Alarm calling behavior of the thirteen-lined ground squirrel, Spermophilus tridecemlineatus

Alarm calling in a population of thirteenlined ground squirrels, Spermophilus tridecemlineatus , was studied over a three-year period. Data on ground squirrel reactions to human and canine approaches and to the approach or presence of avian predators were used to quantify alarm calling behavior.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46905/1/265_2004_Article_BF00299364.pd

Optimal foraging and fitness in Columbian ground squirrels

Optimal diets were determined for each of 109 individual Columbian ground squirrels ( Spermophilus columbianus ) at two sites in northwestern Montana. Body mass, daily activity time, and vegetation consumption rates for individuals were measured in the field, along with the average water content of vegetation at each ground squirrel colony. I also measured stomach and caecal capacity and turnover rate of plant food through the digestive tract for individuals in the laboratory to construct regressions of digestive capacity as a function of individual body mass. Finally, I obtained literature estimates of average daily energy requirements as a function of body mass and digestible energy content of vegetation. These data were used to construct a linear programming diet model for each individual. The model for each individual was used to predict the proportion of two food types (monocots and dicots) that maximized daily energy intake, given time and digestive constraints on foraging. Individuals were classified as “optimal” or “deviating”, depending on whether their observed diet was significantly different from their predicted optimal diet. I determined the consequences of selecting an optimal diet for energy intake and fitness. As expected, daily energy intake calculated for deviators (based on their observed diet proportion) was less than that for optimal foragers. Deviating foragers do not appear to compensate for their lower calculated energy intake through other factors such as body size or physiological efficiency of processing food. Growth rate, yearly survivorship, and litter size increase with calculated energy intake, and optimal foragers have six times the reproductive success of deviators by age three. Optimal foraging behavior, therefore, appears to confer a considerable fitness advantage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47783/1/442_2004_Article_BF00318534.pd

Cues cattle use to avoid stepping on crested wheatgrass tussocks

This paper tests 2 hypotheses regarding the cues cattle use to avoid stepping on crested wheatgrass (Agropyron cristatum (L.) Gaertner) tussocks. The first hypothesis is that cattle are attentive to shade and avoid tussocks by stepping on light areas (soil interstices) and avoiding dark areas (tussocks). In an experiment with 90 Angus heifers placed in a short-duration grazing paddock of 8.5 ha, the animals stepped with equal relative frequency on 28 patches of bare ground, 37 disks painted the shade and color of bare ground, and 37 disks painted to match vegetation over a 24-h period. We therefore reject the shade-cue hypothesis. The second hypothesis is that cattle are attentive to the vegetation itself in their avoidance behavior, and that as they crop the vegetation the frequency of trampling increases. In experiments similar to the first, cattle stepped on 85 intact tussocks 9 times, on 85 clipped (3 to 4 cm above litter) tussocks 28 times, on 85 vegetation-free tussock mounds 107 times and on 35 patches of bare ground 130 times. These differences are statistically significant. The data are consistent with the vegetation-cue hypothesis, except that the cattle also were attentive to the elevated substrate upon which the tussock grew. We conclude that, under the test conditions, hoof action does not have an important impact on crested wheatgrass pastures used for short-duration grazing. The impact could approach importance, however, if the pasture was grazed more heavily and if the vegetation was dry and dusty.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Development of Dietary Choice in Livestock on Rangelands and Its Implications for Management

Plant species that constitute forage for a given species of livestock vary tremendously throughout the diverse environments inhabited by domestic livestock. Within neurological, morphological and physiological constraints, learning early in life enables herbivores to develop preferences for or aversions to available plants and to acquire the motor skills necessary to harvest and ingest those forages efficiently. Hence, the foraging experiences of young herbivores undoubtedly affect their dietary habits as adults. Three mechanisms help young herbivores to learn efficiently to select appropriate foods: 1) food imprinting, 2) social models and 3) trial and error. Dietary habits of adults apparently are more stable than those of young herbivores. Adults accept new foods less readily, avoid foods that cause gastrointestinal distress to a greater degree, and are influenced less in choice of diet by social models than young animals are. The ability of livestock to learn dietary habits early in life presents both problems and opportunities for managers. Livestock that forage efficiently in the environment where they are reared may not forage as efficiently in a new environment. Diet training may enable managers to create a foraging group more suited to management goals. Additional research is needed to determine how age at which exposure occurs, as well as how duration, intensity, variability and complexity of exposure early in life affect dietary habits of adults. These variables affect the efficiency of learning and the persistence of dietary habits and thus are crucial to the development of cost-effective management based on diet training

Applicability of Five Diet-Selection Models to Various Foraging Challenges Ruminants Encounter

It is common knowledge that ruminants do not forage at random, but select a diet from the plants available to them. We believe foraging environments present at least five problems or challenges to ruminants selecting dietary items: (1) variation among dietary items in kind and amount of nutritional constituents, (2) variation among potential dietary items in kind and amount of chemical defenses, (3) plant morphological defenses, (4) temporal and spatial variation in the quantity and quality of forage, and (5) exposure of ruminants to unfamiliar foraging environments. Our objective is to assess the ability of five explanations of diet selection to provide insights into the responses of ruminants to these challenges. The models are: (1) endogenously-generated hungers (euphagia), (2) immediate sensory consequences (hedyphagia), (3) body morpho-physiology and size (morphophysiology), (4) learning through foraging consequences (learning), and (5) nutritional optimization (optimal foraging). We make the assessment by first describing the diet-selection challenges and then discussing the models and their applications to the challenges