Red Knots Return to Mispillion Harbor

We all know the saying, “April showers bring May flowers,” but what does May bring? Along the coast in Delaware, that answer is clear: May brings vast numbers of spawning horseshoe crabs and migrating shorebirds, including red knots.

Hungry red knots feed on the eggs of horseshoe crabs that come ashore in May on Delaware Bay. Photo by Gregory Breese/USFWS.

Red knots complete one of the longest migrations of any species, traveling annually between their Arctic breeding grounds to the warmth of South America where they over winter. These rusty-colored, robin-sized shorebirds fly uninterrupted for thousands of miles, not stopping to rest or eat. And during their northern spring migration, the rufa subspecies of red knots time their arrival in the Delaware region with another important natural event: horseshoe crab mating season. Why? To feast on the protein-rich and fatty crustacean eggs to replenish their energy and finish their epic migration.

However, the number of rufa red knots using Delaware Bay is down nearly 80 percent when comparing aerial survey data from the most recent 3-year period (2020-2022) to the earliest period (1981- 1983). In response to this population decrease, the rufa red knots were listed as a threatened species in 2015, and the U.S. Fish and Wildlife Service (USFWS) announced in 2023 a proposed expansion of the red knot’s critical habitat designation under the Endangered Species Act.

Red knots feed on horseshoe crab eggs along the shore in May at Mispillion Harbor, Delaware. Photo by Gregory Breese/USFWS.

Each year, the return of these mighty migrators reminds me of the years of dedication and effort that The Conservation Fund and our partners invested into efforts to protect key red knot habitat in Delaware. In 2021, our efforts culminated in protecting the last critical piece of unprotected land in Mispillion Harbor — one of the most critical stopover points in the red knot’s migration journey.

Situated on the west shore of Delaware Bay, Mispillion Harbor’s protected cove provides a safe and dependable habitat for horseshoe crabs and shorebirds. The shallow waters warm up quickly in the spring, the jetty provides protection from waves, and the sloping sandy beaches are perfect for the crabs to lay their eggs. In fact, Delaware Bay hosts the largest population of spawning horseshoe crabs in the world and provides ideal habitat for the baby crabs to hatch and grow. Hungry red knots and other migrating shorebirds devour the eggs and restore their strength — sometimes as much as doubling their body weight. After a week or two in Mispillion Harbor, they leave well fed and rested to continue their migration north to begin nesting.

Photo by Ann Marie Morrison/Flickr.

Recognizing this site’s critical importance, The Conservation Fund purchased most of the Mispillion Harbor shoreline in 2006 to prevent any development that would harm the habitat. Over the years, most of that land was transferred to the State of Delaware for permanent protection and the final piece was transferred in 2021. Now protected, Mispillion Harbor provides critical habitat for spawning horseshoe crabs and the migrating shorebirds that feed on them.

“Though this project was small in size, it has a disproportionately positive impact and provides a brighter future for migratory and resident wildlife, as well as higher quality of life and cleaner water supplies for humans.”

- Kate Hackett, Executive Director of Delaware Wild Lands

Aerial view of Mispillion Harbor. Photo by Andrew Martin, Delaware Wild Lands.

Delaware’s Department of Natural Resources and Environmental Control (DNREC) is completing important restoration work and has been operating the DuPont Nature Center, a science-based educational and interpretive facility with interactive exhibits designed to connect people with the Delaware Bay’s natural history and ecology.

Visitors to the DuPont Nature Center have the best opportunity to witness this amazing convergence of wildlife in May and early June, often during or right after a high tide. It is important to remember to always observe shorebirds from a distance to avoid disturbing them and disrupting their feeding. If you can’t come in person, you can check out their Harbor Cam.

Mispillion Harbor was one of the first projects that I worked on when I came to The Conservation Fund twenty years ago. The ultimate protection of this globally significant resource is testament to not only the time and persistence that many habitat protection projects take, but to the dedicated partnerships that made it possible. We worked closely with our partners at the Allerton Foundation, the Campbell Foundation, the State of Delaware, U.S. Fish and Wildlife Service, the Delmarva Ornithological Society and Delaware Wild Lands to complete multiple acquisitions over the years. It is also remarkable that for an organization that has protected millions of acres across the country, some of our greatest impact, at least in my experience, has been in saving these relatively few acres of sandy shoreline along the Delaware Bay.