It’s that time of year again when the tide comes in. Not the twice-daily ocean tides. We’re talking about the bird tide, that incredible movement of billions of birds from south to north every spring and back again in the fall. The flow of birds north is reaching its peak in the southern U.S. now and will hit its maximum flow for us here in Maine in a couple of weeks.

Most of these birds do most of their big migratory movements at night, which is part of the reason most people don’t realize the magnitude of the migration. Some species, of course, do migrate during the day (some both day and night). Observers on the coast have likely seen strings of cormorants, eiders, and other sea ducks, low over the water, furiously beating their wings as they head northward.

Other freshwater-loving ducks occur together sometimes in numbers that, in our area, can reach into the hundreds. Red-winged blackbirds and grackles are daytime migrants that travel in flocks. Swallows also migrate during the day and sometimes amass together.

But the largest numbers of birds — the waves of warblers, sparrows, grosbeaks, orioles, tanagers, thrushes and more — move northward across our continent at night. We delight in seeing their bright colors and hearing their songs as they search for food in our backyards, parks, woods, and wetlands, after a long night of traveling.

There are many on a good May morning: tail-wagging palm warblers and vibrant yellow warblers in the shrubbery, eye-shocking orange Baltimore orioles feeding at the orange halves hanging in the lilac tree, wood ducks in the pond, and the much welcomed “Old Sam Peabody, Peabody, Peabody” whistle of the white-throated sparrow echoing through the woods.

For more than 20 years people have been celebrating the exciting return of migratory birds each spring, during International Migratory Bird Day. Hundreds of events take place across the Americas each spring under the auspices of International Migratory Bird Day, with many of the events in our area taking place the weekend of May 9 this year.

Each year, International Migratory Bird Day has a different theme; this year the theme is “Restore Habitat, Restore Birds,” which focuses on the ways that bird habitats can be restored and protected so that there will always be places for birds to find food and shelter on their long migratory journeys, and places to raise their young when they return home.

At www.migratorybirdday.org you can find all sorts of educational materials about this year’s theme as well as past year’s themes. You can also find out about events taking place through the state and the country.

One of the most important ways that habitat for all those birds is maintained and restored in Maine is through efforts of land trusts like the Boothbay Region Land Trust. These vital land conservation efforts at land trusts have been supported for decades through support and funding of the Land for Maine’s Future program.

Join the tens of millions of bird enthusiasts around the country and in Maine in celebration of International Migratory Bird Day and find ways to help make sure generations to come will also be able to rejoice in the return of those beautiful birds every spring!

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists. His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine. Both are widely published natural history writers and are the authors of the book, “Maine’s Favorite Birds.”