Fossils show that ospreys have been on earth for 13 million years! Ancient ospreys were smaller than those of today, but their range was similar. They are found on every continent but Antarctica. Four subspecies are currently recognized, two of which occur in the Americas; P.h. carolinensus in North America (including Iowa) and P.h. ridgwayi in the Caribbean.
According to tribal elders of the Omaha nation, accounts of ospreys nesting along Iowa waterways are included in their oral traditional stories. These first nation people have lived throughout northwestern Iowa for thousands of years. No successful osprey nesting had been documented in Iowa since European settlement. A report in 1892 indicated a nesting might have occurred along the Cedar River, but it was not recognized as positive proof of nesting.
In recent history, the continental osprey population plummeted in the 1950s due to the use of DDT. The pesticide caused the ospreys' eggshells to thin and break. Numbers were reduced throughout their range, but were hardest hit in Great Lakes and Atlantic coast areas. The use of DDT was banned in the U.S. in 1972; populations have shown a gradual increase. In 1981, 8,000 osprey pairs were in the lower 48 states, and by 1994 a national survey tallied 14,109 pairs. In 2000, an osprey nesting attempt occurred in northwestern Iowa. No eggs were laid that year, but they successfully nested in Spirit Lake three years later. Also, 2003 hailed the first successful nesting at Macbride Raptor Project in over a century.
IDENTIFICATION
Opreys, Pandion haliaetus, commonly called fish hawks or fish eagles, are neither a hawk nor eagle. They are presently classified near the kite family. Ospreys are large, narrow-winged raptors, weighing between 2.5 and 4.5 pounds. An osprey's six-foot wingspan is often mistaken for an eagle's, but an osprey's wing is narrower and curves backward at the wrist, like the wing of a gull. An eagle's wing is flat. Ospreys also have smooth foreheads, without the brow ridge other raptors display.
An osprey's field mark is a dark carpal (wrist) patch on the underside of each wing. The belly is light and the feathers on top are dark. The light stomach camouflages them from their prey (fish) below, while the dark color hides them from owls that might attack an adult from above. Predators of young include raccoons, gulls and crows.
To camouflage its head, an osprey wears dark spots on top, and a dark "maylar stripe" through its eye area. This may reduce sun glare like the black grease used under the eyes of athletes.
EXPERT ANGLERS
Ospreys are well-equipped to capture their favorite prey: fish. An osprey is a strong flier, flying about 25 mph. Their vision is 5 times better than ours; they can easily spot a fish underwater from a height of 100 feet.
While diving for its prey an osprey enters the water talons first at about 40 mph. Their eyes are protected from wind and water by nictitating membranes, which are like thin, clear eyelids. They are the only raptors with closing nose flaps, so they can completely submerge themselves while fishing. They can catch a fish up to three feet underwater. Ospreys are successful about one in three attempts.
Their pale blue toes are tipped with needle-sharp talons that act as fishhooks. They are able to swivel the outside toe, so they can clamp two toes by two toes. The toes also have roughened "spicules" for grip to prevent a slippery escape by fish.
Ospreys have specialized joints at the wing wrists or "carpals" that help them lift vertically out of the water. Research indicates a family with two young needs four to five fish per day, with each fish five to twelve inches long.
REINTRODUCTION
With the construction of lakes and reservoirs, Iowa has potential osprey habitat that did not exist historically. There are numerous osprey summer sightings in Iowa. Yet, despite an overall population growth, ospreys have demonstrated little breeding range expansion. Ospreys (especially males) show strong fidelity to ancestral breeding areas.
To address this issue, young from Wisconsin and Minnesota are being relocated to areas with suitable habitat in southern Minnesota, Iowa, Kansas, Missouri, and Ohio. Projects are designed to place young in areas where ospreys do not currently nest. This will improve nestling survival in the osprey rich areas, and complete continental population distribution.
The Iowa DNR has assisted conservation partners with technical assistance, encouragement, and fish to successfully release ospreys in Iowa. To date, ospreys have been placed at: Macbride Raptor Project at Coralville Reservoir, Cedar Falls, Saylorville Reservoir, Don Williams Lake, Clear Lake, Cedar Rapids, Red Rock Reservoir, White Rock Conservancy, Spirit Lake, and Dubuque. Project fundraising is provided by the conservation organizations doing the releases. Birds cost $525 per bird. A four year minimum commitment of releasing ospreys is required at each site.
Young ospreys are placed at hack towers before being released. The birds will return to area of release sites to nest.
Osprey chicks' availability for potential relocation is evaluated in early July in Minnesota and Wisconsin. Nests with more than one 42-day-old chick are located. At this stage, chicks are able to tear fish and feed themselves. The chicks are examined for relocation suitability. Approved birds are driven to release sites and placed in carefully constructed 8'x8'x8' predator-proof release towers or "hack sites." Volunteers feed the birds in a way that the birds do not imprint on humans. By viewing the birds through one-way mirrored glass or video cameras, observations of temperament and condition of each bird are logged daily.
At 53 days of age, the birds are full-grown and feathers have developed. They are ready for release. The bars of the hack tower are opened and the young attempt their first flight. They continue to be monitored and fed by volunteers until they begin fishing on their own.
Young birds begin range expansion in late August and migrate up to 4,000 miles in September. Immature ospreys spend up to 18 months at their over-wintering sites in Central and South America during their first two years. After that first migration cycle, they will spend just the winter months in the over-wintering area. Average life expectancy is 15 years, so an osprey travels over 62,000 miles in its lifetime. That's 2½ times around the Earth!
Dr. Larry Rymon, noted Pennsylvania ornithologist who initiated osprey relocations on the eastern seaboard, observes that 45% of the continental osprey population nest upon manmade structures. Nesting platforms are placed near release sites to ensure adults have a predator proof nest site. Ospreys reach sexual maturity at three to four years of age.
Thanks to the assistance of volunteers and conservation partners, ospreys have returned to Iowa. They are at the top of the aquatic food chain, so they are a good indicator of a healthy environment. By preserving habitat and clean water, we can hope for continued population growth in the future.
