They’re back — in record numbers.

After capturing and releasing four osprey fledglings last week from two Island locations, Dr. Rob Bierregaard said the Island now hosts 70 pair of summering osprey, “as many as there have ever been [in recorded history] on the Island.”

The University of North Carolina biologist should know. He’s been researching the Island osprey population since the early 1970s, shortly after Island naturalist Gus Ben David set about protecting and expanding the handful of surviving osprey pairs in 1969.

In fact, after clambering down from a 25-foot-high nest in Aquinnah late last week with not one, but two, fledglings, Mr. Bierregaard said “this year may have been ‘the perfect storm’ in a positive sense for osprey hatching.

“Weather and available food play a big part in the osprey life cycle and we’ve had no big storms to blow the birds off track and there is plenty of fish on the Island this spring,” he said.

Noting that the nest near the Batzer house off Lighthouse Road in Aquinnah held four fledglings, the most ever fledged in his experience, Mr. Bierregaard noted he and fellow researcher Dick Jennings had also retrieved a pair of fledglings from a nest at Long Point Wildlife Refuge on Wednesday morning.

“In 25 years of tagging and releasing, retrieving two birds from the same nest has never happened to me until this year,” he said.

“This is a record for us. We’ve counted 121 chicks this year compared with 85 last year,” said Mr. Jennings, who is also the natural resources tour guide for The Trustees of Reservations property on Chappaquiddick.

If his good luck holds, Mr. Bierregaard is hoping to tag and release another fledgling from a nest in Tashmoo this week. The pair fitted last week brings the number of Island ospreys fitted with one ounce global positioning system devices to four.

The devices allow researchers to monitor the activities of the birds in real time, including the height at which they are flying, their speed of flight and exact location. That’s important because of the enormous range possessed by these raptors. They can fly up to 60 hours nonstop, covering up to 1,500 miles to Caribbean and South American wintering spots.

“We’ve got 25 birds along the East Coast with monitoring devices,” he said.

Unlike most tag-and-release teams, his team monitors only fledglings.

“These GPS devices can cost up to $4,000 and the mortality rate of fledglings can be up to 80 per cent, so it’s expensive,” he said.

“We monitor the young so we can better understand their habits and patterns,” Mr. Bierregaard said. “We already know that adults use the sun, their internal navigation system and landmarks they’ve developed over the years to get where they are going. Fledglings only have a direction — south — to guide them in their twice-a-year migrations. We don’t know how the fledglings really do it.”

Twentieth-century insecticides reduced the New England osprey population from 1,200 to only 107 pairs before DDT, the most common insecticide, was banned in the early 1970s, Mr. Bierregaard said.

“Today, the New England population has recovered to more than 1,000 pair,” he said. “The Island recovered more quickly than the rest of the region because of the leaching effect of the soil and because people followed Gus’s lead and began putting up poles more than 25 years ago.”

While technology offers insight and perhaps additional future protection to the raptors, the process of gently capturing, tagging and affixing monitors to the birds is a very human process.

Mr. Bierregaard and Mr. Jennings place sturdy netting with imbedded slipknots over the nest in early morning along with several menhaden to attract the birds. As they land and begin to feed, their four-inch talons engage in the slipknots.

Then Mr. Bierregaard ascends the poles, which often wobble as four-foot wings beat powerfully against the restraints. He then must calm the bird by hooding it, remove it from the netting and lower it gently to the ground.

Each bird is weighed and measured and given a quick physical exam before being released back into its world, generally a 15-minute process. As was the case this week, not every bird is a positioning system candidate. Only the best conditioned birds are selected.

Twenty minutes after release yesterday morning, both fledglings were back in their nest, happily brunching on menhaden.

There’s no place like home. While ospreys can be finicky about just the right nesting place, once they decide, they fix it up to their satisfaction, Mr. Bierregaard said.

“They are real junk collectors. One nest I visited had a small teddy bear in it,” he said with a chuckle.