Foraging Technique Research Articles

Vision and the foraging technique of Great Cormorants Phalacrocorax carbo: pursuit or close‐quarter foraging?

Predatory diving birds, such as cormorants (Phalacrocoracidae), have been generally regarded as visually guided pursuit foragers. However, due to their poor visual resolution underwater, it has recently been hypothesized that Great Cormorants do not in fact employ a pursuit‐dive foraging technique. They appear capable of detecting typical prey only at short distances, and primarily use a foraging technique in which prey may be detected only at close quarters or flushed from a substratum or hiding place. In birds, visual field parameters, such as the position and extent of the region of binocular vision, and how these are altered by eye movements, appear to be determined primarily by feeding ecology. Therefore, to understand further the feeding technique of Great Cormorants we have determined retinal visual fields and eye movement amplitudes using an ophthalmoscopic reflex technique. We show that visual fields and eye movements in cormorants exhibit close similarity with those of other birds, such as herons (Ardeidae) and hornbills (Bucerotidae), which forage terrestrially typically using a close‐quarter prey detection or flushing technique and/or which need to examine items held in the bill before ingestion. We argue that this visual field topography and associated eye movements is a general characteristic of birds whose foraging requires the detection of nearby mobile prey items from within a wide arc around the head, accurate capture of that prey using the bill, and visual examination of the caught prey held in the bill. This supports the idea that cormorants, although visually guided predators, are not primarily pursuit predators, and that their visual fields exhibit convergence towards a set of characteristics that meet the perceptual challenges of close‐quarter prey detection or flush foraging in both aquatic and terrestrial environments.

Bacterial foraging optimisation: Nelder–Mead hybrid algorithm for economic load dispatch

A novel stochastic optimisation approach to solve constrained economic load dispatch problem using hybrid bacterial foraging (BF) technique is presented. In order to explore the search space for finding the local minima of the current location, the simplex algorithm called Nelder–Mead is used along with BF algorithm. The proposed methodology easily takes care of solving non-convex economic dispatch problems along with different constraints such as transmission losses, dynamic operation constraints (ramp rate limits) and prohibited zones. Simulations were performed over various standard test systems with different number of generating units and comparisons are performed with other existing relevant approaches. The findings affirmed the robustness and proficiency of proposed methodology over other existing techniques.

SELECTION OF FORAGING SITES BY DESERT GRANIVOROUS BIRDS: VEGETATION STRUCTURE, SEED AVAILABILITY, SPECIES-SPECIFIC FORAGING TACTICS, AND SPATIAL SCALE

Abstract Seed availability in the algarrobal of the Monte desert, Argentina, as in other deserts, is highly heterogeneous at small scales and is associated with vegetation structure. Granivores are expected to use space selectively (within the capacities of their foraging techniques), resulting in a heterogeneous effect on the seed bank. First, we describe the foraging repertoire of granivorous birds in the algarrobal to develop predictions about their expected use of space. Although the granivory guild as a whole tracked the temporal availability of seeds, species within the guild differed in foraging behavior and seasonal changes. We assessed selection of space by foraging birds through a two-scale bird-centered analysis, comparing the distributions of used and available sites. Granivorous birds, considered as a guild, used the whole range of available microsites, though as a result of an aggregation of contrasting partial patterns. Microsites with more cover of shrubs, grasses, and litter were preferre...

Response to conspecific and heterospecific alarm calls in mixed-species bird flocks of a Sri Lankan rainforest

The flow of information about predators in mixed-species groups is likely to influence the structure and organization of these communities. To map this flow, it is necessary to demonstrate in a playback experiment that animals use the information provided in heterospecific calls. We investigated the response of birds to conspecific and heterospecific calls in a mixed-species flock system of a Sri Lankan rainforest. We played back the aerial alarm calls of the species that produce the most alarms, the Orange-billed Babbler (Turdoides rufescens) and the Greater Racket-tailed Drongo (Dicrurus paradiseus), as well as natural choruses of alarm calls of several species, to 4 species of birds. We found that babblers moved quickly away from the playback speaker after hearing either babbler or drongo alarm calls. Ashy-headed Laughingthrushes (Garrulax cinereifrons) responded similarly to drongo alarm calls. Response by other species was less clear: Malabar Trogons (Harpectes fasciatus) stayed perched for longer during alarms of several species; drongos showed no difference in response to any treatment. We conclude that birds are listening to heterospecifics and suggest that their response is influenced by several factors, including their foraging technique. The fact that the babbler, the gregarious leading species of the flocks, gains information from another species is one of the first indications that such a “nuclear” species can benefit from its participation in mixed-species flocks, and the response of at least 2 species to drongo alarms emphasizes the importance sentinel species such as drongos may play in flock communities.

Ringed seal post-moulting movement tactics and habitat selection

Intra-specific and intra-population variation in movement tactics have been observed in many species, sometimes in association with alternative foraging techniques or large-scale habitat selection. However, whether animals adjust their small-scale habitat selection according to their large-scale tactics has rarely been studied. This study identified two large-scale movement tactics in ringed seals (Phoca hispida) during their non-breeding, post-moulting period. First-passage times (FPT) were used to explore these large-scale patterns. Subsequently, habitat selection was quantified by modelling the FPTs as a function of habitat attributes using Cox proportional hazards models. Some seals moved far offshore into areas preferentially containing 40-80% ice coverage, while other individuals spread along the coasts of Svalbard concentrating their time near glacier fronts. Both tactics resulted in ringed seals being in highly productive areas where they had access to ice-platforms to rest. When offshore, habitat selection was influenced mainly by sea ice concentration and season. Late in the season (autumn), increased risk of leaving an area was identified, even when ice conditions were still favourable, reflecting their need to return to over-wintering/breeding areas before the fjords of the archipelago freeze. For ringed seals that remained inshore, habitat use intensities were influenced mainly by the distance to glacier fronts and season. These animals were already close to their over-wintering habitat and hence their risk of leaving an area decreased as winter approached. This study of ringed seals habitat selection reveals how they fulfil their biological requirements in this dynamic, heterogeneous habitat. Individuals within the same population employed two distinct large-scale movement tactics, adjusting their decisions for small-scale habitat selection accordingly. This flexibility in ringed seal spatial ecology during summer and fall is expected to result in increased population viability in this high Arctic environment.

Through Birds' Eyes: What does vision tell us about foraging in cormorants?

AbstractGreat Cormorants Phalacrocorax carbo are regarded as visually-guided, pursuit-dive foragers, so it would be expected that they have excellent vision much like aerial predators, such as hawks which detect and pursue prey from a distance. However, my research shows that underwater the visual acuity of Cormorants is surprisingly poor (in fact, similar or worse than unaided humans under water) and very inferior to that of aerial predatory birds. I suggest that Cormorants are able to detect typical prey items only at close range and conclude that cormorants are not the aquatic equivalent of hawks. It seems that their efficient hunting involves the use of specialised foraging techniques which employ rapid neck extension to capture prey that cormorants flush from hiding places; much like the foraging techniques of herons. Cormorants seem to be hunting an “escaping blur”. Like herons, the eye movements and visual fields of cormorants allow visual scanning for escaping prey in a wide arc about the head. The ability of cormorants to see prey held in the mouth may help to aid its identification when it is brought to the surface before swallowing.

Vision and Foraging in Cormorants: More like Herons than Hawks?

BackgroundGreat cormorants (Phalacrocorax carbo L.) show the highest known foraging yield for a marine predator and they are often perceived to be in conflict with human economic interests. They are generally regarded as visually-guided, pursuit-dive foragers, so it would be expected that cormorants have excellent vision much like aerial predators, such as hawks which detect and pursue prey from a distance. Indeed cormorant eyes appear to show some specific adaptations to the amphibious life style. They are reported to have a highly pliable lens and powerful intraocular muscles which are thought to accommodate for the loss of corneal refractive power that accompanies immersion and ensures a well focussed image on the retina. However, nothing is known of the visual performance of these birds and how this might influence their prey capture technique.Methodology/Principal FindingsWe measured the aquatic visual acuity of great cormorants under a range of viewing conditions (illuminance, target contrast, viewing distance) and found it to be unexpectedly poor. Cormorant visual acuity under a range of viewing conditions is in fact comparable to unaided humans under water, and very inferior to that of aerial predators. We present a prey detectability model based upon the known acuity of cormorants at different illuminances, target contrasts and viewing distances. This shows that cormorants are able to detect individual prey only at close range (less than 1 m).Conclusions/SignificanceWe conclude that cormorants are not the aquatic equivalent of hawks. Their efficient hunting involves the use of specialised foraging techniques which employ brief short-distance pursuit and/or rapid neck extension to capture prey that is visually detected or flushed only at short range. This technique appears to be driven proximately by the cormorant's limited visual capacities, and is analogous to the foraging techniques employed by herons.

Searching efficiency and the functional response of a pause‐travel forager

Summary The feeding rates of many predators and parasitoids exhibit type II functional responses, with a decelerating rate of increase to reach an asymptotic value as the density of their prey or hosts increases. Holling's disc equation describes such relationships and predicts that the asymptotic feeding rate at high prey densities is set by handling time, while the rate at which feeding rate increases with increased prey density is determined by searching efficiency. Searching efficiency and handling time are also parameters in other models which describe the functional response. Models which incorporate functional responses in order to make predictions of the effects of food shortage thus rely upon a clear understanding and accurate quantification of searching efficiency and handling time. Blackbird Turdus merula exhibit a type II functional response and use pause‐travel foraging, a foraging technique in which animals search for prey while stationary and then move to capture prey. Pause‐travel foraging allows accurate direct measurement of feeding rate and both searching efficiency and handling time. We use Blackbirds as a model species to: (i) compare observed measures of both searching efficiency and handling time with those estimated by statistically fitting the disc equation to the observed functional response; and (ii) investigate alternative measures of searching efficiency derived by the established method where search area is assumed to be circular and a new method that we propose where it is not. We find that the disc equation can adequately explain the functional response of blackbirds feeding on artificial prey. However, this depends critically upon how searching efficiency is measured. Two variations on the previous method of measuring search area (a component of searching efficiency) overestimated searching efficiency, and hence predicted feeding rates higher than those observed. Two variations of our alternative approach produced lower estimates of searching efficiency, closer to that estimated by fitting the disc equation, and hence more accurately predicted feeding rate. Our study shows the limitations of the previous method of measuring searching efficiency, and describes a new method for measuring searching efficiency more accurately.

Transmission of Multiple Traditions within and between Chimpanzee Groups

Field reports provide increasing evidence for local behavioral traditions among fish, birds, and mammals. These findings are significant for evolutionary biology because social learning affords faster adaptation than genetic change and has generated new (cultural) forms of evolution. Orangutan and chimpanzee field studies suggest that like humans, these apes are distinctive among animals in each exhibiting over 30 local traditions. However, direct evidence is lacking in apes and, with the exception of vocal dialects, in animals generally for the intergroup transmission that would allow innovations to spread widely and become evolutionarily significant phenomena. Here, we provide robust experimental evidence that alternative foraging techniques seeded in different groups of chimpanzees spread differentially not only within groups but serially across two further groups with substantial fidelity. Combining these results with those from recent social-diffusion studies in two larger groups offers the first experimental evidence that a nonhuman species can sustain unique local cultures, each constituted by multiple traditions. The convergence of these results with those from the wild implies a richness in chimpanzees' capacity for culture, a richness that parsimony suggests was shared with our common ancestor.

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.

Application of bacterial foraging technique trained artificial and wavelet neural networks in load forecasting

A new load forecasting (LF) approach using bacterial foraging technique (BFT) trained wavelet neural network (WNN) is proposed in this paper. Artificial neural network (ANN) is combined with wavelet transform called wavelet neural network is applied for LF. The parameters of translation and dilation in the wavelet nodes and the weighting factors in the weighting nodes are tuned using BFT optimization. With the advantages of global search abilities of BFT as well as the multiresolution and localizing natures of wavelets, the networks are constructed which identifies the inherent non-linear characteristics of power system loads. The proposed approach is validated with Tamil Nadu Electricity Board (TNEB) system, India. The comparison of Delta Rule and BFT-based LF for different periods are depicted with their mean absolute percentage errors (MAPE).

A Comparison of Two Diet Analysis Techniques for a Browsing Megaherbivore

Diet assessment of herbivores provides insight into trophic relationships, the potential for competition, and the influences herbivores may have on an ecosystem (Bookhout 1996). Thus, the determination of their food requirements is imperative prior to the implementation of any management decisions, which must be based on reliable data (Bookhout 1996). Direct observations and fecal analysis are 2 commonly employed techniques for assessing the diet of wild herbivores (Van Aarde and Skinner 1975, Field and Ross 1976, McInnes et al. 1983, Landman and Kerley 2001, Parker et al. 2003). However, both methods are biased in the way in which they quantify herbivore diets (for review see: Dearden et al. 1975, McInnes et al. 1983, Norbury and Sanson 1992, Bookhout 1996). Traditionally, the diet of megaherbivores (herbivores that exceed 1,000 kg; Owen-Smith 1992) was quantified using direct observations because megaherbivores are conspicuous and easy to observe compared to smaller, more cryptic ungulates. The giraffe (Giraffa camelopardalis) is no exception (Leuthold and Leuthold 1972, Van Aarde and Skinner 1975, Parker et al. 2003). They are large, browsing ruminants (Owen-Smith 1992) that favor open or broken savanna habitats (Skinner and Smithers 1990) and browse exclusively on woody vegetation (Owen-Smith 1992). Giraffes are highly selective compared to other megaherbivores due to their unique foraging technique, whereby they strip the leaves off the terminal shoots of trees with their long tongue (Cooper and Owen-Smith 1986, Owen-Smith 1992). Typically, trees from the genus Acacia are the mainstay of giraffe diet (Du Toit et al. 1990). However, most Acacia species are deciduous and lose their leaves during the dry or cold season (Parker et al. 2003). Consequently, giraffes include a greater proportion of evergreen or semi-deciduous vegetation in their diet during this period (Sauer 1983, Parker et al. 2003). Apart from males having higher forage intake rates than females (Ginnett and Demment 1997), no sex differences in diet composition have been reported in the literature. We compared direct observations and fecal analysis to determine the diet of a megaherbivore on a regional scale, using the giraffe as a model. We tested the ability of the 2 methods to detect the most important plant species and the seasonal changes in the diet. There is no a priori reason to suggest that one method will perform better than the other, and we predicted that it is most likely that the 2 methods together will give the most robust results.

Faithful replication of foraging techniques along cultural transmission chains by chimpanzees and children

Observational studies of wild chimpanzees (Pan troglodytes) have revealed population-specific differences in behavior, thought to represent cultural variation. Field studies have also reported behaviors indicative of cultural learning, such as close observation of adult skills by infants, and the use of similar foraging techniques within a population over many generations. Although experimental studies have shown that chimpanzees are able to learn complex behaviors by observation, it is unclear how closely these studies simulate the learning environment found in the wild. In the present study we have used a diffusion chain paradigm, whereby a behavior is passed from one individual to the next in a linear sequence in an attempt to simulate intergenerational transmission of a foraging skill. Using a powerful three-group, two-action methodology, we found that alternative methods used to obtain food from a foraging device ("lift door" versus "slide door") were accurately transmitted along two chains of six and five chimpanzees, respectively, such that the last chimpanzee in the chain used the same method as the original trained model. The fidelity of transmission within each chain is remarkable given that several individuals in the no-model control group were able to discover either method by individual exploration. A comparative study with human children revealed similar results. This study is the first to experimentally demonstrate the linear transmission of alternative foraging techniques by non-human primates. Our results show that chimpanzees have a capacity to sustain local traditions across multiple simulated generations.

Bottlenose Dolphin (<I>Tursiops truncatus</I>) Predation on a Marine Fin Fish Farm: Some Underwater Observations

This paper reports on the results of underwater observations of bottlenose dolphin feeding behaviour in a marine fin fish farm on the Sardinian coast in Italy from 2000 to 2005. During the study period, 178 underwater encounters were noted during 79 sightings of bottlenose dolphins at a fish farm. Total time spent underwater in the presence of dolphins was 284 min, with a mean encounter duration of 1.6 ± 1.3 min. Bottlenose dolphins were primarily observed hunting both schooling and solitary prey around the fish farm cages, using seven cooperative and individual feeding strategies throughout the water column. The underwater observations suggest that the use of different feeding strategies is consistent with the hypothesis that bottlenose dolphins apply common decision rules in relation to prey availability, resulting in the use of different foraging techniques. The observed frequency of the feeding strategies employed by dolphins preying directly on farmed fish could be worrisome for aquaculture.

Wind-dependent foraging flight in the Osprey Pandion haliaetus

We studied the foraging technique of Ospreys Pandion haliaetus during different wind speed conditions at Lake Hammarsjön, Sweden in autumn 2003. Different fishing techniques were used with a shift in relation to wind speed: (1) without hovering, (2) hovering with pure flapping flight, (3) hovering with flapping flight and gliding into the wind, and (4) hovering with pure gliding. The results supported our predictions that hovering is constrained at low wind speeds and gliding restricted to wind speeds exceeding 7 m/s. Mixing flapping and gliding flight when hovering may be done as a trade-off between increased fishing efficiency associated with flapping flight and energy-saving combined with gain in total hovering time associated with gliding intervals. The relationship between hovering time and wind speed differed significantly between males and females. At wind speeds up to about 3.0 m/s, the hovering time increased more steeply with increasing wind speed for males than for females. In contrast, hovering time was shorter for males than for females at high wind speeds. The juveniles showed a lower mean, smaller scatter, and less increase in hovering time along the wind speed gradient.

FORAGING BEHAVIOR OF EURASIAN THREE-TOED WOODPECKERS (PICOIDES TRIDACTYLUS ALPINUS) IN RELATION TO SEX AND SEASON IN GERMANY

I studied year-round foraging behavior of 28 color-banded Eurasian Three-toed Woodpeckers (Picoides tridactylus alpinus) from 1995 to 1999 in Berchtesgaden National Park, Germany. My research focused on how foraging time was divided among various substrates and foraging techniques. Foraging behavior was recorded by instantaneous sampling during independent observation sessions (i.e. foraging bouts). A combination of tapping and pecking was the most important foraging technique used during breeding (>43%) and nonbreeding (>59%). Both mean and maximum foraging bouts (mean ± SD) lasted longer during nonbreeding periods (mean: 17.0 ± 3.7 min, maximum: 61.9 ± 30.2 min) than during breeding periods (4.3 ± 3.0 min, 15.5 ± 16.1 min). Sap-sucking was observed rarely during breeding. Males spent less time foraging on branches, whereas females spent less time in the lower third of trees on which they foraged. Males also manipulated foraging substrates more by pecking and digging (probing), whereas females did more climbing and position-changing on foraging trees. I concluded that Eurasian Threetoed Woodpeckers changed their foraging techniques according to seasonal changes in diet and that, during breeding, males used better foraging grounds than females. Le Comportement de Quête Alimentaire chez Picoides tridactylus alpinus en Relation avec le Sexe et la Saison en Allemagne

Foraging Behavior of Eurasian Three-Toed Woodpeckers (Picoides Tridactylus Alpinus) in Relation to Sex and Season in Germany

Abstract I studied year-round foraging behavior of 28 color-banded Eurasian Three-toed Woodpeckers (Picoides tridactylus alpinus) from 1995 to 1999 in Berchtesgaden National Park, Germany. My research focused on how foraging time was divided among various substrates and foraging techniques. Foraging behavior was recorded by instantaneous sampling during independent observation sessions (i.e. foraging bouts). A combination of tapping and pecking was the most important foraging technique used during breeding (>43%) and nonbreeding (>59%). Both mean and maximum foraging bouts (mean ± SD) lasted longer during nonbreeding periods (mean: 17.0 ± 3.7 min, maximum: 61.9 ± 30.2 min) than during breeding periods (4.3 ± 3.0 min, 15.5 ± 16.1 min). Sap-sucking was observed rarely during breeding. Males spent less time foraging on branches, whereas females spent less time in the lower third of trees on which they foraged. Males also manipulated foraging substrates more by pecking and digging (probing), whereas females did more climbing and position-changing on foraging trees. I concluded that Eurasian Threetoed Woodpeckers changed their foraging techniques according to seasonal changes in diet and that, during breeding, males used better foraging grounds than females. Le Comportement de Quête Alimentaire chez Picoides tridactylus alpinus en Relation avec le Sexe et la Saison en Allemagne

Effects of visual stimuli, substrate-borne vibrations and air current stimuli on escape reactions in insect prey of flush-pursuing birds and their implications for evolution of flush-pursuers

Insects use escape behaviors to avoid predators. Some insectivorous birds evolved a unique flush-pursue foraging technique that exploits their insect prey escape responses. Flush-pursers use visual stimulation from spreading of tails and wings and from pivoting body movements as well as plumage contrast to trigger escapes in prey. The escaping prey is subsequently pursued in aerial chases. By simulating approaches of one such flush-pursuer, the painted redstart (Myioborus pictus), to moths, flies, and homopteran insects we studied the effect of visual stimulation as well as possible effects of subtle air-currents from pivoting element of flush-displays and the effect of substrate borne vibrations that might be produced by moving bird. We confirm the importance of visual stimulation in triggering the prey escape behavior by flush-displaying birds. Effect of air currents was only important for relatively strong experimental air-puffs, which may approximate a situation of a bird displaying by moving its open tail and wings at a close distance to its prey. Substrate-borne vibrations positively contributed to the visually elicited escape reaction of moths. The results suggest that the visual predator-to-prey signal used by extant flush-pursuers for exploitative foraging could be aided in certain situations by substrate-borne vibrations or air currents produced by flush-displaying birds. Hypothetical role of non-visual stimuli in the initial evolution of flush-pursue strategy is discussed.

Capuchin Stone Tool Use in Caatinga Dry Forest

Wild capuchin monkeys inhabiting dry forest were found to customarily use tools as part of their extractive foraging techniques. Tools consisted of twigs and sticks, often modified, which were used to probe for insects and, most frequently, of stones of a variety of sizes and shapes used for cracking and digging. The use of tools for digging has been thought to be restricted to humans. These monkeys, living in a harsh dry habitat, survive food limitation and foraging time constraints through their extensive tool use.

Redstart Phoenicurus phoenicurus and black redstart P. ochruros in a mosaic urban environment: neighbours or rivals?

Redstart and black redstart inhabit different types of habitats under natural conditions. However, they come into close contact in a mosaic urban environment. Mechanisms enabling their local coexistence were looked for. We found that: 1) The two species occupied exclusive territories of different habitat compositions. 2) Territories differed in the proportion of trees and buildings. 3) Within their territories, the two species used the same foraging techniques, but with different frequencies. 4) Prey size was similar, but the proportions of taxonomic groups differed. 5) Spontaneous interspecific conflicts were observed. Interspecific aggression was confirmed in playback experiments. The black redstart was dominant in both natural and simulated encounters. We conclude that the main mechanism enabling coexistence of the two redstarts in a mosaic urban environment is different habitat selection with the proportion of trees as a key parameter. This proportion was always below 26% in black redstart territories, and above 27% in redstart territories. This is consistent with the habitat preferences these two species show in non‐urban conditions. This pattern is compared to the other cases of coexistence of congeneric bird species such as chickadees Poecile or Sylvia warblers. As the two redstart species are able to hybridise in the wild, the observed interspecific aggression may operate as a pre‐copulation barrier.