RED KNOT
Biology
On a sandy beach along the Delaware Bay, scientists and birders are gathered to catch a glimpse of a very special shore bird known as the Red Knot. Thousands of these birds will be arriving, exhausted and hungry after flying for four long days, -over 4,000 miles- without stopping. Landing gracefully in the sand, the birds immediately begin gorging
on protein-rich horseshoe crab eggs, eating as many as 18,000 eggs each day!. It is important the birds eat up because they have only two weeks to double their weight and prepare for the next leg of their journey, one that will take them an additional 1,800 miles, flying non-stop to the Red Knots’ summer breeding grounds in the Arctic tundra. If world records were awarded to animals, this small bird the size of cafeteria milk carton would win a prize for one of the longest migratory trips on the planet. Red knots travel an astonishing 9,300 miles in one season, stopping only two to three times to refuel.
Image: Public Domain: US Fish & Wildlife
Once reaching the tundra, a treeless habitat with short summers, cool temperatures and perma-frost (permanently frozen soil underneath the surface layer), red knots quickly find mates and make a nest. They make a nest on the ground in a shallow hole that the male bird excavates with his feet. The female usually lays four brown and green camouflaged eggs in the nest and then both birds take turns incubating the eggs. Within 3 weeks, the eggs hatch and the young red knots emerge from the egg covered in down and with eyes wide open. They are ready to leave the nest and follow their parents within a day! Growing quickly is important because summers are short in the arctic and the birds must be ready for the fall migration – another 9000 mile journey – within a month of hatching. By early August, when Connecticut is still in the midst of summer, red knots are already on their way south.
Global Changes
Red knots have lived this way for a long time, probably thousands of years. But recently,something has changed, and it is affecting these birds in a very serious way. In the past twenty-five years, the population of Red Knots has crashed. This species is showing the most rapid decline in numbers ever recorded – down almost 70%, causing much concern among scientists. The red knot is being considered for protection under the Endangered Species Act. What is to blame for the loss of one of the world’s most amazing birds?
Some of the things that make this bird so unique also place them in danger. Red knots travel together in large flocks, a behavior that helps them to survive when they are facing natural predators such as hawksand foxes. But traveling in large flocks puts them at risk in countries where humans still hunt these birds. It can also increase the loss of birds in areas where their habitat has been developed and there are no longer enough resources for the large numbers of birds.
Another reason for the steep drop in the Red Knot population has to do with their eating habits during migration. Because the knots fly such long distances, and stop to eat so infrequently, it is important for them to find enough food at each stop along the way. Without enough to eat, the birds will not be strong enough to reach the arctic, lay eggs and raise their young. Perhaps their most important refueling stop is the Delaware Bay, which divides Delaware from southern New Jersey. It is here that the red knots find the energy they need to complete their journey to the arctic. They get that energy from horseshoe crab eggs, which are being deposited about the same time the red knots arrive each spring. Horseshoe crabs have been around longer than the dinosaurs, each spring finding a shore somewhere to crawl up on to lay their eggs. There were always plenty of eggs for the red knots and plenty more that would hatch into young horseshoe crabs. But then something changed.
Humans had sometimes collected horseshoe crabs to use as food for livestock or as fertilizer for farm crops, but they had other choices as well and didn’t have to rely only on horseshoe crabs for these needs. But beginning in the 1990’s, many horseshoe crabs began to be collected for use as bait for eels and whelk. Scientists also began to collect them to extract some of their blood, which has special properties that can help in medical research. Perhaps most importantly, the sandy beach habitat where horseshoe crabs lay their eggs was rapidly changing, being developed into beach front homes and resorts. To protect many of these homes, sandy beaches were replaced by stone or concrete walls to prevent erosion and flooding. The walls also prevent horseshoe crabs from crawling up on shore to lay their eggs. Many factors contributed to fewer horseshoe crab eggs being available for the red knots. Without this important food source, many red knots died during migration, and the population dropped quickly.
Conservation:
Once biologists and wildlife managers began to discover the important ecological link between horseshoe crabs and red knots, they urged local, state and the federal government to put strict regulations in place. Laws were passed to limit the number of horseshoe crabs that can be caught for bait and for medical research. Also, much of the remaining shore habitat is now protected from development. These controls will help the red knot and the horseshoe crab, but further research must be done to study other factors that can have a positive effect on this important migratory bird.
Sources:
Willis, N.C. (2006). Red Knot: A Shorebird’s Incredible Journey. United States: Birdsong Books