A fiery red sun dipped below the western bank of the Connecticut River earlier this week just as a silvery full moon rose to the east, a signal that the show was about to begin.

“Here they come!” a nearby kayaker exclaimed, and a handful of tree swallows, like the first few flakes of an approaching snowstorm, flew by. In seconds, a blizzard of birds that swooped and dived in great swirling swarms filled the sky.

The annual late-summer migration of swallows to Goose Island off Lyme can overwhelm first-time observers and veteran viewers alike.

A couple years ago, one friend, an avowed atheist, stared silently for several minutes at the hundreds of thousands of birds before whispering, “There is a God.”

Renowned naturalist/ornithologist/bird guide author Roger Tory Peterson, who lived not far from the marshy island, once remarked, “I have seen a million flamingos on the lakes of East Africa and as many seabirds on the cliffs of the Alaska Pribilofs, but for sheer drama, the tornadoes of tree swallows eclipsed any other avian spectacle I have ever seen.”

I have witnessed this extraordinary phenomenon, called a murmuration, more than a dozen times over the past several years, and no two have been alike. On one occasion, the swallows formed a tornado-like vortex and descended to the island in an instantaneous whoosh; another time, they circled lazily for nearly half an hour before dropping to Earth.

The other day, the birds appeared less organized, flitting about haphazardly for 15 minutes or so and then — hey, what happened? — they all wound up among the reeds. Scientists explain that many creatures, from schools of fish to herds of wildebeest, exhibit such “hide mentality” to ward off predators.

No one seems to know for certain how long swallows have been drawn to Goose Island by swarms of migrating insects, their favorite food, but it’s only been in the past few years that people other than dedicated birdwatchers have taken much notice. Now fleets of vessels ranging from canoes and kayaks to large tour boats bearing scores of passengers and professional guides descend on the lower Connecticut River during swallow season, roughly from late August through the end of September.

If you’re planning to paddle, I suggest car pooling and arriving a couple hours before sundown in order to get a parking place at a public launch on Pilgrim Landing Road, which is off Route 156 north of the Baldwin Bridge.

Goose Island is less than a mile north of the launch, and if there’s a stiff west wind, as was the case this week, I suggest steering up Lord Creek on the east side of the island. It’s also better protected there from boat wakes on the main part of the river. You never know exactly where the swallows are going to land, so the best strategy is to take a position midway up the island and be prepared to follow the flight of fancy.

Bring a headlamp because if you stay for the whole show, or just want to linger and enjoy a quiet paddle on the river, it will be dark by the time you return to Pilgrim Landing Road.

I view swallow season with mixed emotions — elation, of course, but also wistfulness. Another long, languid summer is over, and before long we will be stoking the wood stove and shoveling the driveway.

On the other hand, the lower Connecticut River also is temporary home of another migratory species — the bald eagle. Scores of these magnificent birds fly here in winter from points north to fish in ice-free water.

During the rest of the year, there are great blue herons, ospreys, hawks, falcons, mergansers, cormorants, gulls, terns, kingfishers, and any number of other shore birds. The Connecticut indeed is a river for all seasons.