Red knots are medium-sized shorebirds with a plump body, short legs, and a bill slightly longer than their head. During breeding season, their underparts display a reddish-cinnamon hue, with black, brown, and chestnut plumage on their upperparts. In winter, their feathers shift to paler gray above and white below, with greenish legs. The red knot is currently listed as “Near Threatened” by the IUCN, though some populations, like the rufa subspecies, are considered federally threatened in the United States due to significant declines.
The Marathon Migrators
Red knots embark on a migratory journey each year, covering thousands of miles between their Arctic breeding grounds and wintering sites. Different subspecies have distinct routes, with some populations breeding in the high Arctic tundra of Canada, Europe, and Russia. For instance, the rufa subspecies breeds in the central Canadian Arctic and journeys to wintering grounds as far south as Tierra del Fuego. This round-trip migration can exceed 18,000 miles annually, an astonishing feat for a bird with a wingspan of about 20 inches.
Along these routes, red knots rely on stopover sites to rest and refuel, necessary for their survival. One of the most significant stopovers for the rufa red knot during its northbound spring migration is the Delaware Bay, located between Delaware and New Jersey. Here, nearly 90% of the entire rufa population can gather at once, timing their arrival with the spawning of horseshoe crabs in May and June.
Horseshoe crab eggs provide a rich, easily digestible food source, allowing the knots to rapidly gain weight for their journey to the Arctic breeding grounds. Other important stopover locations include coastal areas in Argentina, Brazil, the southeastern United States, and the Virginia barrier islands. These sites offer similar intertidal habitats with exposed mudflats or sandy beaches where the birds can forage for mollusks, marine worms, and other invertebrates. Finding sufficient food at these locations is important, as red knots need to double their body weight quickly to complete migration and arrive in good condition for breeding.
Why They Are Vulnerable
Red knot populations are declining due to environmental pressures across their vast range. One major factor is the loss and degradation of their coastal habitats, affected by human development and erosion. Rising sea levels, a consequence of climate change, further diminish foraging and roosting areas, particularly at coastal stopover sites and wintering grounds. For example, Hurricane Sandy destroyed about 70% of New Jersey’s horseshoe crab spawning beaches in the Delaware Bay, directly impacting an important red knot feeding ground.
A major threat is reduced availability of their primary food source, especially horseshoe crab eggs, at key stopover points like the Delaware Bay. The rufa red knot relies on these eggs to build fat reserves before continuing to their Arctic breeding grounds. Over-harvesting of horseshoe crabs for bait in eel and conch fisheries, and for their blood in biomedical testing, has severely depleted crab populations since the late 1990s. When horseshoe crab egg abundance decreases, red knots cannot gain enough weight, leading to increased mortality or reduced reproductive success.
Climate change also impacts red knots by altering food availability and disrupting the timing of their migration. Warmer coastal waters can affect the timing of horseshoe crab spawning, causing a mismatch between the birds’ arrival and the peak availability of eggs. In the Arctic, warming temperatures can shrink tundra breeding habitats and alter insect hatches, a food source for breeding knots. Additionally, human disturbance at stopover sites, from activities like jogging, beachcombing, or unleashed dogs, forces birds to expend energy, further hindering their ability to refuel.
Global Conservation Initiatives
Addressing the decline of red knots involves a coordinated international effort to protect the birds and their habitats. International cooperation agreements help manage species that cross multiple national borders, recognizing their hemispheric migration. These agreements facilitate shared research, monitoring, and conservation strategies. Ongoing scientific research, including geolocator devices, tracks individual bird movements and helps identify where conservation efforts should be focused.
Habitat restoration projects are underway at many important sites, aiming to reverse coastal degradation and provide suitable foraging and roosting areas. For example, efforts focus on reducing erosion and improving spawning habitat for horseshoe crabs in the Delaware Bay, increasing egg resources for red knots. These projects often involve restoring sandy beaches and mudflats, preferred coastal habitats for red knots during migration and winter.
Regulations on horseshoe crab harvesting have been implemented by bodies like the Atlantic States Marine Fisheries Commission (ASMFC) to manage crab populations. The Adaptive Resource Management (ARM) framework, adopted by ASMFC, links horseshoe crab and red knot population dynamics to make annual harvest recommendations, ensuring crab harvesting does not limit red knot population growth. Public awareness campaigns also educate beachgoers about minimizing disturbance to feeding and roosting birds, such as following posted rules and keeping pets leashed. While challenges remain, these multifaceted initiatives seek to create a more secure future for the red knot.