Species Spotlight: the rufa red knot

By Susan Sorg, nature writer

Using its internal compass and the moon, stars, and sun, the rufa red knot makes one of the longest migrations on Earth, nearly a 20,000 mile round-trip flight from the southernmost tip of South America to its Arctic nesting grounds. Along the way, the red knot may face multiple risks—peregrine falcons, coastal development, and hurricanes. But since the overfishing of horseshoe crab in the 1990s, which caused a decline of the red knots’ critical food, the population has plummeted.

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The migration route of red knots from Tierra del Fuego in South America to their breeding grounds in Canada. Graphic: Guilbert Gates.

Rufa red knot (Calidris canutus rufa) is a large sandpiper weighing an average 4.8 ounces with a 20-inch wingspan, about the size of an American robin. There are three subspecies in North America and six species worldwide; rufa red knot is the eastern North American species. Their characteristic rusty ‘rufous’ plumage is the perfect camouflage in the Arctic breeding grounds to blend with wild grasses and wildflowers. In the fall they molt to a bland grey and white coloring for protection on the beaches of their South American wintering grounds.

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Rufa red knot. Photo: Dick Daniels.

Red knots and horseshoe crabs share a long history of interconnection, a delicate synchronicity of nature—the spawning of millions of horseshoe crab eggs in the Delaware Bay each spring is precisely timed with the red knots’ arrival in May. On its northward migration, the red knots’ key stopover is Delaware Bay—roughly half-way from their wintering grounds, Tierra del Fuego in Argentina to the Arctic nesting grounds.

Nothing in nature exists alone. The fragile relationship of the rufa red knot and the ancient horseshoe crab is one of nature’s many delicate partnerships. With the decline of horseshoe crabs came the quick decline of the red knot—both populations have dropped about 75% since the 1990s. The rufa red knot is one of the most rapid and serious shorebird declines.

At Delaware Bay, the red knot must quickly refuel for energy to successfully complete the last leg of the long journey to the Arctic and breed. This event has been evolutionarily perfected over millions of years. When the red knots arrive, they are exhausted and starved after four or more days flying nonstop from South America and must refuel with horseshoe crab eggs which provide easily digested protein. They can double their weight during this 12-14 day stopover, and this body fat is necessary to reach the Arctic and successfully breed.

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The red knot survival is profoundly linked to the crabs, a species older than dinosaurs. Photo: Jan Van De Kam.

Almost the entire eastern North American population of red knots will congregate in Delaware Bay during spring migration. “Historically, more than 100,000 red knots stopped at Delaware Bay each spring. By 2004, this number had dropped to little more than 13,000” (American Bird Conservancy, February 2015). Although the horseshoe crab population is reported to have stabilized since improved protections restrict overfishing, concerns remain as to whether the crab population will recover fast enough for the red knot. Volunteers protect the Delaware Bay during spawning season, and horseshoe crabs used in medical research are also returned alive back to the ocean.

Climate change has now emerged as a greater threat. In 2014, the rufa red knot was listed as Threatened under the Endangered Species Act and is the “first bird listed explicitly because its existence is imperiled by global warming” (“Red Knots Are Battling Climate Change—On Both Ends of the Earth,” Deborah Cramer, Audubon Magazine; May/June 2016). Rising sea levels and storms may engulf the red knots’ coastal habitat, and erratic temperatures can cause timing ‘mismatches’ (asynchronies) in nesting. Chicks need to hatch simultaneously with the insects’ hatching to guarantee abundant food.

Coastal habitat conservation efforts in Michigan which benefit the endangered piping plover, pitcher’s thistle, Houghton’s goldenrod, and Lake Huron tansy also benefit the rufa red knot, as the species utilize similar habitat. Red knots are an uncommon migrant in Michigan and never abundant here, but could be spotted along Great Lakes shorelines heading north in late May or again in late July through September on their southern migration. In Michigan’s Upper Peninsula it is possible to spot a red knot at MNA’s Lake Superior Nature Sanctuary or Whitefish Point, and in the Lower Peninsula, Point Mouillee State Game Area, Tawas Point State Park, and Lake Erie Metropark at the southeastern point of the state.

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Climate change may extensively reduce the red knot’s breeding and roosting habitats. Photo: Greg Breese.

Half the species of shorebirds in the United States and Canada are either endangered or of special concern, according to the U.S. and Canadian Shorebird Conservation Plans. The Western Hemisphere Shorebird Reserve Network has adopted a conservation strategy that is currently focusing on protecting 97 critical sites internationally, which includes Delaware Bay. For more information visit http://www.whsrn.org/western-hemisphere-shorebird-reserve-network and the USFWS at http://www.fws.gov/northeast/redknot/ to learn more.


Invasive species, Great Lakes, and biodiversity: this week in environmental news

Each week, MNA gathers news stories from around the state and country related to nature and the environment. Here is some of what happened this week in environmental news:

Water levels in Lakes Superior, Michigan and Huron continue to be above their monthly averages for the first time in 16 years. Photo: NOAA

Upper Great Lakes water levels are up. Here’s why. (Michigan Radio): Water levels in Lakes Superior, Michigan and Huron are above their monthly averages for the first time in 16 years. According to the Great Lakes Environmental Research Laboratory, water levels dropped in the late 1990s and remained low. Since 2013, water levels have surged, mainly due to increased precipitation. A seasonal forecast predicts a typical seasonal cycle with no extreme changes in water level.

Invasive species can dramatically alter landscapes, study shows (Science Daily): A study from Purdue University and the University of Kentucky reviewed research on how life forms interact with and influence their surroundings. The review concluded that invasive species can cause serious problems that may have an impact for decades, or longer. The review showed that areas where land and water systems overlap are particularly vulnerable to invasives.

Rufa Red Knot Gets Listed (Audubon Magazine): The US Fish and Wildlife Service announced this week that the Rufa Red Knot will be listed as threatened under the Endangered Species Act. This coastal shorebird has experienced a population drop of more than 75 percent since the 1980s. The Rufa Red breeds in the Arctic tundra in the summer and then migrates more than 9,000 miles to the tip of South America – passing through parts of Michigan on its journey. The bird’s primary threat is climate change – rising water levels and storms are harming the coastal habitat used by the bird for migration.

Scientists oppose bill to keep DNR from considering biodiversity (Michigan Radio): The state legislature is considering a bill that would forbid the Michigan Department of Natural Resources from considering biodiversity along with other uses of state lands. Introduced by State Sen. Tom Casperson , the bill would prohibit the DNR from enforcing the rule that designates an area of land specifically for maintaining biological diversity, limiting the ability to fight invasive species

Study shows that 270,000 tons of plastic float in the ocean (AP): A new study estimates that 270,000 tons of plastic, enough to fill 38,500 garbage trucks, is floating in the world’s oceans. The study, led by the 5 Gyres Institute, aims to understand how synthetic materials are entering the oceans and how they affect fish, seabirds, and the ecosystem. The study only measured plastic floating on the ocean’s surface – plastic on the ocean floor was not included.