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La precision des modeles naturalises chauffes pour evaluer la temperature operationnelle standard (T ES ) de mammiferes vivants a ete recemment critiquee (Walsberg and Wolf 1996). Dans le but d'evaluer davantage cette question, j'ai fait des simulations de Monte Carlo pour estimer la variation inter-individuelle associees a la T ES moyenne de spermophiles a manteau dore (Spermophilus lateralis) et de spermophiles bigarres (S. variegatus) exposes a diverses conditions de vent. La T ES des rongeurs vivants etait significativement plus variable que celle des modeles naturalises. A mesure que la vitesse du vent augmentait, les animaux vivants et leurs modeles naturalises tendaient a produire des T ES significativement differentes. Les causes possibles de ces differences sont proposees.

Information on geographic distribution, habitat, measurements, and reproductive condition of five species of mammals from Guerrero, Mexico, is provided. Two species are new records for the State (Nyctinomops femorosaccus and Sigmodon leucotis), one is the second record (Spermophilus variegatus variegatus), one is the third record (Nyctinomops macrotis), and one is the fourth record (Herpailurus yagouaroundi tolteca).

Taxidermic mounts are frequently used to quantify the operative temperature or standard operative temperature of complex natural environments. These thermal indices are subsequently used to estimate the metabolic heat production of freeliving animals. Such use has often entailed violation of two standards for biological data collection: that multiple samples be analyzed and that instruments be calibrated under the range of conditions used in empirical analyses. To explore the consequences of these practices, we compared the responses of both heated and unheated taxidermic mounts with those of live animals when exposed to combinations of wind and radiation that normally could be experienced in nature. Two mammals, the rock squirrel Spermophilus variegatus and the golden-mantled ground squirrel Spermophilus lateralis, as well as a bird, the verdin, Auriparus flaviceps, were studied. For all species, there was substantial individual variation in mount responses. Under a single set of environmental conditions...

Home-range sizes of adult rock squirrels ( Spermophilus variegatus ) were studied in southeastern Arizona. Twenty-eight adult rock squirrels were radiocollared for various periods from 28 May 1986 to 7 November 1986 and from 15 May 1987 to 19 June 1987. Home-range size was determined by the 95% minimum-convex-polygon method. Data were analyzed monthly and according to reproductive condition. Ranges of adult males were largest during the breeding season (May and June) and generally decreased in size during the remainder of the year. Home-range size of adult females did not vary significantly according to month when all individuals were considered. Also, there was considerable intra- and intersexual overlap of home ranges.

The antisnake behavior of rock squirrels (Spermophilus variegatus) was examined to determine the role of the orbital frontal cortex in regulating physiological arousal and behavioral excitability during encounters with a rattlesnake predator. Rock squirrels with orbital frontal cortex ablations and sham-surgery control squirrels were presented with a caged rattlesnake pre- and postsurgery. Orbital frontal cortex ablations had no substantial effect on the expression of gross motor behavior in dealing with the rattlesnake, but they augmented the speed of snake recognition and clearly disinhibited sympathetic arousal as manifested by increased tail piloerection and tail-flagging activity, which is a specific antisnake behavior. Natural selection from snakes has probably shaped the neural organization of the orbital frontal cortex to afford adaptive behavioral flexibility during snake encounters.

Spermophilus variegatus (Erxleben, 1777). Syst. Regn. Anim., 1:421. TYPE LOCALITY: "in Mexico." Restricted by Nelson (1898:898) to "Valley of Mexico, near City of Mexico," [Distrito Federal, Mexico]. DISTRIBUTION: S Nevada to SW Texas and Utah (USA) to Puebla (C Mexico). SYNONYMS: buccatus (Lichtenstein, 1830); buckleyi Slack, 1861; couchii Baird, 1855; grammurus (Say, 1823); jugions (V. Bailey, 1913); macrourus Bennett, 1833; robustus (Durrant and Hansen, 1954); rupestris (J. Allen, 1903); tiburonensis Jones and Manning, 1989; tularosae (Benson, 1932); Utah (Merriam, 1903). COMMENTS: Subgenus Otospermophilus (Hall, 1981:399). Reviewed by Oaks et al. (1987, Mammalian Species, 272)., Published as part of Robert S. Hoffmann & Charles G. Anderson, 1993, Order Rodentia - Family Sciuridae, pp. 419-465 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 450, DOI: 10.5281/zenodo.7353130, {"references":["Nelson, E. W. 1898. What is Sciurus variegatus Erxleben? Science, n. s., 8: 897 - 898.","Manning, R. W., and J. K. Jones, Jr. 1989. Myotis evotis. Mammalian Species, 329: 1 - 5.","Hall, E. R. 1981. The mammals of North America. Second ed. John Wiley and Sons, New York, 1: 1 - 600 + 90, 2: 601 - 1181 + 90.","Oaks, E. C., P. J. Young, G. L. Kirkland, Jr., and D. F. Schmidt. 1987. Spermophilus variegatus. Mammalian Species, 272: 1 - 8."]}

Rock squirrels (Spermophilus variegatus) were studied from July 1983 to June 1987 in an oak (Quercus sp.) savanna in southeastern Arizona. Adults were relatively inactive from late October through February. In the autumn, adult males generally were significantly less active (and immerged earlier) than females. Juveniles first appeared aboveground in July, and they were active throughout the autumn. Annual activity patterns of juvenile males and females did not differ. While adult males were significantly heavier than females in late May and early June, the middle of the mating season, there were no significant differences in mean weights between adult males and females during any other half-month period. Juvenile males and females emerged aboveground at similar weights and, thereafter, had similar rates of postemergent weight gain.

Physical theory predicts that animals with fur or feather coats can adjust solar heat gain independently of surface coloration or environmental factors by altering coat structure or hair optical properties. This hypothesis is tested by examining seasonal changes in the solar heat load transferred to the skin by the pelage of a desert-dwelling mammal, the rock squirrel (Spermophilus variegatus). Although coat colour remains constant, solar heat gain at low wind speeds is about 20% greater in winter coats than in summer coats. This change is in an apparently adaptive direction and is predicted to have a major effect on the animal’s heat balance in nature. The determinants of these alterations in solar heat gain are explored using an empirically validated biophysical model and are found to result from changes in hair optics and coat structure. These results suggest the existence of a previously unknown mode of long-term thermoregulation that allows adjustment of solar heat gain without affecting the animal’s external appearance.

Physical and vegetational characteristics of rock squirrel ( Spermophilus variegatus ) den sites were investigated during 1983, 1984, and 1985 at the National Audubon Society's Appleton-Whittell Biological Research Sanctuary in southeastern Arizona. Relative to habitat availability, rock squirrel den sites occurred in greater than expected frequencies in oak savanna and riparian habitats. A comparison between 56 den sites and 40 control locations in rock squirrel-occupied habitat revealed significant differences ( P ≤ 0.002) for 12 (52.2%) of 23 physical and vegetational variables. Compared to control locations, dens were located 1) on steeper slopes, 2) in shadier sites, 3) closer to oaks, Quercus spp., 4) closer to washes, 5) associated with prominent potential lookout points, 6) in areas with less ground cover, and 7) associated to a lesser degree with more northerly facing slopes. Discriminant function analysis correctly classified 81.3% of den locations and control sites using only two variables, percent shade and angle of slope.

Spermophilus variegatus (Erxleben, 1777). Syst. Regn. Anim., 1:421. TYPE LOCALITY: Mexico, Distrito Federal, Valley of Mexico, near Mexico City. DISTRIBUTION: S. Nevada to S.W. Texas and Utah (U.S.A.) to Puebla (C. Mexico). COMMENT: Subgenus Otospermophilus; see Hall, 1981:399. Gromov et al., 1965: 145, considered Otospermophilus a distinct genus. Nelson, 1898, Science, n.s., 8:897, fixed the type locality. ISIS NUMBER: 5301410002032029001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 1), pp. 345-382 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 371, DOI: 10.5281/zenodo.7353023, {"references":["Hall, E. R. 1981. The mammals of North America. Second ed. John Wiley and Sons, New York, 1: 1 - 600 + 90, 2: 601 - 1181 + 90.","Gromov, I. M., D. I. Bibikov, N. I. Kalabukhov, and M. N. N. Meier. 1965. Fauna SSSR, Mlekopitayushchie, tom. 3, vyp. 2 [Fauna of the U. S. S. R. Mammals. vol. 3, No. 2]. Nazemnye belich'e [Ground Squirrels]. Nauka, Moscow-Leningrad, 467 pp. (in Russian).","Nelson, E. W. 1898. What is Sciurus variegatus Erxleben? Science, n. s., 8: 897 - 898."]}

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Experimental infections with Yersinia pestis were followed in groups of rock squirrels. Development of coagulopathy and pneumonia were observed in 2-4% and 11-12% of the test animals, respectively. Susceptibility to experimental infection was heterogeneous with some animals surviving inoculation with large numbers of organisms and others succumbing after inoculation with small numbers. Production and longevity of serum antibody titers, as measured by passive hemagglutination tests, were variable as well, and apparently unrelated to dose. The data presented attest to the need for care in interpreting serologic tests results for individual animals.