Knot

Bird of the Month November 2023: Knot

Our wintering waders are a definite highlight of this time of year, and possibly none more so than the knot, or red knot as it is also sometimes known. It may seem fairly nondescript to some with its silvery grey winter plumage. But when hundreds of thousands of birds are gathered together at a high tide roost, the sight is truly mindboggling. Even if you don’t manage to visit one of these spectacular gatherings, look out for smaller groups of this lovely wader if you are heading to the coast this winter.

Fade to Grey

Knots are medium-sized, stocky waders, much bigger than dunlins or sanderlings, but smaller than godwits or oystercatchers. Like many waders, they undergo quite a dramatic transformation between summer and winter. Birds in full breeding plumage have beautiful, brick red undersides, hence the alternative name red knot. Their upperparts are a spangly mix of reds, browns, greys and black. A fairly long, black bill and black legs complete the look. We rarely get to see this plumage in the UK. If you are lucky, though, you might spot the odd bird coming into their finery or not fully moulted out of it at the start and end of the breeding season.

Knot
This autumn bird is still showing much of its breeding plumage

At first sight the winter plumage we usually see might seem fairly dull. But have a closer look and you will see it is actually subtly beautiful. A lovely mix of soft, silvery greys and browns cover the upper part of the bird while the underside is white. In the right light, they can really stand out against dark mud or rocks. A white supercilium, or eyebrow, gives the face definition. Although their bills remain black, in winter their legs are yellowish green. In flight, they display a white wing-bar. Newly arrived juveniles have a peachy wash to their undersides and more obviously scalloped edges to the feathers on their upperparts.

Juvenile knot
The strongly marked scallops and peachy wash show this is a juvenile

Long-haul Travellers

Knots breed on tundra in the high Arctic. Six subspecies have their own distinct breeding and wintering grounds. Our wintering birds all come from groups breeding in Greenland and northeast Canadian. In fact, over 65% of this breeding population winters in the UK and Ireland. The rest head to Continental Europe. Two other groups breed in Canada and Alaska. Both winter in different parts of South America. The remaining three subspecies breed across Arctic Russia. Those breeding furthest west travel to western and southern Africa for the winter. Central Russian birds winter on Australia’s western coasts, while those from further east winter in Papua New Guinea, eastern Australia and New Zealand.

These birds had newly arrived in Shetland from their Arctic breeding grounds this August

These migration routes span many thousands of kilometres. To cope with these distances, most populations have favoured stopping off sites en route. These locations are incredibly important, especially to birds heading north to breed in spring when they need to build up their fat reserves quickly. One of the most well-studied sites is Delaware Bay in the US. Here, rufa subspecies knots time their May visit to coincide exactly with horseshoe crab spawning so they can eat millions of their fat-rich eggs. This vital, but finely balanced, relationship between crab and knot, however, is under threat. Habitat loss, along with overharvesting for bait and use in the pharmaceutical industry are affecting crab populations. In addition, climate change means they spawn earlier, out of sync with the knots’ arrival.

Knot
Winter knot have yellowish green legs

A Bird in a Million

Wintering knots in the UK start arriving from August onwards. Later in the autumn they often gather in huge aggregations at suitable sites. They particularly like estuaries like the Wash in East Anglia and parts of the Moray coast which have large expanses of mud. Birds can number in the hundreds of thousands at some regular wintering sites. RSPB Snettisham is one of the best places to see them, particularly at high tide when birds have to stop feeding and gather in large roosts at the top of the shore. To give some idea of numbers, October 2020 saw the previous count record broken when approximately 140,000 birds were logged. Periodically, birds will take off and fly in huge murmurations as the rising tide forces them off the mud or as predators such as peregrine falcons turn up.

Steart knot
This flock of knots is a fraction of the size they can reach

At low tide they range across the mud feeding. They use their specially adapted bills, equipped with sensors to detect pressure changes within the mud, to find food. Knots’ movement with the tide, from feeding to roosting, is one possible explanation for both their common name and the second part of their scientific name, Calidris canutus. Eleventh century king of Denmark, Norway and England, Canute (pronounced Knut in Scandinavia) supposedly used his inability to stop the incoming tide as a demonstration of his power’s limits. The story was almost certainly invented long after his reign. It lives on, though, in the connection with these waders whose behaviour is also determined by the state of the tide.

Knot
On a bright day, winter knot can really stand out

Fears for the Future

Worryingly, as well as its impact on horseshoe crab spawning, climate change also seems to be affecting the knot’s survival in other ways. First, it leads to the earlier emergence of the insects knot feed to their newly hatched young on the tundra. With peak insect hatching over before they even arrive to breed, adults are struggling to feed their chicks. Some adults abandon the nest completely, heading off to find food for themselves elsewhere. Those that stay are often only able to rear smaller chicks due to the lack of food. These smaller chicks risk not having the fat reserves to survive autumn migration. Additionally, undernourished chicks tend to have shorter beaks. Research suggests that this inhibits them from reaching their preferred prey in the mud of their wintering grounds.

Knot on rocks
Knots don’t always feed on mud; they will use rocks as well

This one small wader is a perfect illustration of the intricacies of ecosystems and food webs. Thousands of years of evolution have resulted in a perfectly timed relationship between knots and peak food availability, whether this is insect emergence on the tundra or horseshoe crab spawning as they travel north. Evolution has also resulted in the knot’s particular physiology, producing the right length beak to access food in winter mud flats. What is increasingly, and worryingly, clear, is that we are attacking these finely balanced relationships on multiple fronts, via climate change, habitat destruction, disturbance and overharvesting of prey items. Could it be that at some point in the future those enormous flocks of wintering knot will be no more?

Knot
Winter knot are a beautiful mix of soft greys

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