MILFORD >> Ospreys are flying high in Connecticut, beloved by bird lovers who flock to specially constructed platforms where the raptors, which mate for life, build their nests and raise their young.

There are more than 600 fledglings in the state this year, with more getting ready to take flight in the next week or two.

It’s the highest total at least since the mid-20th century, when the pesticide DDT threatened the birds with extinction, according to Milan Bull, senior director of science and conservation for the Connecticut Audubon Society.

“We’ve only been keeping records of ospreys I think since the 1970s, so I don’t know what the numbers were before they began to decline in the ’40s and ’50s … but it’s the highest we know of,” Bull said.

Connecticut Audubon knows how many ospreys migrate to the state because of the 287 “stewards” in the ranks of the 3-year-old Osprey Nation, who are devoted to keeping track of the birds and post photos and comments on www.ctaudubon.org.

The success of the osprey population in Connecticut — up about 40 birds from 2016 — is especially gratifying to Bull because of a worrisome report out of Maryland, where there was a devastating decline in the number of new hatchlings.

“The Patuxent River population declined this year and that sent alarm bells across the Northeast,” Bull said, watching an adult male and a juvenile sitting on nests off Connecticut Audubon’s Milford Coastal Center, next to the salt marsh in the Charles E. Wheeler Wildlife Management Area.

“This is the first year there’s been a significant decline in productivity.”

Even though the adults returned from their winter homes in South America, “the failure rate at the Patuxent River … was twice as high as the Maryland wildlife officials expected,” Bull said.

The Patuxent is a major tributary to Chesapeake Bay, where 6,000 to 8,000 pairs make their nests.

“It was a wake-up call for us, but we didn’t see any decline at all,” Bull said. In fact, given the increasing numbers each year, “It’s going to be interesting to see where it levels off,” he said.

Bad weather

The best guess as to why Maryland’s ospreys produced so few young birds is bad weather. That’s Bull’s theory, and it’s also the opinion of Greg Kearns, park naturalist and biologist for the Patuxent River Park.

“Two years in a row the thing I’ve seen … is when we get really cool weather in early to mid-May” the new generation of ospreys suffers, Kearns said. “This year was disastrous.”

Kearns suspects that during a freak hailstorm in early May, “birds literally got knocked off the nest.” A friend showed him a photo of an osprey nest covered in hailstones.

The problem was particularly severe down river, where there was only a 25 percent success rate, Kearns said. “The further I go up the river, where I am, the nesting is close to normal,” in the 60 percent to 70 percent range.

“I really believe there was an intense thunderstorm on that lower section of the river,” where the Patuxent is 1 to 2 miles wide and more susceptible to high winds.

Kearns doesn’t see the problem as long term, however. “I think the ospreys can bounce back. … The population had been steadily growing for years. … Fortunately, they’ve had so many banner years over the last 10 or 15 years.”

There are four nests in the Wheeler management area at the confluence of the Housatonic River and Long Island Sound, but Bull said, “I’ve got over 70 osprey nests in a 2-square-mile area at the mouth of the Connecticut River.”

A worldwide raptor

Ospreys are found on every continent except Antarctica, but South America is only home to them during the winter migration. While the pairs will reunite each spring, usually at the same nest, they don’t winter together.

“These guys will migrate south to places like the Amazon basin in October and the females and the young will migrate first and the males will migrate later,” Bull said. “And they don’t go to the same places. It’s clearly key to a long marriage: separate vacations.”

Kearns said he has one pair that’s been returning to its nest for 20 years, far longer than the average lifespan of 10 years or less.

The key to attracting ospreys is having an abundance of herring, which feed on algae near the water’s surface and make up the bulk of the birds’ diet. The males return in March and feed on three small species of herring: alewives, Atlantic herring and blueback herring. The females arrive in late March or early April.

The larger species of herring, menhaden, also known as bunkers, come back in mid- to late April, early May, and that’s when the young ospreys — an average of three to a nest — are out and looking for food. Fledglings are heavier than their parents in order to give them “enough body weight to learn to hunt on their own,” Bull said.

They also aren’t taught to fly; they have to learn themselves. And the ospreys will only eat fish they catch themselves, which they do by diving and snagging their meal in their talons.

While they nest near water, even fresh water at times, ospreys aren’t picky about where they make their homes, Bull said. Nests can be found on statues, telephone poles, cellphone towers, buoys and even cranes. “If you’re not using your crane this year, you could find an osprey nest next year,” he said.

Into the future

Bull’s biggest worry for the birds is commercial fishing. “There’s concern that the commercial fishing industry wants to increase the take of herring next year,” he said.

That limit is determined by the National Marine Fisheries Service. While the agency is concerned about overfishing, its primary consideration is the economic health of the industry.

“It’s really the commercial fishermen that dictate the tons of species they’re allowed to take,” Bull said. The service doesn’t take into account how important a species is “to the overall ecosystem. There hasn’t been much concern about that,” he said.

In the Chesapeake Bay, factory ships use giant nets to catch tons of menhaden.

“We’re trying to get the Marine Fisheries Service to study the ecological importance of these commercially available herring,” Bull said, which are used in pet food and fish oil pills. “How much can we take before it begins to impact these birds? I don’t know. I’m not sure they know.”

In Connecticut, however, “the curve is going up” for the ospreys, Bull said. Connecticut Audubon has mapped 680 nests in the state, 394 of which are known to be active, Bull said. Osprey Nation is thriving.

“So many people are interested in ospreys,” Bull said. “They’re big, beautiful white birds. … They nest in visible locations.” Among the stewards is everyone from retirees to young families and their children.

Genevieve Nuttall of Waterford, who will be a senior at the University of Connecticut, is in her second year as coordinator of Osprey Nation.

“I collect data from all of our stewards,” she said. “At the end of the season I collect all of the numbers to see how our osprey population compares to the year before and how it’s growing.

“We are at record numbers of nests being monitored by our volunteers, the number of nests being used,” as well as record numbers of ospreys being born, Nuttall said.

She is in a five-year program that will lead to a master’s in conservation biology. “I’m focusing on bird conservation so this program is really great because ospreys are one of conservation’s biggest success stories. … They were almost extinct in the 1970s.”

DDT caused the ospreys and other birds to lay eggs with weak shells and was banned in 1972. As the species rebounded, nesting platforms became popular. “People love these birds because they’re so charismatic and they didn’t want them to go extinct,” Nuttall said.

“They bring up their young together. … It’s this nice kind of love story and … you can see it right in front of you.”

Call Ed Stannard at 203-680-9382.