Breeding-plumage Dunlin in Dungeness Bay during May. Photo by Bob Boekelheide
Dunlin of Dungeness Bay
by Bob Boekelheide
November 2024
October and November are times of change in Dungeness. If you watch birds, you can’t help but notice the goose flocks cackling overhead and the Golden-crowned Sparrows returning once again to your bird feeders. Change also comes to the mudflats of Dungeness Bay. Western and Least Sandpipers, so abundant in August and September, have mostly fled south for the winter. In their place, thousands of Dunlin now arrive from Alaska.
What makes Dunlin so special? Probably not their non-breeding “basic” plumage. During winter, Dunlin look like generic brown-backed shorebirds with white bellies, black legs, and long droopy bills. They are small shorebirds about the size of a Sanderling, yet larger than a “peep,” the collective word used to describe the smallest sandpipers like Westerns and Leasts. Their name “Dunlin” comes from their plain grayish-brown “dun” colors, as in “dunling,” a little brown-colored bird.
Non-breeding plumage Dunlin in Dungeness Bay. Photo: by Dow Lambert
What’s most notable about Dunlin during winter isn’t their appearance, but their abundance. They typically gather in large flocks during migration and winter, often forming flashy murmurations when pursued by predators like Merlins and Peregrine Falcons.
Dunlin are almost always the most abundant shorebird species on our Sequim-Dungeness Christmas Bird Count. For 45 of the 48 years we have held the SDCBC, Dunlin out-numbered all the other shorebirds, including the other two members of the “Big Three” – Black-bellied Plovers and Sanderlings. These three species always make up the great majority of shorebird flocks in Dungeness Bay during winter.
Dunlin flock feeding on the mudflats of Dungeness Bay. Photo: by Bob Boekelheide
Black-bellied Plovers and Sanderlings typically number a few hundred on the CBC, whereas Dunlin often number several thousand. Dunlin’s long-term average count on the CBC is over 2100 per year (Figure 1). Their highest count ever on the SDCBC was 7,610 Dunlin counted in 1985.
In Figure 1, it looks like annual SDCBC numbers of Dunlin are all over the map, sometimes over 5000 and sometimes below 100. Do their numbers really fluctuate that much between years? Likely not. Using our Christmas Bird Counts to follow annual changes in Dunlin is questionable. For one, Christmas Counts occur on just one day out of the whole year. Weather on CBC day, along with shorebird-viewing, can be a bit of a crapshoot – it might be calm with great visibility, or it might be windy and rainy, even snowy and icy.
Additionally, our CBC occurs in mid-December, when tides are high through daylight hours and the lowest tides occur in the middle of the night. This means that Dunlin might be at high-tide roosts during the day, not easily found by our intrepid counters. I’ve seen a few thousand barely-visible Dunlin roosting on logs in the middle of the closed area on Graveyard Spit, where they can’t be found unless someone knew exactly where to look. At the other extreme, it’s easy to over-count Dunlin, because flocks fly all around the count area. Dunlin also fly inland to feed in agricultural fields during the day, where they might be double-counted coming and going as well.
Thankfully, we have other Dunlin data than just the CBC. Figure 2 shows the annual cycle of Dunlin in Dungeness Bay, using monthly high counts at Three Crabs from 2014 to 2018. During these surveys, OPAS volunteers counted Dunlin and other species three times each month, as part of the Three Crabs Restoration Project. These counts purposely took place during favorable tides for shorebird viewing, not always possible during the CBC.
In fall, peak arrival in Dungeness Bay by migrating Dunlin occurs in November, much later than most other migrant shorebirds. (Figure 2). It turns out that Dunlin don’t depart their coastal Alaska breeding areas until after they finish their big annual molt, delaying their fall migration until the seasons are turning and snows begin to fly in Alaska.
Figure 2 also shows that peak numbers of Dunlin in Dungeness Bay actually occur in February, then tails off a little in March and April. It turns out that during fall migration it looks like many southbound Dunlin don’t stop here but continue on to California, or else stop for such a short period that we don’t see very high numbers. By January and February, though, the California birds may have already turned around and began migrating north once again.
From February through April, they stop at estuaries along the coast to feed and rest, including Dungeness Bay. Grays Harbor, a much larger estuary on the south side of the Olympic Peninsula, gets tens of thousands of Dunlin in late winter and early spring, whereas smaller Dungeness Bay gets a few thousand. The data suggest that Dunlin numbers in Dungeness Bay may double or triple during spring migration compared with those during fall migration.
Flock of Dunlin in Dungeness Bay. Photo by Dow Lambert
The Dunlin subspecies that winters along the West Coast of North America, including Dungeness Bay, is the subspecies Calidris alpina pacifica. This subspecies nests in western Alaska, from the Alaska Peninsula northward through the Yukon-Kuskokwim delta to the Seward Peninsula. Another subspecies, C. a. arcticola, nests further north in Alaska, particularly along the North Slope of Alaska from Point Barrow to the Canadian border.
Curiously, sightings of marked birds suggest that after molting C. a. arcticola migrates southwest from Alaska to the coast of Asia, spending the winter from southern Japan to Southeast Asia. This means that C. a. pacifica and C. a. articola might be neighboring subspecies in Alaska, but they travel totally different directions during migration.
Dunlin seem quite good at handling cold weather. I remember one cold winter’s day at Dungeness Landing Park with temperatures in the single digits, so cold that slush ice formed in the bay and rime ice coated the shoreline. Despite the cold, there were stalwart Dunlin flocks feeding on the icy mudflats right next to shore. Maybe their tolerance to cold is what enables them to stay later in Alaska before fall migration.
Non-breeding Dunlin (upper right) with Western Sandpipers. Photo by Bob Boekelheide
After April, Dunlin on the West Coast make a mad dash to their nesting areas in Alaska. By this time, they’ve molted into their spectacular breeding plumage, with a flashy red and black back, a black belly patch, and whitish-gray heads and breasts covered in fine black streaks. At one time, Dunlin in North America were known as the Red-backed Sandpiper, in reference to their breeding plumage.
On the way north nearly all West Coast Dunlin stage at the Copper River delta near Cordova, AK, where they gorge on invertebrates before continuing to breeding areas. The Copper River Delta is critical habitat for West Coast shorebirds, not only for Dunlin, but particularly for Western Sandpipers. Likely the entire world’s population of Western Sandpipers passes through the Copper River Delta during migration, along with the bulk of Dunlin that winter in western North America.
Breeding plumage Dunlin. Photo by Dow Lambert
Once at their breeding grounds, male Dunlin quickly establish breeding territories and begin courting females. They nest in a two-dimensional flat world of tundra, so the males use showy aerial displays to increase their visibility, flying over the tundra with cocked wings making noisy call notes. Males raise their wings when approaching females on the ground, revealing their very sexy bright-white underwings.
We think of Dunlin as social creatures, considering they spend their non-breeding season in tight flocks of thousands of birds. When nesting, however, their sociality goes out the window. A Dunlin pair defends a surprisingly large territory from all other nesting Dunlin, usually covering several acres of tundra. Once chicks have hatched, territories dissolve and broods begin to move freely to find food.
Dunlin are monogamous, and both male and female help build their nest out of tundra grasses. The female then lays four camouflaged eggs, one egg per day or a little longer, in late May or early June. They hide their nests in the tundra grasses, hopefully out of sight from marauding arctic foxes and jaegers. Both male and female incubate, with the male taking longer incubation duties as the eggs near hatching.
Dunlin eggs are relatively large in relation to the size of the female, because their precocial chicks require lots of energy for quick growth. A female Dunlin that normally weighs 60 to 65 grams lays four eggs weighing about 11 grams each. This means the entire clutch totals about 70 to 75 percent of the female’s normal body mass, an amazing output for a little bird that has just migrated long distances. This compares with a 75-gram female American Robin that lays four eggs weighing about 6 grams each, or about 32 percent of the female robin’s normal body mass.
Adult Dunlin don’t start incubating their eggs until the female has laid all four eggs in the clutch. This ensures that all four eggs hatch about the same time, usually within 21 or 22 days. Upon hatching, the chicks become mobile within hours, little fuzzballs with big feet that leave the nest as soon as their feathers have dried. The chicks feed themselves without any help from their parents, but the parents stay with them, brooding them if necessary, and sounding the alarm when predators lurk nearby.
Breeding plumage Dunlin on the left, Sanderling on the right. Photo by Bob Boekelheide
Like many shorebirds that nest on the tundra, their main prey items are mostly fly larvae and adults, particularly chironomids (aka midges) and tipulids (aka crane flies). Eventually the parents abandon their children and gather at shorelines of the Arctic Ocean or Bering Sea. The juveniles later join them prior to southward migration.
Considering their challenging lives, studies show that the average Dunlin has a life expectancy of only about five years. Some Dunlin can live a long time – in Europe the longest-lived marked Dunlin was at least 24 years old. Among our local subspecies, the oldest on record was 14 years old. Studies with banded birds show that only about three out of four adult Dunlins return to the nesting area from one year to the next.
One of the most amazing things about Dunlin is how faithful they are to both nesting areas and wintering areas. In one study in Scotland, 90 percent of the males and 65 percent of the females returned to nest within 100 m of their previous year’s nest. Another study of wintering birds at Bolinas Lagoon in California showed a resighting probability of 97 percent for some years. It’s mind-boggling that these little birds have this phenomenal awareness about where they are on Planet Earth.
Please visit Dungeness Bay this winter to observe Dunlin as they pick and probe on the mudflats. It’s one of the wonders of nature, right here on our doorstep.
Breeding-plumage Dunlin in Dungeness Bay during May. Photo by Bob Boekelheide
Many of the interesting facts about Dunlin contained in this story came from Birds of the World, an on-line resource available through Cornell Lab of Ornithology. I highly recommend that all bird aficionados subscribe to Birds of the World, both for the information and to support the Lab of Ornithology.