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Determining herbage intake is pivotal for studies on grazing ecology. Direct observation of animals allows describing the interactions of animals with the pastoral environment along the complex grazing process. The objectives of the study were to evaluate the reliability of the continuous bite monitoring (CBM) method in determining herbage intake in grazing sheep compared to the standard double‐weighing technique method during 45‐min feeding bouts; evaluate the degree of agreement between the two techniques; and to test the effect of different potential sources of variation on the reliability of the CBM. The CBM method has been used to describe the intake behavior of grazing herbivores. In this study, we evaluated a new approach to this method, that is, whether it is a good proxy for determining the intake of grazing animals. Three experiments with grazing sheep were carried out in which we tested for different sources of variations, such as the number of observers, level of detail of bite coding grid, forage species, forage allowance, sward surface height heterogeneity, experiment site, and animal weight, to determine the short‐term intake rate (45 min). Observer (Pexp1 = 0.018, Pexp2 = 0.078, and Pexp3 = 0.006), sward surface height (Pexp2, We showed an agreement between the Continuous bite Monitoring method and Double‐Weighing Technique method; Continuous Bite Monitoring method is a good proxy for determining the intake of grazing animals; Direct observation is not invasive nor disrupts natural animal behavior.

A feeding experiment was carried out to determine the effects of different proportions of alfalfa hay and maize stover on the growth performance and carcass characteristics of fattening lambs. Forty-two healthy 3.5-month-old male Small-tail Han lambs of 23.89 ± 0.38 kg body mass were assigned to seven groups, which were fed mixed diets composed of maize stover and alfalfa hay containing 0%, 30%, 40%, 50%, 60%, 70% or 100% maize stover on a dry matter (DM) basis. Each lamb received 1.5 kg DM of forage mixture three times daily and supplementary concentrate (0.5 kg corn per lamb per day) for 60 days. Compared with the control forage diet of maize stover only, forage intake rate and forage conversion rate on the 40% maize stover/60% alfalfa hay mixture were 30% and 5% higher, respectively. Body weight, dressing percentage and net income were 6.7 kg, 8% and 94.37 Yuan higher per lamb, respectively. Thus, feeding lambs with a forage mixture of maize stover and alfalfa hay in a ratio of 40:60 optimized the production performance, slaughter performance, and the income derived from lambs.

Annual temperate grasses go through abrupt changes in morphological composition during the growing season, which can affect ingestive behavior of grazing cattle. However, few studies have examined the effects of gradual structural changes in annual temperate pastures on the herbage intake rate during the growing season. We hypothesized that lenient grazing (removal of 40% of the initial pre-grazing height) maintains short-term intake rate (STIR) of grazing cattle over the entire growing season, even with decreased leaf/stem ratios. The studied pastures contained Avena strigosa, Lolium multiflorum and a mixture of the two species. Short-term intake rate was measured using the double weighing technique, evaluating both bite rate and bite mass. The percentage of stem + pseudostem and leaf lamina lengths in the herbage mass were measured. Relationships between sward structure and animal ingestive behavior were also examined. As the pasture growing season progressed, the STIR of heifers grazing annual temperate grass swards was affected more by the time required to take a bite than by bite mass. Moreover, the sward structure also changed after each grazing cycle, reducing the pre-grazing leaf/stem ratio. However, reductions in the pre-grazing leaf lamina mass (up to 37% of the sward herbage mass) and/or in the leaf lamina length (up to 52% of the extended tiller height) did not affect the STIR of grazing heifers, since the animals maintained their bite mass and time per bite. In summary, with a grazing down target of 40% of the pre-grazing height, reductions in STIR of heifers grazing annual temperate grasses occurred when the pre-grazing leaf lamina percentage was

The history of the idea that predation rates are functions of the ratio of prey density to predator density, known as ratio dependence, is reviewed and updated. When the term was introduced in 1989, it was already known that higher predator abundance often reduced an individual predator's average intake rate of prey. However, the idea that this effect was a universally applicable inverse proportionality was new. That idea was widely criticized in many articles in the early 1990s, and many of these criticisms have never been addressed. Nevertheless, ratio dependence seems to be gaining in popularity and is the subject of a recent monograph by the originators. This article revisits the most important objections to this theory, and assesses to what extent they have been answered by the theory's proponents. In this process, several new objections are raised. The counterarguments begin with the lack of a plausible, generally applicable mechanism that could produce ratio dependence. They include the fact that ratio dependence is a special case of predator-density effects, which, in turn, are only one of many non-prey species effects that influence the consumption rate of a particular prey. The proclaimed simplicity advantage of ratio dependence is at best small and is outweighed by its disadvantages; it predicts biologically implausible phenomena, and cannot easily be extended to describe multi-species systems, trait-mediated interactions, coevolution, and a number of other important ecological phenomena. Any potential small simplicity advantage disappears with corrections to remove unrealistic low-density dynamics caused by ratio dependence. The frequent occurrence of strong predator dependence does not make ratio dependence a better ‘default’ model of predation than prey dependence, and empirical studies of the full range of non-prey species effects on the consumption rates of predators are needed.

Aim To examine the effects of “Comfort upon Rising” care (CUR) as a new type of early morning care. Methods This was a quasi-experimental study using a convenience sampling and non-random assignment of 80 orthopedic postoperative inpatients needing ambulation assistance. The intervention group of 40 inpatients was given CUR designed to support the patients' needs. The control group of 40 inpatients was given conventional early morning care (CMC). Floor nurses conducted either CMC or CUR for subjects beginning the morning after surgery and continuing for 3 days. Mood was measured by the Wake-up Questionnaire (question I) and Profile of Mood States (POMS). Morning activities, which were daily living activities, breakfast behaviors including breakfast intake rate, were measured by Wake-up Questionnaire (question IV) and observation. Results Completing the study were 36 patients from the control group and 36 patients from the intervention group. Mood and activities in the morning were improved in the CUR group. Conclusion CUR is a patient-centered care based on patients' individual needs and promotes self-care. CUR is more effective than CMC in promoting natural recovery after an operation.

We studied movements and conflicts within a small flock of free-living black-tailed godwits foraging on benthic invertebrates in a brackish lagoon. To interpret our results in the framework of foraging theory, we studied the influence of individual feeding rate on the decisions to move and to attack flock companions. Birds changed their position within the flock more often when their intake rate was low and sometimes attacked conspecifics to supplant them from their feeding place. Aggressors significantly avoided front attacks and were almost always successful. They attacked individuals having higher feeding rates than themselves and their own feeding rate significantly increased after the attack, although victims were not chased off to particularly poor sites. Our results suggest that aggressors could obtain reliable information about the quality of the foraging site they coveted by observing their victim’s feeding activity before attacking. Although aggression seemed to be caused by a low intake rate, we show that displacing another bird was more time-consuming than independent foraging. We conclude that it was not the most profitable behaviour in terms of energy intake. Foraging site displacement probably also had social functions, such as reinforcement of social status in a flock of birds preparing for pre-breeding migration.

1. Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2. Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3. The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4. These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5. Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6. These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7. The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models.

Numerous studies have shown that juvenile birds obtain food at a slower rate than do adults (Norton-Griffiths 1968, Recher & Recher 1969, Orians 1969, Dunn 1972, Davies& Green 1976, Groves 1978), We compared the foraging behaviour of adult and juvenile Moorhens Gallinula chloropus and tried to assess the relative importance of different components of feeding in determining the intake rate.

The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile-resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m(-2)) and two ages of cattle (1- and 3-year-old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf-only swards, mature cattle achieved a much greater BA (106.5 vs. 57.9 cm(2)), BM (0.88 vs. 0.47 g DM) and IIR (46.9 vs. 17.2 g DM min(-1)) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile-resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.

Food intake is difficult to estimate under natural conditions. We investigated ingestion rates of 14 different food types in 26 captive capuchin monkeys (Cebus apella). The procedure consisted in weighing a piece of food and using a two alternative choice tests to present food to the subject, alone in its cage. We recorded the food chosen and the time it took the subject to consume the food entirely. Consumption time was converted into ingestion rates (g/s) for each food type. Ingestion rates of food types significantly differed, and the difference was significantly higher among foods than among subjects. In particular, ingestion rates of the fruits were higher than those of human-processed food. Interestingly, food preferences were significantly related to energy intake rate, i.e., to the amount of energy ingested per unit of time, but not with ingestion rates or energy content alone. The energy acquired by eating different types of food cannot be calculated on the basis of the time spent eating unless a correction factor for each given food (or similar ones) is applied. Future controlled studies should provide field researchers with such corrections factors, possibly using foods collected in the wild. Am. J. Primatol. 70:510–513, 2008. © 2008 Wiley-Liss, Inc.

Organisms respond to their heterogeneous environment in complex ways at many temporal and spatial scales. Here, I examine how the smallest scale process in foraging by mammalian herbivores, taking a bite, influences plants and herbivores over larger scales. First, because cropping bites competes with chewing them, bite size influences short-term intake rate of herbivores within plant patches. On the other hand, herbivores can chew bites while searching for new ones, thus influencing the time spent vigilant and intake rate as animals move among food patches. Therefore, bite size affects how much time herbivores must spend foraging each day. Because acquiring energy is necessary for fitness, herbivores recognize the importance of bite size and select bites, patches and diets based on tradeoffs between harvesting rates, digestion, and sheering forces. In turn, induced structural defenses of plants, such as thorns, allow plants to respond immediately to herbivory by reducing bite size and thus tissue loss. Over evolutionary time, herbivores have adapted mouth morphology that allows them to maximize bite size on their primary forage plant, whereas plants faced with large mammalian herbivores have adapted structures such as divarication that minimize bite size and protect themselves from herbivory. Finally, bite size available among plant communities can drive habitat segregation and migration of larger herbivores across landscapes.

The impact of manipulating ruminal fill (RF) on intake rate of herbage and grazing dynamics was measured with three rumen-cannulated beef heifers grazing Bermudagrass pastures individually. The treatments compared were removal of proportions of rumen contents of 0 (treatment RF0), 0·33 (treatment RF33), 0·66 (treatment RF66) and 1·00 (treatment RF100). Treatments were randomly applied in a 3 x 4 Youden-square design. The rumens were emptied before and after planned grazing sessions (30 min) to set up the treatments, and to estimate intake rate and bite mass, respectively. Measurements were made of bite rate, bites per feeding station, feeding stations per minute, intake per feeding station, time per feeding station, eating and searching step rates and times. Apparent bite area and area grazed per feeding station were calculated. Ruminal fill affected short-term intake rate and changed grazing dynamics. As RF increased, step rates, searching times, bite mass, apparent bite area, bites per feeding station, area grazed per feeding station, time per feeding station and intake per feeding station decreased (P < 0·01) while step times, eating step rates and bite depth increased (P < 0·01). The results of the present study indicate that RF is an important factor governing the intake characteristics and behaviour of grazing beef heifers.

We present a novel technique using a video serial interface to link a motion-activated, infrared video camera and a weigh-scale to measure supplemental feed consumption by wildlife. This “video-scale” allows us to quantify consumption of various feeds by individual animals to an accuracy of 5 g and to record feeding duration to the second. Using intake rate and total time spent feeding, we calculated comparative use of supplemental feed by animals categorized by species, age, and sex. We present preliminary data on feed consumption and intake rates of wild and tame white-tailed deer (Odocoileus virginianus) and raccoons (Procyon lotor) eating shelled corn, pelleted supplement, and whole cottonseed. Other uses and limitations of the video-scale are discussed.

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type 11 ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81 % of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3 %), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93 % of cases.We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested.As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.

in reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems' barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20-cm leaves and 15-cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m(-2)) and two levels of stem tensile resistance [low (LTRS) and high tensile-resisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13.4, 13.6 and 5.1 cut for 0, 100 and 400 stems m(-2), respectively), bite area (89.3, 50.8 and 47.6 cm(2) for 0, 100 and 400 stems M-2, respectively), bite mass (0.51, 0.29 and 0.11 g for 0, 100 and 400 stems m(-2), respectively) and IIR (23.8, 10.5 and 3.6 g sec(-2) for 0, 100 and 400 Stems m(-2), respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems' barrier effect on bite dimensions and IIR.

The distance that mammalian herbivores can travel without interrupting food processing corresponds to a distance threshold (d*) in plant spacing where change occurs in the mechanisms regulating the functional response. The instantaneous rate of food consumption is controlled by food encounter rate when plant spacing exceeds d*. Below this threshold, food processing in the mouth controls instantaneous intake rate. The distance threshold provides a mechanistic definition of the scale of heterogeneity of the food resource. Recent work indicates that d* should scale positively with the body mass of mammalian herbivores. Here I evaluated the empirical evidence for this positive scaling by investigating (1) herbivores consuming only alfalfa (Medicago sativa), (2) grazers, and (3) herbivores consuming any kind of vegetation. Overall, I found greater evidence for a negative than for a positive scaling of d*. Out of the three groups, only herbivores consuming alfalfa could yield a positive covariation between d* and body mass. However, even this positive scaling became negative when herbivores consumed bites of alfalfa that were only a fraction of their maximum size. Finally, d* also scaled negatively among herbivores foraging in similar food patches. Overall, differences in foraging decisions among mammalian herbivores seem more likely to have been shaped by a negative than a positive scaling of d*.

The question of how much time a foraging herbivore should spend in a patch of food poses a central challenge in classical foraging theory. However, there remains uncertainty about the relevance of the patch paradigm to foraging decisions by large herbivores. This paper examines evidence for successfully predicting and quantifying patch departure decisions for large mammalian herbivores foraging across several spatial and temporal scales. Departure decisions at fine scales are influenced by tradeoffs between maximizing intake rate and food quality. Classical models for departure decisions at larger spatial scales, particularly the marginal value theorem, appear inadequate. We advocate exploring alternative models for predictions of residence time at the patch scale.

1. Rate-maximizing foragers that only divide their time between searching and handling prey should, according to the classical contingency model (CM), only select those prey whose energy content per unit handling time (i.e. profitability) exceeds or equals long-term average energy intake rate.2. However, if digestively constrained foragers were to follow this so-called 'zero-one rule', they would need to take digestive breaks and their energy intake over total time would not be maximized. They should, according to the digestive rate model (DRM), also consider the rate at which a prey type is digested (i.e. digestive quality), such that time lost to digestive breaks is minimized.3. In three different contexts, we tested these competing models in a mollusc-eating shorebird, the red knot (Calidris canutus), that is often digestively constrained due to its habit of ingesting its bulky prey whole. Measurements on gizzard size (using ultrasonography) and prey-characteristics confirmed that in each test the birds were digestively bottlenecked and should thus follow the DRM in order to maximize long-term energy intake.4. In the first experiment, knots were offered a choice between two fully exposed prey, and tended to select prey by the criterion of digestive quality rather than profitability.5. In the second experiment, knots were offered two buried prey types and preferred the highest quality prey to the most profitable prey.6. In the wild, knots mainly fed on high quality Mya and largely ignored poor quality, but equally profitable, Cerastoderma.7. Thus, each test verified the predictions of the DRM and rejected those of the CM. Given that many species face digestion constraints, we expect that the DRM is likely to explain diet composition in many more studies.

The effects of genotypic variation in ryegrasses on sward structure, bite dimensions and intake rate by dairy cows were investigated. Two experiments were conducted. In Experiment 1, swards were in a vegetative state whereas, in Experiment 2, they were partly reproductive and were taller with higher herbage mass but lower leaf proportion than in Experiment 1. Applicability of relationships between sward structure and bite characteristics, previously established from artificial or hand-constructed swards, to field conditions were tested. Additional short-term intake rates and/or sward structural characteristics were considered as indicators of potential intake for use in protocols for the evaluation of grass varieties. Four cultivars were studied: AberElan, Twins (diploid and tetraploid perennial ryegrasses respectively), Polly, a hybrid ryegrass (perennial × Italian ryegrass) and Multimo (Italian ryegrass), each established in 200-m2 plots in four replicated blocks. Herbage intake rate was determined by short-term liveweight change (taking account of insensible weight loss) using 16 dairy cows allocated to four balanced groups with each plot grazed by one group for a 1-h assessment period. One block was grazed per day, over a 4-d experimental period, with each group grazing each variety in a complete crossover design. Sward characteristics and bite rate were also measured in both experiments. Bite dimensions were subsequently estimated, with bite depth being determined as a function of extended tiller height (ETH) in both experiments. Within both experiments, bite mass and intake rate did not differ significantly between swards of different cultivars despite swards containing Multimo generally having a higher ETH and water-soluble carbohydrate concentration and lower green leaf mass, sward bulk density and neutral-detergent fibre concentration than the other swards. However, bite depth was significantly higher (P

To allow improved prediction of daily herbage intake of dairy cows in rotational grazing systems, intake behaviour was assessed throughout the day in 24-h paddocks. Herbage intake in 16 lactating Holstein–Friesian cows was assessed using the short-term (1-h) weight gain method at four predetermined natural meal times throughout the day (early morning, T1; late morning, T2; mid-afternoon, T3; and early evening, T4). The study comprised two 4-day experiments, each with a cross-over design of four blocks. In both experiments, cows grazed a 24-h paddock daily, and the effect of the immediately previous grazing experience on intake behaviour was investigated throughout the day, taking account of daily fluctuations in the short-term physiological condition of the cows. Experiment 1 was carried out to investigate overall grazing behaviour during meals as a sward is progressively depleted during the day, with intake being assessed within the paddock and, hence, on a depleted sward. Experiment 2 similarly investigated the effect of sward depletion and physiological condition throughout the day on intake, but cows were removed to fresh, undefoliated swards during intake measurement periods; thus, intake rate was not influenced by differences in sward condition. Intake behaviour from both experiments was compared to establish the effect on herbage intake of changes in sward state and non-sward factors. In Experiment 1, sward surface height, available herbage mass, proportion of leaf and green leaf mass declined as the day progressed. Bite mass declined with sward depletion, and mean intake rate was 1·64 kg dry matter (DM) h–1, which was significantly lower at T3 (P

Non-pregnant, non-lactating ewes grazed adjacent monocultures of white clover and perennial ryegrass with three sward surface height (SSH) combinations [6 cm white clover: 6 cm perennial ryegrass (c6g6), 3 cm white clover: 6 cm perennial ryegrass (c3g6), 3 cm white clover: 9 cm perennial ryegrass (c3g9)] at two stocking densities (21·3 or 29·8 ewes ha–1). Immediately prior to the experiment, all ewes grazed a c6g6 sward. Grazing time on each plant species was recorded during daylight over two 48 h-test periods. Subsequently, herbage intake rates for each species at each SSH were measured allowing intakes of each species to be calculated. For the first 24 h of both test periods (D1), ewes on treatment c3g6 spent less time grazing white clover than those on treatment c6g6 (228 vs. 362 min) and more time grazing perennial ryegrass (360 vs. 182 min). Total grazing time on treatment c3g6 was more than on treatment c6g6 (587 vs. 544 min) but the difference was not significant. Perennial ryegrass intake was higher (895 vs. 452 g), and white clover intake (814 vs. 1687 g), total intake (1719 vs. 2140 g) and proportion of white clover in the diet (0·460 vs. 0·794) were lower for treatment c3g6 than treatment c6g6. There were no significant differences in total grazing time, grazing time on either species, proportion of grazing time on white clover or proportion of white clover in the diet between treatment c3g6 and treatment c3g9. However, the higher intake rate of perennial ryegrass in treatment c3g9 led to higher perennial ryegrass and total intakes. For the second 24 h of both test periods (D2), ewes on treatment c3g6 again spent more time grazing perennial ryegrass than on treatment c6g6 (270 vs. 161 min) but time spent grazing white clover was similar (318 vs. 308 min). Total grazing time was significantly higher on treatment c3g6 than on treatment c6g6 (588 vs. 469 min) but proportion of grazing time on white clover was similar (0·554 vs. 0·668). Perennial ryegrass intake was significantly higher for treatment c3g6 than for treatment c6g6 (672 vs. 402 g) while white clover intake was significantly lower (1140 vs. 1435 g) but total intake was similar (1812 vs. 1836 g). The proportion of white clover in the diet was significantly lower for treatment c3g6 (0.628 vs. 0.785) than for treatment c6g6. The only significant differences between treatments c3g6 and c3g9 were in perennial ryegrass intake (672 vs. 906 g) and in total intake (1812 vs. 2287 g). Intake of perennial ryegrass on treatment c3g9 was also significantly greater than on treatment c6g6 (906 vs. 402 g) and total intake was higher (2287 vs. 1836 g). At the higher stocking density, time spent grazing perennial ryegrass and perennial ryegrass intake were significantly lower on D1 and D2 while total grazing time was also significantly lower and proportion of time grazing white clover and proportion of white clover in the diet were significantly higher at the higher stocking rate on D2. The results indicate that behaviour changed over the 48 h observation period for treatments c3g6 and c3g9 but behaviour remained relatively constant for animals on treatment c6g6. Ewes traded off dietary preference against total intake by altering grazing times on perennial ryegrass and white clover to achieve maximum net benefit.

Summary 1. The effect of predation risk on the distribution of animals foraging in a patchy environment was explored using a simulation model based on the work of Bernstein, Kacelnik & Krebs (1988, 1991), extended to incorporate predation risk. 2. Modelled foragers consume prey within patches, having different prey densities, at a rate that depends only on prey density and interference from other foragers in the patch. Prey density remains constant (no depletion). A forager leaves a patch if its intake rate drops below its estimate of the average intake rate available in the environment. This estimate is continually updated by taking a weighted average of current intake and the previous estimate, giving a simple learning process. Decisions on whether to leave are made at regular intervals and a forager leaving a patch may arrive at random at any other patch. 3. Simulation results were sensitive to the computational scheme used to represent estimates of average intake rate in the environment and to the way in which foragers’ decisions were distributed over time, illustrating the need for careful formulation of such models. 4. Predation risk was modelled as a cost that reduced effective intake, and could be distributed uniformly or skewed to patches of high prey density. The effects of different levels and distributions of predation risk on distribution of foragers were examined using model parameters broadly appropriate to hedgehogs (Erinaceous europaeus L.) foraging for earthworms (Lumbricus spp.) and risking opportunistic predation by badgers (Meles meles L.). The distribution of foragers with respect to prey density took an ‘ideal free’ form for zero or uniform risk, and was domed when cost of predation risk was relatively high and concentrated in the richer patches, as might be the case when predators and foragers share a common food resource.

When a three-spined stickleback Gasterosteus aculeatus encountered prey simultaneously the probability of hanging and the median pursuit time were greater than when prey were encountered sequentially. During simultaneous prey encounter fish did not choose to attack the more profitable prey but instead the nearer prey was handled first except when the difference between the two prey sizes was large. No difference was found in the level of total energetic intake by the fish regardless of prey size pairing. Fish that handled and ate the first prey of a pair in

The mechanisms of diet choice by herbivores are poorly understood. We tested whether the preference of goats among five grass species was accounted for by differences in intake rate or differences in species-specific attributes of the grasses. When offered a choice between grass species, the goats selected diets that tended to maximize intake rate. Only a small amount of the residual variation was explained by the individual preference of goats for each grass species. The animals exhibited partial preferences, only leaving the lower intake-rate alternative ungrazed in a quarter of the trials. It is argued that the most likely explanation of this is the difficulty of discriminating between alternatives of similar intake rate. Discrimination error is likely to be a general explanation of mixed diets in herbivores, regardless of whether other explanations, such as rate maximization subject to nutrient constraints, also apply.

An experiment was conducted to examine the effect of time of day on the rate of intake of herbage by grazing dairy cows. Eight unsupplemented Holstein Friesian cows in their fourth month of lactation grazed grass swards maintained at a sward surface height of 6·5 cm. Commencing at 07.00, 11.30, 16.00 and 19.00 h, intake rates were estimated by measuring the liveweight change, corrected for insensible weight loss, over a period of 1 h while grazing. During the period of grazing, recordings of jaw movement activity were made to determine total eating time, number of grazing jaw movements (GJMs) and bites. Total eating time over 24 h was measured: once before and once after determination of intake rate. Although time of day did not affect GJM rate, it had a quadratic effect on the proportion of GJMs represented by biting and non-biting jaw movements, resulting in a significant effect on bite rate. Bite rate showed a quadratic effect of time, decreasing between 07.00 and 11.30 h, and then increasing by 16.00 h to reach a maximum at 19.00 h (52·6, 47·5, 51·6 and 59·4 bites min−1 respectively). Bite mass (mg fresh matter bite−1) was greatest at 07.00 h because of the lower dry-matter (DM) content of the herbage and the presence of surface moisture at that time, but the effect of time of day was not significant. Mean bite mass measured as DM or organic matter (OM) differed significantly between the different times of day (332, 384, 481 and 402 mg DM and 302, 348, 438 and 367 mg OM bite−1 respectively). The net result of these differences in bite rate and bite mass was a linear increase in DM and OM intake rate over the day. The magnitude of such differences will have profound effects on mean daily intakes when calculated as the product of total eating time and intake rate.

Foraging efficiencies of bushbuck (Tragelaphus scriptus Pallas) and boergoats (Capra hircus Linnaeus) were evaluated in terms of browse intake rates attained when foraging from a selection of Valley Bushveld plants. Intake rates were calculated as the product of bite size and bite rate. Boergoats were capable of greater bite sizes and bite rates and were therefore more efficient foragers in terms of intake rates. Intake rates increased with increasing bite size and conformed to an asymptotic relationship, while bite rates declined with increasing bite sizes. Plant spinescence and fibre content influenced the intake rates of both species.

Bears consuming wild fruits for fall energy accumulation are constrained by several factors, including intake rate, the physiological capacity of the gastrointestinal tract, and the metabolic efficiency of gain in body mass. We measured these relationships through foraging and feeding trials using captive and wild black bears (Ursus americanus) and grizzly bears (Ursus arctos). Four fruit types covering a range of sizes and clustering were offered to captive bears to determine the effect of density, size, and presentation on intake rate. Intake rate (in grams per minute) and bite rates (in bites per minute) increased cur- vilinearly with increasing fruit density in singly spaced fruits. Maximum intakes ranged from 30 g/min for 0.5-g berries to >200 g/min for 4.2-g fruits. The highest bite rates were obtained during the initial encounter with each patch as bears consumed all visually apparent fruits on the surface. Bite rates quickly dropped by 15-20% as foraging continued within the patch. Maximum bite rates were not depressed until initial fruit density fell to 100 kg. We concluded that large bears, such as grizzlies, must depend on plants that permit large bite sizes or high bite rates through fruit clustering and bush configuration that reduce leaf-to-fruit ratios.

The ability to increase energy storage when food is abundant for later use during late gestation and early lactation is often considered the primary benefit of the capital breeding strategy (clustering conceptions during high food periods, HFP) that promotes reproductive success among females living in unpredictable environments. Capital breeding, however, may also enable preconceptive females to increase hormone production for ovulation, which has been linked to energetic condition in capital breeders, and/or allow females entering the subsequent HFP to increase their energetic condition in order to continue nursing unweaned infants. Here, we investigate whether capital breeding provides these additional benefits in 16 female Sanje mangabeys (Cercocebus sanjei) and determine the dietary strategies used to increase energetic condition (measured by urinary C-peptide: UCP) during the HFP. Fecal estradiol (fE2) and UCP were negatively correlated with number of cycles before conception (r = −0.591, r = −0.646, P

This study used both experimental evidence and a mathematical model to address some differences in interpretation in the literature on the relationship between sward height and the bite dimensions (bite depth, bite area and bite mass) of sheep grazing contrasting vegetation types. Individual non-fasted sheep were released onto small areas (10 × 10m) of white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) and bite dimensions were measured as they grazed across patches (0·7 × 0·7 m) of predetermined sward surface height (SSH). Sward heights were 4, 7, 10, 13 and 16cm for white clover patches and 4, 6, 5, 9, 11·5 and 14cm for ryegrass patches. Four sheep were assigned to each plant species and each sheep grazed one patch of each height (five patches/sheep). Bite depth, bite area and bite mass increased linearly with SSH in both white clover and ryegrass. At a given SSH, bite depth was similar in white clover and ryegrass, but bite area and bite mass were greater in white clover than in ryegrass. The linear relationships observed between bite mass and SSH contrasted with the asymptotic relationships observed in some other studies, but it is suggested that different relationships may arise because of methodological differences between studies. Furthermore, when linear relationships for bite mass were compared with asymptotic relationships for bite mass in a mechanistic model of animals grazing from ryegrass-white clover pastures it was demonstrated that the nature of the relationship had relatively little effect on the relationship between intake rate and SSH. This was because intake rate depended on the fundamental mechanistic relationship between bite mass and prehension bite rate. This relationship meant that the greater bite masses found when linear relationship were assumed were associated with reduced prehension bite rates and thus the effect on intake rate was relatively small. In addition, the predictions of the model regarding the bases of diet selection by animals grazing ryegrass-white clover mixtures were simplified, and stabilized, when linear relationships were assumed.

Performance of three fire zone models BRI2, CCFM.VENTS and CFAST in simulating forced ventilation fires with low heat release and high ventilation rates were studied experimentally. A fire chamber of length 4.0 m, width 3.0 m and height 2.8 m with adjustable ventilation rates was used. Burning tests were carried out with wood cribs and methanol to study the preflashover stage of a compartmental fire and the effect of ventilation. The mass loss rate of fuel, temperature distribution of the compartment and the air intake rate were measured. The beat release rates of the fuel were calculated from the measured mass loss rate. The smoke temperature was used as the validation parameter. A scoring system is proposed to compare the results predicted by the three models. An empirical expression for calculating the smoke temperature is assessed. Lastly, the Computational Fluid Dynamics technique is also used for comparing the simulated fire environment.

A 10-week grazing experiment was conducted on a perennial ryegrass sward with lactating ewes and their twin lambs. Three paddocks were rotationally grazed with rest periods of from 4 to 5 weeks. Sward surface heights at the start of each grazing were 145, 259 and 250mni for treatments RG1, RG2 and RG3. A further four paddocks were maintained by continuous variable stocking (CS) at sward surface heights (SSHs) of about 30, 60, 90 and 120mm. Sward and animal measurements were made on the two different grazing managements as the RG swards were grazed down, giving measurements at similar sward heights for treatments RG and CS. There was less green leaf and the total herbage mass present under RG was less than on CS swards at the same sward heights, demonstrating the differences in structure between rotationally and continuously grazed swards. Regression analysis of animal factors on sward factors showed that grazing behaviour was more highly correlated with green leaf mass than SSH or any of the other sward measurements. On the RG swards, maximum intake per animal was reached at about 1500 kg green leaf mass ha−1. A SSH of 60mm allowed the CS ewes to achieve the highest intake rate, but at this height the ewes on treatments RG2 and RG3 were restricted to approximately half this rate. The results suggest that green leaf mass or leaf area index, rather than sward surface height, could be used as a rational basis to relate intake of herbage to sward state for swards changing rapidly in leaf to stem ratio.

Type II functional responses are frequently observed in herbivores feeding in patches where plants are concentrated in space. We tested a mechanistic model of regulation of intake rate of herbivores foraging in food—concentration patches (Laca and Demment 1992, Spalinger and Hobbs 1992) that accounts for asymptotic, Type II responses. The model is based on the hypothesis that competition between cropping and chewing regulates instataneous intake rate in response to changes in the size of bites obtained by the forager. We tested this hypothesis and examined the ability of our model to account for observations of intake rate of 12 species of mammalian herbivores ranging in body mass over 4 orders of magnitude. We measured short—term intake rates of mammalian herbivores feeding in hand—assembled patches of plants. We varied bite size by changing plant height and density in patches offered to herbivores, and observed dry matter intake rates in response to this variation. Averaged across species, our model acc...

Grazing studies are hampered by difficulty in controlling the characteristics of that part of the sward encountered by animals. A methodology was developed to study the effects of sward height, density and spatial arrangement on bite dimensions, bite weight and instantaneous intake rate by cattle. Hand-constructed swards (HCS) consisted of tillers threaded through wooden modules and attached to a base board. The microphone of a cordless transmitter was attached to the forehead of steers before swards were grazed. HCS were bolted onto a force plate which recorded the forces exerted during grazing. Grazing sessions were videotaped. Height and density of swards were successfully controlled by hand-construction. Bite weight was determined more accurately by dry matter (DM) disappearance than by the reduction of fresh weight corrected for moisture loss and herbage DM content. Bite area and bite depth were precisely measured by counting and measuring the residual height of grazed plant parts. Bites and chews were identified and counted from the soundtrack of video tapes. Visual count of chews was inaccurate because animals can prehend new herbage and chew herbage previously gathered with the same jaw movement. Many jaw movements involve only manipulation of herbage without biting or chewing. Bite dimensions result from the physical interaction of relatively fixed motor patterns, such as tongue sweeps, with vegetation structure. Thus, bite dimensions measured by this technique are relevant to field situations.

The objectives of this study were to contribute to the understanding and quantification of the effect of sward structure on the ingestive behavior and intake of livestock. Hand-constructed swards of approximately 0.43 m 2 were used to determine the bite dimensions, bite weight, and short-term intake rate of steers (Bos taurus L.) grazing short swards. Swards were constructed of leaf blades of Paspalum dilatatum Poir. at homogeneous height of 0.04, 0.06, 0.08, and 0.10 m and heterogeneous heights with means of 0.06 and 0.10 m at two leaf densities (...)

Perennial ryegrass pastures were maintained at sward surface heights (SSH) of 30, 60, 90 and 120 mm by continuous variable stocking using lactating ewes and their twin lambs in spring and non-lactating (dry) ewes in autumn. The effects of SSH on ingestive behaviour, herbage intake, animal performance and sward structure and production were measured in spring, and again in autumn, when an additional SSH of 20 mm was also established. In spring, differences in sward structure were quickly established with mean tiller numbers of 41 000, 30 000, 21 000 and 19 000 m−2 and leaf area indices (LAI) of 1·5, 2·2, 3·3 and 4·1 at SSH of 30 to 120, respectively. By autumn the mean tiller numbers had fallen to 26 000, 26 000, 23 000, 18 000 and 13 000 m−2 and LAI to 1·0, 1·1, 1·5. 2·0 and 1·5 for treatments 20 to 120. The mean stocking rates for the ewes in spring were 27, 20, 22, and 19 ewes ha−1 and growth rates of their lambs were 208, 275, 250 and 263 g d−1 for treatments 30 to 120. In autumn the stocking rates maintained for dry ewes were 22, 15, 9, 4 and 0 for treatments 20 to 120. In spring, both grazing times (GT) and prehension biting rate (BR) were negatively correlated with SSH, while bite mass (BM) was positively correlated with SSH. However, mean daily intakes of organic matter (OM), were reduced only for animals grazing the 30 mm sward. In autumn, intake rate was lower only for the animals grazing the 20mm sward and GT and BR were not significantly affected by SSH. Relationships between SSH and, components of ingestive behaviour and intake, are presented and the control mechanisms involved are discussed. The results showed that the optimum sward surface height for continuously stocked swards, grazed by sheep, Was between 30 mm and 60 mm.

It seems an obvious truism that purely phenomenological models of animal interactions will always compare unfavourably to those based on the actual mechanisms by which individuals interact with each other and their environment. This is a conclusion drawn by van der Meer & Ens (1997) in their comprehensive comparison of model predictions for ideal free predators, and echoed by Weber (1998). We cannot do without phenomenological models, however, since they provide the conceptual framework of key processes, such as density-dependent food intake for 'ideal' and 'free' predators, upon which to model the particular mechanisms, such as food-searching behaviour and time-wasting interactions. Phenomenological models often get a rough ride in the ecological literature because they are matched against mechanistic models as if the two types were alternatives. They accomplish different tasks, with the former type predicting the outcome of underlying processes while the latter distinguishes between alternative mechanisms. It is an incomplete appreciation of this difference that leads van der Meer & Ens (1997) to unfairly criticise the searching rate equation of Hassell & Varley (1969), which is one of the more popular phenomenological models of interference. My intention here is to show how this model can make useful predictions about the exploitation of renewable standing stock, when it is used in an appropriate setting. In common with other authors (e.g. Sutherland 1996), van der Meer & Ens draw on a simple conceptual framework to infer that without interference all ideal free predators will aggregate in the patch or patches with the highest standing stock of prey. This result arises because each predator's intake rate of prey is a function of prey density only, and not predator density if there is no interference between predators. The patches with the highest prey density therefore yield the highest intake for all. Van der Meer & Ens note that 'such strong aggregation is, of course, rather unlikely.' Their conclusion is that ideal free exploitation is insufficient in many cases to explain

A generalized solution to the moisture flow (Richards') equation is developed for infiltration. The equation is expressed in terms of dimensionless time, depth, and water content. The reduced form applies for the hydraulic functions of van Genuchten or of Brooks and Corey as well as to other scaled forms and the solution utilizes the procedure of Philip. Answers are presented in concise tables which, in principle, allow for finding moisture profiles, wetting front, intake rate and cumulative intake for a variety of soils and for varying initial water contents. For application, specifically measured hydraulic conductivities can be best-fitted to the forms used here or generalized empirical values can be used from the literature. Thus, either specific or generic parameters may be used, depending on availability for a given problem.

Four questions relative to suction lysimeter performance have been raised by operators of land treatment systems. These questions deal with plugging of the porous segments of the lysimeters, soil suction operational ranges, adsorption onto and screening by the materials comprising the various lysimeter parts, and loss of volatile organics under negative pressures. This article first describes the physical operation of a lysimeter, the characteristics of the lysimeters tested (high- and low-flow lysimeters with porous ceramic cups and lysimeters with porous PTFE (polytetrafluo-roethylene) cups, and procedures followed in preparing them for testing. The results of experiments dealing with the first two questions plugging and operational ranges are then discussed. It was found that the intake rate of suction lysimeters placed in the vadose zone, in most types of soils, will initially drop off rapidly, but will stabilize after about 15 liters of moisture have been drawn through the porous cups. Packing a crystalline silica flour slurry around the cups of PTFE lysimeters negates most of the plugging associated with finer particles in soils. The effective operating range of ceramic lysimeters is between 0 and 60 centibars of suction independent of the use of silica flour. The operating range of PTFE lysimeters without silica flour is extremely narrow, but with the use of silica flour is extended to about 7 centibars of suction. The testing program indicates that all lysimeters should be checked for leaks using pressure techniques before field installation and that lysimeters have “dead” spaces, or reservoirs of from 34 to 80 mL of moisture that cannot be extracted from the cups, which must be taken into account when determining moisture collection rates. Information gathered in the test program is planned for inclusion in an EPA guidance document entitled “Unsaturated Zone Monitoring at Hazardous Waste Land Treatment Units.”

The potential for artificial ground-water recharge through shallow shafts is being conducted at the Leaky Acres Recharge Project in Fresno, California. The research is directed toward developing methods for constructing and placing filter-pack materials and procedures for periodically cleaning filter materials to regenerate initial intake rates. This report presents preliminary results of two differently constructed shallow shafts. Over a period of 94 days, 50.8 X 103 cu m (13.4 million gals) of screened canal water was recharged. Redevelopment with a submersible pump regenerated one shaft to 109 percent of its original intake rate. Piezometric observations indicated that most of the clogging occurred within the filter-pack material.

A technique for estimating herbage intake by weighing sheep before and after grazing, with an allowance for insensible weight loss (IWL) was evaluated. Live weights were estimated by weighing each animal 200 times using an electronic balance and a microcomputer. This enabled each sheep to be weighed to ± 10 g and overcame the problem of fluctuation in weight due to movement. Mean rates of IWL in housed sheep were 2·3, 1·4, and 0·8 g min−1 for walking, standing eating or idling and when lying ruminating respectively. Intake rate (IR) estimated by weighing gave a small but significant bias of −0·8 g min−1 when compared with measurements of IR made using housed sheep. Estimates of IWL and IR were made with ewes grazing continuously stocked ryegrass swards maintained at surface heights of 3,6,9 and 12 cm. IWL was higher outdoors than indoors and tended to be higher on the longer swards. IR estimated by weighing gave similar results to those obtained using the chromic oxide technique. At a sward surface height of 3 cm, IR and total intake were lower than for taller swards and total time spent grazing decreased with increasing sward surface height.

I tested predictions from three models of central place foraging (CPF) in two field experiments with Calliope Hummingbirds (Stellula calliope). The models were based on different "currencies," or optimization criteria: (a) maximization of net rate of energy intake while foraging and traveling between a central place and feeding areas; (b) mini- mization of proportion of total time spent foraging and traveling; (c) maximization of energetic efficiency while foraging and traveling. All three models differ from most CPF models in that I assumed that gross rate of energy intake while foraging in a patch remained constant. Net rate of energy intake decreased with time spent foraging because the cost of hovering flight increased during foraging bouts due to the accumulating mass of ingested nectar. In a dual choice experiment repeated with the same male in two years, I offered a choice between a "fast-weak" feeder that provided a fast instantaneous energy intake rate but low sucrose concentration (low energy/mass ratio), and a "slow-rich" feeder with slow instan- taneous intake rate and high concentration (high energy/mass ratio). As predicted by all three models, the male preferred the fast-weak feeder when the feeders were near his central place, and he increased his relative use of the slow-rich feeder when they were farther away. In another experiment in which I offered only one type of feeder at a time, males increased meal size with travel distance from their perches to feeders, and took larger, heavier meals from fast-weak than from slow-rich feeders. Both of these results were predicted by the time minimization and efficiency maximization models, but not the rate maximization model. Females who were incubating or feeding young did not change meal size significantly with travel distance from their nests to feeders. This qualitative result was predicted by the rate maximization model but not the time minimization and efficiency maximization models. Females took larger, heavier meals from slow-rich than from fast- weak feeders, and this was not predicted by any of the models. Mean meal sizes of both males and females were smaller than predicted by any of the models at all travel distances.

The effect of sward surface height (SSH) on grazing behaviour and intake by lactating Holstein Friesian cows on continuously stocked grass pastures maintained at mean heights of 5, 7 and 9 cm was studied during the growing season. Intake rate was estimated over periods of 1 h by weighing animals before and after grazing, with a correction made for insensible weight loss. Grazing behaviour during that hour and over 24 h was recorded automatically using sensors to measure jaw movements. Although maintained at the overall mean SSH, swards had a patchy appearance with short, frequently grazed areas interspersed with taller, infrequently grazed areas, which is typical of pastures continuously stocked with cattle. Daily organic matter (OM) intake, calculated as the product of daily grazing time and intake rate, was greater at a SSH of 7 cm than at 5 or 9 cm (14.1 vs. 10.5 and 12.1 kg respectively). On the 5-cm sward, OM intake per grazing jaw movement (GJM) was reduced compared with that on the 7-cm sward (0.182 vs. 0.264 g respectively), and because cows were unable either to increase significantly GJM rate (95.8 vs. 90.1 GJM min(-1)) or the proportion of GJM that were bites (0.80 vs. 0.81) OM intake rate was reduced (16.9 vs. 23.5 g min(-1)). Cows were unable to increase their grazing time significantly (628 vs. 604 min d(-1)) to compensate for the reduction in intake rate, and as a result daily intakes were lower. Cows grazing the 9-cm sward also incurred a reduction in OM intake GJM(-1) compared with those on the 7-cm sward (0.237 vs. 0.264 g respectively) and therefore there was a reduction in OM intake rate (21.6 vs. 23.5 g min(-1)). These animals did not compensate by increasing the time spent grazing (581 min d(-1)), probably owing to an increased ruminating requirement per kg of herbage ingested compared with those on 7 cm SSH (2264 vs. 1780 ruminating jaw movements respectively). The results show that SSH can significantly influence intake rate, but, while the cow's only effective strategy to compensate for any reduction in intake rate is to increase grazing time, this may be limited by the requirement for ruminating and non-grazing, non-ruminating activities, which is influenced by qualitative and quantitative aspects of the herbage ingested, whereas the cows' only effective strategy to compensate for any reduction in intake rate is to increase grazing time.