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Cheney, D. L., & Seyfarth, R. M. (1988). Social and non.social knowledge in vervet monkeys. In Machiavellian Intelligence (pp. 255–270). Oxford: Oxford Univ Press.
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Houpt Ka, H. T. (1988). Social and illumination preferences of mares. J Anim Sci, 66, 2159–2164.
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Berger, J., & Cunningham, C. (1988). Size-Related Effects on Search Times in North American Grassland Female Ungulates. Ecology, 69(1), 177–183.
Abstract: Feeding and searching (= vigilance) rates arise as a result of many interrelated factors including trophic level, diet, reproductive condition, sex, habitat, body mass, and potential predation pressure. Because of unique ecological conditions in which the confounding influences of all but two of these variables could be minimized, we examined the hypothesis that body mass alone accounts for interspecific differences in search times, and tested it with females of four sympatric native North American ungulates (Bison bison, Antilocapra americana, Ovis canadensis, and Odocoileus hemionus). When the effects of group size were controlled, smaller bodied species were more vigilant (per unit body mass) than larger ones. However, search times (ST) also scaled to body mass, and between 81 and 97% of the ST variance was explained by either exponential or power functions. To remove the potential bias that predators exert different influences on species of varying size, search times of bison in areas with and without their major predator, wolves (Canis lupus), were contrasted; search times did not differ between sites. Our results highlight the importance of designing field research that controls for confounding variables prior to attempting to scale behavioral processes to ecological events. See full-text article at JSTOR
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Huff, A. N. (1988). Safety. Journal of Equine Veterinary Science, 8(1), 81.
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Fielding D,. (1988). Reproductive characteristics of the Jenny donkey – Equus Asinus: a review. Trop Anim Hlth Prod, 20, 161–166.
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Westlin-van Aarde, L. M., van Aarde, R. J., & Skinner, J. D. (1988). Reproduction in female Hartmann's zebra. J Reprod Fert, 84, 505–511.
Abstract: Ovaries, fetuses and plasma were collected from zebra mares shot in the Etosha National Park in Namibia between 15 and 25 August 1983. Ovarian weight was affected by reproductive status and most of the non-pregnant mares were anoestrous. The number of follicles varied between individuals and only pro-oestrous/oestrous mares had follicles larger than 20 mm in diameter. The largest follicle in pregnant mares was only 9 mm in diameter. Corpora lutea and corpora albicantia were found in non-pregnant as well as pregnant mares: 4 pregnant mares had only corpora albicantia. The presence of secondary corpora lutea could not be confirmed in any of the pregnant mares. Implantation was estimated to occur at around 73 days of gestation, and most mares (84%) had conceived between November and April. Peripheral concentrations of plasma progesterone during pregnancy varied from 0·5 to 2·4 ng/ml.
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Ryder, O. A. (1988). Przewalski's horse – putting the wild horse back in the wild. Oryx, 22, 154–157.
Abstract: The Asian wild horse, or Przewalski's horse (Equus przewalskii), is believed to currently survive only in captivity. There are more than 660 individuals in over 70 zoological collections, and animals are available for reintroduction. The Przewalski's horse had been bred in captivity for 12 generations, and inbreeding has occurred. Genetic variability has been lost, and released animals will require acclimatization on or near release sites. In China, a program is under way for acclimatization, breeding, and release of wild horses, and plans are being made for a similar program in Mongolia. (LCA)
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Houpt, K. A., & Fraser, A. F. (1988). Przewalski horses. Appl. Anim. Behav. Sci., 21(1-2), 1–3.
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KIRKPATRICK JF et al,. (1988). Pregnancy determination in uncaptured feral Horses based on steroid metabolites in urine – soaked snow and free steroids in feces.
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Kirkpatrick, J. F., Kasman, L. H., Lasley,, B. L., & Turner, J. W. J. (1988). Pregnancy Determination in Uncaptured Feral Horses. J Wildl Manag, 52(2), 305–308.
Abstract: The urinary excretion of estrone sulfate ($\text{E}{1}\text{S}$) by 25 free-roaming feral horses (Equus caballus) was measured by radioimmunoassay applied to extracts of urine-soaked soil. Twelve of 15 mares having $\text{E}{1}\text{S}$ concentrations >1.0 mg/mg creatinine (x = 2.64 +- 1.02 [SD]) produced foals. All 10 mares with $\text{E}{1}\text{S}$ concentrations <1.0 mg/mg creatinine (x = 0.44 +- 0.26) did not foal. Extracting urine from soil and measuring $\text{E}{1}\text{S}$ and creatinine can be used to determine pregnancy in free-roaming feral horses without the stress of capture or immobilization.
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