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Sexual segregation in desert-dwelling mountain sheep Item Type Thesis Authors Bleich, Vernon Charles Download date 02/10/2021 22:18:29 Link to Item http://hdl.handle.net/11122/9364 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. 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Order Number 9S20755 Sexual segregation in desert-dwelling mountain sheep Bleich, Vernon Charles, Ph.D. University of Alaska Fairbanks, 1993 UMI 300 N. ZeebRd. Ann Arbor, MI 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEXUAL SEGREGATION IN DESERT-DWELLING MOUNTAIN SHEEP A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Vernon Charles Bleich, B.S., M.A. Fairbanks, Alaska May 1993 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEXUAL SEGREGATION IN DESERT-DWELLING MOUNTAIN SHEEP By Vernon Charles Bleich RECOMMENDED: APPROVED: Dean, College of Natural Sciences &&mdl CT)^ Dean of the Graduateiat$ School H/M ] 73 Date ' ' Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Mountain sheep (Ovis canadensis nelsoni) were studied in the eastern Mojave Desert, San Bernardino Co., California to test 4 hypotheses potentially explaining sexual segregation in ungulates. Mature males and females were segregated from December to July, and aggregated from August to November. Mature males obtained higher quality diets than did females (based on fecal crude protein) and forage was more abundant on ranges used by these males. Indices of predator abundance were substantially lower on ranges used by females and young than on those used by mature males. Females occurred closer to permanent sources of water, and in steeper, more rugged, and more open habitats than did mature males. Female groups with and without lambs did not differ in their distance from water during aggregation or segregation. Female groups with lambs, however, occurred on steeper slopes and in more rugged and open habitats during segregation, when lambs were very young. I refute the hypotheses that: 1) Males enhance their fitness by segregating from females and their own offspring; 2) Females outcompete males for available resources, and allometric differences between the sexes lead to sexual iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iv segregation; and 3) The constraints of lactation may be important in explaining sexual segregation in this desert- adapted ungulate. In contrast, my observations strongly support the hypothesis that, because of their smaller body size and potentially greater vulnerability to predation, female ungulates use habitats with fewer predators and more opportunities to evade predation than do males, but males are able to exploit nutritionally superior areas. Sexual segregation likely results from differing reproductive strategies of males and females among sexually dimorphic mammals. Males may enhance their fitness by exploiting habitats with superior forage, and thereby enhance body condition, while simultaneously incurring greater risks than do females. In contrast, females appear to enhance their fitness by minimizing risks to their offspring, albeit at the expense of nutrient intake. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT................................................ iii TABLE OF CONTENTS...................................... v LIST OF FIGURES........................................ viii LIST OF TABLES.......................................... x ACKNOWLEDGMENTS..........................................xi INTRODUCTION............................................ 1 Sexual Segregation in Ungulates................... 1 Biology of Mountain Sheep in Desert Environments ... 5 Hypothesized Explanations of Sexual Segregation, and Associated Predictions................... 6 Objectives and Implications of the Research........ 15 STUDY A R E A ............................................... 18 Location, Topography, and Geology..................18 Climate............................................. 20 Water Sources.......................................20 Flora............................................... 22 Fauna............................................... 22 Human Influences....................................25 METHODS................................................ 26 Capturing Mountain Sheep........................... 26 Radiotelemetry......................................26 Aerial Surveys...................................... 27 Ground Observations.................................28 v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vi Time-Lapse Photography........................... 28 Group Composition.................................. 29 Vegetation Sampling................................ 30 Habitat Characteristics............................ 32 D iet............................................... 34 Diet Quality..................................... 35 Forage Quality..................................... 36 Relative Abundance of Predators................... 36 Predator Food Habits............................... 38 Body Mass of Sheep................................. 38 Statistical Analyses............................... 38 RESULTS............................................... 40 Sexual Dimorphism.................................. 40 Social Aggregation and Segregation................. 40 Group Size......................................... 45 Spatial Distribution............................... 45 Composition of Plant Communities................. 48 Habitat Use ...................................... 52 Habitat Selection.................................. 60 Forage Availability and Quality................... 64 D iet............................................... 6 8 Diet Quality..................................... 71 Abundance of Predators........................... 74 Causes of Mortality and Evidence of Sheep in Carnivore Diets............................... 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vii DISCUSSION.............................................. 77 Sexual Dimorphism and Hypotheses Explaining Sexual Segregation............................ 77 Predictions of Hypotheses Versus Empirical Observations ..............................83 CONCLUSIONS............................................. 96 MANAGEMENT IMPLICATIONS................................. 98 LITERATURE CITED....................................... 102 APPENDIX A. Frequency and Cover of Vegetation in 6 Habitat Types............................. 119 APPENDIX B. Causes of Mountain Sheep Mortality........ 126 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Fig. Page 1. Study area in San Bernardino Co., California showing the desert mountain ranges inhabited by mountain sheep..................................... 19 2. Thermograph of monthly precipitation and temperature 30 km NW of Old Dad Mountain, San Bernardino Co., California, 1983-89............... 21 3. Distribution of vegetation types in the Old Dad Peak/Kelso Mountains study area, San Bernardino County, California................. 23 4. Percent of social groups for mountain sheep based on ground and aerial sampling, San Bernardino Co., California, 1981-90............... 42 5. Associations of class II males (as determined by ground and aerial observation) in other social groups of mountain sheep, during periods of aggregation and segregation,

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