My bird of the month for May, the whimbrel, is appropriately enough sometimes called the ‘May Bird’. This is because May is the month most of us encounter this migratory wader as it stops off at coastal sites on the way to its breeding grounds further north. Similar to curlews, but with a few tell-tale differences, the whimbrel is a subtly beautiful bird with a distinctive call. They often travel in small parties, so it is well worth looking, and listening, out for this summer visitor if you are out and about this month.
The Diminutive Curlew
At first glance Eurasian whimbrels look extremely similar to curlews. Both have mottled brown and creamy white plumages with long bills and long legs. However, there are some key differences to help tell them apart. The most useful feature is the bill. Whereas curlews have long, evenly curved bills, more than two thirds of a whimbrel’s bill is more or less straight, with only the end curving down. Their bills are shorter than on curlews as well. Bear in mind, though, that curlew bills do show large variations in size. Juvenile male curlews, in particular, have much shorter bills than females.
Whimbrels are also smaller overall than curlews, with shorter necks. Of course, this is harder to appreciate if the two species aren’t actually standing near to each other. Waders generally are quite good at seeming small one moment as they hunch up at a roost, and much larger when actively feeding to add to the difficulty of judging size!
The two species also have some plumage differences. Curlews tend to be a warmer brown colour while whimbrels often have a ‘colder’, greyer tone. Crucially, though, whimbrels have a pale stripe dividing their dark brown crown caps. While some curlews do have more of an obvious cap than others, it never has a dividing stripe. Whimbrels also have an obvious pale supercilium, or eyebrow, and dark stripe through the eye, both of which are much less obvious in curlews. The two species’ calls are different as well. Instead of the curlew’s bubbling call, the whimbrel’s is a series of seven notes, a little like the whinnying of a little grebe. Whimbrels often call frequently while on migration and as they sometimes move overnight, you will often hear rather than see them. If seen in flight, whimbrels have a more fluttering style, while curlews use stronger, deeper wing strokes.
Bird of the North
Many of us only ever see whimbrels on passage to and from their breeding grounds. Birds often travel in small flocks while on migration, though, and suitable coastal sites can sometimes play host to a number of birds stopping off to refuel. In fact, this is another way of separating them from their larger cousin. By late April and early May when whimbrels pass through, curlews are already paired up and on territories, so any flocks of curlew-like birds on the coast are much more likely to be whimbrels. The UK does have a tiny breeding population, however. Centred predominantly in Shetland, there are also a few pairs in Orkney, the Outer Hebrides and Caithness and Sutherland on the Scottish mainland. The latest British Trust for Ornithology figures show 310 pairs recorded in 2009. Outside the UK, the Eurasian species breeds across the subarctic from Greenland to eastern Russia.
On the breeding grounds, whimbrels nest on the ground on tundra or moorland, making a shallow scrape for their eggs. Like many waders, chicks are precocial. This means that they are already well developed when they hatch and can very quickly start foraging themselves for their insect and berry food. Once breeding is over for the year, whimbrels migrate south, with western birds wintering in Africa and Asian breeders heading to southeast Asia and Australasia. Wintering sites are coastal and here birds eat a range of foods including molluscs, worms, crabs and other crustaceans. Since the 1980s, some whimbrels have begun wintering in the UK and Ireland, predominantly on the two countries’ south coasts. Although at present only around 40 or so birds per year do so, the trend is definitely upwards. This could be a result of climate change and an overall trend of milder winters.
A Hudsonian Cousin
Whimbrels breeding in subarctic North America have had a bit of a complicated taxonomic history. Until 2011 they were classed as a subspecies of what was, up to then, called the common whimbrel. They were then promoted to full species status, in what is known in taxonomical terms as a ‘split’ between the Eurasian and North American birds. In 2018, though, they were once again demoted to subspecies status. However, a study published in 2019 led to its restoration as a full, separate species. Researchers essentially found enough biological evidence to show that the birds were different enough genetically to be distinct species. Ornithology and taxonomy, however, are fraught with politics and differences of opinion, and not every authority recognises the split. Either way, the North American bird breeds solely in northern Canada and Alaska and winters on more southern USA coasts as well as South America.
Tagging shows that individual Hudsonian whimbrels, like many of their Eurasian cousins, carry out incredible feats of migration. In 2008, a female bird was recorded flying more than 5,000 km in approximately 146 hours: just 6 days. Occasionally, this long migration means Hudsonian birds lose their way and turn up in the UK. The first record is from 1955 and there have been approximately 15 recorded here since. One marked difference between Hudsonian birds and Eurasian whimbrels is that our birds have a white rump that shows as a ‘V’ shape in flight. Hudsonian whimbrels, meanwhile, have mottled brown rumps, the same colour as the rest of the body. They are also slightly paler than our UK birds, and their head patterns are even more obvious and clearly defined. This gives them a smart, dapper appearance.
The May Bird
Despite only breeding, in a UK context at least, in the Northern Isles, Outer Hebrides and northern Scottish mainland, whimbrels often stop off around our coasts at this time of year. Their sudden appearance and then disappearance led to many coastal communities naming it the May Bird. So, if you are able to head to the coast this May, look out for small flocks of this lovely little cousin of the curlew and perhaps marvel at how far it has travelled to get there and how far it still has to go.