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The Osprey in our Bays - April 5, 2015

    According to the calendar, it is officially spring, despite the odd snow flurries here and there. Spring time means warmer weather, longer days, and getting out of the house to enjoy the great outdoors. Spring also signals the start for many different animal species to undergo migration and head off to their summer grounds. One such animal that migrates back to the Chesapeake and Coastal bays during this time of year is the Osprey, Pandion haliaetus. This amazing bird, also nicknamed the “fish hawk,” is a migratory staple here in Maryland and can be found here from spring, through summer and into the beginning of fall. 

    Most Maryland Osprey overwinter in 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 in October these Osprey stay throughout the winter, and most will start their journey back to Maryland beginning in February. Juvenile Osprey born in Maryland will spend at least 16 consecutive months in South and Central America before returning to the U.S. Only about 50% of the two-year old Osprey will return, however these birds will not mate or build a nest yet as they do not reach sexual maturity until around the age of three. 

    Once the Osprey return to Maryland in the spring, they have a lot to do in a relatively short time. Beginning in late February to early March, Osprey who have already breed before will start returning to Maryland, with males arriving a few days before females. Osprey are monogamous, meaning that once they mate, they will tend to stay with that partner for life. Once the pair is reunited they usually use the same nest and nesting site they used in previous years, if it has not been destroyed, to begin courtship and nest repair. Osprey with less nesting experience will arrive in mid March to start courtship and nest repair, while first-time nesting Osprey 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 things like channel markers, power lines, and dead trees.

    Once the nesting pair have built or repaired their nest for the season, they soon put it to good use. Egg laying and incubation occur mostly during mid April to late May, and 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 will be fed fish and cared for by the parents until around late July to early August, by which time the juveniles will resemble the adults and be able to fly and fish independently of their parents. The parents will migrate south before the Juveniles, which stay later and start their migration along the Atlantic flyway around the last week of August. 

    Adult Osprey 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, the Osprey is generally smaller than the Bald Eagle and has distinctive crooked wings when flying. 

    Osprey might be known best for their diet; they feed almost exclusively on medium-sized fish like Perch, Shad, Menhaden and sometimes Flounder. The Osprey hunts 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. The water quality can play a major role in fishing success of Osprey 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. During this time period the widespread use of Organochlorine pesticides, or DDT, resulted in heavy  concentrations of this chemical in waterways and subsequently fish. As a top predator of almost exclusively 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 public outcry. Since the banning of DDTs in the 1970s, Osprey populations have slowly recovered in most coastal states, however some inland states still have them listed as endangered or threatened. 

    Osprey are truly amazing birds and, here in Maryland, their return means warmer spring days are almost here. 

 

 

Harrison Jackson is the Coastal Stewards Coordinator for the Maryland Coastal Bays Program.

 


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