Spotted Sandpipers, An Example of Avian Polyandry
by Ro Wauer
A recent visit to Lassen Volcanic National Park in northern California reminded me how different breeding spotted sandpipers appear from when they are over wintering in South Texas. They are a Jeckel and Hyde bird that sports a spotted breast on their breeding grounds but possess an immaculate white breast in winter. But what is most amazing about these little sandpipers is that they are one of nature’s most fascinating experiments. They are one of the few bird species in which the female is dominant. She will entice two or more males into her harem to incubate the eggs and care for the youngsters. She arrives on the breeding grounds first and selects and defends her territory and her mates. This example of avian polyandry is an apparent success story because spotted sandpipers are among our most widespread and abundant shorebirds.
Betty and I discovered a very defensive female near Manzanita Lake at Lassen. She flew about the little stream where we were searching for butterflies, perched on an adjacent tree, and constantly scolded us with shrill “peet-weep” calls. Then she would fly off again, flying stiff-winged in a sporadic flight-and-glide manner to the next landing spot. We did not search for a nest, but moved away so as not to disturb her or her mates who we assumed were sitting tight on a nest. She continued her frantic calls for a long time as we moved further away.
Spotted sandpipers are often finished with their nesting chores by late July, and some of the earliest birds can arrive on their winter homes soon afterwards. They normally utilize lake shores and streams where they wander about searching for insects and various other invertebrates such as worms, crustaceans and mollusks. But they may even catch small fish and on occasion feed on carrion. But whether they are on their nesting or winter grounds they are easily identified by their small size (smaller than a killdeer), long yellowish legs, yellowish bill, and unusual behavior of constant teetering.
The spotted sandpiper is the most widespread sandpiper in North America with a breeding range that extends throughout North America from coast to coast and from the extreme north Texas to Alaska. Because of its odd nesting behavior it can be characterized as a “pioneering species.” It “quickly and frequently colonizes new sites, emigrates in response to reproductive failure, breeds at an early age, and lives a relatively short time (breeding females live an average of only 3.7 years), lays many eggs per female per year, and has relatively low nest success,” according to “The Birder’s Handbook.”
“The maximum clutch size is four eggs, each of which weighs about 20 percent of the adult female’s body weight. Apparently, it is physiologically impossible for a female to increase the clutch size beyond four, but during the six-to-seven-week breeding season she can lay up to five complete clutches of four eggs each. Each clutch requires about three weeks of incubation, so a female would be hard-pressed to hatch and raise even two broods. Multiple males enable a female to increase her reproduction output by freeing her from the responsibility for incubation and care of the young.” Her free time at Lassen allowed her to properly chastise us for invading her territory.