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Field Notes: Migration at the Delaware Bay

While most people flock to the Delaware shores for some rest and relaxation, migratory birds have an entirely different mindset during their visit: refuel. The Delaware Bay is a key stopover site for red knots, sanderlings, ruddy turnstones and other birds who pause their marvelous migrations to gorge themselves on horseshoe crab eggs. Bird House curator Sara Hallager, animal keeper Debi Talbott and assistant curator of nutrition sciences Lori Smith traveled to the Bay in May 2018 to assist the New Jersey Department of Environmental Protection’s Endangered and Nongame Species Program as they researched and banded birds along the coast.

Experience Migration, a first-of-its-kind attraction that will immerse visitors in the annual journeys of western hemisphere birds, is slated to open at the Zoo in 2021. While the Bird House is closed for renovation, visitors can see birds at Amazonia, American Trail and the Cheetah Conservation Station. 
Curator Sara hallager learns how to band birds on the Delaware Bay
“One of the volunteers is teaching me how to band a sanderling. In addition to banding, the researchers also weigh birds and measure the wing and bill length, as well as the length from back of the head to the tip of the bill. They record if the bird has any distinguishing or unusual characteristics and if it sports breeding plumage. Once a chart is complete, volunteers will enter all of the information into the database.”—Sara Hallager, curator
Bird banding tools
“We use a variety of supplies when we band birds in the field. There were six stations of five people each; everyone has a full set of tools, equipment and charts. The pair of scissors on our makeshift table are used to collect biological samples. Researchers snip a section of the bird’s covert feather, then place it in a labeled bag. Clipping the feathers does not harm the bird or impede its ability to fly. Back at the lab, researchers can analyze the isotopes in the feathers to determine the wintering locations where birds grew those feathers. All of the birds receive a metal band (strung along the pink wire) and a light green, unique alpha-numeric leg flag (strung along the black wire), which signify that the birds were tagged in the Delaware Bay.” – Sara Hallager, curator
Bird bander's grip

“It took a bit of dexterity and practice to band a bird! One has to hold it in a position called “the bird bander’s grip” while extending the leg so that one can attach the band. The bird’s wings must be firmly tucked in your hand so it cannot wiggle or fly away.”—Sara Hallager, curator

Sanderling ID chart

“This chart shows different plumages of a sanderling. Younger birds have lighter feathers, which darken as they age. The final photo in the bottom-right corner shows an adult in full breeding plumage.”—Sara Hallager, curator

Securing sanderling tag with banding pliers

“After slipping an open metal band over the bird’s leg, we secure it using special banding pliers, shown in this photo. Depending on the size of the band, we use the corresponding circle on the tool to close the band around the bird’s leg. For these sanderlings, we use the second smallest hole. To secure the leg flag, we loop it around the bird’s leg and glue it closed. We ensure the flag is right-side up so that someone who is looking through a pair of binoculars can read the alpha-numerical sequence on the flag properly.”—Sara Hallager, curator

Bird tagged in Greenland

“This sanderling was banded in Greenland two years ago as a chick. This is the first time a sanderling was documented having flown from Greenland to North America!”—Lori Smith, assistant curator

Lori Smith bands a red knot at the Delaware Bay.

“This red knot is ready for release! The process of placing a band and flag on the bird and taking its head, wing and bill measurements takes about two-to-three minutes. We processed around 200 red knots that day.”—Lori Smith, assistant curator

Lori Smith holds a sanderling with a green flag at the Delaware Bay.

“If you are bird watching and spot one with a flag, you can help scientists track that bird’s flight patterns! Visit and enter the alpha-numerical sequence printed on the flag, along with the bird’s location.”—Lori Smith, assistant curator

Debi Talbott Sanderling Weighing

“One of our animal keepers, Debi Talbott, is weighing a sanderling. The bird is carefully placed within a PVC tube to keep it secure. Some sanderlings weighed as little as 50 grams; others weighed as much as 80 grams. The difference was that the smaller birds had just arrived at the Delaware Bay, so their resources were depleted after migrating, and they were rather thin. The larger birds, on the other hand, had been at that location for a couple of weeks. They were plump from eating horseshoe crab eggs and ready to migrate north for the summer.”—Sara Hallager, curator

Lori Smith holding a cluster of horseshoe crab eggs

“Horseshoe crabs lay their eggs near the high tide line of the beach. Sometimes, we even find them in the grasses. This year, I collected eight clusters of horseshoe crab eggs and brought them back to the Zoo. (In this photo, I am holding one cluster of eggs.) At the Department of Nutrition Sciences research lab, I wash the crabs’ eggs to remove the sand and other tiny particles and dry them in an oven. Now we can run tests on the sample to find out the amounts of nutrients, such as fat and protein, to see why these eggs are so significant to migratory birds. It is thought that the horseshoe crab eggs are easily digestible, enabling the birds to gain a huge amount of weight in a short period of time.”—Lori Smith, assistant curator

Horseshoe crab eggs

“We can read about shorebirds and horseshoe crabs, but to go to the Delaware Bay and witness how vital the shore, the crabs and the birds are to one another is a truly spectacular event. They are all intrinsically linked. Horseshoe crabs are a keystone species; when their populations decline, the populations of migratory shorebirds who rely on their eggs for nutrients follow suit. If the birds do not get enough to eat, they may not be able to make the journey to their breeding grounds, or they may be unable to breed due to lack of nutrients. Shorebirds are not the only animals that rely on this seasonally abundant food source; fish, eels and crabs do, too. It is incumbent on all of us to do what we can to help save these animals from extinction.”—Sara Hallager, curator

This story was featured in the June 2018 issue of National Zoo News.