Notes From the Naturalist
Fall is a great time to pay attention to the natural world. There is so much life activity now that will soon be gone. The buzzing insects are still active on the warm days, but some of their company is moving out. Dragonflies are leaving the fields and coastal marshes and heading south along the Atlantic coast. The same can be said of monarch butterflies, which I can happily report that I have seen more of this year than in the recent past.
The stars of the show are the birds and the fall season, which give us the stirring sights of migration, as skeins of birds assemble and fly in great numbers to the warmer climes. A rise in hormonal levels causes coastal birds to begin to prepare for their long migrations to Central and South America. Shorter days trigger enhanced appetites, as those on the move accumulate energy for the journey. Some birds are able to take advantage of the rich carbohydrates in late summer-fall berries, while many others like ospreys and egrets gorge on migratory fish headed to sea. The birds accumulate fat and store it as energy. Different species begin to gather in huge flocks called staging, awaiting the right mix of conditions. And when they arrive, some silent trigger causes them to rise as one, and away! 1
Some migrate non-stop, which means they must accumulate enough energy and fat to fly continuously, and still have enough in reserve to survive and reproduce lest they risk falling out of the sky. Others migrate in stages, spending their days eating and flying by night, where the cooler denser air helps keep them aloft with fewer wing beats. Birds also use the changing and then clearing weather of fall storms and the resulting tailwinds to help them conserve and save energy.2 No matter how they travel, whether it be by a genetically coded imprint, sunlight, starlight or the earth's magnetic field, birds find their way to wintering grounds beyond the Gulf of Maine.
Birds undergo changes in appearance in late summer, as breeding plumage fades away. Off the Massachusetts and New Hampshire coast in August, flocks of small gulls appear with a black spot on their head. These are the Bonaparte gulls, and they keep their distance from the much larger herring and black-backed gulls. The black spot is the only remnant of the jet-black head plumage of the breeding season. Migrating birds have different strategies for navigating and also for the paths they take. Many birds follow a leading line approach either following the spine of a mountain chain or the coast. They are attracted by buoyant updrafts and ample food along the way. Shorebirds fly great distances over open water, but most birds avoid this and follow the coastline south.
In the upper reaches of the Bay of Fundy, the semipalmated sandpiper congregates in great swarms over the very productive mud flats. Over 95% of this bird's population stops on the Bay to feed enough to provide the energy for their flight to South America. The principal prey is the amphipod Corophium volutator, commonly known as the mud shrimp.3 This fat rich crustacean feeds on benthic (bottom growing) algae, which cover the flats. Meanwhile, at the other end of the Gulf of Maine, the pelagic seabirds are spreading further in their search for food. Pelagic birds are seen on the open ocean only and are not usually seen from land. They hunt the ocean and return to offshore rookeries. The most easily seen are shearwaters, storm petrels, and gannets, which often approach only a few miles from shore. The storm petrels forage far out to sea, returning to their colonies at night. Fishermen call them the "Jesus" bird because they seem to be walking on water as they stir up plankton with their feet.
Gannets are a large and quite magnificent seabird that gathers in tight-packed colonies on offshore rocks and cliffs. They are expert fliers and plunge divers. Their vertical descent into the sea from hundreds of feet to snare a mackerel is a thrilling sight only to be outdone by dozens of them working a shoal of fish. Shearwaters are also magnificent fliers that glide over the wave tops seemingly "shearing off” the top of the wave as they snatch small fish. Shearwaters are here to avoid the winter in the South Atlantic to which they will soon return as our winter approaches. These pelagic birds are fishing near shore this third week of September, so close that you can see them less than half a mile from shore along with another open water resident of the Gulf...humpback whales.
Everything in the marine and nearshore environment is in transition as the migratory animals store energy in the form of fat in preparation for their migrations.
1 Schmitt, Catherine A Coastal Companion, Gardiner, Maine 2008 Tillbury House
3 Thurston, Harry The Atlantic Coast: A Natural History, Vancouver, Canada 2011, Greystone Books
John Halloran is the Director of Science for GOMI and a member of the GOMI Guide Team. John’s interests focus on the ocean environment where he pursues educational adventure travel, research, and recreation by sail, paddle, and scuba.John is the founder and director of Adventure Learning, Newburyport, MA, which has been involved with educational outreach in area