Foraging strategy of cattle in patchy grassland

We tested several strategies of foraging that grazing herbivores may adopt in a patchy habitat in relation to energy intake. The patch selection of cattle was investigated in an Agrostis/Festuca grassland and in a Lolium grassland in 13 observation periods over 2 years. Both grasslands were stocked with five yearling steers. Bite counts were made on patches of different vegetation structure: short, tall and mature stemmy grass. Bite size of each patch category was determined by hand-plucking. Samples of patch types were analysed for organic matter digestibility, as a measure of energy content. There was a large seasonal variation in relative patch cover and in forage characteristics. However, the differences between patches in bite size, bite rate and digestibility were consistent over time. In short patches digestibility was high, bite size was low and bite rate was high compared to stemmy patches. In tall patches digestibility was only little lower than in short patches and bite size and bite rate were intermediate between short and stemmy patches. The steers selected the short and tall patches over the stemmy patches, despite a relatively low intake rate of digestible organic matter in the short patches. Four hypotheses on foraging strategy were examined to explain the allocation of time or bites between patches: random allocation according to bites, random allocation according to grazing time, matching of time in proportion to digestibility, and matching of time in proportion to intake rate of digestible organic matter. The observed distribution of bites and time between patches was significantly different from the predictions of the various hypotheses. Patch choice was better explained by a random allocation of grazing time than by a random allocation of bites. Matching for digestible organic matter intake rate yielded the worst predictions of patch selection. Matching for digestibility gave the best explanation of patch selection, but the improvement compared to a random allocation of grazing time was not significant. The significance of the contribution of digestibility to selection may have been confounded by the effect of increased selectivity within tall patches. Observed patch selection was considered in relation to the maximization of energy intake rate. The selectivity of cattle was not pronounced, but it was consistent with a principle of maximization of energy intake on a daily basis instead of a short-term basis. Selectivity appeared to be constrained by costs of searching for and discriminating between different forage resources. It is concluded that a flexible selection for short patches over tall patches and avoidance of stemmy patches provides a good approximation of energy intake maximization in a complex and changing environment.     

From feeding station to patch: scaling up food intake measurements in grazing cattle

The technique of grazing cut sods was used in combination with sound and video recording to examine the feasibility of using small-scale depletion curves derived from stall trials to estimate forage intake of cattle at the pasture. Setaria lutescens sods were grazed for a variable number of bites to generate patch depletion curves. Depletion curves characterize forage intake as a function of the number of bites taken at a single feeding station. Thus, the method agrees with a hierarchical approach to foraging and it could be used as a basis for scaling up food intake measurements to larger spatial scales. Two sod experiments were carried out, with the second experiment as a validation for predictions of intake. A field experiment was carried out to validate the predictions from the sod experiments with respect to both the amount and the rate of intake. Bite weight was largely determined by initial sward height and depletion level. Cumulative dry matter intake from the sods was well described by a rectangular hyperbola including the variables of number of bites and sward height. Bulk density added little to the explained variation, but was an important factor to account for the dry matter intake on short, dense sods from the second experiment. Feeding time could be explained to a great extent by the number of bites and chews taken, both in the sod and in the field experiments. However, the animals were substantially faster when grazing in the field than on the sods due to a relatively smaller chewing effort. The estimate of bite weight in the field based on the sod depletion curves was validated by an independent estimate derived from the chew to bite ratio. Bite weight estimates that ignored feeding station depletion were significantly greater than the independent estimates. We conclude that the sod grazing technique is an adequate tool to investigate food intake and forage depletion by grazing. It shows promise as a tool to explicitly scale up of foraging behaviour from the level of the feeding station to that of larger patches.     

The importance of scale of patchiness for selectivity in grazing herbivores

The notion that spatial scale is an important determinant of foraging selectivity and habitat utilization has only recently been recognized. We predicted and tested the effects of scale of patchiness on movements and selectivity of a large grazer in a controlled field experiment. We created random mosaics of short/high-quality and tall/low-quality grass patches in equal proportion at grid sizes of 2×2 m and 5×5 m. Subsequently, we monitored the foraging behaviour of four steers in 16 20×40 m plots over 30-min periods. As predicted on the basis of nutrient intake maximization, the animals selected the short patches, both by walking in a non-random manner and by additional selectivity for feeding stations. The tortuosity of foraging paths was similar at both scales of patchiness but selectivity was more pronounced in large patches than in small ones. In contrast, the number of bites per feeding station was not affected by patch size, suggesting that selection between and within feeding stations are essentially different processes. Mean residence time at individual feeding stations could not be successfully predicted on the basis of the marginal-value theorem: the animals stayed longer than expected, especially in the less profitable patch type. The distribution of the number of bites per feeding station suggests a constant probability to stay to feed or to move on to the next feeding station. This implies that the animals do not treat larger patches as discrete feeding stations but rather as a continuous resource. Our results have important implications for the application of optimal foraging theory in patchy environments. We conclude that selectivity in grazers is facilitated by large-scale heterogeneity, particularly by enhancing discrimination between feeding stations and larger selection units. Received: 1 March 1999 / Accepted: 14 July 1999     

Taste agents as modulators of the feeding behaviour of grazing yaks in alpine meadows

Feeding behaviour plays a significant role in promoting good animal health and welfare. It is also reflective of the quality and quantity of available feed. In fact, grazing livestock do not select their feed randomly, rather their behaviour is influenced by the texture, taste, and smell of each pasture species. Although taste agents are often used to modify feed intake for captive livestock, the effect on the feeding behaviour of grazing livestock has not yet been extensively evaluated in native grasslands. To address this gap in knowledge, herein, we sprayed three types of taste agents—salty (SA), sweet (SW), and bitter (BT)—on alpine meadows to investigate their effect on the grazing behaviour of yaks (Bos Grunniens) on the Qinghai-Tibetan Plateau (QTP). Behavioural observations showed that grazing was concentrated primarily in the morning and afternoon, while ruminating/resting peaked at noon; however, the diurnal behavioural patterns of grazing yaks were not affected by the taste agents. Application of the SA agent significantly increased the yaks’ grazing time, bites per minute, bites per step, time per feeding station, and steps per feeding station, while significantly reducing walking time, steps per minute, and number of feeding stations per minute. Meanwhile, application of the SW agent significantly increased the yaks’ time per feeding station, however, significantly reduced the steps per minute and number of feeding stations per minute. In contrast, the BT agent significantly increased the yaks’ walking time, steps per minute, and number of feeding stations per minute, while significantly reducing grazing time, bites per minute, bites per step, and time per feeding station. Application of the SA agent also significantly increased the intake of favoured, edible, and inedible forage, while the SW agent improved inedible forage intake, however, had a more subtle effect on favoured and edible forage intake. Meanwhile, the BT agent had an inhibitory effect on grazing intake. Hence, the structural equation model suggested that taste agents may directly or indirectly influence grazing behaviour by regulating feeding behaviour. Our findings provide a theoretical basis for using taste agents in grasslands to control the grazing behaviour of livestock and provide a method to promote the stability of grassland communities, while mitigating the degradation of grasslands in the QTP.     

Patch depression in grazers: the roles of biomass distribution and residual stems

1. In this paper the results are presented of two experiments designed to examine the relationship between sward structure variables and the nature of patch depression experienced by a large grazing herbivore, Bos taurus, grazing from small patches of forage. In experiment 1 the spatial distribution of leaves within patches was varied. In experiment 2 the role of reproductive stems of different lengths as potential intake rate inhibitors was examined.
2. Both experiments were conducted by offering cattle hand-constructed swards of Orchardgrass ( Dactylis glomerata ) leaves attached to plywood boards. Each of three experimental animals was allowed to take 10, 20, 30, 45 or 60 bites from a patch and intake was estimated on the basis of pregrazing and postgrazing dry-matter. All trials were videotaped and the trial length in seconds was determined from playback of the tapes.
3. In both experiments patch depression (reduction in instantaneous intake rate) was due to decreases in bite mass concomitant with patch depletion. Handling time per bite was unaffected by depletion level. In experiment 1, different spatial configurations resulted in markedly different gain functions ranging from linear to sigmoid. In experiment 2, the presence in the sward of long (15 cm) reproductive stems slowed cumulative gains by restricting bite mass and by increasing the per-bite handling time relative to patches with shorter (5 cm) or no stems.
4. The study of patch depression mechanisms now needs to be generalized over a range of herbivore body sizes and feeding styles.     

Influence of size and density of browse patches on intake rates and foraging decisions of young moose and white-tailed deer

We examined the functional response and foraging behavior of young moose (Alces alces) and white-tailed deer (Odocoileus virginianus) relative to animal size and the size and distribution of browse patches. The animals were offered one, three, or nine stems of dormant red maple (Acer rubrum) in hand-assembled patches spaced 2.33, 7, 14, or 21 m apart along a runway. Moose took larger twig diameters and bites and had greater dry matter and digestible energy intake rates than did deer, but had lower cropping rates. Moose and deer travelled at similar velocities between patches and took similar numbers of bites per stem. We found that a model of intake rate, based on the mechanics of cropping, chewing, and encountering bites, effectively described the intake rate of moose and deer feeding in heterogeneous distributions of browses. As patch size and density declined, the animals walked faster between patches, cropped larger bites, and cropped more bites per stem, and hence, dry matter intake rates remained relatively constant. As is characteristic of many hardwood browse stems, however, potential digestible energy concentration of the red maple stems declined as the size and number of bites removed (i.e., stem diameter at point of clipping) by the animals increased. Therefore, the digestible energy content of the diet declined with decreasing patch size and density. Time spent foraging within a patch increased as patch size increased and as distance between patches increased, which qualitatively supported the marginal-value theorem. However, actual patch residence times for deer and moose exceeded those predicted by the marginal-value theorem (MVT) by approximately 250%. The difference between actual and predicted residence time may have been a result of (1) an unknown or complex gain function, (2) the artificial conditions of the experiments, or (3) assumptions of MVT that do not apply to herbivores.     

Forage quality and patch choice by wapiti (Cervus elaphus)

Recent models suggest that herbivores might optimize energygain by selecting patches of intermediate vegetation biomass.We tested this hypothesis in wapiti (Cervus elaphus) by estimatingdaily rates of energy gain in relation to grass biomass andby measuring patch choice in experimental pastures in whichgrass biomass was manipulated by mowing. The digestible energycontent of grasses declined with increasing biomass due to maturationalchanges in fiber and lignin content. Daily rates of dry matterintake by wapiti increased with grass biomass at a deceleratingrate, implying a Type II functional response. Linking thesevalues to published ad libitum energy intake and energy expenditureparameters, Fryxell's (1991) model predicted that the dailyrate of energy gain should be highest when wapiti feed in grasslandswith 1000–1100 kg/ha. In trials in which grass biomasswithin a mosaic of patches was manipulated experimentally between800–2900 kg/ha, wapiti preferred patches of 1200 kg/ha,close to the value predicted by the energy gain model. Our resultssuggest that the rate of energy gain by wapiti is constrainedby both grass biomass and grass fiber content, the latter ofwhich varies inversely with grass biomass. Behavioral preferencefor grass patches of intermediate biomass and fiber contentcould help explain patterns of aggregation and seasonal migrationreported previously for wapiti.     

Seasonal foraging behavioural compensation in reproductive wapiti hinds (Cervus elaphus canadensis)

Captive wapiti hinds were observed during seven periods between June 1996 and November 1997. We investigated their activity and foraging behaviour on two pastures, heavily and lightly grazed, during four phases of the reproductive cycle (early gestation, late gestation, peak lactation, and late lactation). Within season, differences in forage availability between pastures had little apparent effect on wapiti feeding behaviour (p0.05). However, within each pasture, hinds tended to select locations of higher phytomass than the pasture average. Among seasons, effects of forage availability on feeding behaviour were pronounced. Hinds grazed longest in late lactation (12.8 h/day), when they spent 94% of their active time foraging, whereas during early gestation they foraged fewer hours (8.2 h/day) and less intensively (66% of active time). The longest foraging bouts also occurred in late lactation (100 min) and decreased linearly as the number of bouts per day increased (R(2)=0.88). The annual peak bite rate (BR) was in late lactation (62 bites/min), whereas the annual nadir occurred in early gestation (37 bites/min). Smallest bite sizes (BS) (mg) were recorded in late gestation (127 mg), and increased linearly with forage availability (R(2)=0.46), with largest BS occurring during peak lactation (280 mg). This study demonstrated how seasonal modifications in activity and foraging behaviour enabled gestating and lactating wapiti hinds to satisfy their changing nutritional requirements on seasonal pastures. Knowledge of behavioural compensation in response to nutritional demand and pasture conditions will be useful in designing supplementation program for farmed wapiti.     

The importance of post‐fire regrowth for sable antelope in a Southern African savanna

Burning is commonly used in savannas to stimulate grass regrowth for grazing ungulates. We recorded the relative use of burns occurring at different stages in the seasonal cycle, as well as in different regions of the landscape by two herds of sable. We also recorded behavioural measures of foraging efficiency and faecal nutrient contents as an indication of nutrient gains. Sable consistently concentrated their grazing on burned areas provided there was sufficient green regrowth during the dry season. In these circumstances they grazed for longer per feeding station, showed a slower step rate while foraging, and shorter between‐patch moves, and a higher probability of encountering acceptable food per step taken while foraging than on unburnt areas. In the year when only a burn with insufficient regrowth was available, sable continued to forage in the area that had been burned during the previous year. Faecal crude protein was substantially higher at the end of the dry season in the year when burned areas were utilized. Accordingly early dry season fires can be important in helping sable bridge the nutritional limitations posed by the dry season, provided sufficient soil moisture remains to promote adequate grass regrowth.     

Seasonal and interannual variations in feeding station behavior of cattle: effects of sward and meteorological conditions

A feeding station is the area of forage a grazing animal can reach without moving its forefeet. Grazing behavior can be divided into residence within feeding stations (with bites as benefits) and movement between feeding stations (with steps as costs). However, relatively little information has been reported on how grazing animals modify their feeding station behavior seasonally and interannually in response to varying environmental conditions. The feeding station behavior of beef cows (Japanese Black) stocked on a tropical grass pasture (bahiagrass dominant) was monitored for 4 years (2010 to 2013) in order to investigate the association of feeding station behavior with meteorological and sward conditions across the seasons and years. Mean air temperature during stocking often exceeded 30°C during summer months. A severe summer drought in 2013 decreased herbage mass and sward height of the pasture and increased nitrogen concentration of herbage from summer to autumn. A markedly high feeding station number per unit foraging time, low bite numbers per feeding station and a low bite rate were observed in summer 2013 compared with the other seasons and years. Bite number per feeding station was explained by a multiple regression equation, where sward height and dry matter digestibility of herbage had a positive effect, whereas air temperature during stocking had a negative effect (R²=0.658, P<0.01). Feeding station number per minute was negatively correlated with bite number per feeding station (r=–0.838, P<0.001). It was interpreted that cows modified bite number per feeding station in response to the sward and meteorological conditions, and this largely determined the number of feeding stations the animals visited per minute. The results indicate potential value of bite number per feeding station as an indicator of daily intake in grazing animals, and an opportunity for livestock and pasture managers to control feeding station behavior of animals through managements (e.g. fertilizer application, manipulation of stocking intensity and stocking time within the day).     

Selection of feeding areas by cattle in a spatially heterogeneous environment: selection between two tropical grasses

A herd of 28–33 Japanese Black cows (Bos taurus) were allowed to graze on an experimental plot comprising monoculture swards of centipedegrass (Eremochloa ophiuroides) and bahiagrass (Paspalum notatum) (0.39 and 0.61 ha, respectively) for 3–5 days each month (from 0850 to 1600 hours) between May (late spring) and October (mid-autumn). On a monthly basis, the animals showed an increasing trend to select centipedegrass in preference to bahiagrass as the relative crude protein (CP) concentration of the former increased relative to the latter. On a daily basis, the animals showed a decreased selectivity for centipedegrass with the progression of grazing days, as centipedegrass sward lost both quantity and quality faster than bahiagrass sward under higher degrees of defoliation. Animals maintained similar bite rates on the two swards by modifying feeding station behavior as soon as they switched between the swards, i.e., they increased the number of bites per feeding station and decreased the number of feeding stations selected per unit grazing time soon after switching to centipedegrass, with the reverse process occurring soon after the switch to bahiagrass. The results show CP concentration to be a partial forage factor influencing animals’ choice between tropical grasses growing as patches. The results also demonstrate that animals have an ability to adapt their foraging behavior flexibly and rapidly to varying types of vegetation.     

Winter foraging by muskoxen: a hierarchical approach to patch residence time and cratering behaviour

We examined the temporal and spatial patterns of feeding behaviours of muskoxen during winter in the High Arctic. Pawing motions (to uncover forages beneath snow cover) were strongly aggregated into temporal bouts. Similarly, feeding stations (areas exploitable without motion of the forelegs) were aggregated into spatial patches. Muskoxen responded to greater snow accumulation at feeding sites by increasing the rates of pawing, rates of pawing bouts, number of pawing strokes per bout, and station residence times. Patch residence times showed little relationship to snow or forage abundance because, as muskoxen increased station residence times, they decreased the number of stations per patch. Muskoxen displaced one another from feeding stations more frequently as snow thickness and group size increased. Time spent at feeding stations was positively correlated to travel costs, in accordance with the marginal value model of patch residence. The model was not supported, however, at the scale of the feeding patch. The results indicate that behavioural responses of muskoxen to foraging conditions differ across scales.     

Configuration of daily grazing and searching of growing beef cattle in grassland: observational study

Many of the studies in Campos grasslands focus on management aspects such as the control of herbage allowance, and application of nutrients and/or overseeding with legumes. However, there is little literature on how the Campos grassland resource is utilised, especially regarding the grazing pattern and the relationship between pasture quantity and quality on daily grazing activities. The study of the ingestive behaviour in species-rich and heterogeneous native grasslands during daylight hours, and understanding how animals prioritise quality or quantity of intake in relation to pasture attributes, are important to comprehend the ingestive-digestive processes modulating the energy intake of animals and to achieve a better grazing management. Therefore, the objective was to describe and quantify the daily grazing behaviour of growing cattle grazing native pasture with different structures as a result of different management practices, and study the relationship of pasture attributes and intake through multivariate analysis. The study was carried out at the Faculty of Agronomy, Paysandú, Uruguay. Treatments were native grassland, overseeding with Trifolium pratense and Lotus tenuis + phosphorus, and native pasture + nitrogen-phosphorus. Grazing activities were discriminated into grazing, searching (defined when animals take 1–2 bites in one feeding station and then change to another feeding station and so on), ruminating and idling. The probability of time allocated to each activity was continuously measured during daylight hours (0700–1930) and was related to pasture structure and forage quality using regression tree models, while the bite rate was determined every 2 h. The diurnal pattern of growing cattle showed grazing and searching sessions, followed by ruminating and idling sessions. The length of sessions (as the probability of time allocated to each activity) varied throughout the day. The grazing probability was greater during afternoon than morning and midday (0.74 vs 0.45 vs 0.46, respectively), and it was associated with higher bite rate (34.2 bites/min). Regression tree models showed different grazing, searching and ruminating strategies according to pasture attributes. During the morning, animals modified grazing, searching, ruminating and idling strategies according to bite rate, crude protein in diet and herbage allowance. At midday, they only adjusted ruminating and idling, while during afternoon sessions, grazing activities were modified by pasture quantity attributes such as herbage mass and herbage allowance. By controlling the herbage allowance, herbage mass and pasture height, animals prioritise quality in the morning and quantity in the afternoon, integrating and modifying the grazing-searching and ruminating-idling pattern.     

Effects of grazing pattern and nitrogen availability on primary productivity

A major part of the impact of grazing on primary productivity results from the joint action of tissue removal and nutrient return to the soil via dung and urine. Grazing, however, is not uniformly distributed in space: grazed grasslands show a matrix of grazed and ungrazed patches, which in turn, may or may not be affected by faecal or urine deposition. This paper investigates the effects of grazing spatial pattern and nitrogen availability on primary productivity. We propose that grazed plants located at the edge of a grazed patch are more shaded by their taller ungrazed neighbours than plants at the center. Since the border effect is less important as patch size increases, the effects of grazing will be more positive, or less negative, when grazing pattern is coarse-grained than when it is fine-grained. We also propose that nitrogen availability will affect this response to grazing through its effects on the intensity of competition for light and on the amount of compensatory growth. We performed a field experiment in a grassland community of the Flooding Pampa, Argentina, in which we compared the productivity of undefoliated controls and defoliated patches of different size, with and without nitrogen application. Defoliation reduced primary productivity and this effect was greater in the smallest, fertilized patches. Productivity was highest at patches of intermediate and large sizes. Nitrogen addition increased productivity by two-fold. The integrated photon flux density reaching the base of the canopy was affected by defoliation and by patch size: it was lower in controls than in defoliated patches and increased with patch size. Our results showed that (a) the size of the defoliated patch modified the response of this grassland to defoliation, (b) this response was correlated with light availability, and (c) nitrogen addition, simulating urine depositions, increased primary productivity and affected the response to defoliation of the smallest patches.     

Grassland structure in native pastures: links to soil surface condition

Summary When grassland is grazed by livestock, the structure of the sward changes in a patchy manner. With continuous selective grazing there is a mosaic of short and tall patches but as grazing intensifies the area of short‐grazed patch increases until the paddock has a lawn‐like appearance. This mosaic of patch structures can be stable, as short patches tend to attract repeated grazing and tall patches tend to be avoided. Because heavy grazing can detrimentally affect soil and water functions in grassland (ultimately resulting in erosion), we aimed to assess how well the physical structure of the sward reflects soil surface condition. We described four grassland patch structures that were assumed to reflect different levels of present grazing, and to some extent, past grazing pressure. We assessed patch structure and two other grass‐related variables (basal area of a ‘large tussock’ functional group and basal area of all perennial grass) as possible indicators of soil surface condition. Three indices of condition were measured in the field. The infiltration and nutrient cycling index declined progressively across patch structures, consistent with increasing grazing pressure. The stability index was found to be reduced only for the most heavily grazed grass structure (short patches). We found the ‘large tussock’ grass functional group to be a more sensitive indicator of soil surface condition than the group consisting of all perennial grasses. We found no evidence of sudden soil surface condition decline beyond a certain level of grass basal area, that is, there was no evidence of thresholds, rather, incremental loss of condition accompanied grass decline. We are thus not able to further refine an earlier proposed management recommendation ‘Graze conservatively to maintain dominance of large and medium tussock grasses over 60–70% of the native pastures’, except to suggest the use of short patches as a more practical indicator, rephrasing the recommendation as ‘Graze conservatively to allow a maximum of 30% short‐grazed patches in native pastures’.     

Patch dynamics in grazed subtropical native pastures in south‐east Queensland

Abstract Patch formation is common in grazed grasslands but the mechanisms involved in the formation and maintenance of patches are not clear. To increase our knowledge on this subject we examined possible reasons for patch formation and the influence of management on changes between patch states in three experiments in native pasture communities in the Crows Nest district, south‐east Queensland. In these communities, small‐scale patches (tall grassland (dominated by large and medium tussock grasses), short swards (dominated by short tussock grasses and sedges), and lawns (dominated by stoloniferous and/or rhizomatous grasses)) are readily apparent. We hypothesized that the formation of short sward and lawn patches in areas of tall grassland was due to combinations of grazing and soil fertility effects. This was tested in Experiment 1 by applying a factorial combination of defoliation, nutrient application and transplants of short tussock and stoloniferous species to a uniform area of tall grassland. Total species density declined during the experiment, was lower with high nutrient applications, but was not affected by defoliation. There were significant changes in abundance of species that provided support for our hypotheses. With light defoliation and low nutrients, the tall grassland remained dominated by large tussock grasses and contained considerable amounts of forbs. With heavy defoliation, the pastures were dominated by medium tussock grasses and there were significant decreases in forbs and increases in sedges (mainly with low nutrients) and stoloniferous grasses (mainly with high nutrients). Total germinable seed densities and those of most species groups were significantly lower in the heavy defoliation than the light defoliation plots. Total soil seed numbers were not affected by nutrient application but there were fewer seeds of the erect forbs and more sedge seeds in plots with high nutrients. The use of resting from grazing and fire to manage transitions between patches was tested. In Experiment 2 , changes in species density and abundance were measured for 5 years in the three patch types with and without grazing. Experiment 3 examined the effects of fire, grazing and resting on short sward patches over 4 years. In Experiment 2 , total species density was lower in lawn than short sward or tall grassland patches, and there were more species of erect forbs than other plant groups in all patch types. The lawn patches were originally dominated by Cynodon spp. This dominance continued with grazing but in ungrazed patches the abundance of Cynodon spp. declined and that of forbs increased. In the short sward patches, dominance of short tussock grasses continued with grazing but in ungrazed plots their abundance declined while that of large tussock grasses increased. The tall grassland patches remained dominated by large and medium tussock species. In Experiment 3 , fire had no effect on species abundance. On the grazed plots the short tussock grasses remained dominant but where the plots were rested from grazing the small tussock grasses declined and the large tussock grasses increased in abundance. The slow and relatively small changes in these experiments over 4 or 5 years showed how stable the composition of these pastures is, and that rapid changes between patch types are unlikely.     

Effect of cattle grazing a species-rich mountain pasture under different stocking rates on the dynamics of diet selection and sward structure

Although stocking rate is a key management variable influencing the structure and composition of pastures, only few studies have simultaneously analysed the seasonal patterns of pasture use by cattle, and the adjustments the animals make to maintain intake of a high-quality diet over the grazing season. Therefore, over a 3-year study, we recorded diet selection, plot use and impact of heifers on sward structure and quality under three different stocking rates (0.6, 1.0 and 1.4 livestock units (LU) per ha) in a species-rich mountain pasture of central France. Measurements were made on three occasions between early June and the end of September each year. Overall, heifers selected for bites dominated by legumes or forbs, and against reproductive grass, whatever the stocking rate or season. Selection for tall mixed (P < 0.05), short mixed (P < 0.05) and short pure grass bites (P < 0.01) was more pronounced in plots grazed at the lowest stocking rate. Although heifers' selection for short patches decreased at the end of the season (P < 0.001), they continued to graze previously grazed areas, thus exhibiting a typical 'patch grazing' pattern, with the animals that grazed at the lowest stocking rate tending to better maintain their selection for short patches in September (treatment × period: P = 0.078). Neither diet quality nor individual animal performance were affected by the different stocking rate treatments despite high variability in the quantity and quality of herbage offered and differences in diet selection. However, at the 1.4 LU per ha stocking rate, the quantity of forage available per animal at the end of the season, 0.79 t dry matter (DM) per ha of green leaves with the median of sward height at 4.6 cm, approached levels limiting cattle's ability to compensate for the effects of increasing stocking rate. In plots grazed at 0.6 LU per ha, the total herbage biomass remained higher than 3 t DM per ha with more than 30% of plot area still covered by reproductive grass patches at the end of the grazing season, which in the medium term should affect the botanical composition of these pastures. Sward heterogeneity was high in plots grazed at 1.0 LU per ha, with sufficient herbage availability (1.1 t DM per ha of green leaves) to maintain animal performance, and more than 15% of plot area was kept at a reproductive stage at the end of the grazing season. Hence, it could represent the optimal balance to satisfy both livestock production and conservation management objectives.     

Feeding rate as valuable information in primate feeding ecology

In this review I outline studies on wild non-human primates using information on feeding rate, which is defined as the food intake per minute on a dry-weight basis; further, I summarize the significance of feeding rate in primate feeding ecology. The optimal foraging theory has addressed three aspects of animal feeding: (1) optimal food patch choice, (2) optimal time allocation to different patches, and (3) optimal food choice. In order to gain a better understanding of these three aspects, the feeding rate itself or its relevance indices (e.g., rates of calorie and protein intake) could be appropriate measures to assess the quality of food and food patches. Moreover, the feeding rate plays an essential role in estimation of total food intake, because it varies greatly for different food items and the feeding time is not a precise measure. The feeding rate could also vary across individuals who simultaneously feed on the same food items in the same food patch. Body size-dependent and rank-dependent differences in the feeding rate sometimes cause individuals to take strategic behavioral options. In the closing remarks, I discuss the usefulness of even limited data on feeding rate obtained under adverse observational conditions in understanding primate feeding ecology.     

Environmental and land use determinants of grassland patch diversity in the western and eastern Alps under agro-pastoral abandonment

Agro-pastoral decline in European mountain areas has recently caused changes to traditional landscapes with negative consequences on semi-natural grassland conservation and the associated biodiversity and ecosystem services. In the Italian Alps, grassland patches enclosed in a forest matrix are progressively disappearing. Two alpine valleys (Pesio and Pejo), having similar land-use history, were chosen as representative of management conditions of western and eastern Italian Alps, respectively. This study aims at interpreting the effect of abandonment on grassland patch plant diversity, considering land cover changes of the last 60 years, and assessing the role of ecological, topographic, management and landscape configuration on current grassland species richness. The total area of grassland patches has declined by 54 and 91 % at Pesio and at Pejo, respectively. Actual grassland patch species richness was mostly influenced by ecological factors, such as quantity of light, soil moisture and reaction, then by topographic features, especially slope, and finally by management intensity. Landscape factors exerted a slightly significant effect on plant diversity. In the two valleys, differences on management practices were detected. Even though in the western valley the conservation of several grazing activities contributed to slow down the process of patch reduction, many species-rich grasslands were generally under-grazed. Conversely, in the eastern valley, despite a denser road network, the stronger decline of grassland patch extension was linked to the hay making decline. At the same time, overuse of grassland patches near farms reduced plant species richness. As a conclusion, plant species richness was weakly related to the area of grassland patches and current and historical landscape configuration were of relatively lower importance than ecological, topographic and management factors, when evaluated at patch-level.     

Uncertain availability of a preferred food affects choice in a captive group of chimpanzees (Pan troglodytes)

Food-choice was investigated in a social group of 16 chimpanzees (Pan troglodytes) maintained in a large outdoor compound. Three feeding stations located along the periphery of the compound were considered analogous to food patches. Color-coded aluminum panels temporarily covered each feeding apparatus, with one color corresponding to nonpreferred food (commercial biscuits) available at two locations and other colors corresponding to the certain or uncertain availability of preferred food (oranges) available at one location. Only nine chimpanzees met the criterion for learning the color/food associations and thus only those animals were included in the analysis. There was a significant decrease in choosing the station associated with oranges when the probability of availability of oranges was reduced from 0.5 to 0.1 but not from 1.0 to 0.5. In addition, there was a significant increase in the frequency with which the subjects made no choice when the probability of availability of oranges was reduced from 1.0 to 0.1. The data indicate that the uncertain availability of preferred food in a choice situation affects choice behavior in a social group of chimpanzees studied under controlled conditions.