Behaviour, gastrointestinal parasites, and stress hormones of the South Thompson California Bighorn Sheep (Ovis canadensis) herd
Bighorn sheep (Ovis canadensis) populations are characterized by drastic all-age respiratory disease related die-offs. Conservation efforts and management are often limited by the vulnerability of bighorn sheep to a multitude of pathogens and concurrent natural and anthropogenic stressors. Furthermore, the effects of human development, infrastructure and activities on local bighorn sheep behaviour, physiology, and population demographics are not fully understood. There is an urgency to determine the mechanisms accountable for bighorn sheep population declines and to understand the dynamics of local populations in order to effectively manage sustainable populations. The South Thompson California bighorn sheep herd located in the southern interior of British Columbia has been rapidly increasing in numbers and is considered a resident herd remaining in the same general area year round. The abundance of sheep and their use of human-developed areas raise concerns regarding the effects of anthropogenic pressures, the capacity of the habitat to sustain the population, and the vulnerability of the herd to a die-off. The specific thesis objectives were: (1) determine whether behaviours are affected by habitat, season, and sex with a focus on developed landscapes; and (2) compare gastrointestinal parasitology and physiological stress levels of ewes in three areas by season and anthropogenic influence to evaluate the impacts of human development. From summer 2008 to fall 2009, behaviour observations were collected from unmarked individuals from the South Thompson herd. During the spring, summer, and fall of 2009, 90 fecal pellet samples were collected opportunistically and noninvasively from unmarked ewes. The frequency of various behavioural categories differed seasonally, among habitat types, and between sexes. The gastrointestinal parasite levels varied by season and location; whereas, stress hormones varied only by location. Based on the behavioural observation results, the urban and agricultural developed lands appear to be an integral part of the South Thompson range. Presently this may be having a positive effect on the herd health by providing high quality forage at key times. However, the population numbers are increasing and this may lead to issues associated with overcrowding. Additionally, land use changes that result in reduced access to these lands may have a major impact on the herd. Parasites were found in all of the bighorn sheep including those in a remote area. Similar results have been reported from other bighorn sheep populations and the presence of gastrointestinal parasites alone does not appear to be a major contributing factor to die-offs. However, if the population continues to expand, or if portions of their range become unavailable, parasite loadings could contribute to health problems. This may be exacerbated if habitat use by bighorn sheep becomes concentrated in the developed areas. Stress hormones were not significantly higher for the bighorn sheep using the developed areas compared to the remote area. However, as numbers increase and more development occurs it will be important to continue to monitor gastrointestinal parasites and stress levels as they may indicate potential problem developing. The results of this study support herd-specific management efforts, help with the development of land use guidelines, aid prioritization of stewardship activities, and identify knowledge gaps for the South Thompson herd.