators frequently must detect and localize their prey in challenging environments. Noisy environments have been prevalent across the evolutionary history of predator–prey relationships, but now with increasing anthropogenic activities noise is becoming a more prominent feature of many landscapes. Here, we use the gleaning pallid bat, Antrozous pallidus, to investigate the mechanism by which noise disrupts hunting behaviour. Noise can primarily function to mask—obscure by spectrally overlapping a cue of interest, or distract—occupy an animal''s attentional or other cognitive resources. Using band-limited white noise treatments that either overlapped the frequencies of a prey cue or did not overlap this cue, we find evidence that distraction is a primary driver of reduced hunting efficacy in an acoustically mediated predator. Under exposure to both noise types successful prey localization declined by half, search time nearly tripled, and bats used 25% more sonar pulses than when hunting in ambient conditions. Overall, the pallid bat does not seem capable of compensating for environmental noise. These findings have implications for mitigation strategies, specifically the importance of reducing sources of noise on the landscape rather than attempting to reduce the bandwidth of anthropogenic noise.     

Modelling social insect foraging

Foraging in the social insects can be viewed as a provisioning process, in which workers are powered by one resource (e.g. nectar) to deliver another (e.g. pollen) for the colony. The rate of delivery of a resource depends on the number of workers and how hard they work, which may depend on self-feeding rate. Whether individuals sacrifice their own foraging efficiency in favour of colony performance is unclear, as theory and experiment have not yet properly addressed these issues.     

The locust foraging gene

Our knowledge of how genes act on the nervous system in response to the environment to generate behavioral plasticity is limited. A number of recent advancements in this area concern food‐related behaviors and a specific gene family called foraging (for), which encodes a cGMP‐dependent protein kinase (PKG). The desert locust (Schistocerca gregaria) is notorious for its destructive feeding and long‐term migratory behavior. Locust phase polyphenism is an extreme example of environmentally induced behavioral plasticity. In response to changes in population density, locusts dramatically alter their behavior, from solitary and relatively sedentary behavior to active aggregation and swarming. Very little is known about the molecular and genetic basis of this striking behavioral phenomenon. Here we initiated studies into the locust for gene by identifying, cloning, and studying expression of the gene in the locust brain. We determined the phylogenetic relationships between the locust PKG and other known PKG proteins in insects. FOR expression was found to be confined to neurons of the anterior midline of the brain, the pars intercerebralis. Our results suggest that differences in PKG enzyme activity are correlated to well‐established phase‐related behavioral differences. These results lay the groundwork for functional studies of the locust for gene and its possible relations to locust phase polyphenism. © 2010 Wiley Periodicals, Inc.     

Optimizing foraging behaviour through learning

Manifestation of life-history strategy is through the allocation of resources acquired by foraging. Foraging efficiency can be improved by learning, as fishes adjust their behaviour to changing circumstances. We briefly review the influence of learning on the foraging behaviour of fishes and make recommendations for further research. We stress the importance of quantifying learning and memory in relation to ontogeny and life history.     

Structure-guided foraging in long-tailed macaques

The aim of this study was to identify some of the cues that macaques follow when they search for new food sites. A social group of 37 long-tailed macaques was confined to a holding cage while an experimenter concealed food in an outdoor enclosure according to one of the following rules: (1) along the edge of a visible environmental border, (2) within structures of the same general type, or (3) along an ecologically irrelevant, invisible straight line. To provide the animals with a cue for detecting the rule, three piles of visible food were also presented according to the rule. Each of the 60 trials involved a different location in the 880 m² enclosure. The animals showed clear evidence of utilizing the first two rules from the outset of testing and the third rule about five trials. The animals found concealed food along environmental borders and within matching objects more quickly than along invisible lines. They also showed a rapid improvement in food finding on the invisible line. The results suggest that long-tailed macaques extend their search for food to a given class of environmental structure rather than exclusively by pure spatial gradients. © 1996 Wiley-Liss, Inc.     

The foraging behavior of honeybees on hairy vetch foraging methods and learning to forage

Summary The honeybee can reach the nectar from the mouth of the hairy vetch blossom by tripping it, or she can insert her tongue between the petals at the base of the corolla tube and reach the nectar. These non-trippers are called base workers. The foraging method is learned and becomes fixed through success at foraging from a very few blossoms in one manner during almost random attempts to reach the nectar. A slightly larger percentage of trippers reached the nectar by inserting the tongue to their right than to their left of the sexual column. There were never many bees in the field that foraged some blossoms as trippers and others as base workers, nor were there many that foraged for pollen only. When there was a good nectar flow early in the season there were few bees foraging as base workers, and the number of trippers foraging for nectar only was about equal to the number gathering both pollen and nectar. After a few days with a poor nectar flow the percentage of tripping bees gathering nectar only decreased sharply, the percentage gathering both nectar and pollen increased slightly, and the percentage of base workers increased sharply. There was a larger proportion of base workers in vetch with scattered blossoms than in vetch with numerous blossoms, and also a larger proportion of base workers in vetch with a heavy aphid infestation than in vetch in which these insects were controlled. During a poor nectar flow base worker gathered larger loads of nectar than trippers. To explain these observations, it is proposed that bees prefer to gather nectar which yields the greatest return in sugar per unit expenditure of energy, and that base workers expend less energy in foraging from blossoms than trippers. It is believed that base workers are more sensitive than trippers to competing foragers, and thus are more likely to be forced into areas with the least competition, that as the nectar flow deteriorates more trippers than base workers cease to forage, and that most of the bees that normally trip blossoms but have had some experience as base workers, and possibly some other trippers, begin to forage exclusively as base workers.

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Zusammenfassung Die Honigbiene kann vom Munde der behaarten rauhhaarigen Wickenblüte (Vicia villosa) aus an den Nektar kommen, indem sie die Blüte oben aufschnellen läßt, oder sie kann den Rüssel, zwischen den Blütenblättern am unteren Ende der Korollenröhre hindurchzwängen und so den Nektar erreichen. Diese Blüten nicht schnellenden öffnenden Arbeitsbienen nennt man Bodenarbeiterinnen. Die Sammelmethode wird erlernt und beibehalten durch erfolgreiches Sammeln nach derselben Methode an einigen wenigen Blüten bei fast planlosen Versuchen, den Nektar zu erreichen Ein etwas größerer Prozentsatz von blutenschnellendern Bienen erreichten den Nektar, indem sie den Rüssel rechts statt links an dem Stempel vorbeizwängten. Es gab nur wenige Bienen im Felde, die einige Blüten als Schnellerinnen, andere Blüten dagegen als Bodenarbeiterinnen besuchten; auch waren nicht viele da, die nur Pollen einsammelten. Bei reichlicher Nektartracht im Frühjahr gab es nur wenige Bodensammlerinnen, und die Anzahl von Schnellerinnen, die nur Nektar sammelten, war etwa der Anzahl derer gleich, die sowohl Nektar als auch Pollen sammelten. Nach ein paar Tagen mit schlechtem Nektarertrag ging der Prozentsatz von schnellenden Nur-Nektar-Sammlerinnen stark zurück; der Prozentsatz von Bienen, die zugleich Nektar und Pollen sammelten, nahm um ein weniges zu; und der Prozentsatz von Bodensammlerinnen erfuhr eine starke Erhöhung. Es wurden mehr Bodensammlerinnen in Wicken mit verstreuten Blüten festgestellt als in denen mit zahlreichen Blüten. Dasselbe gilt für Wicken, die stark mit Blattläusen verseucht sind, gegenüber solchen worin die Schädlinge im Zaum gehalten werden. Wenn wenig Nektar erzeugt wird, sammeln die Bodensammlerinnen mehr Nektar als die Schnellerinnen. Um diese Beobachtungen zu deuten, folgern wir so: die Bienen sammeln am liebsten da, wo die größte Ausbeute an Zucker je Einheit Energieverbrauch zu erzielen ist, und die Bodensammlerinnen verbrauchen weniger Energie beim Besuch der Blüten als die Schnellerinnen. Man glaubt weiter, daß die Bodenarbeiterinnen konkurrierenden Insekten gegenüber empfindlicher als die Schnellerinnen seien, und daß sie so mit größerer Häufigkeit gezwungen werden, Gebiete mit wenigern Konkurrenten zu besuchen; daß wenn die Tracht versiegt, mehr Schnellerinnen als Bodenarbeiterinnen zu sammeln aufhören, und daß die meisten Bienen, die normalerweise zu den Schnellerinnen gehören, aber außerdem etwas Erfahrung als Bodenarbeiterinnen haben (und vielleicht auch einige andere Schnellerinnen) jetzt ausschließlich als Bodenarbeiterinnen zu sammeln anfangen.

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Sommaire L'Abeille peut atteindre par la bouche le nectar de la fleur de la vesce velue (Vicia villosa) en la tripping ou elle peut insérer la langue entre les pétales à la base de la corolle et ainsi attindre le nectar. Ces Abeilles non-tripping s'appellent les ouvrières de base. Cette méthode de butiner est apprise et devient fixe à cause du succès à butiner une petite quantité de fluers d'une seule façon pendant pour ainsi dire des essais d'atteindre le nectar à l'aventure. Un pourcentage plus grand de trippers ont atteint le nectar en insérant la langue à droite de la colonne sexuelle que celles qui l'ont insérée à gauche. Il n'y avait jamais beaucoup d'Abeilles dans le champ qui butinaient les fleurs tantôt comme trippers, tantôt comme ouvrières de base. Il n'y avait pas non plus beaucoup d'Abeilles qui butinaient le pollen uniquement. Quand il y avait une bonne miellée dans la première partie de la saison, il y avait peu d'Abeilles butinant comme ouvrières de base, et le nombre d'Abeilles tripping butinant le nectar uniquement était à peu près égal au nombre recueillant et le nectar et le pollen. Après quelques jours d'une miellée pauvre, le pourcentage des Abeilles tripping recueillant le nectar uniquement diminuait nettement, le pourcentage des Abeilles recueillant et le nectar et le pollen augmentait un peu, et le pourcentage des ouvrières de base augmentait nettement. Il y avait une plus grande proportion d'ouvrières de base dans la vesce aux fleurs dispersées que dans la vesce aux nombreuses fleurs, et aussi une plus grande proportion d'ouvrières de base dans la vesce infestée d'Aphides que dans la vesce dans laquelle les insectes étaient maîtrisés. Pendant une miellée pauvre, les ouvrières de base ont recueilli de plus grandes quantités de nectar que les trippers. Pour expliquer ces observations, il pense que les Abeilles aiment mieux recueillir le nectar qui donne le plus grand renvoi de sucre par unité d'énergie dépensée et que les ouvrières de base dépensent moins d'énergie à butiner les fleurs que les trippers. Je crois que les ouvrières de base sont plus sensibles que les trippers à la concurrence des autres butineuses et, donc, peuvent être plus facilement obligées d'aller dans les sections moins compétitives, que plus de trippers que d'ouvrières de base cessent de butiner quand la miellée s'amenuise, et que la plupart des Abeilles qui trip les fleurs habituellement, mais qui ont un peu d'expérience comme ouvrières de base, et, probablement quelques autres trippers, commencent à butiner exclusivement comme ouvrières de base.

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Published as technical contribution No. 2403, Texas Agricultural Experiment Station.     

King Penguins adjust foraging effort rather than diet when faced with poor foraging conditions

The links between foraging success, foraging effort and diet in a myctophid specialist seabird, the King Penguin Aptenodytes patagonicus, were investigated during seven breeding seasons using tracking and isotopic data. Despite the variable foraging conditions encountered by the birds, isotopic signatures (a proxy for diet) were invariable throughout the study. On the other hand, penguins stayed longer at sea when the foraging success indices (i.e. prey capture attempts per day and mass gained per day) were low. Although King Penguins can compensate for low prey capture rates by increasing foraging effort, their specialist diet during reproduction makes the species particularly sensitive to prey availability, with its conservation tightly linked to its main prey.     

How anthropogenic noise affects foraging

The influence of human activity on the biosphere is increasing. While direct damage (e.g. habitat destruction) is relatively well understood, many activities affect wildlife in less apparent ways. Here, we investigate how anthropogenic noise impairs foraging, which has direct consequences for animal survival and reproductive success. Noise can disturb foraging via several mechanisms that may operate simultaneously, and thus, their effects could not be disentangled hitherto. We developed a diagnostic framework that can be applied to identify the potential mechanisms of disturbance in any species capable of detecting the noise. We tested this framework using Daubenton's bats, which find prey by echolocation. We found that traffic noise reduced foraging efficiency in most bats. Unexpectedly, this effect was present even if the playback noise did not overlap in frequency with the prey echoes. Neither overlapping noise nor nonoverlapping noise influenced the search effort required for a successful prey capture. Hence, noise did not mask prey echoes or reduce the attention of bats. Instead, noise acted as an aversive stimulus that caused avoidance response, thereby reducing foraging efficiency. We conclude that conservation policies may seriously underestimate numbers of species affected and the multilevel effects on animal fitness, if the mechanisms of disturbance are not considered.     

Risk-indifferent foraging behaviour in honeybees

We studied the influence of variance in reward volume on choice behaviour of honeybees, Apis mellifera carnica, by training bees to collect sucrose solution from four newly developed artificial feeders. The feeders were electromechanical devices, each controlled by a microprocessor, which monitored the experiments, controlled reward delivery and stored the data. The parameters that varied between the feeders were the amount and variance of reward. The four feeders were arranged in two pairs, with the two feeders in each pair set to the same reward parameters. Constant feeders offered a fixed amount of sucrose solution at each bee visit; variable feeders offered a normally distributed reward with a standard deviation equal to the mean. We tested three reward combinations under two variance conditions. The bees matched their choice frequencies to the mean amount of reward. This applied both to the constant and the variable feeders. Thus the bees were able to discriminate feeders by the amount of reward and were able to estimate the mean reward for the variable flowers. The proportion of immediate returns to the same feeder increased with the amount of sucrose solution imbibed at each visit, indicating that bees were able to perceive the amount of reward at each visit. However, there was no influence of variance on the choice behaviour of the bees, ruling out the possibility that bees are risk sensitive under these conditions. We discuss risk indifference in choice behaviour of bees in the context of several models of risk sensitivity. Copyright 2000 The Association for the Study of Animal Behaviour.     

Neandertal energetics and foraging efficiency

Mechanical interpretations of Neandertal skeletal robusticity suggest extremely high activity levels compared to modern humans. Such activity patterns imply high energy requirements; yet it has been argued that Neandertals were also inefficient foragers. The present study addresses this apparent conflict by estimating energy needs in Neandertals and then evaluating those estimates in the context of energetic and foraging data compiled for contemporary human foragers and nonhuman primates. Energy demands for Neandertals were determined by first predicting basal metabolic rates (BMR) from body weight estimates using human standards developed by the World Health Organization [FAO/WHO/UNU (1985) Energy and Protein Requirements. Report of the Joint FAO/WHO/UNU Export Committee, Geneva: WHO]. Total daily energy expenditure (kcal/day) was then estimated assuming high levels of physical activity (i.e., 2--3 x BMR), comparable to those observed among subsistence-level populations today. These estimates of energy requirements (ranging from 3000--5500 kcal/day) were then used to determine Neandertal foraging efficiency assuming (1) minimal survival-level foraging returns, and (2) daily foraging times longer than those observed among any contemporary foraging group and comparable to a nonhuman primate. Even with these extremely conservative parameters, estimates of Neandertal foraging efficiency (approximately 800--1150 kcal/h foraged) were comparable to those observed among living hunter-gatherers. These results indicate that if Neandertals did have heavy activity levels, as implied by their skeletal robusticity, they would have required foraging efficiencies within the range observed among modern groups. Thus, Neandertals could have been either highly active or poor foragers, but they could not have been both.