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PubMed2006

Hierarchical patch dynamics and animal movement pattern.

In hierarchical patch systems, small-scale patches of high density are nested within large-scale patches of low density. The organization of multiple-scale hierarchical systems makes non-random strategies for dispersal and movement particularly important. Here, we apply a new method based on first-passage time on the pathway of a foraging seabird, the Antarctic petrel (Thalassoica antarctica), to quantify its foraging pattern and the spatial dynamics of its foraging areas. Our results suggest that Antarctic petrels used a nested search strategy to track a highly dynamic hierarchical patch system where small-scale patches were congregated within patches at larger scales. The birds searched for large-scale patches by traveling fast and over long distances. Once within a large-scale patch, the birds concentrated their search to find smaller scale patches. By comparing the pathway of different birds we were able to quantify the spatial scale and turnover of their foraging areas. On the largest scale we found foraging areas with a characteristic scale of about 400 km. Nested within these areas we found foraging areas with a characteristic scale of about 100 km. The large-scale areas disappeared or moved within a time frame of weeks while the nested small-scale areas disappeared or moved within days. Antarctic krill (Euphausia superba) is the dominant food item of Antarctic petrels and we suggest that our findings reflect the spatial dynamics of krill in the area.

Animal Migration↗
PubMed2005

Nest paper absorbency, toughness, and protein concentration of a native vs. an invasive social wasp.

The amount of proteinaceous food that was allocated to nest construction by a native wasp (Polistes fuscatus) vs. an invasive wasp (Polistes dominulus) in North America was examined following a field experiment under natural and surplus prey foraging conditions. Wasps of the surplus prey foraging conditions were provided with prey ad libitum within an enclosed area, while wasps of the natural treatment foraged in an adjacent field-woodland site. At the end of the field experiment, each nest was tested for water absorbency, toughness, and protein concentration. The hypotheses were: (1) When all nests are equally sheltered, the invasive P. dominulus (PD) allocates less protein to nest paper construction (for waterproofing and strengthening) and more protein to developing larvae than the native P. fuscatus (PF). (2) Nests of P. dominulus are more absorbent (less waterproof) and less tough than nests of P. fuscatus. Results indicate that P. fuscatus nests from surplus prey foraging conditions were more absorbent (less waterproof) to artificial rain drops than P. dominulus nests. The toughness of nests was similar between wasp species. However, nests from the natural treatment were tougher than those from the surplus prey treatment. Nests from the natural foraging conditions had half as much protein as those from surplus prey foraging conditions. There was no correlation between nest protein concentration and the number of prey taken, the number of cells, the number of adult offspring produced, or the total wasp biomass produced per colony. For PF under surplus prey conditions, protein concentration and absorbency were negatively correlated, but for PD the correlation was positive. In conclusion, when prey were scarce, Polistes wasps allocated less protein to nest construction. Also, the introduced P. dominulus may increase production of offspring by allocating less to nest construction than that of the native P. fuscatus, and so more protein to offspring production.

Adaptation, Physiological↗
PubMedDate not supplied

Interactions between cattle and badgers at pasture with reference to bovine tuberculosis transmission.

The normal behaviour of badgers, as described here, would not result in direct transmission of tuberculosis from badgers to cattle via air expired by badgers or via bodily contact. All activities of wild badgers in cattle fields at three different sites were observed at night for a total of 359 h. In addition, all activities of pairs of wild caught badgers were observed in a 0.5 ha enclosure with an artificial sett on 20 nights when cattle were present. Badger foraging in cattle fields was infrequent during dry conditions and variable at other times. Clover fields were preferred to grass pastures in two autumnal studies and under dry conditions the badgers did not prefer to forage on short pasture. Badgers consistently avoided close contact with cattle by changing routes from sett to foraging site and by foraging much less in areas of fields occupied by cattle. When foraging they preferred to remain at least 10-15 m from cattle and they avoided compact groups of cattle more than individuals. Some cattle would move towards badgers, especially if they were carrying out unusual behaviour, but badgers fled rapidly from every approach. In all potential encounters badgers were able to keep at least 2-3 m from approaching cattle. Badgers in the artificial sett delayed entering the enclosure if cattle were within 15 m of the entrance. When cattle were managed on a strip-grazing (rotational) system the whole area which they occupied was avoided by the badgers. However, badgers came closer to individual cattle and foraged in areas grazed by the cattle more if the cattle were set-stocked. If cattle are managed so that they are concentrated in a small area (rotational) system the risk of disease transmission is minimized because they are less likely to encounter badgers or their fresh products than are cattle managed on a large area (set-stocked) system.

Animals↗
PubMed2006

Recruitment calling: a novel form of extended parental care in an altricial species.

In many altricial birds, fledglings disperse when they are no longer fed, and this dispersal marks the end of parental care. In some species, however, young remain in close association with their parents after nutritional independence. Because juveniles are still inferior foragers at this stage, they might benefit from parental assistance in locating good feeding sites, but this possibility remains largely unexplored. Here, we show that parents and helpers in pied babbler (Turdoides bicolor) societies use a recruitment call to direct nutritionally independent, but inexperienced, foragers to particular food patches. Observations and a playback experiment indicated that adult babblers use a "purr" call to recruit group members to a foraging patch. Creation of experimental foraging patches supported observations that individuals tend to give the call when they are foraging on abundant, divisible food sources and when their group contains independent fledglings (youngsters who are no longer fed directly). Fledglings responded to calls more often than adults, who frequently encountered aggression from the caller if they did, and the fledglings gained significant foraging benefits. This is the first study to demonstrate that altricial birds may use recruitment calls to extend parental care past the period of direct provisioning.

Age Factors↗
PubMed2003

The effect of mercury on the feeding behavior of fathead minnows (Pimephales promelas).

Fathead minnows (Pimephales promelas) were exposed to mercury (1.69, 6.79, and 13. 57 microg/L HgCl(2), 10 days exposure), and afterward their foraging ability was tested in a vegetated habitat for 7 days. Among the foraging metrics used were foraging efficiency, capture speed, and the ability to learn and retain information regarding habitat characteristics. In addition to behavioral tests, muscle tissue acetylcholinesterase activity and brain levels of several neurotransmitters were investigated. Comparisons with control fish and fish from the two highest exposure groups revealed consistent performance deficits in foraging efficiency and capture speed. However, no treatment effects on learning were detected, nor were differences in neurotransmitter levels detected. In determining the underlying proximate cause of the foraging deficits, it is believed that the greater pause time exhibited by treatment fish while foraging was the main cause of treatment differences. In the future, behavioral studies will continue to allow toxicity testing of environmentally relevant variables such as those used by behavioral ecologists.

Acetylcholinesterase↗
PubMed2003

Effect of predation risk on selectivity in heteromyid rodents.

Variations in predation risk affect the costs of foraging and may therefore warrant different foraging decisions. One class of models ("higher requisite profit") predicts that foragers should become more selective when predation risk increases, as low-profitability items that do not cover the increased costs are dropped from the diet. An alternative class of models ("reduced finickiness") predicts that foragers should become less selective when predation risk increases, because selectivity requires more extensive assessment and/or search behaviour, prolonging exposure to risk. We assessed the selectivity of foraging heteromyid rodents (Merriam's kangaroo rats, Dipodomys merriami, and pocket mice, Chaetodipus spp.) by comparing differences in "giving up densities" (GUD: the quantity of cryptic food left in a patch by animals for whom the diminishing marginal gains from foraging have dropped below the threshold for continued search) for foods of different value as a measure of selectivity in patches varying in predation risk. Data collected over two field seasons revealed that heteromyids were more selective when predation risk was highest; away from the protective cover of shrubs during the full moon. These findings support the predictions of higher requisite profit models.

Journal Article↗
PubMed1995

Functional differences between the prelimbic and anterior cingulate regions of the rat prefrontal cortex.

The effects of reversible lidocaine-induced lesions of 2 subregions of the rat medial prefrontal cortex (mPFC) were examined on a series of cognitively based foraging behaviors on a radial-arm maze. Lesions of the prelimbic (PL) or anterior cingulate (AC) cortex prior to the retention phase of a delayed-foraging task disrupted performance differentially; rats with PL lesions visited arms in a random manner, whereas rats with AC lesions revisited previously baited arms preferentially. Rats with AC lesions were also impaired on a single-trial foraging task; they made numerous revisits to previously baited arms. PL lesions had no effect on performance of this task in well-trained rats. However, rats trained on the 2-phase task did not adapt to a new foraging strategy after a PL lesions, when they were switched unexpectedly to the single-trial foraging task. These data demonstrate functional heterogeneity within the rat mPFC and suggest that the PL is involved in processes through which recently acquired information is used to organize and modify foraging behavior, whereas the AC may play an important role in response flexibility.

Animals↗
PubMed1986

The efficiency of energy utilization in growing cattle consuming fresh perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca).

1. Twenty Friesian steers (225 kg live weight) were fed on mid- (M) (June-July) and late- (L) (August-September) season crops of either fresh perennial ryegrass (Lolium perenne cv. Melle) (G) or white clover (Trifolium repens cv. Blanca) (C). Each of the forage diets was offered at three restricted planes of nutrition above maintenance to compare the effect of forage species on the efficiency of energy utilization. All diets were harvested daily from swards of regrowth forage of intended equivalent digestibility. 2. Faecal and urine excretions were measured for 7 and 5 d respectively, followed by two consecutive 24 h measurements of methane, carbon dioxide and oxygen exchange in open-circuit respiration chambers. 3. The apparent digestibility of the energy in perennial ryegrass (0.759) was marginally higher (P less than 0.01) than that in white clover (0.748); the mid- and late-season forages were of similar (P greater than 0.05) digestibilities. Metabolizable energy (ME): digestible energy (DE) in diet G (0.837) was significantly (P less than 0.001) different from that in diet C (0.812). The partition of energy losses when expressed as MJ/GJ gross energy intake (GEI) indicated that energy lost as methane was not significantly different (P greater than 0.05) either between forages (G 62.8, C 63.4) or between seasons (M 63.2, L 63.1). Energy excretion in urine was higher for cattle fed on diet C (77.5) compared with diet G (60.5) (P less than 0.001). Heat production was similar (P greater than 0.05) between forages (G 480, C 478), but lower (P less than 0.01) for L (471) compared with M(486). Energy retention (by difference) was lower (P less than 0.001) for diet C (132) than G (156) and for M (138) than L (149) (P less than 0.05). 4. Parallel-line analysis of unscaled ME intake (MEI) in relation to retained energy (RE; MJ/d) indicated that the efficiency of utilization (kt) was similar (P greater than 0.05) between perennial ryegrass (0.42) and white clover (0.46). Linear extrapolation of the values to zero energy retention indicated that maintenance requirements of ME (Em; MJ/d) were 23.3 for diet G and 28.8 for diet C. The extrapolated Em when expressed in relation to a measured fasting heat production (FHP) of 22.8 (MJ/d) resulted in a derived efficiency of utilization of ME for maintenance (km) of 0.97 (G) and 0.79 (C), suggesting an underestimate of Em for diet G.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Cropping systems for phytoremediation of phosphorus-enriched soils.

Eutrophication of freshwater bodies is frequently attributed to elevated phosphorus (P) concentrations in surface runoff from P-enriched agricultural soils. Forage and grain-cropping systems were compared for their effectiveness at remediating P-enriched soils. At each of four locations, one of three forage systems (Forage I = cereal rye silage and corn silage annually; Forage II = alfalfa; Forage III = annual ryegrass and corn silage annually) and the grain system (corn, small grain, and soybean rotation) were maintained for 3 yr on soils with five distinct initial soil P concentrations that were established by using four annual applications (1994-1997) of five different rates (0, 100, 200, 300, and 400 kg total P ha(-1) y(-1)) of poultry manure, dairy manure, or commercial fertilizer. Across all manure P treatments at all locations, the forage systems had greater removal of P than the grain system. Soil P concentration changes (2001-2004) did not reflect differences in crop P removal. Few significant reductions in soil P concentration were observed for either crop system. When reductions did occur, they were for the more highly enriched soil P treatments. No significant reductions in soil P concentration have occurred for the lowest manure P treatments. Considerable variability in crop P concentrations was observed among species at locations and among years produced. However, crop P concentrations did increase uniformly as soil P concentration increased, indicating that luxury consumption of P does occur in agronomic species produced on P-enriched soils.

Biodegradation, Environmental↗
PubMed1993

Use of a combined synthetic fibre bag method to estimate the true total tract digestion of organic matter and nitrogen of hay and grass silage in cows.

A 4 x 4 Latin square experiment was designed to determine and compare the total tract digestion of organic matter (OM) and nitrogen of hay and grass silage by combining the ruminal and intestinal digestion estimates obtained by the rumen bag and mobile bag methods. The diets were composed of forage alone or 30% forage and 70% barley. The rumen degradation (RD) was calculated using the degradation constants a, b, and c obtained to the forages, according to the equation RD = a+bc/(c+k). Intestinal digestion of escape feeds was estimated using the feed residues that resisted rumen degradation during 16 hours. For comparative purposes, the total tract digestion was also calculated based on the actual rumen degradation of forages during 16 hours rumen incubation. The effect of dietary interaction on the digestion of forages was assessed. Rumen degradation values obtained by 16 hours incubation did not provide sufficient basis to estimate reliably the total tract digestion by the combined bag method. Using calculated RD total tract digestion of OM of hay and grass silage were rather close to conventional in vivo digestion coefficient of respective feeds similar in chemical composition, when barley was not included in the diet. With hay, but not with grass silage, barley always markedly reduced the rumen degradation and total digestion of OM. Barley supplementation always increased the proportion of feed digested in the intestine. Nitrogen digestion was always higher with grass silage than with hay, and the combined bag method produced N digestion values 17.6-22.0%-units higher than those in the feed table. Barley supplementation did not affect the N digestion of the forages.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed2005

Influence of type and amount of straw cover on weed emergence.

This research was undertaken during 2003-2004 growing season to evaluate the effects of type [forage sorghum "hybrid Cober Exp" (Sorghum bicolor x Sorghum sudanense), forage millet (Pennisetum americanum "var. BN2"), finger millet (Eleusine coracana), and St Lucia grass (Brachiaria brizantha)] and amount of straw cover (5.5 and 3.0 t ha(-1)) upon the emergence of Bidens pilosa, Chamaesyce spp., Amaranthus spp., and Commelina benghalensis, under field conditions of the Brazilian Cerrado, in the region of Uberlândia--MG. The control consisted additional treatment lacking the straw cover. Emergence of weed depended on the type and amount of straw cover, as well as the weed species. The lowest number of B. pilosa seedlings was found in the presence of forage sorghum straw; Chamaesyce spp. in the lack of straw; Amaranthus spp. in the presence of higher amount of forage sorghum and forage millet, and lower amounts of forage millet and Finger Millet. All the types and amounts of straw reduced the emergency of C. benghalensis, except at the lowest level of St Lucia grass and the lack of straw.

Agriculture↗
PubMedDate not supplied

The ponerine ant Pachycondyla (=Ophthalmopone) berthoudi Forel carries loads economically.

The energy cost of running and carrying a load were measured in the termitophagus ponerine ant Pachycondyla (=Ophthalmopone) berthoudi. This ant species uses the individual foraging method in which there is no cooperation between the foragers in the search for or retrieval of prey items. The foragers also transport workers and brood between the nests of the polydomous colony. Pachycondyla berthoudi foragers ran voluntarily in a running tube respirometer at 25 degrees C. Some of the foragers ran in the running tube carrying their termite load, which enabled the metabolic costs of carrying immobilized prey to be determined. This included the costs of maintaining the prey in the mandibles and of stabilization during running. The minimum cost of unladen running was 165.9 J kg-1 m-1, while that of laden running was 136.1 J kg-1 m-1. The mass used to calculate the cost of laden running included body mass of ant and mass of load carried. Pachycondyla berthoudi foragers carry their loads very cheaply. Load carriage costs were calculated to be about 40% as much as body carriage per unit mass, which is the lowest yet found for ants. Low cost of load carriage could have been selected for in P. berthoudi due to its life history.

Animals↗
PubMed2004

Nine-spined sticklebacks exploit the most reliable source when public and private information conflict.

Social foragers can potentially use private information gained from personal experience and public information gained from observing the foraging success of others to determine the profitability of a foraging patch. We investigated how nine-spined sticklebacks use conflicting public and private information of variable reliability to make foraging decisions. In a first experiment, when private information was reliable, sticklebacks ignored public information and based their foraging decision on private information. However, when private information was less reliable, sticklebacks tended to use public rather than private information. A second experiment investigated how the time since experiencing private information affected sticklebacks' use of this information when it conflicted with recent public information. Fish based their foraging decisions on recently acquired private information, but reliance on private information diminished as the period since experiencing it increased. Fish used public information if 7 days had elapsed since updating their private information. Our findings suggest that nine-spined sticklebacks flexibly adjust their decision making to exploit the most reliable information available, be it public or private, and that animals will weight private and public information appropriately depending on circumstances.

Animals↗
PubMed2006

Phylogenetic and ecological determinants of the neotropical dawn chorus.

The concentration of avian song at first light (i.e. the dawn chorus) is widely appreciated, but has an enigmatic functional significance. One widely accepted explanation is that birds are active at dawn, but light levels are not yet adequate for foraging. In forest communities, the onset to singing should thus be predictable from the species' foraging strata, which is ultimately related to ambient light level. To test this, we collected data from a tropical forest of Ecuador involving 57 species from 27 families of birds. Time of first song was a repeatable, species-specific trait, and the majority of resident birds, including non-passerines, sang in the dawn chorus. For passerine birds, foraging height was the best predictor of time of first song, with canopy birds singing earlier than birds foraging closer to the forest floor. A weak and opposite result was observed for non-passerines. For passerine birds, eye size also predicted time of first song, with larger eyed birds singing earlier, after controlling for body mass, taxonomic group and foraging height. This is the first comparative study of the dawn chorus in the Neotropics, and it provides the first evidence for foraging strata as the primary determinant of scheduling participation in the dawn chorus of birds.

Animals↗
PubMed2002

Managing uncertainty: information and insurance under the risk of starvation.

In an uncertain world, animals face both unexpected opportunities and danger. Such outcomes can select for two potential strategies: collecting information to reduce uncertainty, or insuring against it. We investigate the relative value of information and insurance (energy reserves) under starvation risk by offering model foragers a choice between constant and varying food sources over finite foraging bouts. We show that sampling the variable option (choosing it when it is not expected to be good) should decline both with lower reserves and late in foraging bouts; in order to be able to reap the reduction in uncertainty associated with exploiting a variable resource effectively, foragers must be able to afford and compensate for an initial increase in the risk of an energetic shortfall associated with choosing the option when it is bad. Consequently, expected exploitation of the varying option increases as it becomes less variable, and when the overall risk of energetic shortfall is reduced. In addition, little activity on the variable alternative is expected until reserves are built up early in a foraging bout. This indicates that gathering information is a luxury while insurance is a necessity, at least when foraging on stochastic and variable food under the risk of starvation.

Animals↗
PubMed2000

Generating probabilistic spatially-explicit individual and population exposure estimates for ecological risk assessments.

Exposure to chemical contaminants in various media must be estimated when performing ecological risk assessments. Exposure estimates are often based on the 95th-percentile upper confidence limit on the mean concentration of all samples, calculated without regard to critical ecological and spatial information about the relative relationship of receptors, their habitats, and contaminants. This practice produces exposure estimates that are potentially unrepresentative of the ecology of the receptor. This article proposes a habitat area and quality-conditioned exposure estimator, E[HQ], that requires consideration of these relationships. It describes a spatially explicit ecological exposure model to facilitate calculation of E[HQ]. The model provides (1) a flexible platform for investigating the effect of changes in habitat area, habitat quality, foraging area, and population size on exposure estimates, and (2) a tool for calculating E[HQ] for use in actual risk assessments. The inner loop of a Visual Basic program randomly walks a receptor over a multicelled landscape--each cell of which contains values for cell area, habitat area, habitat quality, and concentration--accumulating an exposure estimate until the total area foraged is less than or equal to a given foraging area. An outer loop then steps through foraging areas of increasing size. This program is iterated by Monte Carlo software, with the number of iterations representing the population size. Results indicate that (1) any single estimator may over- or underestimate exposure, depending on foraging strategy and spatial relationships of habitat and contamination, and (2) changes in exposure estimates in response to changes in foraging and habitat area are not linear.

Animals↗
PubMed2007

Prior knowledge about spatial pattern affects patch assessment rather than movement between patches in tactile-feeding mallard.

1. Heterogeneity in food abundance allows a forager to concentrate foraging effort in patches that are rich in food. This might be problematic when food is cryptic, as the content of patches is unknown prior to foraging. In such case knowledge about the spatial pattern in the distribution of food might be beneficial as this enables a forager to estimate the content of surrounding patches. A forager can benefit from this pre-harvest information about the food distribution by regulating time in patches and/or movement between patches. 2. We conducted an experiment with mallard Anas platyrhynchos foraging in environments with random, regular, and clumped spatial configurations of full and empty patches. An assessment model was used to predict the time in patches for different spatial distributions, in which a mallard is predicted to remain in a patch until its potential intake rate drops to the average intake rate that can be achieved in the environment. A movement model was used to predict lengths of interpatch movements for different spatial distributions, in which a mallard is predicted to travel to the patch where it expects the highest intake rate. 3. Consistent with predictions, in the clumped distribution mallard spent less time in an empty patch when the previously visited neighbouring patch had been empty than when it had been full. This effect was not observed for the random distribution. This shows that mallard use pre-harvest information on spatial pattern to improve patch assessment. Patch assessment could not be evaluated for the regular distribution. 4. Movements that started in an empty patch were longer than movements that started in a full patch. Contrary to model predictions this effect was observed for all spatial distributions, rather than for the clumped distribution only. In this experiment mallard did not regulate movement in relation to pattern. 5. An explanation for the result that pre-harvest information on spatial pattern affected patch assessment rather than movement is that mallard move to the nearest patch where the expected intake rate is higher than the critical value, rather than to the patch where the highest intake rate is expected.

Animals↗
PubMed2006

Evidence that blue petrel, Halobaena caerulea, fledglings can detect and orient to dimethyl sulfide.

Procellariiform seabirds (the petrels, albatrosses and shearwaters) are recognized for their acute sense of smell. These pelagic seabirds forage over thousands of miles of ocean to find patchily distributed prey resources. Over the past decade, much headway has been made in unravelling the variety of olfactory foraging strategies that Antarctic species employ, and it is becoming clearer that olfaction plays a key role in foraging, particularly for burrow nesting species. Now we are beginning to explore how these behaviours develop in chicks. Procellariiform chicks fledge and survive the open seas without aid or instruction from a parent, but how they are able to accomplish this task is unknown. Here we explore whether chicks leave the nest pre-tuned to olfactory cues necessary for foraging. In this study, we tested the hypothesis that blue petrel chicks (Halobaena caerulea) are able to detect and orient to a foraging cue (dimethyl sulphide, DMS) used by adults without ever having experienced this odour at sea. We first established that chicks could detect DMS at a biologically relevant concentration that they will later naturally encounter at sea (<10 pmol l-1). We then performed preference tests in a Y-maze on a group of birds 1-6 days before they fledged. Sixteen out of 20 fledglings preferred DMS (e.g. DMS+propylene glycol) to a ;control' odour (propylene glycol alone). Our results suggest that chicks can detect and may already recognize DMS as an orientation cue even before they leave the nest to forage for the first time.

Animals↗