Red Knot migration reaches Cape May Observatory

[Donkees]

Brian Kushner

The rufa Red Knot's spring migration is timed to coincide with the horseshoe crab's spawning season, as the massive outlay of eggs provides a rich, easily digestible food source for the exhausted birds. Delaware Bay shores provide the single most important spring stopover area for the Red Knot, hosting within a narrow time window up to 90 percent of the North American population. Other key U.S. stopover sites include coastal islands off Georgia, South Carolina, Virginia, and Massachusetts.

When preparing for spring migration, Red Knots pack on extraordinary amounts of weight to fuel their long flights. When they reach the Delaware Bay, exhausted and emaciated, the birds must regain fat they lost in the first leg of their journey, and pile on even more. Often, Red Knots almost double in weight while feasting on protein-rich horseshoe crab eggs, before continuing northward and breeding soon after Arctic arrival. During these periods, these birds exhibit among the highest rates of mass gain of any vertebrate.


Martin Pelanek

The rufa subspecies migrates along the East Coast of the United States. In spring, it depends upon a major Mid-Atlantic rest stop, where ancient sea creatures congregate and sustain these birds during their long journey.

Beginning in the 20th century, horseshoe crab overharvest, paired with coastal development and sea-level rise, began to take a serious toll, and rufa Red Knot numbers declined about 75 percent from the 1980s to the 2000s.

American Bird Conservancy has successfully advocated for horseshoe crab harvest restrictions in Mid-Atlantic states and for the creation of a horseshoe crab sanctuary at the mouth of Delaware Bay. New Jersey has, for 12 years running, maintained a moratorium on any horseshoe crab harvests, while Delaware, Maryland, and Virginia now ban capture of females and shut down their seasons once a quota is reached on males.

https://abcbirds.org/bird/red-knot/

[Easterncedar]

1. Interesting

I didn’t know anything about this horseshoe crab and bird story. Thanks!

[Donkees]

2. Photo: Horseshoe crab eggs along the Delaware Bay

Horseshoe Crabs, Red Knots And Humans: How One Species Affects Them All
https://capemaywhalewatch.com/blog/horseshoe-crabs-red-knots-and-humans-how-one-species-affects-them-all/


Image 1: Horseshoe crab eggs along the Delaware Bay. Photograph taken by Madison Olszewski

The red knot is a shore bird species that visits the shores of Cape May on its migration route. This species has the longest migration route of any species that visits our shores. It travels from tropical and temperate conditions in the winter all the way to the Arctic for breeding, a journey that totals more than 19000 miles (Schwartz, 2016). In order to survive this journey the red knot makes a series of stops along the way in order to refuel. The red knot’s stop at the Delaware bay is the most crucial as it is the final stop before they arrive in the Arctic. The red knot when stopping at the Delaware Bay area is extremely dependent on horseshoe crab eggs as a food source. They need a sustainable food source to help them refuel on their long journey. This stopover is also important because once they reach the harsh conditions of the Arctic, food is low and they must be in good health in order to successfully breed. Horseshoe crab eggs are easy to digest and very high in lipid content which is essential for the red knot to survive it’s intense migration route. The red knot is currently listed as near threatened on the IUCN red list and unfortunately, their populations are continually decreasing.

In recent years, horseshoe crabs have been harvested for much more than just bait. Horseshoe crabs are extremely important for medical research and development. Horseshoe crab blood has incredible antibacterial properties. Horseshoe crab blood is a very distinct blue color which is caused by hemocyanin which is copper based and helps transport oxygen throughout the horseshoe crabs body (Luntz, 2014). Amebocytes play an integral role in fighting off infections in invertebrates but the horseshoe crab has very specialized and effective amebocytes. Their amebocytes are fast reacting and can effectively react in 45 minutes, whereas in mammal species the reaction could take around two whole days (Luntz, 2014). This fast reaction is due to coaglun and this chemical has been utilized for medical testing such as testing vaccines. This has led to the harvesting of a quarter of a million horseshoe crabs.