Master of Science degree with a major in Natural Resources, option Wildlife
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Adult survival is one of the most influential vital rates affecting population growth of iteroparous organisms. Survival often varies annually due to environmental stochasticity. However, drastic variations in annual adult survival rates can have overwhelmingly negative impacts on population viability and growth. In many wild avian populations, adult survival varies between sexes and may owe to unequal risks associated with reproductive roles or predation; this is particularly true among shorebirds. I used mark-resight data from a 19-year study of Western Snowy Plovers (Charadrius nivosus nivosus) in coastal northern California to investigate sex-specific apparent survival of the adult population (N=387). I reported apparent survival (φ) along with standard error (±SE) and 95% confidence intervals, as well as beta estimates (β) with 95% confidence intervals. Apparent survival varied substantially among years (min φ= 0.44±0.07; 0.30-0.57 to max φ = 0.82±0.06; 0.64-0.94), with the minimum occurring in the middle of the study (2006-07) and the maximum occurring in 2009-10. Furthermore, apparent survival varied between sexes, whereby males had higher overall apparent survival (0.72±0.03; 0.30-0.93) than females (0.68±0.03; 0.26-0.91). Average known lifespan of Snowy Plovers within the study was 3.5±2.1 years, with males living longer on average (4.3±2.8 years) than females (3.6±1.9 years). Overall population growth remained stable ( =1.05±0.13 to 1.10±0.12) across the course of the study. Years of substantially low adult survival have directly reduced overall growth potential for the local population. High temporal variance in adult survival produces increased variance in annual population growth rates, with possible implications for extinction risk. Reduced survival in adult female Snowy Plovers has been shown to influence the adult sex ratio of the population, as observed in other Charadrius populations, however that was not evident in this study. Application of demographic parameters in future population viability and growth models will provide a comprehensive understanding of population dynamics and will inform progress toward the recovery of the Pacific Coast population.
Journal of Wildlife Management
Windsor, Justin A., "Apparent survival of snowy plovers varies across years and between sexes in coastal Northern California" (2020). HSU theses and projects. 383.