California Bighorn Sheep Research Articles

Browsing of Antelope Bitterbrush(Purshia tridentata: Rosaceae) in the South Okanagan Valley, British Columbia: Age Preferences and Seasonal Differences

We compared browsing on twigs of small and large antelope bitterbrush (Purshia tridentata) shrubs among ten sites in the south Okanagan valley, British Columbia. We tested whether there were any age preferences by browsers and determined whether these preferences changed between seasons and mode of browsing. Two different types of browsing were observed: leaf stripping which occurred in the summer and twig clipping which occurred predominantly in the winter. We calculated age and size relationships showing that shoot volume and especially stem diameter were good predictors of shrub age. Among the ten sites, clipping removed 0.02 to 15.7% of a shrub's total twig length and stripping removed leaves from 0 to 5.2% of total twig length. Observations suggested that California bighorn sheep (Ovis canadensis california) stripped antelope bitterbrush leaves in late summer, mule deer (Odocoileus hemionus hemionus) clipped twigs in the winter and cattle clipped twigs in the summer. Browsers preferred to clip twigs on smaller and hence younger antelope bitterbrush shrubs. In contrast, larger and older shrubs were preferred for leaf stripping. Since twig clipping was more prevalent than leaf stripping in antelope bitterbrush, overall preference for younger shrubs may lead to difficulties in seedling establishment in regions where it is heavily used as winter forage.

CRANIAL MORPHOMETRIC AND EVOLUTIONARY RELATIONSHIPS IN THE NORTHERN RANGE OFOVIS CANADENSIS

Univariate and multivariate statistical methods were used to examine geographic variation in skull and horn characters of 694 bighorn sheep (Ovis canadensis) specimens from the Great Basin north to British Columbia and Alberta to test previous taxonomic hypotheses. Substantially more morphometric variation in skull and horn size and shape was found west of the Rocky Mountains than within the Rocky Mountains. Our results did not support the recognition of Audubon’s bighorn sheep ( O. c. auduboni) as a subspecies separate from Rocky Mountain bighorn sheep (O. c. canadensis). California bighorn sheep (O. c. californiana) from Washington and British Columbia were not distinguishable from Rocky Mountain bighorn sheep but differed notably from populations in the Sierra Nevada considered part of that subspecies. Extirpated native populations from northeastern California, Oregon, and southwestern Idaho, also considered to be O. c. californiana, shared with Nelson bighorn sheep (O. c. nelsoni) from the Great Basin desert a horn-related character that distinguished them from Rocky Mountain bighorn sheep. Bighorn sheep from the Sierra Nevada were found to be distinguishable from those of the adjacent Great Basin region. Our morphometric results were concordant in geographic patterns with mtDNA data. We synonymize O. c. auduboni with O. c. canadensis. We also assign extant and extinct native populations of O. c. californiana from British Columbia and Washington to O. c. canadensis. Finally, we assign the extinct native populations of O. c. californiana from Oregon, southwestern Idaho, northern Nevada, and northeastern California to the Great Basin Desert form of O. c. nelsoni, recognizing that some transition to Rocky Mountain bighorn sheep probably occurred along that northern boundary. With these taxonomic revisions, the range of O. c. californiana includes only the central and southern Sierra Nevada.

GEOGRAPHIC ANALYSIS OF PATHOGEN EXPOSURE IN BIGHORN SHEEP (OVIS CANADENSIS)

Antibody responses were examined among 998 bighorn sheep (Ovis canadensis) in California (USA) to determine spatial patterns of pathogen exposure. Using a shifting frame analysis, a specific geographic region was delineated that contained bighorn sheep with higher (P < 0.05) levels of multiple exposure (antibodies detected against > or = two pathogens), as well as higher prevalence values for eight of ten individual pathogens. This region in southwestern California encompassed all of the peninsular populations of bighorn sheep recently proposed for listing as endangered by the U.S. Fish and Wildlife Service.

Isolation and In vitro Cultivation of Babesia Parasites from Free-Ranging Desert Bighorn Sheep (Ovis canadensis nelsoni) and Mule Deer (Odocoileus hemionus) in California

Protozoal parasites of the genus Babesia were isolated for the first time from free-ranging desert bighorn sheep (Ovis canadensis nelsoni) and mule deer (Odocoileus hemionus) populations in California by in vitro culture of host blood. These naturally infected animals did not have microscopically detectable parasitemia at the time blood was collected for parasite cultivation. Three isolates of small Babesia parasites were cultured from different sample groups of bighorn sheep, and 2 isolates of large Babesia parasites were cultured from a group of bighorn sheep and a group of mule deer, respectively. The size and structure of the various forms of piroplasms from each isolate remained consistent throughout the period of cultivation. Statistical comparison of the sizes of the piroplasms among the isolates indicated that there were at least 2 distinct morphotypes. Four of the 5 isolates were maintained with continuous growth in cultures containing erythrocytes from uninfected donor bighorn sheep, mule deer, and domestic sheep. Cryopreservation or storage of cultures at 4 C for 7 days did not affect viability of the isolates. These results demonstrate the potential for use of in vitro cultivation methods for the isolation of Babesia parasites from free-ranging artiodactylids.

Culicoides boydi (Diptera: Ceratopogonidae): a potential vector of hemorrhagic disease viruses to desert bighorn sheep in southern California.

Culicoides boydi new species is described from Riverside County, CA. A taxonomic key, table of numerical characters, and female wing photographs are presented to distinguish it from the three other species of the Culicoides pusillus species group of the subgenus Avaritia. Brief notes are presented on its biology and distribution and suspected vector potential in the transmission of bluetongue virus to desert bighorn sheep in California.

Grazing Effects and Range Trend Assessment on California Bighorn Sheep Range

This study investigated the effect of grazing by California bighorn sheep (Ovis canadensis californiana) on plant community structure. Over 28 months from 1977 to 1979, bighorn diet consisted of 79 species, including 14 grasses, 47 forbs and bryophytes, plus 18 trees and shrubs. Grasses, forbs, and shrubs comprised 66.6, 18.9, and 14.5% of the diet, respectively. Three years of bighorn sheep grazing reduced (P < 0.05) leaf and culm lengths of bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith). Grazing generally reduced leaf length, basal diameter, culm (stem) length, and culm (stem) numbers of prairie Junegrass (Koeleria cristata Pers.), Sandberg's bluegrass (Poa sandbergii Vasey), needle-and-thread (Stipa comata Trin. & Rupr.), Thompson's paintbrush (Castilleja thompsonii Pennell), silky lupine (Lupinus sericeus Pursh), and snow buckwheat (Eriogonum niveum Dougl.). Vigor of arrowleaf balsamroot (Balsamorhiza sagittata (Pursh) Nutt.) was unaffected by grazing, despite its dietary importance. Total plant frequency remained unchanged between 1976 and 1983 in areas grazed by bighorn sheep, and in grazing exclosures. Total grass frequency declined from 46.5 to 30.8% within the exclosures, but increased from 44.7 to 48.8% in response to bighorn sheep grazing. Forb frequency remained unchanged after 7 years of bighorn sheep grazing while frequency of yarrow (Achillea millefolium L.) increased more inside exclosures than on the grazed area. Botanical composition of shrubs increased on grazed and ungrazed areas from 1976 to 1983, but frequency was unaffected by bighorn sheep grazing. Snow buckwheat and Wyeth buckwheat (Eriogonum heracleoides Nutt.) declined in response to bighorn sheep grazing. Successional trends caused by California bighorn sheep grazing differed from trends expected from cattle grazing.

Squamous Cell Carcinoma in a Free-ranging Bighorn Sheep (Ovis canadensis californiana)

An oral squamous cell carcinoma which invaded maxillary bones with metastasis to the right retropharyngeal lymph node was diagnosed in a free-ranging California bighorn sheep (Ovis canadensis californiana) from Washington. Much of the maxillae had been replaced with tumor and reactive tissue, and many teeth were missing or loose. The tumor was predominantly confined to the shape of the maxillary bones and was unusual because it was bilaterally symmetrical.

Human Disturbance of Sierra Nevada Bighorn Sheep

California bighorn sheep (Ovis canadensis californiana) and recreationists were studied in the Sierra Nevada Mountains of California from May through August 1976. Direct observation of sheep and people, pellet transects, and hiker interviews were used to assess overlap in areas of use and nature of interactions. Distance, juxtaposition, age and sex composition, and herd size are important factors in reaction of bighorns to humans. Meadows used by humans were inherently poor meadows for bighorn sheep, based on vegetation analysis. Use of meadows by sheep was correlated with amount of preferred forage species and vegetative cover. Hiker foot-trails did not affect sheep movements in the summer range. Bighorn-human encounters were limited to specific locations and were not adversely affecting the bighorn population. Nevertheless, regulations should continue to limit use of the study area by humans. J. WILDL. MANAGE. 43(4):909-915 California bighorn sheep of the Sierra Nevada Mountains in California are the only naturally occurring population of this subspecies in the United States and were classified as rare by the U.S. Department of Interior (1966). Estimated populations declined from 390 in 1950 to 180 in 1972 due to a variety of suspected influences (Jones 1950, McCullough and Schneegas 1966, Dunaway 1971b, Jorgensen and Schaub 1972, Weaver 1972). Hansen (1971), Woodward et al. (1974), Geist (1971:87-88, 1975), and others have described the impact of human activities on populations of bighorn sheep. Dunaway (1971b) concluded that disturbance by humans was the most important factor limiting populations of bighorns in the Sierra Nevada. Gaps between existing herds were areas of high human use, and there was an apparent correlation between the recent increase in recreational activity and the decline in bighorn numbers. However, little supporting data were available. Acting on Dunaway's hypothesis, the U.S. Forest Service established the California Bighorn Sheep Zoological Area in 1971. Regulations limited entrance to 25 hikers per day, and prohibited off-trail hiking and grazing of recreation and saddle stock (Dunaway 1971a). The purposes of this study were to determine the amount of overlap in current use by humans and bighorns, the nature and extent of the interactions, and whether the interactions have a deleterious effect on the bighorns. The study extended from May through August 1976, and coincided with the peak periods of activity of both humans and sheep. The U.S. Forest Service and the National Park Service provided financial support. D. R. McCullough and S. R. Tocher, University of Michigan, provided guidance and assistance throughout the study. D. Garber (Forest Service) and D. Parsons (Park Service) provided logistical support. We thank J. Wehausen for his assistance in formulating the study and participating in the fieldwork. G. Smith, J. Elder, S. Sherwood, D. Asay, and H. W. Elliot, III also assisted in the fieldwork. STUDY AREA AND METHODS The Mt. Baxter herd area was chosen as the study site because it supports the largest herd of California bighorns in the 1Present address: Burlington Northern Resources Div., 700 South Ave. West, Missoula, MT 59801. 2 Present address: 9430 Edward, Brighton, MI 48116. J. Wildl. Manage. 43(4):1979 909 This content downloaded from 207.46.13.129 on Fri, 01 Jul 2016 05:34:37 UTC All use subject to http://about.jstor.org/terms 910 DISTURBANCE OF BIGHORN SHEEP. Hicks and Elder

Transplacental transmission of Protostrongylus sp. in California bighorn sheep (Ovis canadensis californiana) in Oregon.

Transplacental transmission of Protostrongylus sp. was documented for the first time in California bighorn sheep (Ovis canadensis californiana) by recovery of third stage larvae from two fetuses.

Group size, foraging, and antipredator ploys: An analysis of bighorn sheep decisions

1. Several aspects of the foraging behavior of California bighorn sheep (Ovis canadensis californiana) were studied in homogeneous habitats in the interior of British Columbia, Canada. The manner in which an individual sheep foraged was based upon the size of group within which it was found. 2. In small groups (five or less individuals) sheep foraging efficiency was poor and interruptions of foraging to scan the environment were frequent. 3. Alarm vocalizations and other conspicuous behaviors tend to alert their neighbors to the presence of disturbances. It appears that these signals cannot be based solely as the result of kin selection.

Wyominia tetoni (Cestoda: Thysanosomatinae) from bighorn sheep in Washington.

In washington, eitht California bighorn sheep, Ovis canadensis californiana, were necropsied to ascertain age and general physical condition. Four were found to harbor Wyominia tetoni.

Abundance and Distribution of California Bighorn Sheep in North America

There is a minimum of 3,000 California bighorn sheep (Ovis canadensis californiana) in several herds (native and introduced) from central British Columbia south to central California. Recent field studies by several members of the British Columbia Fish and Wildlife Branch have increased our knowledge of the numbers and distribution of California bighorns in British Columbia. In addition, several successful introductions of this subspecies of bighorn sheep have been made in the states of Washington, Oregon, North Dakota, Idaho, and Nevada (Mitchell in press). We have combined these data to estimate a total population.