The salt ponds along the southern edge of San Francisco Bay provide critical nesting grounds for almost ten percent of the Pacific Coast population of the federally threatened Western snowy plover, a bird with creative breeding rituals and a need for enhanced habitat. The Snowy Plover Recovery Project, a program launched in 2003 by the San Francisco Bay Bird Observatory (SFBBO) to help the plover, is now turning to high technology to find the nesting sites of the secretive birds and to learn which predators are stealing their eggs and threatening their survival.
Western snowy plovers are small shorebirds about the size of sparrows, with ashen-colored wings and backs, white bellies, and black-trimmed faces. These plovers, which nest along the Pacific Coast, are behaviorally different from the plover populations in the interior West, and are considered a subspecies. They were listed as threatened by the federal government in 1993 due to low population and decreased habitat; in 2007, the US Fish and Wildlife Service estimated that there were only about 2,100 snowy plovers breeding on the Pacific Coast, and that the number of major nesting areas was down to 28. Today there are fewer than 150 plovers nesting in the San Francisco Bay salt ponds.
“The western snowy plover population is declining for several reasons,” says Caitlin Robinson, director of the SFBBO’s waterbird program, which is heading up the observatory’s plover project. “Their primary nesting habitat has been encroached upon by human development, especially buildings right on the beach and the disturbance caused by recreation activities on beaches,” she says.
Worse, she adds, “Along with the human development on beaches also come more predators.” Snowy plovers have natural predators such as red-tailed hawks, northern harriers, raccoons, coyotes, and owls, but people have introduced—or the human population has attracted—other predators including crows, common ravens, red foxes, and domestic dogs.
Founded in 1981 by a group of biology graduates from San Jose State University, the SFBBO is a nonprofit research and education organization that works to conserve birds and their habitats. The objective of the Snowy Plover Recovery Project is to identify the plovers’ foraging or nesting sites, and to find ways to optimize their habitat on the dry salt ponds, in the hope of boosting the Bay Area’s population of adult plovers to 500. Hitting this target number for the San Francisco Bay would serve as a step towards getting the birds delisted as a threatened species.
But before the researchers can count the birds, first they have to find them—and that’s harder than it sounds. First of all, the birds usually avoid humans, setting up their nesting and breeding areas far from human disturbance, and in large, open areas like the salt flats where they can forage for brine flies. The pale plovers also naturally blend in with the shoreline around them; they like areas with light-colored soil and objects that can camouflage them and their nests while providing cover for chicks. “Their bellies are fat and white like salt,” says Jocelyn Davidson, an assistant on the Snowy Plover Recovery Project, “and their backs are light brown like the dirt.”
So this year to aid them in distinguishing bird from background, the researchers began using Kowa and Swarovski “spotting scopes” designed to help them see natural colors precisely and in high contrast. The tripod-mounted scopes have high-definition lenses that contain fluoride, and have a much higher magnification power than ordinary binoculars. With these high-power lenses, the researchers hope to spot not only the plovers, but also the nests they build in the ground, called scrapes. These are just small divots in the substrate, decorated with small sticks or pieces of shell, but it’s important to find them because they can tell the researchers a lot about the birds’ nesting success and the impact that predators are having on their population.
Each researcher has to cover quite a bit of turf—the research area includes salt flats in Hayward, Fremont, Alviso, and East Palo Alto. “When we go out to find the plovers we are given an area of about one to five salt ponds to survey, depending on their size,” says Davidson. “We drive the levees around the salt pond and use the scopes, and write what we see in our field notebooks.”
With some high-tech help from the scopes, assistants can see everything from nesting areas to, well, other things. “It’s easy to tell when the plovers are copulating,” says Davidson. After the male and the female meet, she explains, “He goes to work building a scrape. When he is done and the girl is interested, she tries out the scrape by sitting in it and seeing if she ‘fits’ and likes it.’ If so, then she gets out and they copulate. If not, she runs away…and then the male will try again.”
After Cinderella finds her scrape, the researchers use the scopes to determine if the plovers are sitting on an empty nest, a brood, or simply chilling out, plover-style. This helps them determine where plovers like to nest. It is not yet known why females prefer one scrape over another—researchers believe the choice may have something to do with location—but identifying the nests early on tells scientists which areas to keep monitoring.
Western snowy plovers usually lay three eggs. Once the eggs are laid, “The female incubates during the day and switches off at night with the male,” says Davidson. “The dad takes over when they hatch.” But these eggs are very small—much too small to see from a distance, even with a scope—so researchers have to rely on watching plover behavior to find the nests. For example, when plovers are incubating, they sit lower to the ground and look puffed out to keep the eggs warm. But this is not always an exact science. “If they have a nest and perceive a threat, they will start sitting in random areas to confuse you [about where the eggs are]. We’re always complaining about the ‘sneaky’ plovers,” says Davidson.
Once a nest is found, an assistant floats the eggs in a water bath to test their age. If an egg floats at an angle, it means the chicks are under a week old, but if the top of the egg is exposed while floating, the chicks are almost here. The number of eggs discovered tells the researchers how well the plovers are reproducing, as well as when the plovers are using the pond for mating.
Determining the age of the eggs is important, because the researchers want to band the chicks within a few hours of hatching. During the spring of 2008, the observatory teamed with the US Fish and Wildlife Service to band snowy plover chicks, each with an individually identifiable color combination, to track their survival rate and their movements. But the chicks are precocial, which means they are up and running within a few hours and can feed themselves, much like ducklings, so there isn’t much time to band them before they can get away.
By estimating when the eggs will hatch, researchers can also know whether to blame disappearing eggs on chicks hatching or on predators raiding the nest. “Sometimes it’s an obvious predation with egg yolk everywhere,” says Davidson. But sometimes predators eat the egg whole, leaving no sign of their presence.
“One of the key factors limiting Western snowy plover population growth is poor reproductive success due to predators and human disturbance,” says Robinson. “Identifying nest predators can often be difficult if researchers do not observe the predation event or predators do not leave tracks around the nest.” As a result, SFBBO researchers have also started using remote camera monitoring at the salt flats to identify these elusive nest predators and capture footage of them stealing the eggs. The cameras have night vision and work from up to thirty meters away; they can record continuous footage of plovers incubating their nests. The cameras are camouflaged and connected by a thousand feet of cable to DVR systems that record the footage. The long cable allows the researchers to change the batteries and swap out the entire DVR without disturbing the incubating plover.
The preliminary data is already exciting, says Robinson. “During the 2009 pilot season of this project, we recorded footage of red-tailed hawks, common ravens, northern harriers, and California gulls depredating snowy plover nests,” she says. “We also captured footage of a California gull depredating newly hatched snowy plover chicks. By knowing what predators are depredating snowy plover nests and chicks, we will be able to manage snowy plover nesting areas to accommodate plover’s needs more effectively.”
As the study progresses, the observatory researchers will be continuing the camera observations, banding the newly hatched chicks, monitoring how many chicks survive the year, and watching how the plovers move around the salt ponds. They have also made a simple change to the landscape to aid the birds—after careful scientific research to determine the plovers’ proclivities, researchers and volunteers from SFBBO added oyster shells to the bottoms of the salt ponds to make the soil, which is usually dark brown or red, a lighter color that will help the plover avoid predators. The team hopes to continue their project until the plovers have been delisted—and then maybe the birds can get a little privacy.