David F. Balph

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.

Ability of lambs to learn about novel foods while observing or participating with social models

We studied the influence of different social models on the intake of novel foods by lambs. The lambs were 6–7 weeks old during exposure to the novel foods. Lambs that ate novel foods for 16 min per day for 5 days with their mothers consumed about twice (P<0.05) as much of the foods after weaning as lambs that ate the foods with a dry ewe. Lambs exposed alone five times to the novel foods consumed about half (P<0.05) as much as lambs that ate with a dry ewe. Lambs did not learn to eat novel foods by observing, but not concurrently participating, while social models (mother, ewe) ate the foods. However, lambs that observed their mother eat and subsequently avoid a harmful food, ate less (P<0.05) after weaning than lambs that had observed the food only during exposure. Results were the same when lambs were tested 2 months later.

Sound Communication of Uinta Ground Squirrels

The purpose of this study was to catalog the calls given by Uinta ground squirrels, Citellus armatus , and to determine the cause and function of each. Spectrographic analysis permitted graphic descriptions and quantitative comparisons of the sounds. Records of the behavior of animals before and after each call, as well as the environmental situation, were the basis for determining the causes and functions of these signals. The squirrels produced six different calls: chirp, churr, squeal, squawk, teeth-clatter and growl. They used all the calls in agonistic behavior. An attack, approach or sight of another animal nearby elicited most of the calls. The signals functioned to intimidate others or to inhibit them from moving closer. Squirrels chirped in response to airborne predators and churred in response to ground predators. Spectrographic analysis indicated that these were the same calls the squirrels used in intraspecific threat. Their system of sound communication was simple and unspecific. Its primary use seemed to be as a general attention-getter. Perhaps relying on visual and scent communication and living in relatively open habitat promoted the development of their generalized system of sound communication.

Effects of predator fecal odors on feed selection by sheep and cattle.

The effectiveness of predator fecal odors in modifying feeding selection by sheep and cattle was investigated in two trials. In trial 1, animals could select from feed bins contaminated with coyote, fox, cougar, or bear fecal odor, and oil of wintergreen, or select the control feed. All odors were rejected (P<0.01) by sheep and cattle, except bear odors by sheep. In trial 2, animals could select feed during 10-min periods in an open 11-m × 16-m arena. Fecal odor did not influence approaches to feed bins, or head entries into bins. Only coyote fecal odor reduced (P<0.05) the time spent feeding in the contaminated bin, and increased (P<0.05) consumption from the control bin by both cattle and sheep. Some animals on some test days refused to feed from either feed bin, although cattle and sheep closely inspected bins. Results suggest that fecal odors may not prevent livestock from entering a treated area but may reduce the time spent grazing in such an area.

The Role of the Mother in the Intake of Harmful Foods by Lambs

Abstract In two experiments, we studied whether a conditioned food aversion in the mother affected intake of the same food by her lamb in the absence of the mother. Mothers averted to a palatable food ate very little of the food in the presence of their lambs during the 4-day exposure in Experiment 1 and the 5-day exposure in Experiment 2. In Experiment 1 the feeding behavior of mothers during exposure did not ( P >0.05) affect the intake of novel foods by lambs during the 10-day trial after weaning. However, in Experiment 2 lambs exposed with averted mothers ate less ( P =0.001) of the food (16 g per day) than lambs whose mothers ate the food in their presence (80 g per day) during an 8-day trial after weaning. Results persisted during an 8-day trial 3 months later. Differences in ages of lambs and exposure procedures may have caused different outcomes in Experiments 1 and 2. In Experiment 1, lambs were > 11 weeks of age during exposure, while in Experiment 2 they were 8 weeks of age. Moreover, mothers and treatment lambs in Experiment 1 were given the experimental and the alternative food simultaneously during the 4-day exposure, while in Experiment 2 mothers and lambs were given only one food at a time during the 5-day exposure.

The effect of experience on the foraging skill of lambs: Importance of plant form☆

Livestock moved often from one area to another are required to forage on plants of different life form. The degree to which experience foraging on one plant form affects foraging performance on another plant form is unknown. We compared the foraging skills of grass- vs. shrub-experienced lambs on monocultures of mature crested wheatgrass (Agropyron cristatum × Agropyron desertorum) and the shrub serviceberry (Amelanchier alnifolia). Grass-experienced lambs were more successful (P 0.05), more successful than grass-experienced lambs at prehending (93% vs. 86% success) and ingesting (5.0 vs. 4.5 g min−1) shrub. Shrub-experienced lambs had a higher (P 0.05). We conclude that the skills acquired by foraging on one plant form are to an important extent specific to that plant form. However, grass-experienced lambs foraging on shrubs were aided more than shrub-experienced lambs foraging on grass by their respective experiences.

Social Influences on Conditioned Food Aversions in Sheep

Abstract We conditioned ewes and 10-week-old lambs to avoid calfmanna pellets by giving them capsules of lithium chloride following ingestion of calfmanna. We then exposed conditioned ewes and lambs to calfmanna in the presence of similar aged conspecifics that ate calfmanna. Intake of calfmanna by sheep with the conditioned food aversion increased ( P P

Relationship between Plant Maturity and Foraging Experience of Lambs Grazing Hycrest Crested Wheatgrass

Abstract We compared the ingestive behavior of 8-week-old lambs experienced with either hycrest crested wheatgrass ( Agropyron cristatum × Agropyron desertorum ) or the shrub serviceberry ( Amelanchier alnifolia ) when they grazed on monocultures of vegetative or flowering hycrest crested wheatgrass growing in pots placed in the soil at ground level. A split block design was used to test for the main effects of plant maturity (vegetative or flowering) and experience (grass or shrub), and their interaction. Phenology affected ingestive behavior. Bite size (0.29 vs. 0.10 g per bite) and intake rate (4.2 vs. 3.3 g min −1 ) were higher ( P −1 ) was lower ( P P −1 ). Grass-experienced lambs had slightly higher bite rates (25 vs. 24 bites min −1 ) and took larger bites (0.21 vs. 0.18 g per bite), but differences were not statistically significant ( P > 0.05). The interaction between plant phenology and experience was not significant ( P > 0.05). Grass-experienced lambs were more ( P −1 ) and flowering (4.6 vs. 3.7 g min −1 ) grass than shrub-experienced lambs. Shrub-experienced lambs failed more ( P

The evolution of alarm calling: a cost-benefit analysis

Abstract Three arguments for the likelihood of alarm calling in colonial animals are presented. The first, a game-theoretic portrait, predicts that alarm calling should be less probable per animal in larger groups and also that actual fitness benefits and costs are not quantitatively important in determining the evolutionarily stable probability of calling in large populations. The second is a geometric model of the dependence of risk upon position within a colony of sedentary animals. The two models are integrated to form a third, which predicts that the probability that an animal gives an alarm call is independent of both group size and the ratio of benefits to costs, above some minimum group size. Some of the available data are consistent with the models, and some are not.

Age and seasonal differences in the synthesis and metabolism of testosterone by testicular tissue and pineal HIOMT activity of Uinta ground squirrels (Spermophilus armatus).

Abstract Male Uinta ground squirrels ( Spermophilus armatus ) were sacrificed from a free-living population (a) during the breeding season, which immediately followed emergence from hibernation; (b) after the reproductive season; (c) and just prior to aestivation/hibernation. HIOMT activity of the pineal gland was assayed and related to the ability of the gonads to synthesize and metabolize testosterone. Older squirrels had higher HIOMT activity than did the younger animals. The activity of this enzyme was lowest in squirrels during the breeding season. HIOMT activity increased after the breeding season to its highest level just before the squirrels enter aestivation/hibernation. At this time, testicular weight increased concomitant with an apparent increase in HIOMT activity. Testicular size and weight were largest at the time of emergence of the animals from hibernation. Androgen synthesis was also greatest during the breeding season. As would be expected, both decreased rapidly there-after. The testes formed little 17α,20α-dihydroxyprogesterone during or after the breeding season, contrary to what has been reported for rats and house sparrows. The older squirrels demonstrated a greater capacity for testosterone metabolism during the breeding season than did the younger animals.