Nature Watch: Peeping at Fall Shorebirds

About the author: Steve Ellis is a naturalist and Land Trust member who enjoys sharing his love of the natural world. His blog series, “Nature Watch,” will appear each month in “Habitchat,” chronicling native plants and wildlife you can expect to see during that particular time of year. We thank Steve for sharing his passion, illustrating the importance of island conservation.

Overview

Long before winter grips their nesting areas on the arctic tundra, shorebirds begin migrating southward.

Adults of many species leave the breeding grounds before their young. The latter must bulk up with muscle and fat, activities that require a few extra weeks. This means the majority of shorebirds seen here in late August and September are the young of the year.

What attracts these energetic birds to these islands?

Rocky beaches shelter marine invertebrates such as limpets and snails, while ebbing tides strand small fish. All these are potential prey for Black Turnstones, Black Oystercatchers and Surfbirds.

Waves deposit small clams and other food items on sandy beaches. This is the preferred habitat of Sanderling flocks, those “wind-up toy” shorebirds that race after retreating waves to pick up prey. When the next wave returns, the light-colored birds dash back up the beach again.

By far, the most productive beaches for shorebirds are mudflats. Small clams, shrimp, crabs and other invertebrates burrow into the soft mud. Shorebird species with various bill lengths poke into the burrows of these creatures.

Dowitchers are large, chunky shorebirds with long bills used to probe in the mud. Their feeding action resembles the quick up-and-down motion of a sewing machine.

Dunlins, a smaller species, often probe with the tip of the sensitive bill flexed opened, able to detect prey just below the surface of the mud. These birds may be seen wading in shallow water.

Perhaps the most unusual food on the mudflat menu is the layer of biofilm. This is a sheet of diatoms (single-celled plants), tiny invertebrates, organic detritus, and bacteria. Western Sandpipers spread out across the mud, slurping up this highly-nutritious goop. Biofilm regenerates quickly under the right conditions.

Western Sandpipers feasting on biofilm are one of the small shorebird species known affectionately to birders as “peeps.” Other peeps are Least, Baird’s and Semi-Palmated Sandpipers. Dunlin and Sanderlings are a bit larger and can be thought of as honorary peeps. These species are notoriously difficult to identify. You can test your ID skills by searching for them at Port Susan Bay, Deer Lagoon and Crockett Lake.

By far the most numerous of the peeps are Western Sandpipers. Adult non-breeding Westerns have a pale gray head, grayish-brown upper parts, and are lighter underneath. Juveniles sport some rusty color above, and all Western Sandpipers have a black bill that droops at the tip.

The upper wings and back of Baird’s Sandpipers are brown with a scaly appearance. If you’re having difficulty locating these particular peeps, try the alpine tundra in the North Cascade mountains. Their dichotomous pattern of either coastal mudflats or alpine meadows has to be one of the strangest among all bird migrations.

Many shorebirds only use local beaches to restore their energy and fat reserves after long flights from Alaska and Canada. Some will continue southward to winter in Mexico, Central America and as far away as South America. Enough stay here, however, to make it worthwhile for birders to check out our local mudflat beaches all the way into next June, when the peep flocks again return to the far north.

Least Sandpiper adults arrive in our area as early as the first week of July. Photo by Martha Ellis.

Fauna: Least Sandpiper (Calidris minutilla)

Least Sandpipers have been dubbed “those mice of the mudflats” for their diminutive size. With a length of 6 inches, they’re the world’s smallest shorebird.

They have a short, sharp black bill and the belly and flanks are white. The head is darker than other peeps. Juveniles are a bit brighter in color than adults, with rufous upper parts. All Leasts have yellowish or greenish legs, a field mark which separates them from the other common peeps whose legs are dark.

Least Sandpipers occasionally join Western Sandpipers and other shorebird species in feeding on mudflats or in shallow water. They prefer, however, to search for prey in drier conditions and are often found in the short vegetation bordering mudflats. Their diet includes insects, crustaceans, small snails, and other invertebrates. Seeds are sometimes added to the menu.

Merlins, small but powerfully-built falcons, prey on Least Sandpipers during migration and at overwintering sites.

Least Sandpipers breed in open areas of the boreal forests of Alaska and Canada. Adults arrive in our area as early as the first week of July, with juveniles following in August. Small numbers spend the entire winter here, but most will continue as far south as central coastal Peru.

The northward spring migration brings them back to our islands for a stopover in mid-April through early May.

Places to look for Least Sandpipers include Port Susan Bay, Oak Harbor marina, and Crockett Lake. They can also be located in the drier parts of marshes, and their high-pitched “Kree” calls can be heard from rain pools and flooded fields.

Flowers of pickleweed are tiny, blooming from August through November. Photo by Martha Ellis.

Flora: Pickleweed, also known as Glasswort (Salicornia virginica)

One of the few plants that can thrive next to tide flats is pickleweed. This plant grows as a perennial mat, rising from long, slender rhizomes. The short stems are grayish-green and support leaves resembling scales.

Flowers of pickleweed are tiny, blooming from August through November. Male and female organs are found on separate plants. The blooms are wind-pollinated and the resulting minuscule seeds are dispersed by tides, rain, or by the movements of birds and mammals.

Pickleweed has few competitors and can form large areas of monoculture. The mats shelter Savannah Sparrows and small mammals. Snails and other invertebrates are found on pickleweed and the stems are hosts for some moth species.

Northern Pintail ducks and Canada Geese are among the waterfowl species that graze the seeds and stems. Least and Baird’s Sandpipers prey on invertebrates among the mats.

Pickleweed traps sediments, prevents erosion and helps keep saltwater from impacting upland plant species.

Look for pickleweed along Crockett Lake, Perego’s Lagoon, Iverson Spit and Camano Island State Park. It thrives in other places on our islands not subject to strong wave action.

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