Osprey, Pandion Haliaetus
Osprey, Pandion haliaetus
Status:
State: Threatened
Federal: Not listed
Identification
The osprey is a large raptor
with a wingspan of 4.5 ft. to 6 ft.
When gliding, the osprey’s long,
narrow wings are pulled towards the
body and its silhouette is analogous
to an “M” shape, closely resembling
a gull in flight. In a shallow glide or
full soar, the wings are bowed
downwards. Ospreys fly with stiff
and shallow wing beats, pumping
the head and body up and down
while flapping.
© T.J. Ulrich/ VIREO
The adult osprey is dark brown above and
light below. The underside is white with contrasting dark carpal ("wrist") patches and
barred flight feathers. The head is white with a broad, black eye stripe that extends to the
back of the neck. The tail and flight feathers are dark brown with faint white bands. Adult
females and juveniles of both sexes exhibit a “necklace” of dark feathers contrasting with
the white feathers of the upper breast. The intensity of this necklace varies among
individuals, with some adult males also displaying this trait. Females are only slightly
larger than males and, excluding the necklace, the plumage of both sexes is identical.
Juvenile ospreys closely resemble adults. However, juveniles exhibit buffy tips to the
upperwing coverts, a more heavily streaked crown, mottled carpal patches, and a tawny
wash to the underwing that fades by the following spring.
On all ages, the osprey has a pale blue-gray cere (fleshy area behind the base of
the bill) and legs. Their toes are equipped with tiny spines, or spicules, that enable them
to grasp slippery fish. The bill is black and strongly hooked with a sharp tip for piercing
the skin of fish. The osprey’s eye color changes from blood red in nestlings to orange-
yellow in juveniles to yellow in adults. The osprey’s call is a high-pitched, down-slurred
whistle that is often repeated in a short series.
Habitat
As a piscivorous species, the osprey is strictly associated with bodies of water that
support adequate fish populations. Consequently, ospreys inhabit coastal rivers, marshes,
bays, and inlets as well as inland rivers, lakes, and reservoirs. Ospreys nest on live or
dead trees, man-made nesting platforms, light poles, channel markers, abandoned duck
blinds, or other artificial structures that are in close proximity to fishing areas and offer
an unobstructed view of the surrounding landscape. Infrequently, ospreys nest on the
ground within coastal marshes. Territories typically contain poles, snags, or structures
near the nest on which the ospreys perch.
Status and Conservation
In the 1800s, the osprey was an abundant breeding species along the New Jersey
coast. In 1884, there were 100 nests at Seven Mile Beach, currently Avalon/Stone
Harbor, alone. However, by 1890, the number of ospreys nesting at Seven Mile Beach
shrank to only 25 pairs, and similar declines were evident throughout the state. These
early population declines are attributed to habitat loss, eradication of nest trees, egg
collecting, and shooting. Further declines in the osprey population continued through the
turn of the century and into the 1930s and 1940s. As human settlement along the coast
increased during this time, trees that were used by ospreys as nesting sites were
destroyed.
The pesticide DDT was first used to control mosquitoes in Cape May County
marshes in 1946 and was applied at increasing rates until 1964. When introduced into the
environment, DDT enters the food chain and bioaccumulates at each trophic level,
contaminating top level predators such as the osprey with high doses of this biologically
harmful pesticide. DDT contamination inhibits calcium metabolism in birds, reducing the
thickness of the eggshell. When an adult bird attempts to incubate an egg with a thinned
shell, the egg will break under the weight of the bird. Because DDT contamination may
remain within an adult osprey's body for years, pairs can continue to experience
reproductive failure over a long period of time.
Following the use of DDT, osprey populations in New Jersey plummeted due to
several decades of poor productivity. Prior to the 1950s, the osprey population in New
Jersey was estimated at 500 pairs (Leck 1984). In 1950, there were 253 nesting pairs
along the Atlantic Coast of New Jersey south of Barnegat Light. By 1975, only 53 pairs
remained in this area and a total of only 68 pairs remained statewide.
Due to its disastrous environmental impacts, the use of DDT was banned in New
Jersey in 1968 and in the United States in 1972. However, because of its persistence in
biological systems, contamination from DDT and its metabolite, DDE, continued to
impair osprey productivity. Ospreys in areas that experienced the most severe population
declines and the lowest productivity in the state were also found to contain the highest
DDT levels in their eggs. Osprey eggs collected in New Jersey during the early 1970s
yielded much higher DDT and DDE concentrations than those from other states. In
addition, analysis of eggs from New Jersey ospreys also revealed contamination from
PCBs.
Pesticide contamination and habitat loss had reduced New Jersey’s osprey
population to a tiny fraction of its former level. Consequently, the osprey was one of the
first species to be included on the New Jersey Endangered Species List when the New
Jersey Endangered Species Conservation Act passed in 1974. With this legislation came
the establishment of the New Jersey Endangered and Nongame Species Program (ENSP),
a team of biologists dedicated to the conservation of New Jersey’s imperiled wildlife. In
1979, the ENSP began an osprey reintroduction program in which biologists transplanted
eggs from healthy nests in the Chesapeake Bay area into active, but unsuccessful, New
Jersey nests. In addition, biologists erected nesting platforms to support a growing
population and began annual surveys to monitor osprey productivity.
Slowly, the osprey population began to recover, as nesting success improved and
the number of nesting pairs increased each year. The state population grew from a low of
68 pairs in 1975 to 87 pairs in 1981. Productivity had improved from 0.42 young per
active nest in 1968-1972 to 0.97 in 1979 and to 1.18 in 1982-1984. Due to its improved
reproductive success, its acceptance of man-made nesting structures, and the decline of
persistent pesticides, the status of the osprey was changed from endangered to threatened
in New Jersey in 1985. The osprey, brought back from the brink, was the first to be
removed from the endangered species list in New Jersey. The New Jersey Natural
Heritage Program considers the osprey to be “demonstrably secure globally” yet “rare in
New Jersey” (Office of Natural Lands Management 1992).
After 1985, New Jersey’s osprey population grew beyond 200 pairs and
productivity was stable at around 1.3 to 1.5 young per active nest. The ban of DDT, the
reintroduction of healthy eggs, and the ospreys' acceptance of artificial nest sites are
largely responsible for this species’ recovery.
However, despite increases in productivity along the Atlantic Coast, osprey
production along the Delaware Bay Coast, particularly in Salem County, remained low
throughout the 1980s. Productivity in Salem County, which averaged 0.63 young per
active nest from 1974 to 1984, was well below productivity in other areas of the state,
which often exceeded one young per active nest. In addition, the number of active nests
in Salem County declined from 1984 to 1987. In 1987, ENSP biologists initiated an
investigation into the poor productivity of this population. Contaminant analysis revealed
that Delaware Bay ospreys experienced more severe eggshell thinning and higher levels
of contaminants such as DDE, DDD, PCBs, and dieldrin heptachlor epoxide than Atlantic
Coast ospreys. In addition, fish samples collected from Delaware Bay in 1990 contained
higher contaminant levels than those from the Atlantic Coast. Osprey eggs and blood
collected from Salem County nests from 1991 to 1994 were compared to samples taken
from declining populations around the Great Lakes. The analysis revealed that ospreys
nesting along Delaware Bay had higher organochlorine and PCB levels than Great Lakes
osprey populations. However, by the late 1990s, organochlorine pesticide levels had
declined in osprey eggs and fish collected along the Delaware Bay, allowing for
improved nesting productivity in this area. Productivity among Delaware Bay nests
averaged a very healthy 1.78 young per nest in 2001.
Ospreys nesting along the Atlantic Coast of New Jersey experienced a dramatic
reduction in productivity in 1997 and 1998, possibly due to a scarcity of prey. But
productivity, which averaged only 0.6 young per nest along the Atlantic Coast during
these years, returned to a normal average of 1.3 young per nest in 1999 and 2000, and
increased to nearly 1.6 in 2001. The biennial aerial osprey survey in 2001 tallied 340
pairs in the state, the majority of which were located along the Atlantic Coast.
