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Lifetime reproductive success of snowy plovers in coastal northern California
Conserving threatened and endangered species requires knowledge of species breeding productivity and the factors that cause variation in reproductive success. I summarized 13 years of reproductive data to quantify lifetime reproductive success (LRS) for 195 individually marked Snowy Plovers (Charadrius nivosus) breeding in Humboldt County. In addition, I modeled relationships between LRS and various measures of habitat quality using an information theoretic framework and a model averaging approach. LRS varied appreciably between sexes; males exceeded females in maximum LRS, mean LRS and variance in LRS. Additionally, reproductive success was highly skewed among individuals, with a small proportion of the population contributing most offspring. Thirteen percent (nmales = 12, nfemales = 14) of males and females produced approximately 50% of fledglings. By contrast, 37% (n = 33) of males and 45% (n = 47) of female plovers produced zero fledglings and 71% (n = 64) of males and 72% (n = 76) of females produced two or fewer during their lifetime. Variance in LRS was best explained by breeding substrate, with gravel breeding birds having significantly higher LRS compared to beach breeding birds. Models containing this covariate accounted for nearly 100% of the corrected-Akaike weights based on the relative importance of model covariates. Other measures of habitat quality, including measures of nest exclosures, corvid abundance and human activity, were not significant predictors of LRS. The results from this study provide valuable information regarding the relationship between LRS and habitat quality, and thus can be used to guide management aimed at increasing the reproductive success of this threatened species.