Population Viability Analysis of the Western Snowy Plover
Brian Hudgens1, Luke Eberhart-Phillips2,3, Lynne Stenzel4, Catherine Burns5, Mark Colwell2, Gary Page4
1. Institute for Wildlife Studies
2. Humboldt State University, Department of Wildlife
3. Universität Bielefeld, Department of Animal Behaviour
4. Point Blue Conservation Science
5. San Francisco Bay Bird Observatory
IWS collaborated on a new population viability analysis (PVA) of the threatened Western Snowy Plover. The report to the U. S. Fish and Wildlife Service (USFWS) updates recovery goals and management priorities, which were largely based on a PVA conducted in 1999 by Nur et al., prior to the widespread implementation of annual counts and current management practices.
The Pacific coast breeding population of the Western Snowy Plover has been listed as a threatened population since 1993 under the Endangered Species Act. Since 2005, the estimated breeding population size has varied between 1,537 and 1,877 adults. Currently, most of the U.S. Pacific coast plover population breeds in a few large subpopulations in central and southern California while plovers occur at lower densities in Washington, Oregon and northern California.
Photo's by Matt Brinkman, IWS
Analysis of demographic data from five to nine sites spanning the U.S. Pacific coast revealed latitudinal gradients in both adult survival and fecundity, with plovers from southern populations experiencing greater longevity and producing higher numbers of chicks than plovers from northern populations. These latitudinal gradients in demographic rates resulted in a geographic pattern in population growth potential, with sites south of Point Reyes National Seashore expected to be population sources, and most sites north of Point Reyes expected to be population sinks.
Expected population growth rates for 25 subpopulations along the Pacific Coast (without immigration; BWS - Breeding Window Survey).
Our simulations suggest that ongoing intensive predator management across the range coupled with source-sink population structure substantially reduce the risk of extinction for western snowy plovers. However, reaching the recovery target of 3000 breeding plovers will likely require habitat restoration and more consistent use of currently unoccupied sites. In addition to continued predator management, plover recovery will require a better understanding of:
1. How density dependence and environmental variables relate to plover habitat suitability
2. How much dispersal occurs and what influences rates and distances
3. Mechanisms underlying latitudinal patterns and how they shape the species’ response to global climate change
Cited: Nur, N., G. W. Page, & L. E. Stenzel. 1999. Population viability analysis for pacific coast snowy plovers. Point Reyes Bird Observatory, Stinson Beach, California.