Immature bald eagles do not acquire the typical white head and tail until they are four to five years of age.
New Jersey Endangered and Threatened Species Field Guide
Species Group: Bird
State: Threatened (Breeding)
The osprey, formally known as the “fish hawk,” is one of New Jersey’s largest raptors. They are well known and highly visible along coastal marshes. The bird is distinguished by its dark underwing patches and the crook at the wrist joint of the long, narrow wing. Adult birds have dark brown body feathers on its back and wings contrasting with their white crown, neck and undersides. Broad dark stripes appear on either side of the head, running through the eye. The eye color changes from red to orange to yellow as they mature. The tail is light with fine dark bands and a broad terminal bar edged in white. Both sexes have similar plumage. The female is slightly larger than the male and exhibits a more prominent “necklace” of dark feathers on their chest. Osprey’s average wingspan is 63 inches and weighs about 3 pounds.
Distribution and Habitat
The osprey is one of the most widely distributed birds in the world, yet its preference for fish requires that it live close to the water. In North America, its range extends from Alaska to Baja California, and along the Atlantic coast from Labrador to Florida. In New Jersey, ospreys nest along the Atlantic Coast from Sandy Hook to Cape May, and along the Delaware Bay and River in Cumberland, Salem, and Gloucester counties. As a result of reintroduction efforts on northern New Jersey lakes, ospreys also nest along the upper Delaware River and their range is expanding in the Meadowlands each year. Ospreys prefer to build their large stick nests close to water on tall, dead trees, live trees, channel markers, old duck blinds, and telephone poles. More recently, man-made structures placed on the marsh for their nesting have replaced trees and are largely responsible for the recovery of ospreys in the state.
Ospreys winter in Florida, the Gulf Coast states, and as far down as Central and northern South America. New Jersey ospreys fitted with satellite transmitters have been tracked to Venezuela and Colombia to Brazil’s Amazon River Basin. The majority of New Jersey birds winter in N. South America.
Special adaptations make the osprey exceptional at fishing. Most notable is the bird’s outermost toe, which can reverse to oppose the the other two (most birds grip with three toes in front, and one in back), this attribute is referred to as zygodactyl. It uses this grip to carry fish head first to reduce wind resistance. It has long legs, and its feet and toes are equipped with tiny spines, or spicules, that enable them to grasp slippery fish. The osprey will dive several feet into the water (up to 1 meter), feet first, after fish. An osprey’s diet consists almost entirely of fish, although occasionally during the breeding season some bird carcasses have been observed near nest sites.
Their diet differs throughout their range and the time of year. Ospreys are opportunistic predators. They hunt on the wing and can hover. They have very keen eyesight and percevie light in the UV spectrum, making some fish with iridescent markings, like flounder, easy prey. During early spring when ospreys return in late March the shad and herring migration is getting underway. Then striped bass begin to move inshore and in summer fluke and bunker are plentiful and are often their main prey items.
In New Jersey, ospreys arrive on breeding grounds in late March, usually to the same nests each year, meaning they have a high level of site fidelity. Older more experienced birds arrive first, especially males. Ospreys mate for life and are monogamous. Pairs begin courtship and nest building in early April. Males perform courtship displays that consist of a high undulating flight, called the "sky dance," sometimes after a successful hunt where he holds a fish or nesting material and calls out with a high pitched whistle like sound. This strengthens their pair bond. Males do 100% of the foraging from courtship until the young fledge. Females do around 70% of the incubation duties. Eggs are laid in mid-April to early May, usually three buff colored, brown spotted eggs. Incubation lasts 32-43 days, and most young hatch in late May. The chicks are born semi-altricial or are helpless and require close parental care. To successfully raise a full clutch of young the male must provide enough fish (sometimes up to 6 lbs. a day!) to feed all the hungry mouths. After a successful hunt he almost always stops at a nearby perch and consumes the head of the fish. If he feeds near the nest with the female on the nest she will beg for food from him. Young birds fledge the nest at 7-8 weeks of age in mid-late July. Adults continue to feed young in the area of the nest for several weeks while young ospreys learn flying and hunting skills. In late August and early September, ospreys leave New Jersey for their wintering grounds.
Look up in August and you might see numerous young osprey learning how to soar and ride thermals!
The successful production of young is highly dependent on several factors. Weather plays a huge role in the reproduction of ospreys. Since they rely on fish as their main prey item, high winds and wet weather can have a negative effect on the success of foraging attempts. In years with a wet and cool spring, productivity rates dropped as adults had trouble finding and catching prey. In years with a warm spring and summer, ospreys fair quite well. An adaptation to help control this seasonal changes in their diet is that ospreys exhibit is asyncronous hatching. This is where incubation begins when the first egg is laid (laying occurs in two day intervals), not when the full clutch is laid. This gives the oldest chick the best chance at surviving if food is not plentiful. It is better for a pair to produce one very strong chick than 2-3 meager young. Finally, their success is also highy dependant on the male's ability to successfully find and catch prey. In general, older males are often more experienced and in turn, can produce more young then at nests with young adults.
Current Threats, Status, and Conservation
Prior to 1950, over 500 osprey nests were found along the New Jersey coastline. By 1974, only about 50 nests remained. Loss of nesting sites and widespread food contamination by persistent pesticides (mostly DDT) caused the birds’ decline in New Jersey and throughout the eastern U.S. Consequently, the osprey was listed as “endangered” by New Jersey Division of Fish & Wildlife in 1973.
Efforts to recover the osprey population began in 1974, when biologists built and installed nest structures in and along the coastal marshes, to replace trees that had been lost to development. Biologists also transferred eggs and chicks from a Maryland population to New Jersey nests that were not producing healthy eggs at the time.
Management efforts were successful in restoring osprey nesting in the state. In 1984 there were 108 nests and sustainable production, leading to the down listing of the osprey to “threatened” status in 1985. By 1990 osprey nests numbered 170, and by 1993 there were 200 nests, a four-fold increase since 1974. Today, there are over 600 nesting pairs.
In partnership with the Endangered and Nongame Species Program, our Osprey Project is meant to help monitor, manage, and support New Jersey's ospreys and their role in the ecosystem.
One of the most important management techniques for New Jersey ospreys is providing adequate nest structures along the coast. Over 200 nest platforms have been installed and over 75% of the current population nests on man-made platforms that are specifically designed for them. These structures require maintenance and replacement as they age. Donors and volunteers have been valuable in providing funding and assistance with the installation of artificial nest structures.
Since 2007, over 40 nesting platforms have been installed on Barnegat Bay from Mantoloking south to Little Egg Harbor and west on the Mullica River. About half of these platforms were occupied in 2010, so there are plenty of nest sites available for young adults to nest when they return from their wintering areas (they spend two years on their wintering grounds in northern South America and the Caribbean).
Ospreys are proven indicators of environmental health. Feeding largely on fish, their health reflects the health of a food source shared by humans. A study performed by the Endangered and Nongame Species Program in the late 1990s showed that toxic and persistent pesticides have declined in Ospreys in New Jersey. However, the effects of other contaminants like brominated flame retardants which are used in a large amount of consumer goods are little known. We currently collect addled eggs for future contaminant studies (if funding becomes available).
Another threat to ospreys is pollution. "On several occasions I’ve personally witnessed osprey nestlings that have been entangled in mono-filament or ribbon from balloons" said Ben Wurst, Habitat Program Manager. "I don’t think I’ve ever seen an osprey nest without some kind of trash in it."
Text derived from the book, Endangered and Threatened Wildlife of New Jersey. 2003. Originally written by Sherry Liguori. Originally edited by B.E. Beans & L. Niles. Edited and updated in 2010 by Maria Grace and Ben Wurst.
Species: P. haliaetus
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