Red Knot

Sara Meissner

A Red Knot in breeding plumage. From allaboutbirds.org

Meet the toughest bird on the beach! Weighing in at 4-7 ounces, with wings spreading a mere 22 inches, this stocky sandpiper can migrate up to 9,300 miles per year! Easily identified in breeding plumage (but just as charismatic when grey), Red Knots are a special sight to behold.

The rufa subspecies, migrating along the Atlantic coasts of North and South America, is listed as Threatened in the United States under the Endangered Species Act. A number of compounding factors have jeopardized this small population, but efforts are now underway to protect this species as a flagship for shorebirds everywhere.

allaboutbirds.org

Red Knots in non-breeding plumage. All photos by Sara Meissner unless otherwise credited.

Fun Facts

Knots use special sensory organs in the tip of their bills to feel for changes in pressure under the sand, indicating possible prey.
Knots have the largest gizzards, in relation to body mass, of any shorebird. They use these grinding organs to dissolve mollusk shells that are swallowed whole.
The oldest recorded Red Knot was at least 19 years old.
Up to 90% of the rufa subspecies can be present at one time, at one important stop during migration (Delaware Bay).
Knots continually produce a waxy oil used for preening, but during breeding season it can also be used to disguise the scent of vulnerable chicks.

allaboutbirds.org

Taxonomy

Scientific Name: Calidris canutus rufa

Common Name: Red Knot

Kingdom: Animalia

Phylum: Chordata

Class: Aves

Order: Charadriiformes (Shorebirds)

Family: Scolopacidae (Sandpipers)

Genus: Calidris

Specific epithet: canutus

Subspecies: rufa

https://motus.org/wp-content/uploads/2019/11/REKN_Final.pdf

L-R: Buff-breasted Sandpiper (Tryngites subruficollis), Short-billed Dowitcher (Limnodromus griseus), Red Knot (Calidris canutus rufa).

Niche and Habitat

In winter, the rufa Red Knot utilize a variety of marine habitats along the east coast of the Americas from the mid-Atlantic states down to Tierra del Fuego in Chile and Argentina.

During spring migration, Red Knots feast upon the eggs of spawning horseshoe crabs in the Delaware Bay. This feast allows them to nearly double their bodyweight in two weeks, providing enough energy to complete their journey to the breeding grounds. Occasionally they will be seen on inland bodies of water as well.

The Red Knot breeds in the High Arctic of North America during the summer months. Early in the nesting season, they have been known to eat some tender shoots and seeds. But their preferred meal is small invertebrates of shallow waters: mussels, clams, worms, shrimp, and crabs. They probe the wet sands and marshes for tasty morsels in typical shorebird fashion.

Knots are thought to be monogamous during the breeding season, and both parents work to incubate their 3-4 eggs. The nest is a shallow scrape on bare, stony ground, lined with grasses, leaves, and lichens. The chicks are precocial, meaning they can leave the nest almost immediately after hatching, and eat small insects like midges until they can effectively search for marine food.

allaboutbirds.org

Below: Global range of all Red Knot subspecies.https://fws.gov/northeast/red-knot/Conservation of Arctic Flora and Fauna (CAFF), Arctic Biodiversity Trends 2010.

Above: North American range. The rufa Red Knots are present in the pink breeding area and along the eastern half of the continent down into South America.https://www.allaboutbirds.org/guide/Red_Knot/lifehistory

A Red Knot partially in breeding plumage.
https://macaulaylibrary.org/asset/109897331

In flight, notice the pattern on the wings.
https://macaulaylibrary.org/asset/49222941

Nesting with chicks, well camouflaged.
https://www.audubon.org/magazine/may-june-2016/red-knots-are-battling-climate-change-both-ends

Evolutionary History

For long-distance migrants and Arctic-nesting birds, timing must be precise. Prey abundance along the journey is a rolling gamble of seasonality. Spring migrants are chasing the first appearances of prey, while fall means the dwindling end of supplies. Storms and other harsh weather could easily derail an entire migration by changing the schedule. Red Knots have developed a pattern of long-distance flights (1,500 miles or more) punctuated by intensive feeding stops to sustain them through unexpected delays or deficiencies.

And the Arctic summer is only a brief window. Males must arrive early enough to claim the best nesting locations, tending to avoid areas without lemmings and other rodents. Choosing areas with lemmings allows the birds to face less predation pressures from Arctic Foxes (Alopex lagopus) and have a better chance for chick survival.

FWS.gov [pdf]

A Red Knot taking a well-deserved break during migration.

Friends or Foes?

Predators: Arctic Foxes (Alopex lagopus), Red Foxes (Vulpes vulpes), Arctic Wolves (Canis lupus arctos), feral cats (Felis catus), and a number of avian predators, including: Peregrine Falcons (Falco peregrinus), Merlins (Falco columbarius), Harriers (Circus spp.), Short-eared Owls (Asio flammeus), Jaegers (Sterocorarius spp.). Large gulls like the Greater Black-backed Gulls (Larus marinus) and others will hunt vulnerable chicks.

Competitors: Gulls (more aggressive and disturbance-tolerant) and other shorebirds compete with Red Knots for available food sources, especially during migrations. Arctic-nesting birds also compete for prime nesting space, especially as the climate changes.

Cooperators: Large, mixed flocks of shorebirds provide cover from predators, the same way a school of fish disrupts a predator’s ability to home in on a target.

FWS.gov [pdf]

Conservation and Environmental Impacts

When the rufa Red Knot was proposed as a Threatened species in the United States, the Fish and Wildlife Service compiled a massive document outlining the current and possible future threats to the subspecies.

1: Climate change and sea-level rise are becoming major issues along the Red Knot’s migration routes and wintering zones as coasts change shape and sandy beaches disappear in storms and behind hardened structures. Coastal development is destabilizing necessary habitat with increased human disturbances and invasive species. Additionally, climate change is already affecting the Arctic breeding areas that are so delicate and necessary.

2: In parts of the Caribbean and South America, the Red Knot is hunted as a game animal. The impacts are likely minimal, but information is not reliably gathered. The practice was banned in the United States after substantial population reductions in the 1800s.

3: Predation is a normal experience for any wild animal. But along migration routes, points of high predation and human disturbance can push Knots from prime foraging and roosting, decreasing their physiological fitness. In the breeding range, Knot reproductive success normally cycles along with natural rodent/predator cycles. However, climate change is altering these cycles, leading to longer periods of low productivity and threatening the species.

4: Regulatory protections across the entire Knot range are generally good. But protections for important prey species, like the horseshoe crab, have been late in coming and perhaps not strong enough. Commercial harvests of the crab in Delaware Bay, which hosts the vast majority of Knots along their migration, is considered a primary cause of decline during the 2000s (laws regarding harvesting have since been changed because of this revelation).

5: Additional threats to prey species are numerous and not so easily fixed. Warming oceans and acidification, habitat changes, increasing diseases and invasive species, and the burial and crushing of prey under sand during beach renourishment and recreational activities are all growing threats. Increasing asynchronies between migration timing and prey cycles are also important factors with data currently lacking

FWS.gov [pdf]

All three North American subspecies are declining. In 2012, this larger grouping was estimated at just under 140,000 breeding individuals. Globally, the IUCN lists the entire Red Knot species as Near Threatened.

allaboutbirds.org

Videos:

How to Help

Shorebirds, whether they nest in your area or not, need your help! Check out the content below to explore how you can become a responsible beach visitor.

For More Information:

Crabs: The following sites feature a wealth of information regarding Horseshoe Crabs and their relationship with Red Knots, and how individuals can help.

Banding: These three sites highlight the importance of banding for conservation, including efforts specific to Red Knots, photos, and videos. The last link is for the government site where banded birds can be reported by the public.

Successes and failures: These articles cover a range of topics related to the conservation of shorebirds and Red Knots. All contain pertinent information about past or ongoing efforts as they have faced difficulties or successes.

In-Depth: For further research, try these two sites. The first dives into international agreements for the protection of migratory species around the world, and the second is a compendium of knowledge regarding Red Knots of North America.

Moonbird: For a more light-hearted read in your free time, try learning about the oldest recorded Red Knot and his incredible journey migrating farther than the distance to the moon and back.

Hoose, P. M. (2012). Moonbird: A year on the wind with the great survivor B95. Farrar Straus Giroux.

Resources

Links listed above, plus:

https://www.allaboutbirds.org/guide/Red_Knot/lifehistory

https://abcbirds.org/bird/red-knot/

https://www.audubon.org/news/rufa-red-knot-gets-listed

https://ebird.org/species/redkno

https://motus.org/wp-content/uploads/2019/11/REKN_Final.pdf

http://www.nashorebirds.org/the-red-knot/