When the airplane buzzed over Pierce Country Day Camp in Roslyn Wednesday morning, hundreds of campers turned their eyes to the sky to see it towing a surprise message: “Happy 100th Birthday Pierce Day Camp!”

The plane was part of the family-owned camp’s celebration of its 100th summer — other activities included camp directors riding on a golf cart while shooting confetti; unearthing a time capsule buried 20 summers ago and replanting it with new items to be opened 25 summers from now; presenting an enormous 100th birthday cake; and singing tunes celebrating the camp and its milestone.

Inside the capsule, among other items, was an enormous banner that had been signed with messages from campers at Pierce 20 summers ago. Marie Pierce, 63, one of the camp directors, said she couldn’t believe the moment had finally come to open the capsule and mark the occasion.

“It just seemed so far away and such a milestone. Here we are today. We’re passing the baton on to the fourth generation,” she said, referring to her daughter Courtney and nephew Will taking over the running of the camp that was founded by their great-grandfather, Forrester “Pop” Pierce, in 1918. The next time a capsule is opened at Pierce, Marie Piercewill be 88 and a fifth generation of Pierces may be running things. “I can’t believe that in 25 years my grandchildren will be in their 30s,” she said.

Festive banners surrounded the field Wednesday, made by the camp’s various age groups and held by their counselors. “Each group went to arts and crafts and we designed our own banner,” said Alex Prince, 19, of Howard Beach, who has been spending summers at Pierce since he was 3 years old and is currently a counselor for a group of 6-year-old boys. “Pierce is Having a Treemendous Birthday,” read the group’s banner, with the handprints of the 20-plus boys in the group. Treemendous is a play on the camp’s massive treehouse. Another group’s banner said, “May the Pierce be with you.”

The time capsule and the airplane were the biggest hits for campers Alivia Saunders, 9, of Port Washington, and Victoria Zargari, 9, of Great Neck.

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“It was unexpected,” Alivia said of the plane.

Victoria agreed. “We thought it was just a plane, but then we saw the banner. It had the Pierce logo,” she said. “It blew my eyes.”

“It was really, really fun,” Alivia said. “All my friends were here, and we had confetti and a cake.”