The red knot is a medium-sized shorebird that undertakes one of the longest migrations in the avian world. They breed in the Arctic during the summer months before undertaking long-distance flights to wintering grounds as far away as South America. During these lengthy migrations, red knots exhibit fascinating behaviors related to their extreme endurance travel.
What are some key facts about the red knot?
Here are some quick facts about the red knot:
- Scientific name: Calidris canutus
- Length: 9-11 inches
- Wingspan: 20-24 inches
- Weight: 4-7 ounces
- Lifespan: Up to 15 years
- Population: Around 150,000
- Breeding grounds: Arctic tundra
- Wintering grounds: Coasts of North and South America, Europe, Africa
- Migration: Annual roundtrip up to 19,000 miles
- Diet: Mollusks, crustaceans, insects
- Predators: Falcons, hawks, gulls
The red knot is a medium-sized sandpiper with a stocky body and short legs. In breeding plumage, they have a distinctive red breast and belly. Their body feathers are intricately patterned in browns, grays, and black. During nonbreeding seasons, their plumage fades to a plain gray. Their long curved bill allows them to easily probe into sand or mud to find food.
Where does the red knot breed and nest?
Red knots breed in the high Arctic tundra during the summer months of June and July. They seek out breeding grounds with good supplies of food, wetlands, streams, and ponds. The female lays a clutch of 4 eggs in a simple scrape in the ground lined with lichens and leaves. Both parents share incubating duties for around 22 days until the eggs hatch. The chicks are precocial, meaning they leave the nest within a day and begin feeding on their own. The parents protect and brood the chicks until they fledge at around 18-20 days old.
How far does the red knot migrate?
The red knot is known for undertaking one of the longest migration routes in the animal kingdom. They fly thousands of miles between their Arctic breeding areas to wintering grounds in North and South America, Europe, Africa and beyond. Some populations make annual roundtrip migrations of up to 19,000 miles! Their longest nonstop flight segment can cover around 4,000 miles taking 4-6 days. They travel in large flocks and use a network of strategic stopover sites to rest and refuel along their journey.
Key red knot migration facts:
- Total annual migration up to 19,000 miles roundtrip
- Travel in large flocks
- Use network of stopover sites to rest and feed
- Nonstop flight segment can cover 4,000 miles
- Longest nonstop flight takes 4-6 days
- Fly up to 370 miles in 24 hours
What does the red knot eat?
The red knot is specially adapted for feeding on small marine creatures. Their long curved bill allows them to probe deeply into mud or sand to find prey. They mainly eat mollusks, small crustaceans like crab larvae or brine shrimp, marine worms, and some insects. At stopover sites during migration, they gorge themselves on dense concentrations of eggs and larvae to quickly rebuild energy stores. Some key prey items include:
Red knot diet:
- Mollusks – clams, mussels, snails
- Crustaceans – crab eggs/larvae, brine shrimp
- Marine worms
- Insects – midges, beetles, flies
Their specialized bill allows them to grab and swallow mollusks whole. The knot has a strong muscular gizzard that acts like a grinding stone to crush the shells and digest hard-shelled prey.
How does the red knot migrate?
The red knot is specially adapted for ultra long-distance migratory flight. Here are some key facts about their migration strategy:
- Travel in large flocks to conserve energy
- Use a network of stopover sites to rest and feed
- Fly nonstop for 4+ days by burning fat stores
- Long pointed wings provide aerodynamic flight
- Heart rate slows to conserve energy in flight
- Can sleep while flying by shutting down half their brain
- Orient using celestial cues (stars, sun) and earth’s magnetic field
Knots travel in large flocks up to several thousand birds. By drafting in formations, the flock gains efficiency and reduces drag. The birds conserve energy by riding air currents and the wing vortices of other birds.
On long nonstop flights, the knots can burn through nearly half their body weight in fat stores. Their muscles also transition to burning fat over carbohydrates. Their pointed wings provide lift with minimal drag allowing them to cover thousands of miles efficiently.
Key stopover sites:
On their migration route, red knots stop to rest and feed at critical stopover sites. These areas provide abundant food for them to quickly rebuild energy reserves. Some vital stopover regions include:
- Delaware Bay, New Jersey – Horseshoe crab eggs
- Maranhão, Brazil – Mollusks
- Ría Gallegos, Argentina – Mussels
- Banc d’Arguin, Mauritania – Mollusks
- Yellow Sea, China – Potamiscus snails
How do red knots navigate migrations?
Red knots navigate with incredible precision across thousands of miles to locate breeding and wintering sites. They orient using several cues:
- Celestial cues – Using stars, the moon, and polarization patterns of sunlight
- Earth’s magnetic field – Detecting tiny variations to determine latitude
- Landscape features – Following coastlines and mountain ranges
- Instinct – Inherited genetic program guides navigation
Younger birds learn the migration route and stopover locations from experienced adults. Recent studies also suggest knots may get assistance from “infrasound” – extremely low frequency sound waves below human hearing that can provide positional cues spanning thousands of miles.
How do red knots survive extreme migrations?
Red knots endure some of the most extreme migrations in the natural world. Here are some key adaptations that allow them to complete marathon trips:
- Hyperphagia – Gorging to store fat before migration
- Large liver – Provides energy from stored fats
- Flexible digestive system – Shrinks organs not needed in flight
- Slowed metabolism – Lower energy needs in flight
- unihemispheric sleep – Rest half their brain at a time
- Dense breast muscles – Generates power needed for flapping
- Pointed wings – Reduces drag for energy efficiency
Before migrating, knots go through hyperphagia – a phase of eating voraciously to build up fat deposits. Their liver makes up 10% of body mass to provide sustained energy release. Unneeded digestive organs shrink by up to half. Their metabolic rate also drops by 25%. Amazingly, they can sleep by resting each brain hemisphere separately – allowing aerodynamic flight even while sleeping.
What threats do red knots face?
Red knots face a wide array of threats across their migratory range. Some key dangers include:
- Habitat degradation at stopover sites
- Reduced food availability
- Disturbance by human activity
- Pollution
- Climate change
- Hunting (historically)
- Predation
Destruction or disturbance of critical stopover habitats can significantly impact knots if they cannot refuel efficiently. Spills of oil or chemicals can poison birds. Human disturbance causes stress and excess energy expenditure. Due to climate change, some stopovers may emerge earlier or later than needed. The red knot population declined by up to 75% in recent decades but has rebounded slightly following conservation actions.
Conservation actions:
- Habitat protection
- Restricting human access
- Educating public
- Monitoring populations
- Banning hunting
What is the red knot’s conservation status?
The red knot has been classified on the IUCN Red List as Near Threatened since 2015. This indicates it is close to qualifying for Vulnerable status in the near future. Exact population numbers are uncertain but current estimates are around 150,000 birds globally. Their numbers declined by 50-75% since the 1980s primarily due to habitat destruction and overharvesting of horseshoe crab eggs at Delaware Bay.
Regional conservation status:
- Europe – Least Concern
- Australia – Endangered
- USA – Threatened and endangered (some populations)
Some regional subspecies have greater threats. The Great Knot subspecies in Australia is listed as Endangered. In the US, the Rufa subspecies is listed as Threatened and Endangered in parts of its range. Overall the red knot remains at risk of further declines without continued conservation management.
Conclusion
In summary, the epic migrations of the red knot rank among the most extreme endurance feats in the natural world. They transform their bodies to undertake marathon journeys up to 19,000 miles roundtrip. Along their global flight paths, they rely on a suite of amazing navigational abilities ranging from magnetic sensing to star-guided navigation. Yet despite their supreme adaptations, red knots now face an uncertain future. Conservation efforts to protect their stopover habitats and reduce human pressures have aided recent population rebounds. Ongoing stewardship will be vital to ensure the resilience of one of the champions of animal migration into the future.