HABITAT USE, MOVEMENT PATTERNS, AND BODY CONDITION OF MALE AND FEMALE SNOWY OWLS (BUBO SCANDIACUS) IN WINTER
Chang, Alexander M
Birds that winter in northern latitudes face challenges associated with cold climates, including reduced food abundance and availability. Additionally, metabolic requirements are greater in colder weather and more food is required to meet these demands. Consequently, competition for resources in winter may be greater than in the breeding season. Competitive ability and dominance within species is often related to sex, if there is sexual size dimorphism, as in raptors. I studied various aspects of the winter ecology of male and female Snowy Owls wintering in Saskatchewan. Females are the larger sex and dominant, and I tested hypotheses that female dominance would translate into priority access to resources through sex differences in winter habitat use and home range size and movement patterns. Further, I tested whether differential access to resources manifested as a difference in winter body condition and survival between the sexes. Using information obtained from Global Positioning System - Global System for Mobile Communications (GPS-GSM) satellite transmitters, driven transects, and habitat ground-truthing, I found that females occupied home ranges in areas with lower proportions of canola than males, but males avoided canola fields within their home range. Male home range sizes tended to be smaller than those of females. Females in higher body condition (weight adjusted for body size) had significantly smaller home ranges than individuals in lower body condition. These findings are consistent with the prediction that dominant individuals place home ranges in higher quality habitat and so require smaller areas to meet their food requirements. I extended this finding and demonstrated that there are population level physical consequences to female dominance in winter. Using records from an 18 year-long dataset of Snowy Owl winter trapping and wildlife rehabilitation centers, I found that males have lower body condition than females in winter, carrying lower amounts of fat and muscle energy reserves, and experiencing higher mortality. My research demonstrates the importance of the winter period as a stressful time for owls that stay in northern latitudes year-round. It also raises as yet unanswered questions as potential topics for future research. It would be interesting to extend my findings to determine whether winter body condition has carryover effects to the subsequent breeding season, by investigating the relationship between condition and mating status, breeding territory quality, reproductive output, and survival. Also, as my research focused on differences between males and females, similar work could be done to compare the dominance relationship between age classes and its implications.
DegreeMaster of Science (M.Sc.)
SupervisorWiebe, Karen L
CommitteeClark, Robert; McLoughlin, Phil; Somers, Chris
Copyright DateFebruary 2017