Waterbird Wednesday week 9 - Dunlin
The Dunlin (Calidris alpina) is a very familiar wader to most people. It breeds in small numbers in the north west of the UK, with a population of around 10'000 pairs. However, thousands of birds arrive from their breeding grounds further north in the late summer and autumn, and during the winter the population swells to around 350'000 individuals. During the winter they gather in large flocks at the coast, particularly on estuaries or where there are mudflats. Flocks can reach thousands in there areas.
Identification
Dunlins are rather small, measuring around 17-21cm long. They have medium long, slightly decurved black bills and medium sized dark legs. When the wings are closed, they reach about the end of the tail. They are overall quite dumpy and short necked. In every plumage has a thick white wingbar and a white rump with a thick black line through the middle. This image shows a winter plumage Dunlin.
Adult summer
Birds in breeding plumage have a distinctive black patch on the belly. The upper parts are red-brown and there is obvious thick streaking on the breast and nape. The top of the head is red-brown streaked black but the face is rather plain with a weak supercilium.
Adult winter
Birds in adult winter plumage are plain grey-brown above and white below. There is some weak streaking on the breast, the crown is slightly darker than the rest of the head and there is a weak light supercilium.
First winter
First winter birds are like adult winter birds but the flight feathers are retained from juvenile plumage - they are light edged and give a "scalloped" effect.
Juvenile
Juveniles have an orangeish wash to the head and breast, and black spots on the breast and belly. The back is slightly reddish brown - feathers have dark centres and lighter, coloured edges. Some feathers may have been moulted - these replaced feathers would be greyish brown. Two white stripes on each side of the upperparts form white "V"s on the back. Light supercilium is stronger than in other plumages but still relatively weak. The crown is darker than the rest of the head.
Moult
Dunlins are often encountered during active moult. These can be birds moulting from juvenile to first winter plumage, breeding to winter plumage or winter to breeding plumage. A juvenile entering first winter plumage would have variable spotting on the underparts, and fresh winter-type feathers in the scapulars and/or back. The gingery head feathers would be replaced with plainer winter type feathers.
Breeding plumage birds entering winter plumage would have variable amounts of black on the belly, and winter type feathers in the scapulars and back. The head and breast change into plainer winter plumage, so colour and streaking here can vary.
Birds moulting back into breeding plumage in the spring are very similar, showing variable dark marking on the underside and fresh red-brown feathers in the scapulars and back.
Similar species
Curlew Sandpiper
Frequent passage migrant to the UK. Overall appears more elegant, with longer legs and neck and longer wings. The bill is longer and more decurved, leading to a thin tip. In all plumages has a white rump and a very broad white wingbar. This image shows a juvenile.
Winter
Stronger facial markings than Dunlin with obvious Supercilium, in some cases split. Greyer than Dunlin with less streaking on the breast and sides. Images show adult (left) and first-winter (right).
Juvenile
Juveniles have unmarked bellies with not much streaking on the breast. The breast and face are washed peach, and the supercilium is very prominent, with a slight split (as well as the supercilium another weak light stripe runs along the side of the crown). The face is darker with stronger markings. The back is uniformly scalloped, without "V" marks.
Broad-billed Sandpiper
Rare visitor to the UK, seen when blown off course on migration from breeding grounds in Fennoscandia to wintering grounds further south-east. Overall smaller than Dunlin, with a unique bill shape - straight for about 3/4 of the length before kinking downwards at the tip. Legs are short and greenish. In flight has a similar rump pattern to Dunlin with a slightly weaker wingbar. This image shows a juvenile.
Adult summer
Much darker than Dunlin with thick dark streaks on the breast and very dark back. Lacks black marking on belly. Dark facial markings with an obvious split light supercilium and dark lores. Light line down back gives light "V", similar to juv Dunlin but more prominent.
Winter
Much less plain than winter Dunlin, with streaks on back and scalloping on wing feathers. Strong facial markings with an obvious split light supercilium
Juvenile
Strong white 'V' on back and lightly streaked breast not extending to belly. Light base to bill and bold facial markings with a dark cap and a split supercilium.
White-rumped Sandpiper
Rare visitor to the UK - breeds in northern Canada and winters in southern South America. Overall smaller than Dunlin but with much longer wings, projecting far past the tail when closed. Due to this, it appears much slimmer than Dunlin. In all plumages has a fully white rump and a weak wingbar.
Adult summer
In breeding plumage, the back and crown are patterned rufous. The breast is streaked, and the supercilium is very weak. The base of the bill is light. There is no dark marking on the belly as in Dunlin.
Winter
A White-rumped Sandpiper in winter plumage is much less plain than a winter Dunlin, with dark-centred scapulars giving a 'streaked' effect to the upperparts. The white supercilium is much more prominent than in Dunlin, and the lower mandible is light at the base. The upperparts are lightish grey as oppose to the grey-brown of Dunlin.
Juvenile
In juvenile plumage, a White-rumped Sandpiper would have a light base to the bill and a very prominent supercilium. There would be no streaking on the belly as in Dunlin - The breast has some streaking and is slightly tinged orange. The back has two prominent white 'V' marks. These images show two juveniles (left and centre) and one moulting into juvenile plumage with a first year Dunlin behind (right).
Semipalmated Sandpiper
Very rare visitor to the UK from America. Overall much smaller than Dunlin with a shorter, straighter bill in proportion. It's toes are half webbed, giving it it's name, but this feature is rarely seen. In flight has a weaker white wing bar than Dunlin with a similar rump pattern. This image shows a juvenile.
Adult summer
A breeding bird is grey-brown above, with some variation towards rufous. The underparts are mainly white, with some streaking on the breast.The breast is tinged orange-brown. The scapulars have an obvious pattern, with medium-thick dark centres and light edges. This gives the effect of very large streaks on the side of the bird. The facial pattern is stringer than Dunlin, with a dark mask and a strong supercilium.
Winter
Rather plain grey with black centres to scapulars. Dark facial markings with dark cap and prominent supercilium. Images show winter plumage birds (left and centre) and an adult breeding bird moulting into winter plumage (right).
Juvenile
In juvenile plumage, a Semipalmated Sandpiper wouldn't show any obvious white "V"s. There isn't much streaking on the breast, and the head and breast are washed slightly orange. The back is lighter than in juvenile Dunlin. Images show a full juvenile (left) and a bird moulting into winter plumage (right).
Western Sandpiper
Very rare visitor to the UK from America. Smaller than Dunlin, with a thinner bill. White wingbar less obvious than in Dunlin. Like Semipalmated Sandpiper, has partly webbed toes. Rump pattern is like Dunlin's.
Adult summer
In breeding plumage, a Western Sandpiper would have heavy spotting on the breast - but no black marking on the belly like Dunlin. The crown, ear-coverts and scapulars are light rufous, and there is an obvious white eye-stripe.
Winter
Light grey above with thin 'streaks' in scapulars similar to Semipalmated Sandpiper. Obvious white supercilium but facial markings much lighter than Semipalmated. Images show adult (left) and first winter (right).
Juvenile
Juvenile has slight streaking on the breast, with head and breast washed more orange than in Semipalmated Sandpiper. Streaks do not reach belly, and are relatively weak. The lower scapulars are grey with a black "anchor" mark, and the upper scapulars are rufous. There is a white "V" mark on the back. Facial markings are light, and there is a thick white supercilium.
Pectoral Sandpiper
Pectoral Sandpipers are a relatively frequent passage migrant in the UK. They are, overall, larger than Dunlin, longer legged and longer necked with a more upright posture. The legs are pale yellowish and the bill has a pale base. When resting, the primaries project further than in Dunlin. In flight has a very weak wingbar and similar rump pattern to Dunlin.
Juvenile
A juvenile bird has streaking on the breast, not extending to the belly. The streaking comes to an abrupt end, causing a contrast on the lower parts. There are two obvious white "V" marks on the back, and the face is paler than Dunlin - however the crown is still dark.
