Abnormal Coloration in Bighorn Sheep (Ovis canadensis)

Reports of abnormal coloration in wild vertebrates are encountered frequently in the literature. Abnormal white coloration manifests itself as albinism or leucism, and those terms are often used interchangeably, albeit erroneously (Curatolo 1979; McCardle 2012). Albinistic individuals are characterized by a complete lack of pigmentation in the skin and hair and have pink eyes; leucistic individuals (Fig. 1), however, are deficient in pigmentation and are white in color, but exhibit pigmented skin and eyes that are normally colored or blue (Abreu et al. 2013 for review). Leucism is a double-recessive trait (Cruickshank and Robinson 1997); hence, normally colored parents have the potential to produce leucistic offspring, but the genetics of albinism should not be confused with the genetics of leucism (Searle 1968). Piebaldism involves a lack of pigmentation (Abreu et al. 2013) in some parts of the body, and piebald individuals are characterized by normally colored eyes (Fertl and Rosel 2002; Acevedo and Aguayo 2008). Miller (2005) noted that piebaldism has been referred to as partial albinism by some investigators, whereas others have not considered the differences between piebaldism and leucism; thus, the terminology associated with reports of abnormally pigmented animals frequently is confounded (Abreu et al. 2013). Melanistic individuals exhibit dark or even black pelage or appendages resulting from the excessive deposition of melanin, and this condition occurs less frequently than does albinism (Sage 1963). Shackleton (1985) had reported an absence of records of abnormal coloration in bighorn sheep (Ovis canadensis) despite published reports of white-colored individuals (Jonez 1958; Hansen 1965a; Cooper 1974; O’Connor 1974; Wilson et al. 1975; McQuivey 1975, 1978; Jones 1980). Individuals exhibiting piebaldism also had been previously described (Hansen 1965a, 1965b), as had melanistic bighorn sheep (O’Connor 1974) and others whose coloration was described by Bunch and Nguyen (1982) as “melanistic black”. Similar to Shackleton’s (1985) report, McCardle (2012) did not include any records of white, albinistic, or leucistic bighorn sheep in a much more recent review. My interest in this subject dates to 1976—when I learned that ≥2 white-colored individuals had been seen in the Clark Mountain Range, San Bernardino County, California—and I have since then recorded all records of abnormally colored bighorn sheep that I became aware of. I also used several web-based bibliographic databases (EBSCOhost, JSTOR, Google Scholar, Harzing’s Publish or Perish) and a web-based search engine (Google) to search for words or phrases (albinistic, leucistic, piebald, melanistic, pelage color, etc.) specific to abnormal coloration in bighorn sheep and reviewed results of those searches for references to abnormal coloration in that species. Additionally, I contacted numerous bighorn sheep biologists and other colleagues in the United States and Canada, as well as guides, outfitters, and hunters that had accumulated extended periods of time in the field, and queried each regarding observations of abnormally colored bighorn sheep. Finally, a simple questionnaire was distributed via e-mail to members and affiliates of the Northern Wild Sheep and Goat Council or the Desert Bighorn Council.