Every spring a great convulsion occurs across the earth. Over a few months, without sophisticated logistical coordination or the support of expensive mechanical transportation, fossil fuels, or agricultural food stockpiles, billions of individuals move thousands of mile from one part of the globe to another.

They are generally moving northward, part of an explosion of life there each spring, as longer days and warmer temperatures allows ice to melt, soil to loosen, plants to start making food from the sun again, and insects to resume activity.

Baby eels, born in the warm Sargasso Sea between Bermuda and the Azores, come to rivers and streams along the Atlantic Coast north to Labrador in the billions, where they will spend years reaching maturity, then return to the Sargasso to breed.

Other fish, including alewives by the millions, come back to rivers and streams from the ocean to breed. Waiting for this mass migration of life are birds who have made journeys back north, some from as far away as southern South America or even the sub-Antarctic.

Ospreys, eagles, kingfishers, mergansers, herons, terns and other species feast on the returning fish and feed them to their newly hatched young. Aquatic insects like early-hatching mayflies that have spent a dark winter in the water in an immature stage, emerge into the air as adults just long enough for mating.

Many a hungry tree swallow, newly arrived from a winter in Florida, has found its survival dependent on a hatch of mayflies or other aquatic insects when cool weather prevails on their return north.
The first greening willows and alders along the edges of streams and wetlands are host themselves to other newly active insects, which are the grocery stores for the first returning warblers and sparrows.

Before the maples and birches fully leaf out, evergreen trees like pines and hemlock and spruce provide insect food for the black-throated green warbler that may have spent the winter in the Dominican Republic or Mexico.

As each of the different species of broad-leaved trees leaf out, their soft new leaves become favorites of insects, making them the short-term favorite “restaurant” for migrant songbirds. Birches are among the first to leaf out; maples soon, follow then oaks, and at the very end of the season, the white ash.

Sometimes the one or two white ash trees in late May, amid the already leafed-out sea of green in a neighborhood, will be crawling with warblers and vireos while none can be found anywhere else.

Check out this amazingly interconnected convulsion of life at a natural area near you. Boothbay Land Trust Preserves like Ocean Point Preserve, Zak Preserve, Penny Lake Preserve, Lobster Cove Meadows, Ovens Mouth Preserve, Colby Preserve, Saunders Preserve, and many others are great places to catch a glimpse of this grand global spectacle.

Dr. Jeff Wells is the senior scientist for the Boreal Songbird Initiative. During his time at the famed Cornell Lab of Ornithology and as the Audubon Society's national bird conservation director, Dr. Wells earned a reputation as one of the nation's leading bird experts and conservation biologists. Jeff's grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, also formerly of the Cornell Lab of Ornithology, is a widely published natural history writer and a senior director at the Natural Resources Council of Maine. Together, they have been writing and teaching people about birds for decades. The Maine natives are authors of the highly acclaimed book, “Maine's Favorite Birds.”