Thursday, July 18, 2024

An osprey in Boxborough carries a stick in its talons in May 2020. Ospreys have a brown stripe that runs from their eyes to their neck. (Photo: Brian Rusnica)

Ospreys (Pandion haliaetus) are also called fishhawks, seahawks and riverhawks. (Now you know what kind of bird the Seattle Seahawks are.) But ospreys are not hawks. They are a separate family that includes only osprey.

Ospreys are fish-eaters, and they catch fish about 75 percent of the time. They dive into the water feet first, head between the legs like a guided missile, to seize prey. It takes an osprey on average about 12 minutes to grab a fish with its talons. Then it lifts straight up out of the water clutching the fish. (A well-named military aircraft, the Osprey, can lift straight up off the deck of a ship.) A 3-pound osprey catches fish that weigh on average about half a pound – but have been known to cart away fish that weigh 4 pounds!

An osprey returns to its nest in Allston in June 2017. (Photo: Brian Rusnica)

Osprey carry fish headfirst in their talons while in flight for better streamlining. Its rounded talons help hold onto its catch. Osprey toes are covered with short barbs that grip fish (and tree branches). In addition, they have a reversible outer toe: They can hold fish with two toes in front and two toes in back. Because of their curved talons, ospreys do not walk well on the ground. They are also front heavy because their legs are set far back on their bodies. It is extremely rare, therefore, to see an osprey on the ground.

In the 1940s, an estimated 1,000 active osprey nests lined the coast between New York City and Boston. Partially because of development but mostly because of DDT use, the number of nests fell precipitously – to 11 in Massachusetts by 1964. DDT and some other pesticides were banned in 1972, and osprey populations have been rebounding since the mid-1970s.

An osprey carries a headless fish above the Larchwood neighborhood of Cambridge in July 2021. (Photo: Richard George)

Ospreys sometimes can be observed in Cambridge. During the breeding season, you can see their nests in Boston, Medford, Belle Isle Marsh, Saugus Marsh and many other nearby places. They like to build large stick nests in trees or on cliffs in open areas near shallow water. They also make nests on top of telephone poles, cell towers, tall buildings or artificial nesting platforms.

Ospreys mate for life. When they fly south, though, the females overwinter farther south than the males. In March, male ospreys return north to Massachusetts where they reclaim their old nests and add to them. Because they keep adding to older nests, the nests can become extremely large over time – 6 feet or more in diameter. When the female arrives back at the nest, the happy couple is reunited.

An osprey above Revere carries a fish parallel to its body to reduce drag in August 2022. (Photo: Richard George)

The female osprey lays about three eggs in late April and incubates them until early June, when the chicks hatch. During this time, the male brings fish to the female. After the chicks hatch, the male continues bringing fish to the nest, and the females bites off pieces to feed the chicks. After about two months, the youngsters fly from the nest for the first time. Soon the youngsters learn to fish for themselves, and they spend more and more time away from the nest. In late August, the female flies south first. Then the male heads south in September or early October. The youngsters stay a while longer until their instincts compel them to fly south, too. The youngsters do not return north in the spring but stay in the overwintering grounds for a year or two before they migrate north again. They usually return to breed somewhere near where they were born.

An osprey family in Ayer in July 2017. (Photo: Tom Murray)

Ospreys live 15 to 20 years, and during that time they can migrate more than 160,000 miles. One three-month old osprey named Penelope flew 2,700 miles from Martha’s Vineyard to French Guiana in South America in just 13 days. She lounged in Maryland and North Carolina for three days and relaxed in the Bahamas for four. Then she flew to the Dominican Republic in 29 hours. That evening she set out across the Caribbean, flying all night to an island off Venezuela. Seven days later, she reached French Guiana, where she lived for the next year and a half. Young ospreys such as Penelope wander and loiter on their southern migration route. Older adults fly faster and take more direct routes, as they have more experience and know better where they are going.

An eastern kingbird harasses an osprey in Ayer in June 2017. (Photo: Tom Murray)

Even though pesticides are now banned in the United States and Canada, osprey are still subject to DDT and other pesticides in their overwintering areas in South America. Human development along shorelines reduces the number of places ospreys can build nests. Littering also harms ospreys: Fishing line and six-pack plastic, which ospreys often use to line their nests, can strangle chicks. Fish-farmers shoot osprey in the Caribbean and South America, where the birds stop along their migration route or overwintering area.

In 2019, the Massachusetts Water Resources Authority built an osprey nesting platform on the island in Macdonald Park in Medford. You can see it from the park or from the route 28 bridge. Over the past 10 years, more and more ospreys have been spotted during the annual spring herring migration. A nesting pair lives in the Schrafft’s building in Charlestown, and there’s even an osprey nest in Allston! In the spring or summer, look atop utility poles and other tall structures near rivers or marshes to look for osprey; look up now and you might see them migrating south.

An osprey tangled in human debris flies above Boston Harbor in September. (Photo: Jeanine Farley)

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Reader photo

James Erdenbrack of Quincy, Pennsylvania, spotted this praying mantis this month.

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.