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PubMed1998

Social calls coordinate foraging in greater spear-nosed bats

The function of social calls emitted by foraging bats has received little study. Here we use observations of free-ranging greater spear-nosed bats, Phyllostomus hastatus, and field playbacks to determine whether audible, broad-band 'screech' calls attract mates, warn conspecifics or influence access to food. Five lines of evidence suggest that screech calls enable adult females from the same roosting group to fly together from the day roost to feeding sites. (1) Seasonal differences in diet influenced the rate of screech calling recorded outside the cave roost, as well as how often bats departed together. Bats called more often and flew in larger groups when feeding on a concentrated resource, balsa, Ochroma lagopus, flowers, in winter than on more dispersed Cecropia peltata fruit in spring. (2) Observations of bats flying outside the cave, in flyways and at feeding sites indicated that screech calls occurred more often when bats flew in groups than alone. (3) Females from the same roosting group were netted at the same feeding site, sometimes simultaneously, several kilometres from the cave. (4) Calling colour-marked adult females outside the cave were joined by a female group member, both on initial departures and on second foraging trips, more often than non-calling bats. (5) Playbacks attracted conspecifics at roost and feeding sites. Screech calls appear to function as contact calls that recruit and coordinate foraging among group members. We postulate that females benefit from foraging with unrelated roost-mates because they can defend feeding sites more effectively. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

Foraging bumblebees avoid flowers already visited by conspecifics or by other bumblebee species

Honey bees, Apis mellifera, use short-lived repellent scent marks to distinguish and reject flowers that have recently been visited by themselves or by siblings, and so save time that would otherwise be spent in probing empty flowers. Conversely, both honey bees and bumblebees, Bombus spp., can mark rewarding flowers with scent marks that promote probing by conspecifics. We examined detection of recently visited flowers in a mixed community of bumblebees foraging on comfrey, Symphytum officinale, in southern England. When foraging among inflorescences on a plant, three abundant species of Bombus probed fewer inflorescences more than once than would be expected from random foraging. Bees frequently encountered inflorescences but departed without probing them for nectar. Examination of the incidence of such rejections in the two most common species, B. terrestris and B. pascuorum, revealed that the low incidence of multiple probing visits was due to two factors: bees both foraged systematically and selectively rejected inflorescences that they had previously visited. When presented with inflorescences of known history, bees selectively rejected those that had been recently visited by themselves or by conspecifics compared with randomly selected inflorescences. They were also able to distinguish inflorescences that had been visited by other Bombus species. Bees were unable to distinguish and reject inflorescences from which the nectar had been removed artificially. We conclude that these Bombus species are probably using scent marks left by previous visitors. The significance of deposition and detection of interspecific scent marks for competitive interactions between species is discussed. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

Patch sampling behaviour and future foraging expectations in Argentine ants, Linepithema humile

Nests of Argentine ants, L. humile, were exposed to pairs of foraging patches of varying quality. These patches varied from never having food to having food for 4 h every day. After 15 days, colonies were allowed an added access to a new patch. The new patch, however, never contained food. The sampling behaviour of nests towards the initial patches and the new patch suggested that the nests were using a sampling rule based on maximizing net benefits of finding food minus the cost of sampling. The behaviour of the nests towards the new patch was also significantly affected by what the foraging workers had previouisly encountered in the foraging patches. The behaviour of the L. humile colonies is similar in pattern to what would result by Bayesian updating of expectations for success in novel foraging opportunities. These data are the first suggestions of such an ability in an insect. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

Prey availability and selective foraging in shorebirds.

Accurate measurements of prey availability are vital to our understanding of foraging behaviour, particularly prey selectivity. In the present study, observations of shorebirds foraging for fiddler crabs on intertidal mudflats demonstrate that prey availability depends both on the temporal variation in crab activity and on the crabs' responses to the presence of foraging shorebirds. Our results suggest that measurements of prey availability that do not specifically account for prey activity patterns and their responses to predators are neccessarily inaccurate. Furthermore, our results also show that tests for foraging selectivity are extremely sensitive to the way in which prey availability is measured and can even indicate active prey selectivity when more accurate measures of prey availability show predators to be non-selective. Because inaccurate measures of food resources greatly reduce our ability to detect food preferences, greater care must be taken to account for prey activity patterns and their responses to predators in measurements of prey availability. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

Hunger effects on foraging responses to perceptual cues in immature and adult wolf spiders (Lycosidae).

The wolf spider, Schizocosa ocreata (Hentz), varies foraging patch residence time in the presence of different sensory cues from prey, even without food rewards. This study examines the influence and interaction of hunger state, age and sex on the use of different types of sensory information to determine foraging patch sampling duration. In a series of two-chambered artificial foraging patches, I tested 26 S. ocreata once as immatures, and again as adults, under two hunger states (satiated and 7 days without food). Patches varied in the type of sensory information provided by live prey (crickets) as follows: visual cues alone; vibratory cues alone; combined visual/vibratory cues; and control (no prey). Without feeding in patches, the type of sensory stimuli available from prey strongly affected patch residence time, with spiders using primarily visual rather than vibratory cues. Hunger level as a main effect had no influence on residence time, but hunger state did mediate the importance of visual or vibratory information. Significant age- and sex-related differences in patch residence time in the presence of different sensory cues were found.These data suggest that ontogenetic and sex-specific foraging strategies are influenced by use of prefeeding perceptual cues rather than hunger state in wolf spiders. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

The effect of group size on the foraging behaviour of juvenile coho salmon: reduction of predation risk or increased competition?

Animals often increase their apparent willingness to incur risk when foraging in groups, presumably because group membership reduces an individual's risk of predation. As group size increases, however, competition for resources may also increase, resulting in a decrease in the quantity of resources available to each member of the group. When resources are scarce, individuals might be expected to increase their foraging effort in an attempt to increase their share. Such increases in effort will often appear to increase an individual's risk of predation. Thus, increased competition may contribute to the frequently observed relationship between risk-taking behaviour and group size. To date, no experimental assessment of the relative importance of these two mechanisms exists. We argue that to differentiate between the hypotheses of 'risk reduction' and 'increased competition', it is necessary to quantify the effect of predation risk on the form of the relationship between group size and risk-taking behaviour, and thus, to manipulate both group size and predation risk. We conducted an experiment to determine the relative importance of risk reduction and increased competition to the foraging decisions of juvenile coho salmon, Oncorhynchus kisutch. We recorded the foraging behaviour of 18 focal individuals in the presence and absence of a predator, and in the company of zero, one and three conspecifics. As group size increased from one to four, focal fish captured more prey items, ventured closer to the feeder (and predator) to intercept them, and decreased their use of cover. Furthermore, although focal individuals captured fewer prey items and intercepted them further from the feeder in the presence of the predator than in its absence, the form of the relationship between risk-taking behaviour and group size was not affected by the level of predation risk. The results of our experiment are consistent with the interpretation that increases in risk-taking behaviour with group size occurred primarily as a consequence of increased competition for scarce resources. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1996

Bioextraction of selenium by forage and selected field legume species in selenium-laden soils under minimal field management conditions.

A forage plant, tall fescue (Festuca arundinacea), and a selected field legume species, sour clover (Melilotus indica), were examined for their selenium (Se) bioextraction abilities in Se-laden soils under minimal management conditions. Natural vegetations in a 2-acre plot adjacent to the forage plots were also studied for Se accumulation comparisons. During the dry season, in the fall of 1994, the field plots were either irrigated weekly or without irrigation. No fertilization and weed control were applied. The plants were harvested in May 1995. There were considerable differences in the ability of Se uptake between the forage and the legume species and among the naturally established plant species; the amount of Se accumulated per land area was largely dependent on their respective biomass production. Comparing Se concentration between preplant and postharvest, there was a detectable reduction in the soil selenate, selenite, and water-extractable organic Se in the tall fescue and melilotus plots. The field irrigation provided more favorable conditions for bioextractions and dissipation of Se by the plants. However, the available soil Se only accounts for less than 10% of the total soil Se and no detectable reduction of total soil Se was found. This may be due to the large inventory and variation of Se concentrations in the field soils and therefore obscured the detectable differences. For practical considerations, the forage plants can be repeatedly harvested and used for rangelands of Se deficiency currently seen in some northern California counties.

Analysis of Variance↗

PubMed1999

Learning foraging thresholds for lizards: an analysis of a simple learning algorithm

This paper gives proof of convergence for a learning algorithm that describes how anoles (lizards found in the Caribbean) learn foraging threshold distance. An anole will pursue a prey if and only if it is within this threshold of the anole's perch. The learning algorithm was proposed by Roughgarden and his colleagues. They experimentally determined that this algorithm quickly converges to the foraging threshold that is predicted by optimal foraging theory. We provide analytic confirmation that the optimal foraging behavior as predicted by Roughgarden's model can be attained by a lizard that follows this simple and zoologically plausible rule of thumb. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Prey processing in central place foragers.

The importance of prey processing as an integral part of foraging behaviour has long been acknowledged, but little theoretical consideration has been given to the optimization of the processing behaviour itself. Processing renders food down to ingestible, palatable portions, and also removes non-essential mass thus reducing transport costs. Here, several models of processing are developed for a central place forager. When the forager has to make a simple choice between processing the prey and not, a critical distance from the central place can be calculated, beyond which it is optimal to process prey. If the forager also decides on how much of the prey to remove, the optimal amount to be removed can also be calculated. Imposing a ceiling on overall metabolic expenditure is shown to reduce the distances at which processing becomes the optimal strategy. The models are tested using parameters derived for a provisioning merlin, Falco columbarius, and alternative explanations as to why observed behaviours should differ from the optimal behaviour predicted are discussed.

Animals↗

PubMed2001

The effects of genotype, foraging role, and sucrose responsiveness on the tactile learning performance of honey bees (Apis mellifera L.).

We analyzed sucrose responsiveness and associative tactile learning in two genetic strains of honey bees under laboratory conditions. These strains differ in their foraging behavior. Bees of the "high" strain preferentially collect pollen. "Low"-strain bees mainly forage for nectar. Responsiveness to different sucrose concentrations and tactile learning were examined using the proboscis extension reflex. Acquisition, extinction of conditioned responses, and responses to an alternative tactile stimulus were tested. High-strain bees are more responsive to sucrose than low-strain bees. Regardless of genotype, pollen foragers are more responsive to sucrose than nectar foragers. In bees of both strains we find the same relationship between responsiveness to sucrose and acquisition. Bees responding to low sucrose concentrations show more often the conditioned response during acquisition than those responding only to higher sucrose concentrations. Extinction of conditioned responses depends on the response probability during acquisition. Discrimination between the two tactile stimuli is affected by genotype but not by responsiveness to sucrose. High-strain bees discriminate better than low-strain bees. Our experiments thus establish links between division of labor, responsiveness to sucrose, and associative learning in honey bees.

Animals↗

PubMed1996

Pollinator Foraging Strategies in Mixed Floral Arrays: Density Effects and Floral Constancy

The profitability of any foraging strategy may be in part dependent on the number of foragers adopting it, and so it can be viewed mathematically as a "game." We explore here the implications of a game-theoretic model of pollinators foraging on a mixed array of two flower species, with individual pollinators either specializing on one or the other, or else acting as generalists. We further allow for the possibility of specialist advantages in foraging efficiency. The predicted mixture of pollinator behavioral strategies depends on the overall floral density and the relative densities of the two flower species. Where floral resources are scarce, pollinators should behave as generalists whereas when resources are superabundant, specialization on the single most profitable flower type (all else being equal, the commonest one) is favored. At intermediate floral densities, a mix of floral specializations (floral constancy) is favored, so long as the rarer flower's density does not fall below some critical minimum level. Where the rarer flower is too rare, a mixture of generalists and common-species specialists is favored. Rare flowers are at a reproductive disadvantage in all cases, but their relative success is highest where their pollinators are flower constant.

Journal Article↗

PubMed1992

The foraging locus: behavioral tests for normal muscle movement in rover and sitter Drosophila melanogaster larvae.

We used Drosophila melanogaster larvae with different alleles at the foraging (for) locus in a variety of behavioral tests to evaluate normal muscle usage of rover and sitter phenotypes. The results show that sitter and lethal sitter alleles of for do not affect larval behavior through a mutation which affects larval muscle usage. In general the behavior of rovers and sitters differed on food but not on non-nutritive substrates. Rovers and sitters moved equally well on non-nutritive substrates, and measures such as the time to roll over and length of forward stride showed no significant strain differences. Larvae with different alleles at for did not differ in body length. Rovers took more strides, not longer ones, than sitters while on foraging substrates. We conclude that differences in larval locomotion during foraging found in larvae with different alleles at for can not be explained on the basis of muscle usage alone. It is more likely that for affects larval ability to perceive or respond to the foraging environment.

Alleles↗

PubMed1994

Substrate-gleaning versus aerial-hawking: plasticity in the foraging and echolocation behaviour of the long-eared bat, Myotis evotis.

The foraging and echolocation behaviour of Myotis evotis was investigated during substrate-gleaning and aerial-hawking attacks. Bats gleaned moths from both the ground and a bark-covered trellis, however, they were equally adept at capturing flying moths. The calls emitted by M. evotis during substrate-gleaning sequences were short, broadband, and frequency-modulated (FM). Three behavioural phases were identified: search, hover, and attack. Gleaning search calls were significantly longer in duration, lower in highest frequency, and larger in bandwidth than hover/attack calls. Calls were detected in only 68% of gleaning sequences, and when they were emitted, bats ceased calling approximately 200 ms before attacking. Terminal feeding buzzes, the rapid increase in pulse repetition rate associated with an attempted prey capture, were never recorded during gleaning attacks. The echolocation calls uttered by M. evotis during aerial-hawking foraging sequences were also short duration, high frequency, FM calls. Two distinct acoustic phases were identified: approach and terminal. Approach calls were significantly different from terminal calls in all variables measured. Calls were detected in 100% of aerial-hawking attacks and terminal feeding buzzes were invariably produced. Gleaning hover/attack calls were spectrally similar to aerial approach calls, but were shorter in duration and emitted at a significantly lower (but constant) repetition rate than aerial signals. Although the foraging environment (flight cage contents) remained unchanged between tasks (substrate-gleaning vs. aerial-hawking), bats emitted significantly lower amplitude calls while gleaning. We conclude that M. evotis adjusts its echolocation behaviour to meet the perceptual demands (acoustical constraints) imposed by each foraging situation.

Animals↗

PubMed1977

Intensive fattening of beef cattle by stall feeding on the Lilongwe Plain, Malawi. I. Type of forage and level and type of supplementation.

Experiments were undertaken with Malawi zebu steers over three wet seasons to investigate the effects of feeding improved forages (zero grazed) and supplements on animal performance. The forages fed were Guinea grass and pearl millet and the supplements maize: madeya (maize bran) or maize: madeya: cottonweed cake. The daily allowance of supplement was, on a DM basis, liveweight equivalent to 0-6, 1-1 or 1-5 per cent of cattle (1973, 1974). In 1975 the supplementation treatments were nil, maize: madeya or leucaena fed at 0-6 per cent liveweight. Daily gains of steers were similar with both forages except in 1975 when those fed on pearl millet grew 19 per cent faster than those on Guinea grass. The performance of steers was increased with supplementation only where forage quality declined. The significance of the results are discussed.

Animal Feed↗

PubMed2003

The emergence of collective foraging in the arboreal Gnamptogenys menadensis (Hymenoptera: Formicidae).

Gnamptogenys menadensis is an arboreal nester that forages opportunistically almost exclusively on vegetation, sometimes recruiting others to participate in prey retrieval. The three-dimensional characteristics of vegetation suggest that functions describing recruitment decision thresholds or the pattern of recruitment in arboreal species may differ from those predicted by optimal foraging theory. To examine the effects of prey abundance and distance on the recruitment dynamics of G. menadensis, we baited nests with one termite, five termites or a number of termites between 20 and 40 either near to or far from the entrance and observed the ensuing behaviors. G. menadensis recruited others when encountering multiple termites regardless of the termite pile's distance from the nest, although a few individuals remained at the site and defended the resource. The pattern of arrivals at the site indicates that the majority and sometimes all arrivals were recruited from the branch trails. In combination, these results suggest that the architecture of the foraging habitat, which limits available return routes to the nest and thus increases encounter probabilities with potential recruits, shaped the process of information transfer and generated a collective pattern of foraging and prey retrieval.

Animals↗

PubMed2004

A method to quantify and analyze the foraging activity of honey bees: relevance to the sublethal effects induced by systemic insecticides.

The assessment of agropharmaceuticals' side effects requires more realistic simulations of field conditions than those deduced from the dose-lethality relation obtained under laboratory conditions. Because the presence of sublethal doses or concentrations may also alter the behavior of foraging insects, we attempted to devise a quantifiable and accurate protocol for evidencing various alterations in free-flying bees. Such a protocol was illustrated by testing new classes of systemic insecticides. The protocol focused on video recording to quantify the foraging activity of small colonies of honey bees confined in insect-proof tunnels. The basis of the protocol was not the colony itself but the change in each colony on a specific day and between days. First, the paradigms of attendance at a safe feeding source were established by observing 8 control colonies at different times of the season during 5 days after the necessary forager training was accomplished. Second, on three different colonies we considered the paradigms on the control day before contamination and during 4 days after the feeding source was contaminated. During the same period, one more colony was exclusively fed with safe food to serve as control. Two plant-systemic insecticides were tested at contamination levels 70 times lower than the 50% of the lethal concentration. Imidacloprid, at 6 microg/kg, clearly induced a decrease in the proportion of active bees. Fipronil, at 2 microg/kg, induced an additional decrease in attendance at the feeder. Such levels are still higher than the corresponding lowest observable effect concentration (LOEC). Our protocol, which provided intermediate conditions between field and laboratory conditions, allowed the quantification, with an enhanced level of sensitivity, of sublethal effects on foraging bees.

Agriculture↗

PubMed2005

The status of selected minerals in soil, forage and beef cattle tissues in a semi-arid region of Zimbabwe.

Five districts in the Matabeleland region, an arid western area of Zimbabwe, were investigated for the status of Ca, P, Na, Cu and Zn in soil, forage and cattle during the wet and dry seasons over a period of one year. The cattle came from the natural grazing lands and were not supplemented at the time of sampling. Some deficiencies in soil Zn and P were found in the districts of Lupane and Bulilimamangwe, respectively. Dry season soil Ca, Cu and P concentrations were significantly higher (p < 0.05) than rainy season values owing to leaching in all five districts. Most forage samples had mineral concentrations below the critical levels known to be adequate for animal requirements. Forage levels of Ca, Na. Cu and Zn significantly increased (p < 0.05) with advancing maturity, while P significantly decreased (p < 0.05) in almost all the districts. Marked deficiencies of minerals were found in cattle tissues and these levels followed the seasonal trend seen in the forage. These results indicate that cattle in Matebeleland are deficient in P, Ca, Cu and Zn and that grazing areas in the region cannot provide adequate levels of the five minerals studied.

Abattoirs↗

PubMed1980

Changes in morphology of dendritic spines on honeybee calycal interneurons associated with cumulative nursing and foraging experiences.

Using the rapid Golgi method, the morphology of dendritic spines was quantified in the calyxes of groups of newly emerged, nurse, and forager honeybees. These groups were studied because they represented distinct stages of behavioral development and cumulative experience which, according to recent vertebrate findings, may be associated with enlargement of the spine head and stem shortening. Measurements were made of spine density, overall spine length, stem length, maximum head width, and profile area using eyepiece micrometry and computer image analyses. The results indicated that none of the groups differed appreciably in spine density and overall spine length. Foragers did exhibit spines with markedly larger profile areas and shorter stems than those in newly emerged and nurse honeybees. However, nurses and foragers did not differ appreciably in spine head width, but both groups had markedly wider heads than the newly emerged group did. These findings suggest that elongated growth of the spine head and concomitant stem shortening is an incremental process affecting different portions of the spine population at different rates. In particular, the growth rate of most spines appears to accelerate during the foraging stage in which the diversity of sensory stimulation is greatest.

Animals↗