Breeding patch dynamics of the Western snowy plover (Charadrius alexandrinus nivosus) in Humboldt County, California

Graduation Date

2010

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Wildlife, 2010

Committee Chair Name

Mark A. Colwell

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Density, Charadrius alexandrinus nivosus, Common raven, Patch dynamics, Snowy plover, Breeding, Humboldt State University -- Theses -- Wildlife, Human disturbance, American Crow, Daily predation rate, DPR, Reproductive success

Abstract

Effective management of threatened bird populations relies on identifying factors contributing to population limitation and ameliorating those factors. The U.S. Fish and Wildlife Service identified three factors acting to limit productivity of the Western Snowy Plover (Charadrius alexandrinus nivosus): predation of chicks and eggs, loss and degradation of breeding habitat owing to exotic species, and human disturbance. Using direct and indirect measures of habitat quality, I examined the dynamics of plover occupancy, density and productivity at 19 historic breeding locations in Humboldt County, CA from 2001-09, and compared these measures to indices of limiting factors. To evaluate the relationships of habitat quality and productivity across the breeding sites, I conducted an a priori parsimonious model selection strategy using 13 candidate linear models. I found that breeding site occupancy and density were positively correlated. With both daily predation rate and per capita fledging success as response variables, the covariate representing an index of Common Raven (Corvus corax) activity appeared in the top five most-competitive models, accounting for 99% and 88% of corrected-Akaike weights based on the relative importance of model covariates, respectively. Estimates for the most competitive models suggest that raven incidence correlates positively with daily predation rate and negatively with per capita fledging success. Additionally, I found that there was considerable variability in direct and indirect measures of habitat quality among breeding sites. Based on these results, and other evidence collected over the 9-year study, I consider predation by ravens to be the most important ecological factor limiting the Snowy Plover population in Humboldt County. I recommend that management actions designed to increase the productivity of Snowy Plovers in Humboldt County be directed at ameliorating the effects of predation by ravens.

https://scholarworks.calstate.edu/concern/theses/pz50gz35f

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