- Mule deer (Odocoileus hemionus) populations in south-central Oregon are near their lowest levels since census efforts began in 1961. I investigated fawn survival, cause-specific mortality, and factors contributing to mortality from 2010 – 2012 to identify potential causes for the decline. I also explored pre-parturition and parturition site characteristics.
I studied fawn survival among two different population segments in south-central Oregon. Adult females (n = 126; > 1 year old) were captured on winter ranges to collect biological samples and attach transmitters. Vaginal implant transmitters facilitated the capture of fawns (n = 127). Fawns (birth to < 1 year old) were radio-collared and mortalities investigated. Fawns died primarily as a result of predation, but other sources of mortality included vehicle collisions, fence entanglement, hunter harvest, drowning, disease, and unknown causes. Predation was primarily attributed to coyotes (Canis latrans) but bears (Ursus americanus), cougars (Puma concolor), and bobcats (Lynx rufus) also preyed on study animals. To investigate survival, I developed known-fate models within Program MARK using 9 individual covariates and 3 environmental
covariates. Estimated annual fawn survival was 34% and positively correlated with a linear time trend. Survival was not correlated with indicators of female body condition including rump fat, blood serum non-esterified fatty acids, blood serum triglycerides, and blood serum β-hydroxybutyrate. Survival did not differ by fawn sex, fawn weight, date of birth, wintering area, or whole blood selenium levels. Environmental covariates including precipitation, year, and temperature did not significantly explain fawn survival. I concluded that predation might be limiting mule deer population growth in south-central Oregon. However, I did not explore the full suite of factors that would indicate sources of population regulation.
I also investigated adult female habitat use prior to and during parturition from 2010 – 2013. I measured 10 habitat attributes at all parturition sites for comparison to randomly selected pre-parturition locations within each adult female’s seasonal range. Birth sites that occurred in habitats characterized by juniper (Juniperus occidentalis), were closer to water and within greater vegetative cover compared to summer range sites in the same habitat type. Other birth sites were located in areas characterized by conifer spp. (Abies concolor, Pinus spp., Pseudotsuga menziesii) and in these areas there were no differences in habitat attributes between birth sites and summer range sites. I concluded that within each habitat type birth sites might be chosen to maximize predator avoidance and within juniper habitats low water resources might contribute to site selection.