Portland State University. Department of Biology
Michael T. Murphy
Date of Award
Doctor of Philosophy (Ph.D.) in Biology
1 online resource (xii, 167 pages)
Snowy plover -- Conservation -- Oregon, Snowy plover -- Oregon -- Population, Predatory animals -- Control -- Oregon, Bird populations -- Oregon
A thorough understanding of demographic parameters and their contribution to overall population growth is fundamental to effective conservation of small populations, but this information is often lacking. The Pacific Coast population of the Western Snowy Plover (Charadrius nivosus nivosus) is listed as threatened and has been the target of long-term, multi-pronged management in Oregon. The Oregon coastal population has been intensively monitored since 1990, and over 80% of the population is color banded, but a comprehensive analysis of demographic parameters and the effect of management on vital rates and population growth has been unavailable until now. Here, the author used capture-mark-resight techniques to document survival at each life stage and to explore environmental and management factors that best explained variation in survival over a 25-year study period. The author analyzed the effects of habitat restoration, exclosure use, and lethal predator management on survival at appropriate life stages and evaluated the effects of one management option, lethal predator control, on overall population growth. Chick survival to fledging improved dramatically after the chicks' 5th day, was higher in years with lethal predator management, and was highest during the peak of the long brood-rearing season. Cold weather, particularly during the chicks' first 5 days, had a negative effect on survival to fledging. Juvenile survival from fledging to the following spring declined over the study period, but rebounded after implementation of lethal predator management. Adult survival was lower in wetter-than-average winters and higher in years with predator management. The author used the survival analyses and productivity data collected over 25 years in a matrix population model to reveal that population growth is most sensitive to changes in adult survival, and that while predator management is important for continued growth, its use may be scaled back by as much as 50% and still maintain a growing population. My results, encompassing all phases of this species' life cycle, demonstrate that with holistic and thoughtful adaptive management, and with the cooperation of numerous agencies, a balance can be struck between protection and control of native species to bring about recovery of species threatened with (local) extinction.
Gaines, Eleanor Prindiville, "Snowy Plover Demography in Oregon" (2019). Dissertations and Theses. Paper 5004.
Available for download on Wednesday, June 03, 2020