Ecotypic variation in recruitment of reintroduced bighorn sheep: Implications for translocation

• Published in: The Journal of wildlife management 2014-04, Vol.78 (3), p.394-401
• Main Authors: Wiedmann, Brett P., Sargeant, Glen A.
• Format: Article
• Language: English
• Subjects: Animal populations; Animal, plant and microbial ecology; Applied ecology; bighorn sheep; Biological and medical sciences; Conservation, protection and management of environment and wildlife; Demography; Ecotourism; ecotype; Fundamental and applied biological sciences. Psychology; Game fishes; Geist; General aspects; Goats; Habitat conservation; Mammalia; Mountain sheep; North Dakota; Ovis canadensis; Population Ecology; recruitment; reintroduction; Sheep; Species reintroduction; Translocation; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; wild sheep; Wildlife conservation; Wildlife management
• ISSN: 0022-541X; 1937-2817
• DOI: 10.1002/jwmg.669

European settlement led to extirpation of native Audubon's bighorn sheep (formerly Ovis canadensis auduboni) from North Dakota during the early 20th century. The North Dakota Game and Fish Department subsequently introduced California bighorn sheep (formerly O. c. californiana) that were indigenous to the Williams Lake region of British Columbia, Canada, and Rocky Mountain bighorn sheep (O. c. canadensis) that were indigenous to the Sun River region of Montana. Although California bighorn sheep are no longer recognized as a distinct subspecies, they are smaller and adapted to a milder climate than either the native bighorn sheep of North Dakota or introduced bighorn sheep from Montana. Because reintroductions still play a key role in the management of bighorn sheep and because local adaptation may have substantial demographic consequences, we evaluated causes of variation in recruitment of bighorn sheep reintroduced in North Dakota. During 2006-2011, Montana stock recruited 0.54 juveniles/adult female (n = 113), whereas British Columbia stock recruited 0.24 juveniles/adult female (n = 562). Our most plausible mixed-effects logistic regression model (53% of model weight) attributed variation in recruitment to differences between source populations (odds ratio = 4.5; 90% CI = 1.5, 15.3). Greater recruitment of Montana stock (fitted mean = 0.56 juveniles/adult female; 90% CI = 0.41, 0.70) contributed to a net gain in abundance (r = 0.15), whereas abundance of British Columbia stock declined (fitted mean = 0.24 juveniles/adult female; 90% CI = 0.09, 0.41; r = — 0.04). Translocations have been the primary tool used to augment and restore populations of wild sheep but often have failed to achieve objectives. Our results show that ecotypic differences among source stocks may have long-term implications for recruitment and demographic performance of reintroduced populations.