News and ResourcesFlight of the Ospreys - March 19, 2017
According to the calendar, spring is officially here. Spring time means warmer weather, longer days, and enjoying the great outdoors. Spring time is also when migratory animals begin their journey back to their summering grounds. One such animal that migrates back to the Chesapeake and Coastal Bays is the osprey, Pandion haliaetus. This amazing bird, nicknamed the “fish hawk”, is a migratory staple in Maryland and can be found here from spring into the beginning of fall.
Ospreys mainly overwinter in Central and South America, primarily on the larger islands of the Greater Antilles, lakes and rivers in Venezuela and Columbia, and throughout the tributaries of the Brazilian Amazon. After arriving around October, ospreys will remain throughout the winter before beginning the journey back to Maryland in February. Juvenile ospreys born in Maryland will spend at least 16 consecutive months in Central and South America before returning to North America. Only about 50% of the two-year old osprey will return; however, these birds will not mate or build a nest until they reach sexual maturity until around three-years old.
Once the ospreys return to Maryland in the spring, they have a lot to do in a relatively short amount of time. Beginning in late February to early March, ospreys that have bred before will start returning to Maryland, with males arriving a few days before females. Ospreys are monogamous, meaning they will tend to stay with the same partner for life. Once the pair is reunited, they typically use the same nest they used in previous years and begin their courtship rituals, which includes nest repair. First-time nesters might arrive at a similar time but spend weeks looking for a mate and a suitable nesting site. Nests tend to be around a meter in diameter and built from whatever the nesting pair can find around; like corn stalks, branches, and shoreline debris. Ospreys also tend to build their nests high off the ground, on structures such as channel markers, power lines, and tall dead trees.
Once the nesting pair have built or repaired their nest, egg laying and incubation quickly follows and occurs around mid-April to late May. The average clutch size, or number of eggs in the nest, is around three. If the first clutch is lost before mid-May, due to predators or weather, then the nesting pair might lay another clutch to replace them. After around 38 to 42 days of incubation, the eggs hatch. The young are fed fish and cared for by the parents until around late July to early August, at which time the juveniles resemble the adults and are able to fly and fish independently of their parents. The parents migrate south before the juveniles, which stay later and start their migration along the Atlantic flyway around the last week of August.
Adult ospreys can grow to be about two feet long from head to tail, with a wingspan of around six feet. They have a mostly white belly and head, with brown and black patches and patterns on its back, wings, tail and across its eyes to the back of its head. While it can often be mistaken for a bald eagle due to the white head, ospreys are generally smaller than bald eagles and have distinctive crooked wings when flying.
Ospreys might be best known for their seafood diet. They feed almost exclusively on medium-sized fish like perch, shad, menhaden, flounder, and catfish. Ospreys hunt by flying high above the water, searching for fish. Once it has spotted its prey, it will hover in the air before plunging in, talons-first, to catch it. After capturing its prey the osprey will fly away, maneuvering the fish in its talons so the head is facing forwards to reduce drag. Water quality can play a major role in the fishing success of ospreys as turbid waters, plankton blooms, and other factors can obscure visibility for the birds and drive prey to other areas.
The fish-exclusive diet for the osprey almost proved to be their undoing during the mid-twentieth century. At that time the widespread use of organochlorine pesticides, or DDT, resulted in heavy concentrations of this chemical in waterways and subsequently fish. As a top predator feeding almost exclusively on fish, this resulted in high concentrations of DDT in osprey. High levels of DDE, a metabolite of DDT, in adult ospreys led to eggs being laid with thinner shells and resulted in high numbers of addled, cracked, and broken eggs. Eventually this led to a plummet in osprey populations, which led to Rachel Carson's famous book “Silent Spring,” and subsequent public outcry. Since the banning of DDT in the 1970s, osprey populations have slowly recovered in most coastal states, however some inland states still have them listed as endangered or threatened.
Ospreys are truly amazing birds and their return to our bays can only mean that warmer spring days are truly on the horizon.
Jackson is the former Educational Coordinator for the Maryland Coastal Bays Program and current graduate student at Clemson University.
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