Signs of Spring: May 11, 1998
The bright moon also helps people to see migrants. In the 1950s, ornithologists named Lowery and Newman focused a telescope on the moon and saw hundreds of birds winging past, and learned many things about migration that ornithologists had never known for certain before. They found out that nighttime migrants start flying soon after dark, and that the numbers are greatest between 10 pm and 1 am, with the hugest numbers between 11 pm and midnight. By dawn virtually all nocturnal migrants land to rest and feed. They also found that herons, geese, and shorebirds migrate in close formation, but that virtually all small birds fly alone. When huge numbers of little birds like warblers are migrating at the same time, we can see lots of them in the sky, but they aren't really together--except by chance. They make little "seet" sounds in the sky, probably to keep track of each other to avoid mid- air collisions.
If the moon helps us to see them sometimes, it can be a hindrance to the nighttime migrants themselves. Many scientists believe that the glare of a full moon probably makes it harder for night-time migrants to see the stars, and so their navigation may be at least sometimes a bit less accurate during full moon nights. Nevertheless, the middle of May is the peak of migration for many neotropical migrants, and no matter what phase the moon is in, they are on the move.
The full moon also affects ocean tides, making them stronger than normal, which affects food supplies for many shorebirds. One ocean creature, the horseshoe crab, comes out of deep water to spawn on beaches during high tides, and spawning increases during the strong tides of full and new moons. Kathryn Reshetiloff, a scientist with the U.S. Fish & Wildlife Service's Chesapeake Bay Field Office in Annapolis, wrote that "the horseshoe crab (Limulus polyphemus) is found along the Atlantic Coast from Maine to the Yucatan peninsula. This fierce-looking yet harmless creature is valuable both ecologically and economically. Horseshoe crab eggs are an important food for shorebirds migrating along the Atlantic Coast. Horseshoe crabs are also used as bait in eel, whelk and catfish fisheries. Their importance doesn't end there. Horseshoe crabs are also used extensively for medical research."
Right now, along the Atlantic coast, horseshoe crabs are starting to appear on the beaches, along with the shorebirds that depend on this food to fuel their migration. In Cape May, New Jersey, Red Knots, Ruddy Turnstones, and Sanderlings have been reported this week along with the season's first horseshoe crabs. The Cape May Bird Observatory is trying to protect the crabs from being overharvested, so that the shorebirds that depend on them can survive.
Now Think About This:
Discussion of Challenge Question # 6
Last week we asked you to consider this:
Most hawks catch their prey on the wing. Accipiters and falcons,--bird eating hawks like the Sharp-shinned Hawk
and Merlin--fly about much of the day whether or not they're migrating. On non-migrating days they may fly many
miles just going back and forth patrolling their woods trying to catch birds. When they're migrating, they're doing
pretty much the same thing, only flying in a particular direction. So no matter whether they're migrating or not,
they try to keep their bodies well-fueled and in top condition.
How to Respond to Today's Challenge Question
1. Address an e-mail message to: email@example.com