Cafeteria-style Feeding Trials Research Articles

Palatability of common cover crops to voles (Microtus)

Use of cover crops in intensive row-crop agriculture has dramatically increased over the last decade. Cover crops provide vegetative cover and forage that may support more diverse and abundant rodent communities than those found in conventional row-crop agroecosystems. However, increasing vole populations can lead to depredation of the soybean (Glycine max) commodity crop. We tested for selection of 13 commonly planted cover crops and 4-5 additional benchmark species by meadow (Microtus pennsylvanicus) and prairie (M. ochrogaster) voles using cafeteria-style feeding trials conducted in semi-natural outdoor enclosures. Red clover (Trifolium pratense), alfalfa (Medicago sativa), and hairy vetch (Vicia villosa) were commonly preferred among vole species, and canola (Brassica napus) was avoided. Meadow and prairie voles consistently chose or avoided highly and minimally preferred species, respectively, but were more variable in choosing moderately preferred species. Consumption scores were negatively associated with the number of plants offered in a trial, and the relationship was stronger for males than females. The interaction of protein and fiber content of plants, and vole identity included as a random effect, were also important in predicting score probability for both vole species. Identifying minimally preferred plants and factors that influence selection may allow farmers to manage cover-cropped soybean fields to discourage immigration of small mammals into fields, thus reducing negative consequences that might otherwise limit future adoption of a valuable soil conservation practice.

Cafeteria‐style feeding trials provide new insights into the diet and nutritional strategies of the black snub‐nosed monkey (Rhinopithecus strykeri): Implications for conservation

Anthropogenic changes and fragmentation of natural habitats often exert a negative effect on resource availability and distribution, and the nutritional ecology and feeding behavior of nonhuman primates. The goals of this study are to examine food choice and to identify the nutritional profile of foods consumed by the Critically Endangered black snub-nosed monkey (Rhinopithecus strykeri). To accomplish our study goals, we presented cafeteria-style feeding trials of fresh food items collected in the home range of wild black snub-nosed monkeys to the only two captive R. strykeri, and compared the nutritional profiles of the leafy foods (buds, young, and mature leaves, 100 i23tems from 70 plant species) selected with those avoided (54 items from 48 plant species). Overall, the results indicate that captive R. strykeri selected foods that were higher in moisture (Mo; 77.7%), crude protein (CP; 21.2%), total nonstructural carbohydrates (TNC; 34.9%), and phosphorus (P; 0.37%) while tending to avoid foods with a neutral detergent fiber (NDF) content of greater than 46.8%. Leaves collected in autumn and selected by the monkeys were characterized by a slightly higher amount of metabolizable energy (ME) than those rejected (1,350 kJ/100 g vs. 1,268 kJ/100 g). In contrast, the protein content of foods collected and consumed during the spring was greater (22.9%) than in autumn (16.4%). Random Forests modeling, an ensemble learning method, indicated that the proportion of Mo, NDF, ME, CP, P, and TNC were among the most important factors in predicting which items were consumed by the captive R. strykeri during spring and autumn. On the basis of the nutritional profile of foods consumed across the two seasons, we identified 18 nutrient-rich native plant species that we recommend for use in ex- and in-situ conservation management and reforestation programs to provide long-term access to a nutritionally adequate diet.

Human- and risk-mediated browsing pressure by sympatric antelope in an African savanna

Human activity shapes landscape heterogeneity, which can influence where and how species interact. In African savannas, human-mediated changes to woody cover affect perceptions of risk and foraging decisions by large herbivores. Through cafeteria-style feeding trials, we presented two common, browsing ungulates (Guenther's dik-dik [Madoqua guentheri] and impala [Aepyceros melampus]) with branches from four tree species that varied in their relative investment in mechanical and chemical defenses. We conducted trials in habitats that were perceived as risky to either dik-dik (i.e., open habitat) or impala (i.e., bushland habitat). We found that dik-dik preferred to eat thorny trees low in tannin content within bushland habitats, while the larger-bodied impala preferred tannin-rich but thorn-less branches within open habitats. Risk-induced habitat use homogenized browsing pressure in the lower canopy, but increased heterogeneity in browsing pressure in the upper canopy. In addition, plant defenses neutralized the effects of risk, and foraging height on browsing pressure. Our results demonstrate how foraging experiments—typically the basis for field studies on species coexistence—can be extended to make inferences about consumer-resource dynamics in human-modified landscapes.

Winter Preference for Weed Seed and Waste Grain by Native Mice in Row-Crop Agriculture

Consumption of weed seeds and waste grains by seed predators is an important ecosystem service that helps to regulate weed and volunteer crop populations in many agricultural systems. The prairie deer mouse is found in a variety of sparsely vegetated habitats throughout the central United States and is the dominant vertebrate seed predator in row-crop fields (corn and soybean) in this region. Evaluating the preferences of prairie deer mice for common agricultural weed seeds and waste grain is important to understand the potential ability of native mice to regulate volunteer crops and weed populations. We evaluated winter seed preference of deer mice using cafeteria-style feeding trials presented within row-crop fields in central Indiana and used compositional analysis to compare proportional consumption of seeds from five common agricultural weeds (common ragweed, common cocklebur, common lambsquarters, velvetleaf, and giant foxtail) and two grains (corn and soybean) during overnight feeding trials. Prairie deer mice significantly preferred corn to all other available seed types. Ragweed and soybean were also readily consumed and were preferred over seeds other than corn. Giant foxtail was intermediately preferred. Our results show that prairie deer mice have clear preferences for certain seeds commonly available in row-crop fields; mice likely contribute to reduction of waste grain and some weed seed populations.

Potential role of masting by introduced bamboos in deer mice (Peromyscus maniculatus) population irruptions holds public health consequences.

We hypothesized that the ongoing naturalization of frost/shade tolerant Asian bamboos in North America could cause environmental consequences involving introduced bamboos, native rodents and ultimately humans. More specifically, we asked whether the eventual masting by an abundant leptomorphic (“running”) bamboo within Pacific Northwest coniferous forests could produce a temporary surfeit of food capable of driving a population irruption of a common native seed predator, the deer mouse (Peromyscus maniculatus), a hantavirus carrier. Single-choice and cafeteria-style feeding trials were conducted for deer mice with seeds of two bamboo species (Bambusa distegia and Yushania brevipaniculata), wheat, Pinus ponderosa, and native mixed diets compared to rodent laboratory feed. Adult deer mice consumed bamboo seeds as readily as they consumed native seeds. In the cafeteria-style feeding trials, Y. brevipaniculata seeds were consumed at the same rate as native seeds but more frequently than wheat seeds or rodent laboratory feed. Females produced a median litter of 4 pups on a bamboo diet. Given the ability of deer mice to reproduce frequently whenever food is abundant, we employed our feeding trial results in a modified Rosenzweig-MacArthur consumer-resource model to project the population-level response of deer mice to a suddenly available/rapidly depleted supply of bamboo seeds. The simulations predict rodent population irruptions and declines similar to reported cycles involving Asian and South American rodents but unprecedented in deer mice. Following depletion of a mast seed supply, the incidence of Sin Nombre Virus (SNV) transmission to humans could subsequently rise with dispersal of the peridomestic deer mice into nearby human settlements seeking food.

Salinity-mediated cyanogenesis in white clover (Trifolium repens) affects trophic interactions.

Increasing soil salinity poses a major plant stress in agro-ecosystems worldwide. Surprisingly little is known about the quantitative effect of elevated salinity on secondary metabolism in many agricultural crops. Such salt-mediated changes in defence-associated compounds may significantly alter the quality of food and forage plants as well as their resistance against pests. In the present study, the effects of soil salinity on cyanogenesis in white clover (Trifolium repens), a forage crop of international importance, are analysed. Experimental clonal plants were exposed to five levels of soil salinity, and cyanogenic potential (HCNp, total amount of accumulated cyanide in a given plant tissue), β-glucosidase activity, soluble protein concentration and biomass production were quantified. The attractiveness of plant material grown under the different salt treatments was tested using cafeteria-style feeding trials with a generalist (grey garden slug, Deroceras reticulatum) and a specialist (clover leaf weevil, Hypera punctata) herbivore. Salt treatment resulted in an upregulation of HCNp, whereas β-glucosidase activity and soluble protein concentration showed no significant variation among treatments. Leaf area consumption of both herbivore species was negatively correlated with HCNp, indicating bottom-up effects of salinity-mediated changes in HCNp on plant consumers. The results suggest that soil salinity leads to an upregulation of cyanogenesis in white clover, which results in enhanced resistance against two different natural herbivores. The potential implications for such salinity-mediated changes in plant defence for livestock grazing remain to be tested.

Paper birch (Betula papyrifera) shoot selection by moose (Alces alces) following a forest-cleaning experiment

In order to maximize food intake per harvesting effort and minimize energy expenditures required to move between feeding patches in nature, herbivores such as moose (Alces alces L.) generally select large plant shoots when browsing in winter. To determine moose preferences for shoots of different morphologies, an experiment was conducted in northern British Columbia in which shoots from birches cut at different times of the growing season were fed in 2 consecutive years to eight human-habituated moose in cafeteria-style feeding trials. The results indicate that moose preferred smaller winter shoots of birches regardless of when the parent plant was cut and also appeared to reject larger shoots containing sylleptic branches. It is argued that the preferences for smaller shoots by moose detected in these trials should be observable under natural conditions, but are generally only supported by literature from some parts of Scandinavia. The findings underscore the importance that factors such as mouth filling per harvesting effort, snow depth and consistency, predators and browse patch distribution must have on foraging decisions made by moose while browsing in the wild. Implications of the findings include the significance of cutting time on the size of shoots produced by birch after cutting, how this affects moose browsing birch and, subsequently, how managers can theoretically use cutting time as a tool in forest cleaning operations to direct the foraging efforts of moose towards or away from forest plantations.

Using multivariate techniques to determine if yellow-bellied marmots feed selectively

Understanding how animals select resources provides important information regarding their requirements for survival. One method for studying diet selection is multiple-choice feeding preference experiments, in which animals are offered multiple food items simultaneously. However, because food items are offered simultaneously, the consumer's choices are not independent. They therefore violate assumptions of univariate statistical tests, such as ANOVAs and t-tests, which are most often used in such studies. I used multivariate statistics to examine diet selection of yellowbellied marmots (Marmota flaviventris) for the 7 plants most commonly found in their foraging areas. Using Hotelling's T2, I rejected the null hypothesis that the proportions of plant species consumed were equal to the expected value of 1/7 (T2 = 180.63, P = 0.025). Cafeteria-style feeding trials indicated that dandelions (Taraxacum officianale) were selected significantly more often than expected by a random distribution (P = 0.001), whereas grasses (Bromus spp. and Poa spp.) and cinquefoil (Potentilla gracilis) were avoided (P = 0.002). Use of the remaining species, cow parsnip (Heracleum lanatum), yarrow (Achillea millefolium), mountain blue bells (Mertensia fusiformis), and wild sweet pea (Lathyrus leucanthus), did not differ significantly from random, although cow parsnip and wild sweet pea tended to be more preferred and avoided, respectively, than the remaining species. Preferences in these marmots may have been based on fatty acid content, which is important for hibernation.

Selective feeding of pine voles on roots of tree seedlings

Previous studies have implicated numerous physical and biotic factors as contributing to the failure of oak to regenerate successfully throughout substantial portions of eastern North America. Recent field evidence in southern Indiana implicated belowground herbivory by pine voles ( Microtus pinetorum (LeConte, 1830)) as a potentially important but overlooked mortality agent for oak seedlings. We used cafeteria-style feeding trials to determine whether selection of hardwood seedlings by captive pine voles differed according to species or age. White oak ( Quercus alba L.) was selected more frequently and experienced a greater proportion of root removal by pine voles than same-age seedlings of the other four species tested. Yellow poplar ( Liriodendron tulipifera L.) was never eaten. White oak seedlings 3 and 6 weeks of age suffered proportionately greater root removal than conspecific seedlings 12 and 15 weeks of age; pine voles removed roughly constant levels of root biomass irrespective of seedling age. Our results confirm that pine voles selectively feed on oak seedlings. In areas where pine voles are abundant, belowground herbivory could limit regeneration of oak by reducing seedling growth and survival. The importance of pine voles as factors influencing the success of oak regeneration warrants closer scrutiny in future field studies.

Discrimination of intra- and inter-specific forage quality by collared pikas (Ochotona collaris)

The specific nutritional characteristics by which herbivores evaluate their foraging options are complex. We experimentally manipulated the crude protein and water content of two forage species ( Carex consimilis Holm. (= Carex bigelowii Torr. ex Schwein.) and Polygonum bistorta L.) commonly cached by collared pikas ( Ochotona collaris (Nelson, 1893)) to determine their influence on inter- and intra-specific forage selection. Preference data were collected for 27 pikas using cafeteria-style feeding trials in a randomized block design. A three-way interaction (species × protein × water) suggested that pikas made conditional forage selection decisions while caching these plants. The interaction was driven by greater selection for fresh rather than dried C. consimilis when both were not fertilized. Water content had no effect on the selection of either fertilized C. consimilis or fertilized P. bistorta. Overall, our results indicate that pikas made subtle decisions about their selection of vegetation during caching, based on variation in nitrogen and water content in addition to species-specific selection criteria. Further, our results imply that tests of foraging theory may need to consider intra-specific variation in forage characteristics, as well as inter-specific ranking of forage species.

SELECTION OF MAST BY GRANIVOROUS RODENTS OF THE CENTRAL HARDWOOD FOREST REGION

We used cafeteria-style feeding trials with 8 types of mast in various combinations to examine differences in resource selection among 5 syntopic species of granivorous forest rodents in west-central Indiana. Patterns of resource selection corresponded to differences in phylogeny and body size of granivores, with greatest similarities among closely related species of similar body size. Breadth of resource use varied inversely with body size in our trials. Resource selection by Sciurus carolinensis, S. niger, and Tamiasciurus hudsonicus was correlated positively with caloric and lipid content of mast and its size, whereas selection by Glaucomys volans was correlated negatively with the percentage of protective tissue associated with seeds. Laboratory trials indicated that T. hudsonicus and G. volans discriminate among mast of comparable physical and chemical composition on the basis of size, with a preference for larger seeds. Contrary to our expectations, T. hudsonicus, a recent immigrant from the boreal forest, did not exhibit a preference for seeds of red pine (Pinus resinosa) relative to mast of hardwood species. G. volans and Peromyscus leucopus tended to consume perishable white oak acorns immediately and to cache a substantial portion of less perishable seeds of nonpreferred species. Our results demonstrate the potential for considerable overlap in resource use among members of this guild. Guild members also seem to be affected differentially by physical and chemical properties of mast, and patterns of resource selection reflect contrasting foraging constraints under which these animals operate.

Volatile Oil Contents of Ashe and Redberry Juniper and Its Relationship to Preference by Angora and Spanish Goats

Angora and Spanish goats (Capra bircus) were exposed to ashe (Juniperus ashei Buchholz) female, ashe male, redberry (Juniperus pinchotti Sudw.) female and redberry male branches in cafeteria style feeding trials. Preferences were consistent across seasons (except winter). Spanish goats generally consumed more juniper than Angoras. Both breeds preferred ashe over redberry juniper and female over male plants. Concentrations of volatile oils varied significantly between species of juniper and among seasons, but not between sexes. Concentrations of total oils were greater in the spring and summer than in the fall and winter. Concentrations of sabinine+beta-pinene were greater in redberry than ashe for all seasons. Concentrations of myrcene were significantly greater for redberry during the spring and summer. Significant correlation of oil concentration with grams of juniper consumed indicated that specific oils were influencing preference for juniper. Correlations were similar for Angora and Spanish goats, indicating no differences between goat breeds in sensitivity to oils.

Common Components of Orchard Ground Cover Selected as Food by Captive Woodchucks

I examined diet selection by captive woodchucks (Marmota monax) for 20 species of plants commonly found in ground cover in Connecticut orchards. Cafeteria-style feeding trials indicated that the most frequently selected foods were dandelion (Taraxacum officinale) and common plantain (Plantago major), whereas orchard grass (Dactylis glomerata), Virginia creeper (Parthenocissus quinquefolia), and common toadflax (Linaria vulgaris) were selected least often. Sequential elimination of the most frequently selected foods resulted in increased use of mugwort (Artemisia vulgaris), campion (Lychnis alba), red clover (Trifolium pratense), aster (Aster vimineus), poison ivy (Rhus radicans), common strawberry (Fragaria virginiana), old-field cinquefoil (Potentilla simplex), bird vetch (Vicia cracca), and goldenrod (Solidago rugosa). Management of ground cover to reduce the abundance of plant species selected by woodchucks might reduce woodchuck numbers and the problems they cause. J. WILDL. MANAGE. 54(3):412-417 Woodchucks inhabit orchards throughout eastern North America, and damage due to their burrowing (Byers 1984) and gnawing of fruit trees (Swihart and Conover 1988, Swihart 1990) is a problem for growers. Phillips et al. (1987) estimated annual losses of $240,000 because of woodchuck activity in orchards in the Hudson Valley, New York. Population reduction typically is used to lessen problems caused by woodchucks, although immigration and increased fecundity of survivors may limit the utility of this type of control (Davis et al. 1964). Ground cover in orchards typically is composed of numerous herbaceous species that woodchucks eat. Reducing the abundance of commonly selected plants while encouraging the growth of less palatable species may lessen the suitability of orchards for woodchucks. Information on food habits of woodchucks consists primarily of qualitative observations (Hamilton 1934, Twichell 1939, Grizzell 1955). Moreover, these studies did not examine the relative abundance of each species in determining diet selection. My objectives were to examine selection by captive woodchucks for 20 plant species found in orchards and to determine the extent to which diet selection was affected by removal of the most readily eaten species. I thank M. R. Conover, G. L. Kirkland, Jr., P. M. Picone, and an anonymous reviewer for constructive comments on the manuscript, and P. M. Picone and A. DeNicola for diligent assistance with feeding trials. METHODS Feeding trials were conducted using 15 adult woodchucks (8 M, 7 F) captured in early spring of 1988 and 1989 in agricultural regions of western and central Connecticut. Woodchucks were housed individually in 1.5x 1.5x 0.9-m outdoor pens constructed of galvanized wire mesh and containing a plywood nest box. Animals were kept in cages with access to unlimited rodent chow and water for 10-30 days prior to initiation of feeding trials to permit acclimation to their surroundings and to a diet of rodent chow. Feeding trials were conducted in June and July 1988 and in June 1989. Vegetation used in trials was collected in or near orchards in central Connecticut. Vegetation not used immediately after collection was stored in a cool room (10 C), and any vegetation kept in storage >48 hours was discarded. Vegetation was collected from the same sites in both years to reduce variability in vegetation due to site characteristics. Nonetheless, differences in environmental conditions between years could have caused differences in plant quality and, consequently, selection of plants by woodchucks. However, selection by woodchucks was highly consistent between years (selection between 1988 and 1989, Pearson r = 0.78, 18 df, P 0.10 for all plant species). Hence, results were pooled across years and sexes prior to anal-

Development of food preferences: social learning by Belding's ground squirrels Spermophilus beldingi

The mechanisms by which food selection behavior develops may constrain the evolution of optimal foraging, yet these mechanisms have received relatively little attention in recent optimal foraging studies. We used cafeteria-style feeding trials to examine the role of social learning in the development of food preferences by a generalist mammalian herbivore, Spermophilus beldingi. Naive young spent relatively little time feeding and showed no preferences among five plant species offered in their feeding trials. This random pattern persisted for one set of young during two subsequent trials in the absence of their mother. A second group of young squirrels was tested initially alone, once with their mothers, and then once more alone. These squirrels fed more than those in the control group during their final trials, and showed significant preferences among plant species. These paralleled the preferences of their mothers. These results suggest that social learning may be important in the development of feeding behavior in ground squirrels, and provide a possible mechanism for cultural differences in food preferences among populations.