The red knot is a medium-sized shorebird that is named for its rusty red breast feathers during the breeding season. But why is this particular bird called a “knot”? The origins of its common name provide some interesting linguistic and historical insights.
What is a “knot” in reference to birds?
In ornithological terms, a “knot” refers to a group of shorebirds that are in the genus Calidris. This genus contains around 30 different species of sandpipers and stint that are often collectively referred to as “knots.” Some examples of knots include the red knot, great knot, surfbird, and ruddy turnstone.
The term “knot” originated in the 1500s to describe these chunky-bodied shorebirds in their non-breeding plumage, when their feathers appear gray and knotted or mottled together. This distinguishing pattern evoked the imagery of knotted clumps of material or tangled knots of rope, leading people to refer to the birds as “knots.”
Why is the red knot named for its coloration?
The red knot stands out from other knots due to its vibrant breeding plumage. During spring and summer months, most red knots sport bright rufous or cinnamon-colored feathers on their face, breast, belly and flanks. This reddish-orange hue contrasts sharply with their grayish non-breeding plumage for the rest of the year.
While knots may seem rather nondescript in winter, the red knot’s rusty breeding feathers make it one of the most colorful shorebirds in its range. As a result, the descriptive moniker “red knot” differentiates this species from other duller knots based on its prominent red coloration.
Where does the red knot breed and nest?
The red knot has an expansive breeding range that includes the entire Arctic region. Some key nesting areas include:
- Northern Canada
- Alaska
- Russia
- Siberia
- Northern Scandinavia
- Greenland
Red knots breed in tundra habitats from June to August before migrating southward. They prefer well-drained, elevated nesting spots near water, where the males construct shallow scrapes in the ground lined with lichen and grasses.
Why do red knots migrate such long distances?
Red knots are champion marathon migrants that make some of the longest yearly journeys of any bird. They breed in the Far North during the brief Arctic summer then travel up to 16,000 miles round trip to reach their wintering grounds in southern oceanside habitats. This extreme migration is driven by seasonal food availability and their specialized eating habits.
In the Arctic tundra, red knots feed voraciously on protein-rich insects, arachnids and larvae to store fat for the long flight ahead. But as winter descends, food becomes scarce and difficult to access beneath snow and ice. The birds must seek out new food supplies along their migration route down the coasts of North and South America.
Red knots feast on mollusks, crustaceans and other marine invertebrates in coastal wetlands and mudflats. By migrating huge distances, they follow seasonal bursts of food abundance to fuel up and successfully breed. Their flexible foraging allows them to oscillate between polar opposites!
How do red knots find their way on migration routes?
Red knots navigate with amazing precision across continents and oceans despite having small brains. They are thought to orient themselves using several natural cues:
- The sun – knots calibrate their internal compass based on its location.
- Stars – they also navigate by star positions at night.
- Earth’s magnetic field – they have a sense of direction based on magnetic forces.
- Landscapes – they recognize and follow prominent coastline and mountain features.
- Smell – they may locate breeding sites by detecting plant scents.
Additionally, juvenile red knots learn traditional migration paths and stopover sites by traveling with older birds. Generations follow the same flyways between ancestral Arctic nesting grounds and wintering habitats, a tradition spanning thousands of years.
What are some key red knot migration stopover sites?
Red knots use a network of critical stopover habitats to rest and feed during their marathon migrations between the Arctic and southern tip of South America. Some major sites include:
Delaware Bay, New Jersey and Delaware
Delaware Bay’s extensive mudflats provide an integral rest stop for red knots to gorge on horseshoe crab eggs in May to bulk up before final travels to breeding grounds. Up to 80% of the total population may stop here during spring migration.
Río Grande, Argentina
The vast tidal flats ringing Río Grande in Patagonia host huge numbers of red knots from November to April, providing up to 75% of their diet at this time based on abundant shellfish.
Maranhão, Brazil
The tropical coastal mudflats along Brazil’s northern shore represent the red knot’s final major stop before jumping off on transoceanic flights of 2,500 miles towards Arctic breeding sites in May and June.
Chukchi Peninsula, Alaska
In late summer, up to 80% of the red knot population stops to feed again on the Chukchi Peninsula’s nutrient-rich mudflats to fuel the final southbound leg of migration back towards wintering grounds.
How do red knots eat?
Red knots have a unique, specialized feeding method to target their prey. Here are some of their key adaptations and foraging techniques:
- Sensitive bill tip – Their bills have a dense concentration of nerve endings allowing them to detect prey buried in mud or sand.
- Vibration detection – They can sense minute vibrations to pinpoint active prey moving underground.
- Suction feeding – Creating a vacuum with their buccal cavity, knots swiftly suck up prey as they probe into the substrate.
- Rapid digestion – Their digestive systems are highly efficient at metabolizing food for energy within 1-2 hours.
Knots also have an ingenious trick for the most efficient foraging. They rapidly jab their bill into the wet sand or mud in the same spot to open up a hole, stirring prey from deeper levels up towards the surface where they can reach them.
What are some threats facing red knots?
Red knot populations have plummeted in recent decades due to several key threats, especially along migration routes and in wintering habitats:
- Habitat loss – Coastal development, pollution, and erosion have degraded mudflats and wetlands they rely on for food.
- Overharvest of horseshoe crabs – Declining crab numbers directly reduces eggs that are a critical food source at migration stopovers like Delaware Bay.
- Climate change – Rising temperatures and extreme weather disrupt food supplies and nesting success in the Arctic.
- Disturbance – Human recreational activities on beaches interfere with feeding and rest during migratory stopovers.
Protecting vulnerable coastal ecosystems and controlling horseshoe crab harvests are key to stabilizing red knot populations into the future.
How many red knot subspecies are there?
There are six recognized subspecies of red knot that represent distinct populations:
- Islandica – breeds across northern Greenland, Ellesmere Island and other parts of the far northeast Canadian Arctic.
- Rufa – breeds in central Canadian Arctic islands and winters along Atlantic coast down to Tierra del Fuego.
- Roselaari – breeds in Wrangel Island and northwestern Alaska and winters along Pacific coast.
- Piersmai – breeds in northeast Siberia and winters in southeast Asia and Australia.
- Rogersi – breeds in central Siberia and winters in northwest Australia and New Zealand.
- Canutus – breeds in Taymyr Peninsula of Siberia and winters in west Africa down to South Africa.
The subspecies follow different migration routes across the globe that converge in the high Arctic for summer nesting. However, ongoing population interchange means their isolation is diminishing over time.
How long do red knots live?
The average lifespan of a red knot in the wild is 5 to 7 years. However, one particular knot named B95 demonstrated the incredible endurance of this species by living over 20 years and likely traveling over 400,000 miles in migration during his lifetime!
B95 was first banded as an adult in 1995 on Argentina’s Tierra del Fuego and spotted repeatedly over 20 years along the US Atlantic coast during migrations until he disappeared in 2016. This long-lived individual provided proof of red knots’ impressive longevity despite their strenuous marathon migrations every year.
How has tracking technology expanded knowledge of red knot migrations?
Advanced tracking technologies like geo-locators, satellite transmitters, radio tags and leg banding have revolutionized understanding of red knots’ migration routes, timing and habitat use. Some insights gained include:
- Complete migration maps showing interconnected flyways between Arctic, North America, Europe and South America.
- Precise timing of movements showing consistency year-to-year for individuals.
- Identification of previously unknown stopover and wintering sites.
- Data showing red knots fly up to 6,000 miles nonstop over oceans.
- Demonstration that most red knots pause in the Yucatan Peninsula en route between wintering and breeding grounds.
Tracking devices have revealed the red knot’s full annual cycle for informed conservation planning based on threats at different stages.
What is the red knot’s conservation status?
The dramatic declines of red knots in many regions have led to heightened conservation concerns and actions in recent decades. The current status for major populations includes:
| Subspecies | Population Trend | Conservation Status |
| Rufa | Declining; 85% loss since 1980s | Near Threatened |
| Islandica | Relatively Stable | Least Concern |
| Roselaari | Unknown | Data Deficient |
| Canutus | Declining | Near Threatened |
Intensive conservation efforts for rufa red knots include habitat protection, horseshoe crab harvest limits, and public education along the Atlantic Flyway. Hopefully these initiatives will slow or reverse the worrying declines in many red knot populations.
Conclusion
The red knot is aptly named for its rust-colored breeding plumage, but the origins of “knot” reflect its membership in a shorebird genus known for their mottled gray appearance most of the year. These marathon migrants make heroic intercontinental flights chasing food between summer nesting grounds in the High Arctic to the southern tip of South America. Ongoing conservation efforts aim to protect red knot populations facing an array of threats from climate change, coastal development, and food shortages. Advanced tracking studies continue to provide new insights into the remarkable globe-spanning migrations of the red knot.
