Dunlin by Barry Van Dusen
Once again, Bird Observer offers a painting by the artist who has created many of our covers, Barry Van Dusen. Barry, who lives in Princeton, Massachusetts, is well known in the birding world. Barry has illustrated several nature books and pocket guides, and his articles and paintings have been featured in Birding, Bird Watcher’s Digest, and Yankee Magazine as well as Bird Observer. Barry’s interest in nature subjects began in 1982 with an association with the Massachusetts Audubon Society. He has been influenced by the work of European wildlife artists and has adopted their methodology of direct field sketching. Barry teaches workshops at various locations in Massachusetts. For more information, visit Barry’s website.
The Dunlin (Calidris alpina) is one of our most common small sandpipers, and in spring it is one of our most striking. The species is unmistakable in breeding plumage with its rufous back and cap, black belly, and white flanks. The sexes are similar in plumage. Juveniles are less rufous than adults and are streaked with black on their breast and belly. On the Pacific Coast, Dunlin could be confused with Rock Sandpipers, which are also black below but are lighter rufous above and have pale rather than black legs. In winter plumage, Dunlin are gray tinged with brown, have brownish heads, and exhibit a conspicuous white wing stripe in flight. Their long drooping bill helps distinguish them from other small sandpipers. The similar Curlew Sandpiper is grayer, lacks the brownish head, and has a white rump.
Although controversial, up to nine subspecies are generally accepted worldwide for this Holarctic-breeding sandpiper. Three subspecies breed in North America: C. arcticola and C. a. pacifica in the coastal areas of Alaska; and C. a. hudsonia in northern Canada and its Arctic islands, and south to the western shores of Hudson and James bays. Dunlin are migratory, wintering along the West Coast from southern Alaska as far south as central Mexico, and inland in several locations in California. They also winter along the East Coast from Massachusetts south through coastal Florida and along the Gulf Coast to central Mexico and the Yucatan. In Massachusetts, Dunlin are an abundant spring and fall migrant along the coast, and in some coastal locations are also a common winter resident. In spring, the migration often has a double peak in both early and late May. Fall migration extends from late August to late November with a peak in late October or early November.
Dunlin are generally monogamous although occasionally they are polygamous. The male's song is a series of trills given during courtship flights involving short glides on stiff wings and shallow fluttering. They also vocalize from the ground. The Dunlin's vocal repertoire includes a variety of cheep, treep, chrri, and kree calls. They are gregarious on their wintering grounds.
Dunlin nest in wet coastal tundra or sedge marshes, where they produce a single brood during the short Arctic summer. Males establish a territory and typically make several nest scrapes, one of which the female chooses. The male makes the scrapes with his feet, shapes them with his body, and lines them with fine grass and willow leaves. Dunlin are sometimes site faithful and reuse former nest scrapes. Males tend to be more site faithful than females. The usual clutch is four olive eggs with dark blotches. Both parents develop brood patches and share incubation duties for the three weeks until hatching. Until the chicks hatch, males defend a nesting territory with a threat display of raised wings and flights along the territorial boundary. The chicks are precocial and leave the nest soon after hatching. The parents lead the chicks to areas with abundant insects where the young feed themselves. The male does most of the brooding of the chicks. Both parents tend the chicks but the males stay with them longer, sometimes up to three weeks, until the young can fly.
The Dunlin diet consists of bivalves and arthropods, especially amphipods, but also includes some gastropods, and polychaetes. Dunlin are primarily tactile foragers in winter, probing mud flats of estuaries with their long bills. On the breeding grounds, they are usually visual foragers, pecking and jabbing at terrestrial and fresh water invertebrates from wet grasses, pond edges, and coastal lagoons. Insects and larvae comprise most of their diet on the breeding grounds.
Falcons and owls are the main avian predators on adult Dunlin while jaegers are the predominant egg and chick predators. Arctic foxes also prey on nests. Loss of wintering habitat due to anthropogenic factors has negatively impacted some populations. Christmas Bird Count data suggest a decrease in birds wintering in the Northwest and many experts think that there has been a continent-wide decrease in Dunlin numbers. The effects of global warming on Dunlin and their breeding grounds are not yet known. However, the Dunlin’s Holarctic distribution—with little alteration of breeding habitat to date—suggests that this common and colorful sandpiper is secure.
William E. Davis, Jr.