Browse Consumption Research Articles

Patterns in consumption of woody plants by snowshoe hares in the northwestern United States

Herbivores manifesting spatially variable population densities may elicit geographical differences in the characteristics of the plants upon which they feed. Northern snowshoe hare (Lepus americanus) populations undergo dramatic numerical cycles; during periods of hare abundance, browsing by these populations can result in both absolute food shortage and the production of chemical defenses among browsed plants. Southern hare populations never achieve the densities characteristic of their northern counterparts and, therefore, should be less likely to elicit either food biomass limitation or the production of plant chemical defenses. Thus, hares in these populations should have access to a superabundant food supply and select browse species according to their nutrient content rather than their defensive chemical composition. We measured the extent of browse use by hares in the southwestern portion of the species’ range by calculating per capita winter browse availability (total biomass of potential food divided by winter hare population estimate) on six study sites during the winter of 1999. In addition, we used feeding trials on captive hares to determine patterns of browse consumption. Per capita browse biomass estimates were adequate to support the hares residing on each study site; on average, a 10-fold numerical increase would have been required to produce absolute food shortage. Patterns in consumption of browse by hares were not related to concentrations of plant chemical defenses (total phenols and monoterpenes), but rather to crude protein content. Levels of protein and copper (and possibly selenium) in the major browse species in our area were low, implying that, despite having access to a superabundance of poorly defended food, hares in southwestern populations may be subject to a poor-quality diet. In support of this possibility, we found that free-ranging hares had reproductive rates (potential natality = 5.64 young female-1 year-1) that were qualitatively lower than any reported in the literature (n = 18 studies) and males had relatively poor overwinter condition as well as delayed testes recrudescence. Poor diet quality and, consequently, low reproductive rates may contribute to the allegedly non-cyclic and generally lower densities of southwestern hare populations.Keywords: snowshoe hare, Lepus americanus, browse availability, plant chemical defenses, browse consumption patterns, reproductive rates, protein, copper.

Digestive efficiency in two small, wild ruminants: the dik-dik and suni antelopes

A comparative study, using six dik-dik and eight suni antelope, was undertaken to identify similarities and differences that may exist in the digestive process of these two small, East African ruminant browsers. The suni antelope was the more select feeder, preferring the native, Grewia sinilis leaves over that of lucerne hay. Daily forage consumption rate, per unity body weight, was greater in the dik-dik (40.4 g/kg) than for the suni (30.6 g/kg), while daily fluid intake was considerably less (i.e. dik-dik, 68 ml/kg versus suni, 106 ml/kg body weight). Rumen fermentation studies suggested that the suni antelope attained the more rapid rumen and caecal fermentation activities, when compared to the dik-dik antelope. The difference in ruminal and caecal digestive process of the two antelope is suggested to be partly the result of the dik-dik’s arid-adaptation strategies of less fluid intake and a more diverse (less selective) browse consumption, relative to the suni antelope.

Grazing Steer Fecal Output Dynamics on South Texas Shrubland

Combined with other information, fecal output appears to have potential use in models to predict forage intake. Better understanding of fecal output dynamics relative to forage availability could improve model estimates of animal performance. Field trials were conducted during 4 different periods to investigate the relationship between 1) declining forage mass or forage component availability and beef steer fecal output and between 2) browse consumption and available forage mass. Fecal output was estimated using the rare-earth marker ytterbium. Initial fecal output as a percentage of body weight was greatest in March (1.24%) and least in August (0.96%). Regression slopes were negatively correlated (-0.73) with initial forage mass. As indicated by regression slopes, fecal output declined most rapidly in March (slope = 0.57) and slowest in August (slope = 0.13). Expression of available forage mass as either daily grass allowance or daily grass leaf allowance, both as g dry matter/kg live weight, produced similar regression equation statistics. Development of regressions for individual pastures within trials did, however, improve equation statistics in all trials except August. Browse consumption was < 10% until daily grass allowance fell below 50 g/kg live weight then increased to between 53 and 64% below 25 g/kg live weight, but was not adequate to maintain fecal output. Apparent seasonal differences in fecal output suggest lower forage intake (29%) in August compared to March. Fecal output was not affected by daily grass allowance above 100 g. Fecal output declined to below 0.6% of body weight below 100 g daily grass allowance. Data are interpreted to suggest that different fecal output curves and/or adjustment factors may be needed to account for season and initial forage mass.

Chinese Privet and the Feeding Ecology of White-Tailed Deer: The Role of an Exotic Plant

Exotic plants and overabundant wildlife are apparent indicators of disturbed habitats, yet few studies have investigated their interactions. Chinese privet (Ligustrum sinense) is an abundant, exotic shrub in the southeastern United States, yet little is known about its forage value to white-tailed deer (Odocoileus virginianus) e quantified the seasonal importance of privet browse and fruit in the food habits of deer at Chickamauga Battlefield Park (CBP) in Georgia, and we determined seasonal cycles in crude protein (CP) content from privet browse. Analyses of rumen samples from 146 deer collected during 32 consecutive months (1992-94) revealed total privet (browse and fruit) averaged 11.1% of rumen volume during fall and 13.3% during winter. Fall consumption of privet browse increased almost 2 times, and privet fruit consumption >20 times in a fall of low acorn consumption. Winter browse surveys conducted in February for 2 years revealed privet browse composed >50% of available browse and >75% of browse used. Privet browse maintained a CP content >12% in all months. These results suggest privet is an important component of the fall and winter diets of CBP deer and may serve as a nutritional buffer during years of acorn scarcity. The value of privet as a deer forage must be weighed against the threat it poses to biodiversity conservation.

SPATIAL PATTERNS IN THE MOOSE–FOREST–SOIL ECOSYSTEM ON ISLE ROYALE, MICHIGAN, USA

The effects of herbivores on landscape patterns and ecosystem processes have generally been inferred only from small-plot or exclosure experiments. However, it is important to directly determine the interactions between herbivores and landscape pat- terns, because herbivores range over large portions of the landscape to meet requirements for food and shelter. In two valleys on Isle Royale, Michigan, USA, soil nitrogen availability and its temporal variance decreased rapidly as consumption of browse by moose (Alces alces) increased up to 2 g·m 22 ·yr 21 ; with greater amounts of consumption, nitrogen avail- ability was uniformly low and constant from year to year. We tested three geostatistical models of the spatial distribution of available browse, annual browse consumption, conifer basal area, and soil nitrogen availability across the landscape: (1) no spatial autocorrelation (random spatial distribution); (2) short-range spatial autocorrelation within a patch, but random distribution of patches at larger scales (spherical model); and (3) both short-range autocorrelation within a patch and regular arrangement of patches at larger scales (harmonic oscillator model). Conifer basal area and soil nitrogen availability fit the harmonic oscillator model in both valleys. Annual consumption and available browse showed oscillations in one of the valleys and only short-range autocorrelation in the other. In both valleys, however, the spatial pattern of annual consumption followed that of available browse. The predom- inance of spatially oscillatory patterns suggests that the interactions of moose with the forest ecosystem cause the development of both local patches of vegetation and associated nitrogen cycling rates, as well as the development of higher order patterns across the larger landscape. We suggest a coupled diffusion model of herbivore foraging and plant seed dispersal that may account for these patterns.

Landscape-Scale Foraging Decisions by Reintroduced Arabian Oryx

We evaluated landscape-level movements of reintroduced Arabian oryx (Oryx leucoryx) in relation to rainfall for 8 years (1982-89). For the first 4 years (1982-85), captive-bred oryx released into habitat devoid of conspecifics demonstrated a distinct shift in movement patterns as foraging conditions deteriorated. Based on mean monthly estimates, during the first 2 months after rain, oryx used large areas (297-724 km 2 ), exhibited low site fidelity (15-32%) overlap between consecutive months), high range expansion (45-62%) new area used each month), and undertook more long distance journeys than expected (P < 0.01). From 2 to 3 months after rainfall, oryx reduced the amount of area used by 86%, increased site fidelity by 72%, reduced range expansion by 29%, and gradually suspended long distance forays. We related this shift to the low nutritive quality of the oryx's primary forage species (Stipagrostis spp.). Once Stipagrostis declined to extremely low levels of crude protein, copper, and phosphorus, the oryx apparently suspended their nutritionally costly searching activities, and instead remained in areas where Stipagrostis was most palatable. In contrast, in years 6 through 8 following their release, the oryx responded to rain with no apparent shift in foraging patterns. Instead, they exhibited less variable and reduced levels of range expansion (10-42%) and area use (180-211 km 2 ). In addition, site fidelity was more consistent on a monthly basis (46-65% overlap),. and long distance movements were more random regardless of the influence of rainfall on the nutritive value or palatability of Stipagrostis. The changes in movement patterns over time were attributed to: (1) a reduction in the oryx's threshold of acceptance for low-quality Stipagrostis; (2) decreased consumption of Stipagrostis and a concomitant increase in browse consumption, and (3) greater knowledge of the landscape. Captive-bred oryx released in years 7 and 8 into the existing reintroduced population reacted to changes in forage nutritive quality caused by rain with a similar shift in foraging patterns as exhibited by the first releases during their first 4 years in the desert. This result emphasizes the relative importance of learned foraging behavior in explaining changes over time in the movement patterns of the oryx. Results of this study indicate that reintroductions of social herbivores should be implemented in ways that enhance the transfer of knowledge from experienced to naive individuals.

Stump height effects on sprouting of mountain maple, paper birch and pin cherry — 10 year results

Stump sprouting of mountain maple, paper birch and pin cherry was studied in relation to residual stump height. The three-year-old stems were cut at stump heights of 0, 15, 45 and 75 cm in a completely randomized plot design. Two growing seasons after cutting, the percent of stumps with live sprouts was lower for the low stump heights. Two years after cutting, the mean number of sprouts per stump of the three species significantly increased with stump height but the effect was no more significant after 10 years. Initially, total height of the sprouts was significantly greater for the higher stump heights of the three species, which is explained by the point of origin of the sprouts along the stump. After 10 years, this effect was no more significant. Except for pin cherry after the first growing season, the three species produced sprouts of similar vigor during the first 10 years, expressed in terms of both diameter and height growth, among the four stump heights. In view of the increasing stump mortality of these three species after manual or mechanical release treatments of a conifer regeneration, a cut height of 15 cm is recommended. Conversely, increasing stump height will likely favor sprout production, which could be advantageous in wildlife habitat management for browse consumption. Key words: stump height, vegetation management, sprout production, vegetative reproduction, wildlife habitat

Diet choice and nutrition of captive snowshoe hares (Lepus americanus): Interactions of energy, protein, and plant secondary compounds

:We examined consumption and digestibility of winter browse in captive snowshoe hares (Lepus americanus Erxl.) to determine how energy content, protein quality and plant secondary chemicals interact to affect their diet choice and nutrition. We found that preferred foods of snowshoe hares have higher apparent digestibilities of dry matter and energy than nonpreferred foods. Digested crude protein was unaffected by increased consumption of preferred foods, but declined when hares consumed nonpreferred foods. Rate of weight loss in hares increased with increasing consumption of nonpreferred twigs. Hares did not compensate for low protein or low energy content by eating more twigs. Weight changes were correlated with the energy content of the food and its digestibility, whereas consumption was correlated with phenol and protein content. If hares can increase consumption of preferred foods, they may simultaneously meet both their energy and protein requirements. If they are obliged to increase consumption of nonpreferred foods, then protein requirements may never be met due to the effects of secondary compounds. During periods of limited food availability, snowshoe hares should select a mixed diet that may include small quantities of poor-quality food items, regardless of preference, allowing them time to find good-quality foods.

Epidemiologic evaluation of encephalitic listeriosis in goats

Objective To evaluate host and environmental factors associated with the development of encephalitic listeriosis in goats. Design Retrospective analysis of diagnostic laboratory records and survey of veterinarians and goat producers. Sample Population 355 goat herds accessible through laboratory records; 38 veterinarians who treated goats and 76 goat producers. Procedure Data regarding breed and use for goats affected with encephalitic listeriosis were obtained from surveys and case follow-up information. Listeria monocytogenes isolates from the brains of 7 affected goats were serotyped and subjected to DNA restriction analysis. Results Odds ratio for the development of encephalitis listeriosis in Angora (mohair-producing) goats was 22.9 by use of diagnostic laboratory records. Surveys also revealed a high prevalence in herds of Angora and other breeds that subsisted on woody browse, although Angora goats feeding predominantly on hay or pasture were not affected. Listeria monocytogenes isolates from 4 Angora goats in 3 herds differed in DNA restriction patterns, although the pattern was identical in 3 other goats from another herd. Clinical Implications Encephalitic listeriosis can be observed in all goat breeds, but a lifestyle of heavy browse consumption seems important to the development of disease in some herds. (J Am Vet Med Assoc 1996;208:1695-1699)

Temporal Changes in Winter Diet Selection by White-Tailed Deer in a Northern Deer Yard

We followed short-term changes in the winter foraging behavior of yarded northern white-tailed deer (Odocoileus virginianus) over 3 winters to evaluate the hypothesis that deer forage nonselectively. We used a sequential-clipping, browse-monitoring technique to measure browse use and availability at biweekly (1983-84) or weekly (1984-85, 1985-86) intervals. From initial diets composed of 1-4 browse species, deer expanded their diets to include up to 16 out of 19 species by the end of each winter. Rate and magnitude of diet expansion were influenced by the degree of browsing pressure in the study area. We found partial preferences in diet choice, but important diet items were used in nonrandom runs once adopted into the diet. Proportional representation of all browse species in the diet varied on a short-term basis. Three dominant species, red-osier dogwood (Cornus stolonifera), pussy willow (Salix discolor), and white ash (Fraxinus americana), exhibited gradual compensatory shifts in proportional use over each winter, which reflected early season preferential selection of red-osier dogwood. During the third winter, browsing was nonrandom and selective, and temporal changes in patterns of browse use occurred. Forage ratios and relativized electivity indices of the 3 dominant species also changed gradually, indicating sequential shifts in preference for redosier dogwood, pussy willow, and white ash, respectively. Overall, deer foraging in the winter yard was dynamic, with high diet selectivity at the beginning of the yarding season and gradual diet generalization as browse was depleted in the yard. J, WILDL. MANAGE. 55(3):361-376 In winter, white-tailed deer in north-temperate regions congregate in deer yards, which provide shelter during periods of deep snow and inclement weather (Telfer 1967, Rongstad and Tester 1969, Marchinton and Hirth 1984). However, deer yards only represent a small proportion of the total annual range, resulting in high population densities in areas of limited food availability. Yarded deer meet their energy and nutrient requirements from 2 main sources: catabolization of limited body fat and protein reserves (DelGiudice et al. 1988) and ingestion of woody browse (Mautz 1978). Prolonged confinement of deer to winter yards causes the gradual depletion of the browse supply, often resulting in high deer mortality by starvation late in the yarding season. The consumption of browse in winter slows the rate of tissue catabolization, a process that is critical to survival in northern regions (Mautz 1978). Efficient use of limited browse resources during periods of thermal stress is evolutionarily advantageous; presumably, the selective pressures of overwintering have contributed to the evolution of a particular foraging strategy in deer which is adapted to food-limited situations such as those in a northern deer yard. Several authors have discussed foraging behavio of large ungulates in food-limited environments from a theoretical standpoint. Westoby (1974) and Belovsky (1978) proposed that herbivore diet specialization should occur when food resources are abundant, and diet generalizati n should occur at low food levels. Using data from Wetzel et al. (1975), Nudds (1980) suggested that a shift in foraging strategy from specialist to generalist occurs as winter food resour es are depleted. Though criticized on methodological grounds by Jenkins (1982), Nudds (1980) posed a pertinent question about possible changes in foraging strategy adopted by deer in the face of ever-diminishing winter food resources. To date, most winter field studies of deer foragi g have examined total use of foodstuffs within a given habitat over the entire yarding season. Standard browse inventory techniques involve establishing transects or sample plots at a few critical times in the year (Gysel and Lyon 1980), usually fall and spring, to assess winter browse use. LaGory et al. (1985) employed seasonal totals of browse use to plot relative browse use over an entire winter as a function of estimated relative browse availability at the beginning of the winter. They found significant positiv linear regressions between use and

Timing of Parturition and Lactation in Southern Mule Deer

Factors related to timing of fawning in southern mule deer (Odocoileus hemionus fuliginatus) were studied in montane areas of San Diego Co., California, from June 1977 to January 1979. Mean date of birth was 27 June (SD = 7.4 days). Rates of nursing were highest in June and declined thereafter. Forage available to females following fawning was dry and of low quality; deer increased their consumption of browse during this period. A resultant shortened period of maternal care may have contributed to mortality (50–74%) of fawns. Timing of parturition may be related to the requirements of the maternal female during the last third of gestation when favorable temperatures and adequate precipitation combine to produce abundant forage. Sex ratios (males:females) changed markedly from yearlings (3.1:1) to adults (0.2:1), presumably because rutting activities followed harsh summer conditions.

The rate of consumption of bush and grass by goats in a representativeacacia karroosavanna community in the Eastern Cape

Abstract Consumption of browse and grass in a representative Acacia karroo savanna community was measured. Acacia karroo was preferred to grass. It was selected almost exclusively when available at high leaf densities. Grass was consumed in significant amounts only when approximately 50 % of the available A. karroo leaf had been consumed. Maximum daily intake was 78 g.W−0,75 kg.day−1 and decreased with decreasing amount of browse on offer. When approximately 90 % of the available A. karroo leaf had been removed, the goats had consumed only 30 % of the available grass. Total intake of browse plus grass was lower during the period when the goats changed from consuming mostly A. karroo to consuming mostly grass. Goats did not appear to select a diet according to their nutritional needs, as judged by feeding tables, when this was possible. This may be due to protein indigestibility caused by tannin complexing by A. karroo, luxury consumption of A. karroo as a favoured food, an adaptation by goats to use browse more efficiently than grass, or differences in palatability between A. karroo and grass.

Use of predator odors as repellents to reduce feeding damage by herbivores

The effectiveness of predator odors (fecal, urine, and anal scent gland) in suppressing feeding damage by snowshoe hares was investigated in pen bioassays at the University of British Columbia Research Forest, Maple Ridge, British Columbia, Canada. A total of 28 bioassay trials tested the effects of these odors on hare consumption of willow browse and coniferous seedlings. Lynx and bobcat feces, weasel anal gland secretion, and lynx, bobcat, wolf, coyote, fox, and wolverine urines resulted in the most effective suppression of hare feeding damage. Novel odors of domestic dog urine and 2-methylbutyric acid did not reduce feeding. A field bioassay with lodgepole pine seedlings and weasel scent provided significant results comparable to the pen bioassays. The short-term (up to seven days) effectiveness of these treatments was more likely due to evaporative loss of the active repellent components of a given odor than habituation of hares to the stimulus. Predator odors as repellents have a biological basis compared with the anthropomorphic origins of commercial repellents. When encapsulated in weather-proof controlled-release devices, these odors could provide long-term protection for forestry plantations and agricultural crops which experience hare/rabbit feeding damage.

Estimation of Dry Matter Intake of Free-Ranging Moose

Two free-ranging moose (Alces alces) cows were used to study seasonal changes in voluntary intake between December 1982 and January 1984. Observations of each animal were made during a continuous 24-hour period every 6-8 weeks. Dry matter intake was estimated from the ratio of total dry matter in the feces to the percent indigestibility of dietary dry matter and from the bite-count technique. During the 1-year period, dry matter intake ranged from 37.8 g/kg BWo075 in January to 128.5 g/kg BW0-75 during July. The bite-count technique estimated voluntary intakes which were within 6% of those calculated from total fecal collections. Dry matter digestibility of selected diets ranged from 71% in late May to 44% in late January as estimated by the in situ nylon bag technique. Crude protein content in the feces was correlated (P < 0.05) with digestible dry matter intake (r2 = 0.88) and with the nitrogen content of simulated diets (r2 = 0.95). Nylon bag dry matter digestibility of simulated diets was highly correlated (P < 0.001) with diet dry matter (r2 = 0.73), crude protein (r2 = 0.69), and neutral detergent fiber (r2 = 0.90). The maintenance energy requirement for a free-ranging moose cow, estimated by least squares linear regression, was 399 KJ/ kg BW075 daily. J. WILDL. MANAGE. 49(3):785-792 Seasonal variations in forage intake by freeranging ungulates express the interactions of animal requirements and wide fluctuations in diet quality and availability. Schwartz et al. (1981) showed that penned Alaska moose fed a pelleted ration reached peak intake during summer and low points during the breeding season and late winter. Miquelle (1979) reported dry matter intakes of young moose on Isle Royale during summer from pen trials with clipped browse and of free-ranging moose using the bite-count technique. Crete and Bedard (1975) and Nystr6m (1980) estimated browse consumption for moose in Quebec and Sweden, respectively, using modified versions of the twigcount technique. Approximate calculations of daily food consumption by moose were made by Gasaway and Coady (1974) based on seasonal differences in rumen fill. However, few empirical data are available on seasonal forage intake of free-ranging moose. Several methods for determining forage intake of free-ranging animals have been published. Among these, ratio and bite-count methods are most practical for studies on wild ruminants. The ratio technique (fecal excretion/indigestibility of the diet) appears most reliable for estimations of intake by grazing livestock (Cordova et al. 1978). Measures of fecal output are usually combined with an in vitro estimate of diet digestibility from esophageal samples (Allison et al. 1982, Holechek and Vavra 1982). However, fecal output also can be determined indirectly using external markers (indigestible indicators attached to diet particles) and digestibility can be estimated with indigestible internal markers such as lignin or silica (Langlands 1975, Engdahl 1976). The bitecount technique, a useful alternative for less tractable animals, has been used to estimate feeding rates and daily intake by wapiti (Cervus elaphus nelsoni) (Collins 1977, Hobbs 1979, Ni tfeld 1983, Wickstrom 1983), mule deer (Odocoileus hemionus) (Wickstrom 1983), and moose (Miquelle 1979). Accurate measurement of bite rate, simulated bite size, and total foraging time are required for a reliable predictio of voluntary intake. This study determined seasonal changes in dry matter consumption by habituated freeranging moose using both ratio and bite-count methods. We acknowledge the financial support of Alberta Recreation, Parks and Wildl. Found., Agric. Res. Counc. of Alberta, The Alberta Env ron. Trust, and the Nat. Sci. and Eng. Res. Counc. We wish to thank D. M. Renecker, D. M. Bayne, M. T. Nietfeld, C. D. Olsen, L. R. Griffith, M. H. Griffith, A. J. Keith, K. L. Risenhoover, and D. A. Welch for their skillful assistance in data collection. Special thanks to D. M. Renecker and C. D. Olsen for their helpful comments on the manuscript.

White-Tailed Deer Food Habits and Nutritional Status as Affected by Grazing and Deer-Harvest Management

White-Tailed Deer Food Habits and Nutritional Status as Affected by Grazing and Deer-Harvest Management

Browse Regrowth and Consumption Following Summer Defoliation by Moose

Browse Regrowth and Consumption Following Summer Defoliation by Moose

Consumption of Artificial Browse Supplements by Penned White-Tailed Deer

Four experiments with captive white-tailed deer (Odocoileus virginianus) involving 54 adults of both sexes were conducted to establish if a manufactured protein-energy supplement block would be consumed by deer subsisting on winter browse, and, if so, whether this supplement has po- tential for increasing winter survival. When fed with evergreen and/or hardwood browse, this sup- plement increased dry matter intakes from 39 to 161 percent. This increase was a result of both sup- plement ingestion and increased consumption of browse. Apparent digestibility of the food was not increased, but rumen function appeared more normal and the increased nutrient supply to the tissues resulted in decreased tissue catabolism and less weight loss. The use of attractants on the blocks did not consistently speed their acceptance as food. The opportunity for deer to consume a protein-energy sup- plement, when winter browse is the only other food available, has the potential for reducing weight loss and perhaps reducing death from starvation.

Daily Browse Consumption by Moose in the Gaspe Peninsula, Quebec

Daily Browse Consumption by Moose in the Gaspe Peninsula, Quebec