OSPREY LIFE

Clutch Size:    1-4 eggs

Number of Broods: 1 brood

Egg Length:    2.2-2.7 in (5.5-6.8 cm)

Egg Width:    1.6-2.0 in (4.2-5 cm)

Incubation Period:    36-42 days

Nestling Period:    50-55 days

Egg Description:    Cream to pinkish cinnamon; wreathed and spotted with reddish brown.

Condition at Hatching:    Capable of limited motion. Covered with down and with eyes open.

Egg laying and incubation take place mostly between mid-April and late May, and clutches of two to three beige, chicken-size eggs with blotches of chestnut, olive, and brown are incubated principally by the female for 38–42 days after the first egg is laid. The male will feed the female during incubation. Nestlings are brooded by the female, fed fish, and begin to resemble adults by 40 days of age, when they begin preparation for flight at about 55 days of age. Families stay intact near the nest site through July while the fledglings acquire fishing skills.  

Osprey mate for life and pairs return to the same nest site for years. Here the males arrive first right around St. Patrick's Day and begin staking out their territory constantly enforcing the flightlines to their nest. When their mate arrives, he starts his sky dance, brings her food, and grooms his nest with sticks and grass. That aerial display is something else. Its a high hover, then a dive sometimes with a fish or a stick - proving his mettle to the female.

Since the 1972 ban on the organochlorine pesticide DDT,  which gets concentrated in  Bay ospreys, they have recovered from a population low of 1,500 pairs to an esitmated 10,000+ pairs today.  Our waters support nearly 25% of the entire global population.

Male osprey build homesites in channel markers, treetops, branches, telephone and power poles, road sign structure, duck blinds and man-made platforms. They start small but over the seasons can grow to 6 ft. diameter nurseries.  He brings sticks, marsh grass, sod - anything he can carry to keep his brood contained within and safe from predators. The female tends to the nest constantly and does most of the internal soft grass lining.

As open nest users, osprey are exposed via the open air to vultures, eagles, and the great-horned owl.  From the ground, raccoons are the main predator.  They are fierce protectors of their nest.

What kills osprey?  They are shot at fish farms and run into vehicles. Some are electrocuted around power-lines and cell phone towers.

Man is the biggest threat to our osprey population. Sediment from erosion in the water obscures the clarity of the top of the water column making fish tough to see. 

Plastic fishing nets, monofilament fishing line, plastic six pack ring trash contribute to eating issues.

Heavy metals which build up in their bodies as the top predator of their aquatic ecosystems can kill individual osprey and contribute to breeding failures.

Overfishing of menhaden particularly in Virginia waters reduces the quantity of food sources.

Osprey can dive 3ft. into water dive bombing prey from a hover 100+ ft above the surface.  Nearly all our osprey rely solely on a diet of fish - toadfish, small carp, white and yellow perch,  croaker, shad, menhaden and spot. We have seen small rockfish and eel ripped apart in the nest and tree limbs as well.

 Adults begin fall migration as soon as fledglings become independent. Juveniles normally migrate the last week of August or later along a narrow Atlantic coastal path. They leave the U.S. by September, continue south, and arrive at their wintering grounds by mid-October.  Scientists have tracked Bay osprey and found that bay osprey winter primarily on the Caribbean islands of Cuba, the Dominican Republic,  and Puerto Rico.  A University of Virginia study followed Southern Chesapeake Bay osprey to Venezuela. Juveniles remain south of the U.S. at least 16 months. They do not actively nest until they are three years old and do not fly north until their second spring.

Osprey are a good indicator of the health of our Bay.  Orinthologists agree that mated pairs need to produce an average of 1.15 young per pair per breeding season.  Studies are hard to intrepret but counts show lower successful nestling production. Our nest has demonstrated that food competition is fierce and premature death occurs.   Being at the top of its food chain and relying primarily on only one source of food - fish from the Bay, breeding osprey and its offspring are solid barometers for the health of our river ecosystem. With the help of technology and positive human intervention, we need to figure out a way to monitor osprey and encourage care of the species. Our nest is just a start.

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 William and Mary College Center for   Conservation Biology, Osprey Study July 2023