Signs of Spring: February 16, 1998
Some songbirds and raptors are already moving across South America, Mexico, and parts of Central America in large numbers. Thousands of Purple Martins have left their wintering grounds and will be among the first songbirds to arrive in huge numbers on the Gulf Coast. Purple martins winter in South America. The map above shows in which South American countries banded purple martins have been found. On the heals of Purple Martins are Tree Swallows which are moving through west Mexico right now.
At the time of writing, Swainson's Hawks are departing by the hundreds from the Pampas region of Argentina, and heading for their breeding grounds in the Northern Great Plains. Note the region on the map where banded Swainson's Hawks have been recovered. In 1995, 20,000 Swainson's were killed in a single season from pesticide poisoning in this agricultural pampas region of Argentina. This represent 5% of the entire world's population. Also already on the move are those Coopers and Sharp-shinned hawks which winter in Mexico and Latin America.
Shorebirds Begin their Long Journey North
1. Read the news below about shorebird migration.
3. Imagine all the countries and habitats the Red Knots fly over and visit. If you worked for a Red Knot travel agency, what would your travel brochure for Red Knots contain? Make a set of brochures that would attract Red Knot visitors to each of these sites. Don't forget to include important traveling tips that would appeal to a shorebird. Here's one from the travel brochure made by students in Ms. Devine's class in Tom's River New Jersey.
Red Knots Fly from Argentina to the Arctic
Red Knots are right now winging their way to key stop over sites at Peninsula Valdez and Cabo San Antonio Oeste in Argentina. By mid-March, the Knots will move onto Buenos Aires, Argentina. From here, they will make their way across central Brazil to the northern coast of South America.
The shorebirds will then embark on the most extraordinary leg of their journey, a non-stop flight of some 2,000 miles over open ocean, lasting over 70 hours, before making land-fall at wetlands in and around the Delaware Bay, New Jersey. Why do you think the Delaware Bay is so special for Red Knots?
The availability of food is key to shorebirds' migratory success. Food must be available in abundance at key sites so that shorebirds can go "one stop shopping," fatten up, and move onward towards their breeding grounds in the central Canadian Arctic as quickly and efficiently as possible. Because the need to gain weight quickly is so important to migration, scientists theorize that migrants including migratory songbirds, raptors, waterfowl, and songbirds specifically synchronize their migrations to emergence and availability of food at their stop over sites.
For example, just as huge numbers of Red Knots are flying over the southern Atlantic in early May, thousands of horseshoe crabs are preparing to lay their eggs in coastal areas of the Delaware Bay. By mid-May, enormous flocks of Knots will arrive at Delaware Bay just as the Horseshoe Crabs have laid their eggs providing a huge meal for the voracious shorebirds. Upon arrival, the exhausted and depleted Red Knots weigh an average of only approximately 130 grams. Horseshoe crab eggs represent the large percentage of the Knots diet during their short stay at the Bay. By the time the Knots are ready to leave after just a few short days, they will weigh up to 200 to 230 grams.
Clearly, the horseshoe crabs are important to Red Knots. Because people have been harvesting the horseshoe crabs
for fish bait, there have been fewer and fewer crabs-and eggs--each season. Scientists worry that increased harvests
could reduce the food supply and disrupt Red Knot migratory behavior. The New Jersey Audubon Society and others
who were concerned recommended restrictions on the offshore trawl of Horseshoe Crabs. In the interest of protecting
this important stopover food source for shorebirds, this harvesting has recently been made illegal. So, when the
hungry shorebirds arrive on the New Jersey shore in May, their food supply will be more secure.