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A key component to adaptive management of threatened and endangered species is periodic updating of recovery goals and management priorities after implementation of previous management strategies. This report describes an updated metapopulation viability analysis for the distinct population segment (DPS) of western snowy plover (Charadrius nivosus nivosus) breeding on the U.S. west coast based on monitoring data from across its range for the 12 years after the population’s recovery plan was published. 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 Sea Shore expected to be population sources, and most sites north of Point Reyes expected to be sinks. High adult survival of Oregon birds relative to other northern populations meant that Oregon sites also had relatively high potential growth rates for their latitude. Once dispersal was accounted for, all sites except those in northern California (Recovery Unit 2) and Washington had positive potential growth rates, with populations in southern and central California acting as strong sources (λ>>1). Simulated plover population dynamics were quite stable through time and across replicates, with an average metapopulation size of ~1950 birds. Mean metapopulation size in simulations was more sensitive to adult survival than either fecundity or juvenile survival. Increasing environmental stochasticity had little effect on mean metapopulation size, but large effects on both predicted year to year fluctuations and model uncertainty. Only simulations without dispersal or with continuous habitat loss predicted a sustained decline in plover populations. Overall, intensive predator management across the range coupled with source-sink population structure has substantially reduced the risk of extinction for western snowy plovers as long as current management practices continue and sufficient high quality habitat remains available. However, a single demographic target across the range may be inappropriate, as overall metapopulation dynamics are contingent on high growth potential of southern populations, while lower growth potential in northern populations means that greater effort will be required there to achieve the same growth rate. No simulations reached the 3000 plover target set forth in the current recovery plan. Reaching this target will likely require habitat restoration and more consistent use of currently unoccupied sites. In addition to continued aggressive predator management, plover recovery will require a better understanding of 1) mechanisms through which density dependence acts on plovers and environmental variables that determine habitat suitability, 2) how much dispersal occurs between populations and what influences dispersal rates and distances, and 3) mechanisms underlying latitudinal patterns in demographic rates and how those mechanisms will shape the species’ response to global climate change. Recommended citation: Hudgens, BH, Eberhart-Phillips L, Stenzel L, Burns C, Colwell M and Page G (2014). Population Viability Analysis of the Western Snowy Plover. Report prepared for the U.S. Fish and Wildlife Service. Arcata, CA. |
