It's likely that you've heard of a starling murmuration, when a flock of the birds take to the sky and fly in an astounding, shape-shifting ballet. Starlings aren't the only birds that are able to move in unison as if the massive flock is of one mind. Red knots can also flock, but they add an extra dash of dazzle for spectators thanks to their coloration.
The red knot in non-breeding plumage is dust-colored on its back and the tops of its wings, but it is a silvery white on its belly and the underside of its wings. When in flight, a red knot flashes dark or light depending on which part of the bird you see. And when a flock of red knots changes direction, the whole thing changes color like a wave.
Hotspot Birding posted another amazing example on their Facebook page.
According to Cornell Lab of Ornithology, the red knot "makes one of the longest yearly migrations of any bird, traveling 15,000 km (9,300 mi) from its Arctic breeding grounds to Tierra del Fuego in southern South America."
Indeed, at least one banded red knot has flown the same number of miles during migration as a trip to the moon and back. It is the length of this migration that makes their refueling points particularly important.
Red knots feed on the eggs of spawning horseshoe crabs, and time their migration with the arrival of horseshoe crabs at beaches. Delaware Bay is one such critical refueling point, where red knots line the shores by the thousands during migration season in order to gather enough energy-rich eggs to finish their migration. Unfortunately, humans have harvested huge numbers of horseshoe crabs for fishing bait and for blood collection for medicinal purposes. The decline of the horseshoe crab at the hands of humans is causing the decline of the red knot as well.
"The populations wintering in South America dropped over 50% from the mid-1980s to 2003. The North American population of Red Knot is on the 2014 State of the Birds Watch List, which lists species most in danger of extinction without significant conservation action," reports Cornell Lab of Ornitholoty.
Learn more about the intricate tie between red knots and horseshoe crabs in the PBS Nature episode, "Crash: A Tale of Two Species."