Dall Sheep Reproduction

I studied the reproductive cycle of Dall sheep (Ovis dalli dalli) in 3 herds in the Kenai Mountains, Alaska. The rut was predicted to extend from 16 November through 19 December 1970, and from 18 November through 18 December 1971. All adult ewes collected throughout the winter were pregnant. Three of 4 yearling ewes were pregnant and no female lambs had reached puberty. Although some long yearling rams appeared physiologically capable of reproduction, they were unlikely to participate in breeding activities because of behavioral constraints. The mean gestation period was 171 days. Fetal growth curves are presented. Lambing dates were not uniform between years or herds. Peak dates of lambing for the 3 herds over 4 yr ranged from 20 May to 31 May. Lambing success averaged 31.8 lambs per 100 ewes and was not significantly different from the statewide average of 36.6. There were negative correlations between increasing winter snow depth and lambing success and between average maximum winter winds and snow depth. Positive correlation was found between average maximum winter temperatures and snow hardness, which, in turn, was negatively correlated with lambing success. J. WILDL. MANAGE. 42(3):570-580 The reproductive biology of Dall sheep is poorly documented in the scientific literature. Although several papers deal with phases of the reproductive cycle (Dixon 1938, Murie 1944, Murphy 1974), the only definitive studies available are Geist's (1968, 1971) excellent works on breeding behavior of mountain sheep (primarily concerned with 0. canadensis but including some data on O. dalli stonei and 0. dalli dalli) and Pitzman's (1970) study on birth behavior of Dall sheep. This study examines several aspects of the reproductive cycle in 3 herds, including: chronology of the rut, breeding age, reproductive potential, fetal development, prenatal sex ratio, gestation period, lambing chronology, and reproductive success. It is part of a larger study involving 3 adjacent but distinct herds of Dall sheep occupying mountains in the vicinity of Kenai Lake and Kenai River near the village of Cooper Landing, Alaska. The Crescent Mountain and Surprise Mountain herds, each with about 150 animals, are almost entirely restricted to their respective mountain complexes by physiographic barriers. The 3rd herd has over 250 sheep occupying Cooper Landing Closed Area. It is centered primarily on Slaughter Mountain but ranges over a considerably larger area during the summer. No significant contact is known to occur between herds. The Slaughter Mountain herd has been protected from hunting for many years and represents a nearly natural herd, with many old rams. A small number of these are taken annually beyond the boundaries of the closed area. The other herds are relatively accessible and have long been open to hunting. Nearly all rams with horns of 3/ curl or larger have been removed each hunting season. Since 1970 the Crescent Mountain herd has been subjected to experimental reduction by selective removal of ewes, lambs, and young rams. Older rams have received almost complete protection. The Surprise Mountain herd continues to be hunted for rams and few with horns of 3/? curl or larger survive the August-September season. Although these 3 herds occupy areas only about 32 km apart, winter habitats are dissimilar (Nichols 1976). Forage proI A contribution of Federal Aid in Wildlife Restoration Project W-17-R, Alaska. 570 J. Wildl. Manage. 42(3):1978 This content downloaded from 207.46.13.153 on Fri, 05 Aug 2016 05:14:04 UTC All use subject to http://about.jstor.org/terms DALL SHEEP REPRODUCTION* Nichols 571 duction is greatest on Slaughter Mountain and least on Crescent Mountain, while winter climate is most severe on Crescent and least severe on Slaughter Mountain. Surprise Mountain was intermediate in both respects. I would like to thank the following Alaska Department of Fish and Game employees for field and laboratory assistance: W. Heimer, A. Johnson, N. Johnson, E. Klinkhart, R. LeResche, P. LeRoux, C. Lucier, C. McIlroy, K. Neiland and N. Steen. Mr. H. Hamilton, of Chugach Electric Association, kindly made available rainfall data collected at Kenai Lake over the years of this study. R. Rausch and K. Schneider assisted with direction to the study, and D. McKnight and S. Harbo generously reviewed this manuscript.