Knot (Calidris canutus): long distance traveller.
A BBC TELEVISION PRESENTER once likened the spectacular pre-roost display flight of the red knot to iron filings being attracted to a magnet. Such a description does not fairly depict the scene that draws-in naturalists from all over Britain and Europe -- to the Wash estuary in west Norfolk -- every year during the late summer and autumn. These visitors are hoping to view a spectacular aerial ballet where glistening shoals of shifting quicksilver take on shapes and forms that are hard to imagine; a tornado one moment, a thunder cloud the next, then an hour glass, and more. Why the birds form such huge flocks that often number several tens-of-thousands is not known for certain, although it is most probably a tactical bluff to confuse or disorientate an aerial predator lurking close by. It may be that they simply enjoy it.
The red knot belongs to the family of birds known as Scolopacidae that globally number around eighty-one species, of which many can be seen around the Norfolk coast, and are often referred to collectively as the sandpipers. This family includes the dunlin and sanderling, often found in close association with the knot, yet not in such mind boggling numbers. Accompanying them during their huge roosts, when the flowing tide has consumed the nutritious mud flats, it is possible to distinguish the slightly dumpy knot from its sandpiper cousins by their soft, smoky grey plumage and collective shuffling habit; it is also possible to pick out birds with rufous, brick-red feathers that are yet to fully moult their breeding plumes from the summer. Visiting the estuary during neap or medium tides might leave you wondering where these thousands of birds have gone. The closest views are only possible when the most powerful of spring tides forces the knot and its companions to leave their feeding grounds and take refuge on any exposed area of sand or shingle close to the shoreline: fantastically, up to two-hundred birds can squeeze onto one square meter of dry land!
It is very probable that the Scolopacidae have their origins in the northern hemisphere and show a distinct preference for breeding well above the Arctic Circle. Such high latitudes give them a very hectic and short summer in which to complete their nidifi'cation, where days that have no nights in Canada, Greenland and the Taimyr Peninsula of Northern Siberia provide them with twenty-four hour daylight under which to raise their young on the sparse tundra and barren lands of the far north. The threat of the Arctic winter forces the knot south at the earliest opportunity where they follow ancient aerial migration paths, eventually bringing them to the Wash estuary. It is here that they can rest and feed on the millions of molluscs, worms, crustaceans and insects that the gleaming silt provides when exposed during low water. Few of these travellers will stay for the length of the British winter though. They are bound for the warmth of the southern hemisphere, to the coastlines of South America, South Africa, Asia and the Antipodes. Only in the spring will they return to Norfolk on a brief stop-off before re-commencing their journey north.
To see the spectacle that is ninety thousand knot exploding from the mud flats and perform their abstract dance takes some planning. Spring tides are necessary to push the birds from the safety of the mud and timing on the day is also crucial. The nature reserve at RSPB Snettisham is one of the best locations in the British Isles to observe this dramatic event from, and to help you plan your trip, birdwatchers tidal charts are available from the reserve office to ensure your journey is not wasted.
The scientific name for the knot, Calidris canutus, is thought to be derived from King Canute, the 11th century Viking monarch, who is thought to have been taken aghast at the birds ability to seemingly drive back the fullest of tides at will.
Packed together tightly on a sand bank, thousands of knot roost during a spring tide. It is estimated that up to two-hundred of the birds can squeeze onto a single square metre of land when space is at a premium.
Once the tide has receded, tens-of-thousands of knot break away from their roosting sites to stock-up on the Wash estuary's bounty. Exposing the invertebrate rich mudflats, the tide will soon turn, leaving only a short window of opportunity to restock depleted energy reserves.
Like a genie escaping from a bottle, thousands of red knot reverse the situation, swirling and flocking ever tighter before filtering down onto the last exposed fragments of sandbank in a mesmerising pre-roost display.