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1 Bighorn Lamb Production, Survival, and Mortality in South-Central Colorado Author(s): Thomas N. Woodard, R. J. Gutiérrez, William H. Rutherford Reviewed work(s): Source: The Journal of Wildlife Management, Vol. 38, No. 4 (Oct., 1974), pp Published by: Allen Press Stable URL: Accessed: 15/03/ :12 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Allen Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Wildlife Management.

2 BIGHORN LAMB PRODUCTION, SURVIVAL, AND MORTALITY IN SOUTH-CENTRAL COLORADO1 THOMAS N. WOODARD, Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins R. J. Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins 80521* GUTI:RREZ, WILLIAM H. RUTHERFORD, Colorado Department of Natural Resources, Division of Wildlife, Fort Collins Abstract: A bighorn sheep (Ovis canadensis) herd was observed in the Sangre de Cristo Mountains of Colorado during the spring, summer, and fall of 1969 and the summer and fall of June ewe-lamb ratios were 100:83 in 1969 and 100:72 in High late summer lamb mortality occurred during both years, with the ewe-lamb ratio being 100:17 by September 1969, and 100:22 by September Lamb mortality resulting from predation or accidents was not found to be a factor. Disease, possibly enhanced by inclement weather, was believed to be a significant factor in lamb mortality. Two lambs were collected in 1970, and both displayed a verminous pneumonia of lungworm (Protostrongylus stilesi) origin and a broncho-pneumonia of probable bacterial origin. J. WILDL. MANAGE. 38(4): Many of the Rocky Mountain bighorn sheep herds in Colorado are presently static or decreasing in size (Bear and Jones 1973). As the Sangre de Cristo herd apparently has declined since the mid-1950's, a study to investigate this herd reduction was initiated in The objectives of the study, com- pleted in 1970, were to determine sheep distribution, lamb birth rate, survival, and mortality. We thank D. Post and C. Hibler, Colorado State University, for their guidance. D. Riggs and D. Crane, Colorado Division of Wildlife, and J. Landen of Alamosa, Colorado, assisted in field research. STUDY AREA The study area was centered in the Sand Creek drainage of the Sangre de Cristo Range, located in south-central Colorado, approximately 24 km (15 miles) southwest of the town of Westcliffe. The range is narrow and extremely rugged with many (8) 1 A contribution from Federal Aid Project W-41- R, Colorado. 2 Present address: Colorado Department of Natural Resources, Division of Wildlife, 526 Pine Street, Glenwood Springs Present address: Museum of Vertebrate Zoology, University of California, Berkeley peaks rising above 4,281 m (14,000 feet). Bighorn sheep summer range is mostly above timberline, 3,516 m (11,500 feet) elevation at this latitude, and is characterized by steep slopes, cliffs, rock out-croppings, and talus slides. Winter range has not been well defined (Bear and Jones 1973), but montane, subalpine, and alpine zones typical in the Colorado Front Range are represented (Marr 1961). METHODS Population and distribution data were obtained by 89 ground classification counts, seven helicopter flights (about 13 hours), and four fixed-wing aircraft flights. During the summer of 1969 and 1970, 159 days (approximately 1,315 working hours) were spent in the field. The entire Sand Creek ewe-lamb herd was under observation for approximately 350 hours during this period. An effort was made each day to locate and classify what was thought to be the same group of sheep. These sheep were kept under surveillance for as long as possible to note signs of illness, interaction with predatory species, and injuries or mortalities resulting from accidental falls. Two lambs were collected on 6 August J. Wildl. Manage. 38(4):

3 772 BIGHORN LAMB PRODUCTION * Woodard et al. Table 1. Summary of bighorn sheep classification data, Sangre de Cristo Mountains, Colorado, Number of sheep seen Date Rams Ewes Yearlings Lambs Unclassified Total 1965 Fall Late winter Late summer Late winter Late summer Late winter Early summer (5)a 18 2(3) Early fall (2) 12(3) (1) Early summer Late summer Early fall 1 14(6) 2(2) 3(4) Late summer 1(3) 15(6) 4(2) 5(2) 38 a Numbers in parentheses indicate sheep not included in age ratio calculation; not part of Sand Creek herd. and 9 September Both were necropsied by personnel in the Department of Pathology at Colorado State University. Fresh adult and lamb fecal samples were examined to determine occurrence of lungworm (Protostrongylus sp.) in the herd and the time lambs began shedding Protostrongylus larvae. A standard weather station was installed to collect weather data. RESULTS AND DISCUSSION Herd Composition, Size, and Distribution Moser (1962) estimated that about 135 bighorns inhabited the Sangre de Cristo Range during the mid-1950's. He estimated 25 rams and 35 ewes were in the Crestone Peak-Sand Creek area: 50 sheep were near Horn Peak, 6 km (4 miles) north of Sand Creek headwaters; and 15 sheep were near Mosca Pass, 21 km (13 miles) south of Sand Creek headwaters. Census information between the mid-1950's and mid-1960's is poor. During this period fewer sheep were seen by hikers, hunters, and Division field personnel. Sheep were seen consistently only in the Sand Creek area (Riggs, personal communication). Our observations indicate at least three small sheep herds still remain in the range, one each, at Sand Creek, Horn Peak, and Medano Pass 10 km (6 miles) south of Sand Creek headwaters. Population data since 1965 are presented in Table 1. Sheep Production and Mortality Reproduction in the Sand Creek herd was excellent during 1969 and June ewelamb ratios were 100:72 (18 ewes and 13 lambs) in These are comparable to the best ratios reported in other areas of Colorado (Moser 1962, Streeter 1969). This herd suffered high late summer lamb mortality in both 1969 and Of the 15 lambs located by 3 July 1969 (100:83), a minimum of 11 lambs remained alive until 23 July. Only two lambs were found by 10 September (100:17). Thirteen lambs were located by 30 June 1970 (100:72) and a minimum of 11 lambs were alive by 2 August. Only 3 lambs were found by 18 September 1970 (100:22). The fall ratios were calculated using the number of yearlings J. Wildl. Manage. 38 (4):1974

4 BIGHORN LAMB PRODUCTION - Woodard et al. 773 which were present in the herd the following year and 18 ewes (the number of ewes during 1969 and 1970). No recent adult mortality was noted. MORTALITY FACTORS All observed bighorn lambs appeared to be in excellent condition through the first half of the summers of 1969 and Lambs were not observed during August 1969 because of a prolonged period of inclement weather. In 1970 lambs were observed coughing by the end of July; the frequency of coughing increased through August until over 80 percent of the lambs appeared sick. They were lethargic and would lie down whenever possible. Group play exhibited earlier in the summer was no longer observed. A hunched-up posture and staggering gait were common. They would cough violently up to 20 times, shake their heads, and stand for long periods with their mouths open. During the late summer of 1970, 88 observations of this sick lamb behavior were recorded. Necropsy results on the two lambs collected in 1970 indicated both animals had a verminous pneumonia of Protostrongylus stilesi origin, and a secondary bronchopneumonia of probable bacterial origin. A total of 116,702 first stage P. stilesi larvae were recovered from the lungs of the first lamb. Isolates were also made of an alpha Streptococcus and Pasteurella bacteria. The second lamb had a total of 67,100 first stage larvae. Isolates of a Pasteurella sp. and a gram negative diplococcus, thought to be a species in the genus Neisseria, were made. Twenty-six (100 percent) of the adult fecal samples contained Protostrongylus larvae, as well as 14 (58 percent) lamb fecal samples. Of the earliest lamb samples collected, 3 July 1969, 3 of 6 were positive. This means that within a probable period of 30 to 45 days after birth, these lambs were harboring adult lungworms that were already reproducing and shedding first stage larvae. No predation or accidents were observed during field observations. The time of mortality during coincided with periods of inclement weather (Woodard 1971). Temperatures were low and rain fell frequently, thus the lambs were probably under a prolonged period of physical stress. Our observations of sick lamb behavior and the pathology associated with Sthe two collected lambs indicate a pattern of pneumonia complex described by Post (1971: ). Buechner (1960) and others have reported early lamb mortality. The exact times the mortality has been noted varies and may reflect the consequence of a short term study. The lambs may suffer mortality when severe stress (i.e., cold weather) affects them. Crump (1971) has shown that acquisition of critical winter range reflected an increased lamb survival from 5 lambs:100 ewes to lambs:100 ewes. He stated (Crump 1971: ) that major lamb mortality originally occurred during early winter (November-December) and that the lambing range is directly above the winter range (approximately 2,293-3,058 m; 7,500-10,000 feet). The Sand Creek lambing range is approximately 3,669-3,975 m (12,000-13,000 feet) and winter range approximately 2,599 m (8,500 feet). Inclement weather may arrive sooner at this higher elevation and thus the lambs would encounter physical stress earlier. In 1969, fivefoot snow drifts covered our base camp at 3,363 m (11,000 feet) by 20 October. The long-term population data for the Sangre de Cristo Range indicate a reduction J. Wildl. Manage. 38 (4):1974

5 774 BIGHORN LAMB PRODUCTION Woodard et al. in the herd size. Our ewe-lamb ratios (100: 17 and 100:22 in 1969 and 1970) and yearling ratios (100:12 and 100:17 in 1969 and 1970) indicate the Sand Creek herd may still be decreasing or is stabilizing at a low number. The proximate cause of lamb mortality and the low population density is probably a pneumonia complex operating within the herds (at least the Sand Creek herd). The ultimate cause is unknown but may be related to loss of a historical winter range due to a livestock operation. As the subdivision and development of private land below the sheep range proceed, the sheep herd may receive added pressure. LITERATURE CITED BEAR, C. D., AND G. W. JONES History and distribution of bighorn sheep in Colorado. Colorado Division of Wildlife. P-R Proj. Rep. W-41-R pp. (Multilith). BUECHNER, H. K The bighorn sheep in the United States; its past, present and future. Wildl. Monogr pp. CRUMP, W The Wind River bighorn herd -a new approach to sheep habitat management. Trans. N. Am. Wildl. Sheep Conf. 1: MARR, J. W Ecosystems of the east slope of the Front Range in Colorado. Univ. Colo. Stud. Ser. Biol. 8. University of Colorado Press, Boulder. 134pp. MOSER, C. A The bighorn sheep of Colorado. Colorado Game and Fish Dept. Tech. Publ pp. PosT, G The pneumonia complex in bighorn sheep. Trans. N. Am. Wildl. Sheep Conf. 1: STREETER, R. G Demography of two Rocky Mountain bighorn sheep populations in Colorado. Ph.D. Thesis. Colorado State Univ., Fort Collins. 96pp. WOODARD, T. N Bighorn sheep lamb production, survival and mortality in the Sangre de Cristo Mountains, Colorado. M.S. Thesis. Colorado State Univ., Fort Collins. 84pp. Accepted 5 September J. Wildl. Manage. 38 (4) :1974