Birth site selection and neonate survival in mule deer in the Blue Mountains of Oregon
AuthorWalsh, Danielle R.
AdvisorStewart, Kelley M
Environmental and Natural Resource Sciences
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Mule deer (Odecoilius hemionus) populations have been in decline in recent decades for a variety of reasons including habitat loss, disease, and competition. We were interested in what factors influence survival of neonatal mule deer in the Blue Mountains of Oregon. Individuals should select resources to increase fitness; therefore, females should select parturition sites with characteristics that have the potential to increase survival of their neonates. We examined what habitat characteristics females selected at birth sites as well as how those selected characteristics affected neonate survival. Additionally, we were interested in how changes in forage quality, maternal condition, climate, maternal age, and physical characteristics of neonates affected their survival. We conducted our research at Starkey Experimental Forest and Range in northeast, Oregon, primarily in the Main study area. We captured adult females during the winters of 2013-2014 and 2014-2015, and fitted them with GPS collars as well as inserting vaginally implanted transmitters. When parturition occurred in May and June, we located neonates and birth sites. Neonates were fitted with expandable collars so that we could monitor mortality. We measured metatarsus length, chest girth, and weight for adults and neonates. Additionally, we quantified body condition, measured maximum rump fat, and measured the jaw and body length of adults. At birth sites and 2 adjacent random sites, we measured overstory and hiding cover, the number of trees and shrubs, the distance to the nearest transition in vegetation type, and aspect. We determined selection of habitat characteristics at birth sites with resource selection functions using a mixed effects logistic regression. We chose our best model based on Akaike’s Information Criterion corrected for small sample size. Our best model included significant parameters indicating selection for south facing slopes, increased overstory cover, and increased amounts of woody debris. We modeled neonate survival until weaning using the nest survival module in program MARK. We included different age trends to determine how survival changed. Survival from birth to weaning was 0.3169 (SE 0.706) and did not differ between years. Our best model indicated that survival changed daily from birth to day 30 and then began to stabilize and change weekly until weaning. Additionally our best model included a parameter for birth sites located on south facing slopes. Our results indicate that neonates born on south facing slopes have higher survival rates than those born in other locations. South facing slopes in this montane forested ecosystem are warmer and drier, providing a more stable microclimate for neonates who are born with few energy reserves. South facing slopes likely allow neonates to minimize energy use, which may increase their survival. Results from birth site selection analysis indicates that females selected habitat characteristics that increase hiding cover, potentially decreasing mortality by reducing predation events at birth sites. A better understanding of how deer select habitat characteristics to increase survival as well as what factors increase susceptibility to mortality allows for better management of populations. Management strategies that account for factors influencing survival will be better suited to counter population declines across the west.