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Snowy Plovers: Single Species Study Leads to Ecosystem Insight

Gary Page


Most people who visit California's sandy coastline perceive the beach as largely devoid of life. In fact, a thriving community of plants, invertebrates, mammals and birds depends on sand beaches and dunes. Among these species is the Western Snowy Plover, a small, imperiled shorebird. The Pacific coast population is federally listed as threatened due to intensive recreational use of beaches, destruction of dunes, and expansion of predator populations. Today, some 1,500 Snowy Plovers nest on the 500 miles of California's beaches.
Beach-nesters inhabit an altered ecosystem today. J. Fuhrman / VIREO

To provide information for sound conservation and management, PRBO began studying Snowy Plovers in 1977. Initially, we focused on the factors underlying their reproductive success and the survival of adult and young plovers. We learned that plover egg and chick loss varied widely from place to place and from year to year. Strong winds, high tides, and trampling by humans destroy eggs, but predation by foxes, ravens, skunks or other predators usually outweighs all other factors. Predators, severe weather, and disease all contribute to the annual mortality of adults and juveniles.

Expanding Focus. These findings led us to ask questions about changes to the beach landscape related to human use, beach and dune dynamics, and, most importantly, predator populations. So many people visit some beaches that plovers have no chance of nesting on the sand without their eggs being crushed. The beach grass, Ammophila arenaria, introduced to stabilize dunes, has spread along the California coast, replacing native vegetation that plovers exploit for food and shelter. Changing predator populations are a serious threat. Since 2002, ravens have colonized the coast from San Mateo to San Luis Obispo counties by exploiting human infrastructures and food sources. Once absent from these areas, now ravens can destroy most plover nests along many miles of beach.

Single-species studies are often intensive and garner data essential to understanding a population's viability. Our long-term data on Snowy Plovers at Monterey Bay has been folded into a population viability analysis (see sidebar, page 3), indicating that, on average, each male Snowy Plover must successfully raise one chick per year in order to maintain a target coastal population of 3,000 birds.

Informing Management. Our research and monitoring now provide feedback to wildlife managers on the effectiveness of techniques they use to protect Snowy Plovers. In some locations, upper-beach nesting habitat is fenced off from the public to reduce disturbance. Following the implementation of this practice and of a docent education program at Point Reyes Beach, monitors found that rates of chick loss decreased on weekends, when they had formerly been highest. In many locations, managers enclose individual nests within wire fencing to foil predators. This effectively protects nests but several times has resulted in bouts of adult mortality, when predators keyed in on nesting adults (leading to immediate removal of enclosures).

At Point Reyes Beach, where the National Park Service is restoring the native dune system, newly opened habitat is already in use by post-breeding Snowy Plovers. In 2000, though, PRBO monitors noted that an unusually high percentage of plover eggs failed to hatch. These eggs, subsequently found to contain elevated levels of mercury, signaled the presence of an unexpected contaminant in the beach-dune ecosystem. Research is now under way to find the source of the mercury and solve a potential environmental problem for the plover and other species.

Addressing species-specific problems has led to ecosystem-level inquiries, needed to ensure that coastal dunes and beaches, even in their heavily altered state, will continue to support a thriving wildlife community.