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Accueil du site → Doctorat → États-Unis → 1991 → Deer and cattle foraging strategies under different grazing systems and stocking rates

Texas Tech University (TTU) (1991)

Deer and cattle foraging strategies under different grazing systems and stocking rates

Ortega, Isaac M

Titre : Deer and cattle foraging strategies under different grazing systems and stocking rates

Auteur : Ortega, Isaac M

Université de soutenance : Texas Tech University (TTU)

Grade : Doctor of Philosophy (PhD) 1991

Résumé
The purpose of this research was to determine the foraging strategies of deer and cattle under continuous and short- duration grazing at heavy and moderate stocking rates. The study was conducted from October 1987 through July 1989 at the Welder Wildlife Refuge, Sinton, San Patricio County, Texas. From tame white-tailed deer, I obtained food habits data by direct observation. The esophageal fistula technique was used to determine cattle diets. To understand how different techniques might affect diet estimates for cattle, I compared the esophageal fistula and direct observation techniques using gentle, tractable cattle. I concluded that for the Texas Coastal Bend, an area with highly diverse plant communities, direct observation is not as reliable a technique as the esophageal fistula. These techniques were different in determining the use of forage classes and plant species in cattle diets. The bite-count technique may be acceptable if analyses are limited to only those plant species making up >2% of the diet. Homogeneity of the vegetation community of the study pastures was not affected by the grazing treatments. However, the drought of the second year produced some floral changes. Through use of canonical discriminant analysis, diets of deer and cattle were found to be distinct from each other in every treatment throughout the sampling period. Differences were related to forage classes used by the animal species. Overall, deer used mostly forbs (72%) while cattle primarily used grasses (60%) and forbs (39%). The forbs Oxalls dinellii, Ruellia nudiflora, and Desmanthus virgatus, and the grasses Buchloe dactyloides, Tridens congestus, and Stipa leucotricha were the species that separated deer and cattle diets. Deer were most sensitive to the vegetation conditions within each treatment during the summer months (May through September) and the second winter which was affected by the drought. During these periods deer selected different diets across all treatments. Deer were the least sensitive to the grazing treatments during spring. Their diets were the same across all treatments. The highest diet overlap (range = 43-64%) between deer and cattle occurred in Winter 1 and Spring 1, when deer and cattle were consuming Ambrosia psilostachya. Geranium carolinianum, Oenothera speciosa, O. dillenii and Ratibida columnaris. During the second year, significant overlap occurred only on pastures heavily stocked by cattle. Information on deer foraging behavior, which included grazing time, bites per minute, and distance traveled, was collected under the different treatments. Predictions such as an inverse relationship between search time and grazing time (r = -0.91), or the direct relationship between search time and the distance traveled (r = 0.92), were confirmed for white-tailed deer

Mots Clés : Cattle — Feeding and feeds – Texas — Grazing — White-tailed deer — Feeding and feeds

Présentation (TTU)

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