The sky turned orange, pink, and then several shades of purple as the sun set over Goose Island on the Connecticut River in Lyme this week. We kayakers drifted with the current, waiting for the show to begin.

“Where are they?” Elyse Landesberg demanded.

“They’re up there,” Nick Schade replied, squinting heavenward. The rest of us craned our necks.

“I don’t see anything,” Denise Gautreau complained.

Just then someone shouted: “There’s one!” This late in the season, it was slim pickings for spectators who hoped to view one of nature’s most exquisite displays: huge flocks of migrating tree swallows, swirling in tornadic formation around the half-acre island.

A few weeks earlier, during peak migration, our kayak group was treated to a phenomenal performance, called a murmuration, when enormous clouds of tiny birds swooped and spiraled for more than 45 minutes. This week was a different story. No matter – kayaking in the lower Connecticut River at sunset is sufficiently rewarding, swallows or no swallows.

No one knows exactly when they began arriving at Goose Island – even world-renowned ornithologist Roger Tory Peterson, who moved to nearby Old Lyme in 1954, was unaware of the phenomenon until 1994, two years before his death.

Friends and I have been making late-summer/early-fall pilgrimages to the river for more than a decade, which I’ve chronicled in past columns, and each experience has been unique. Some evenings, the swallows circle high in the air for just a few minutes before descending in unison; other times they fly only inches above the water. On occasion they separate into several flocks; they also have been known to join one gigantic mass.

The swallows feed on bugs that mass amid Goose Island’s tall grasses. This week’s mild weather has allowed the insects, and birds, to linger. Now that cold is settling in, we’ve probably witnessed the last major murmuration of the season – a swan song for tree swallows.

Eagle-eyed Nick proved correct, though: Lots of birds were in fact “up there.” They just didn’t seem in a hurry to descend for the night.

So our flotilla – which included dozens of kayaks, paddleboards and small powerboats – drifted and chatted, making lame jokes about how inconsiderate the birds were to deprive us of our entertainment.

Finally, a collective cry: “Here they come!” A hush then fell over us, as we watched, mouths agape.

One swarm formed a thin spiral and began dropping earthward, as if sucked by a giant vacuum. How had the birds managed to arrange themselves so quickly, in such a tight formation? Moments later, a second flock created the same pattern and began its descent, followed by a third and fourth.

We were aboard only a couple dozen drifting boats but still wound up bumping into one another every so often. Why weren’t hundreds of thousands of zipping birds constantly crashing into each other and tumbling to the ground? A wondrous mystery.

Soon, the last flock settled among Goose Island’s reeds. The sun had long set, and kayakers clicked on head lamps and solar-powered deck lights for the 2.3-mile paddle back to Ferry Landing in Old Lyme, just south of the Baldwin Bridge.

I flushed out a roosting great blue heron while I swept past Calves Island – hard to say who was more startled, the giant, squawking bird or me. Our group hugged the shore along Lords Creek – far from the main river channel, where cigarette boats might tear along at 60 mph after dark. Kayaking at night can be peaceful or perilous.

Over the next several weeks, the swallows will work their way south to Florida and Central America. I’ll be thinking about them in February, when friends and I typically return to the Connecticut River to view migrating bald eagles. The lower river, also home to a wide array of other shore birds, is recognized as “a wetlands of international importance” under the global Ramsar Convention. The Nature Conservancy calls the river “One of the 40 Last Great Places in the Northern Hemisphere.”

We are lucky to have access to such an exceptional waterway, in any season.