(C) Daily Kos This story was originally published by Daily Kos and is unaltered. . . . . . . . . . . Delaware Bay: Where Horseshoe Crabs & Red Knots Reenact an Ancient Ritual of Spring [1] ['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.'] Date: 2024-06-17 During the first weeks of May, in an ancient rite of reproduction that has been replaying since the dinosaurs were here, horseshoe crabs come ashore in Delaware Bay on the lunar high tides to meet and lay eggs. Those eggs become a critical link in the food web of the Bay, but will be especially important to the migratory shorebirds called Red Knots. One of the longest migratory journeys of the bird world Red Knots are long-distance migrators; they travel from their wintering grounds at the southern tip of South America, up the Atlantic flyway, stopping to refuel in Delaware Bay before moving on to the far north to breed on the shores of Baffin, Victoria and Banks islands. There are six recognized subspecies of Knot. The birds we see in Delaware Bay belong to Calidris canutus rufa and represent the second largest population of migrating shorebirds in North America. Other subspecies undertake somewhat less extensive migratory journeys, but all reach breeding grounds in the Arctic, including Ellesmere Island and the northern coast of Greenland. Various subspecies follow different migratory pathways & important site The largest population of horseshoe crabs in the world is found in Delaware Bay. And more than half of the total Atlantic Flyway population of Red Knots as well as Ruddy Turnstones, and Semipalmated Sandpipers depend on Delaware Bay’s horseshoe crab eggs as a rich and critically important food supply. All three birds are considered target species for the Delaware Shorebird Project in which volunteers work alongside professionals in wildlife management from all over the world to trap and band these birds when they pass through Delaware Bay, as part of a program to assess and monitor the success of the populations in the habitats there. I was afforded a wonderful opportunity to work this past May as one of those volunteers, and this blog entry is intended to share some of what I learned. Modification of the first walking leg of the male to grasp the female Horseshoe crabs come ashore on the lunar high tides of May (new and full moons) which occurred about two weeks before I arrived at Delaware Bay. Males follow females onto the beaches and use the modified first pair of walking legs to grasp the female as she moves around the beach. The female crab partially buries herself in the sand and deposits about 4,000 eggs at a time. In an evening of egg laying, a female crab can lay several egg clusters, and she may spawn repeatedly over several nights to lay up to 100,000 eggs. Crabs stranded by a receding high tide will burrow into the sand in order to keep their gills wet and diffuse enough oxygen to survive. Crabs stranded in this way can survive about four days awaiting the next high tide to free them. Standing on the estuary beaches with our spotting scopes sighting previously flagged birds, it seemed the sand was paved with these strange and ancient creatures, looking as though they were somehow suspended between life and death. Occasionally one would remind us that they were very much alive: whipping the sharp propulsive tail or telson back and forth in an apparent attempt to burrow deeper into the damp sand and thus survive until the arrival of that next life-saving high tide. During the spawning season, many of the horseshoe crab’s tiny green eggs are exposed to the surface of the sand due to subsequent high tides or by wave action as well as by the digging behavior of other spawning crabs. Unlike the adult crabs though, once an egg is exposed to air it will dry out quickly and die. However, it still plays a vital role in the ecosystem. These exposed eggs are the primary food source for migrating shore birds who are making the journey from South America to the Arctic along the Atlantic Flyway. The sheltered beaches of the Mispillion River, where we searched the churning flocks for previously banded birds, often sported entire windrows of these eggs looking like nothing quite so much as strangely colored grains of sand. Research suggests that if only 0.5% of the eggs laid here survive, horseshoe crab populations can maintain themselves at equilibrium. One wonders if the crabs, with their primitive cognitive capacity, might know how vital their efforts are to the survival of these long distance travelers. I first learned about the precarious relationship between the Red Knots with the Horseshoe crabs from a wonderful book by Deborah Cramer, The Narrow Edge. But my most recent encounter with the horseshoe crabs, shorebirds and tidal mudflats of the Delaware Bay was made possible by The Delaware Shorebird Project. This diverse group of professionals and volunteers operate under the auspices of the Delaware Department of Natural Resources and Environmental Control (DNREC). The view from Port Mahon Rd into Delaware Bay. I first met a team from the Delaware Shorebird Project in a chance encounter on Port Mahon Rd, amid a rather post-industrial looking landscape, marked by concrete rip-rap but interrupted by stretches of sandy beach virtually paved in spawning horseshoe crabs. Seeing these team members engaged in assessing and banding the very birds I had come to see was serendipitous. That chance encounter was followed by an application process, and a year later I found myself in the midst of an incredible learning experience. This is serious citizen science built on a collaboration between state & federal agencies, professionals from across the globe and a team of volunteers working together to monitor the health of the shorebird populations that depend on the horseshoe crabs that make this area their spawning grounds. During peak spring migration, mixed flocks form on the isolated beaches along Cedar Creek and Mispillion River which drain into Delaware Bay. There are three shorebird species identified by the Delaware Shorebird Project as targets for banding. These are the Red Knots, Ruddy Turnstones and Semipalmated Sandpipers. All three are included in this beach flock photo. Can you pick them out? Click here to see! The net is launched — timing is critical so that no birds are in the safety zone directly in front of the net and the birds in the target zone are settled. For more than 35 years the preferred method for gathering shorebirds and waterfowl has been Cannon Netting (click here for a video). The skilled and highly experienced folks of the Delaware Shorebird Project use this method to collect the birds that they will assess and band as they continue to monitor these populations. The process of choosing a site, setting the net, deciding if or when to fire the net and then extracting the birds safely is a tightly choreographed activity that is amazing to watch! Captured birds are assessed for maturity and health... and measured and weighed... then banded first with a silver colored band that is registered with the Bird Banding Laboratory under the auspices of the US Geological Survey... and then with a band from the local group — green colored bands like this one indicate birds were banded in the United States. The real function of this process of capture, assessment, and banding that I learned about in my time with the DSP comes in something called re-sighting. This involves daily excursions onto the remote beaches and estuaries with spotting scopes, examining each bird of the target species for a colored flag and then recording the three-digit alphanumeric code that flag bears. Statistical analysis of the numbers of birds sighted with flags, compared with the number of those without flags, allows for an estimate of the total population. Re-sighting of previously banded birds…. provides valuable data that tells us how the population is doing. But the real magic of all that I did with these folks came home to me one day out on the banks of an estuary when several members of our team saw this: Look carefully at the upper left leg of the Red Knot standing front and center in this photo. That blue flag tells us that this bird was tagged in Brazil! Against all odds, this shorebird, the weight of a single-serving yogurt cup and the length of a sheet of notebook paper, crossed half a dozen national borders, and despite all of the environmental hazards that would accompany such a journey, came to rest on our muddy river bank to eat horseshoe crab eggs. And with my unlikely contact with that intrepid Red Knot, all the mucky boots, the deer fly and tick bites, and the sun and wind exposure I would accumulate over my time on the Delaware Bay seemed worthwhile! 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