Osprey Status in Iowa Report
From a hundred feet in the air, the hovering angler folded its wings, silently slipping like lightening from the sky. Suddenly a four-foot portion of the lake thundered into prisomed plumes of diamondized droplets. Completely immersed, the feathered predator floated to the surface, struggling to emerge with a fish in its talons. A third, then fourth, labored wing-beat increased the height from the lake's surface. In a remarkable finale, the fishing raptor shook off excess water, gliding ever so closely to the pool's shimmering surface again. While positioning the fish straight ahead, torpedo-style in its talons, the Osprey began stroking upward, its wriggling prey secured. With most efficient style, this lean, flying machine had spied its quarry and with amazing desire, just took it. You thought your tackle box contained everything you needed to catch a fish, but this was truly an incredible display of "fishing perfection!"
Ospreys are well equipped for obtaining a meal. They can see five times more clearly than people, so they easily spot their prey. As bow-hunters realize when spear-fishing, underwater targets are not where they appear, due to water's refraction of sunlight rays. In flight Ospreys close the nictitating membrane, a thin layer of clear tissue like an inner eyelid, over their eyes to keep the eye moist. During a dive the membrane protects the eye when Ospreys hit the water. They are the only raptor with nose flaps that close, so they can go completely under the surface. Also, Ospreys' pale-bluish toes are tipped with nature's finest fishhooks: talons, sharp as needles. Toes have roughened protuberances or "spicules" to hold slippery fish, and outside toes are capable of swiveling backward to join the rear toe or "hallux" (two toes clamping with two toes versus the standard three toes and hallux). This allows grasping fish torpedo style, which reduces wind resistance while in flight. Ospreys also have the ability to lift from water, vertically, using specialized joints at wing wrists or "carpals". These anatomical tools distinguish ospreys as unique in the raptor kingdom. No other birds of prey combine all of these capabilities into one species.
The Osprey’s scientific name (Pandion haliaetus) comes from the mythical king of Athens, Pandion, whose daughters were turned into birds, and by the Greek words halos, referring to the sea, and aetos, or eagle. Ospreys, commonly called fish hawks or fish eagles, are neither a true hawk nor eagle. The species is of ancient lineage and is presently classified near the, hawk-like, kite family. It has a worldwide range and some ornithologists call the Osprey “The Natural Citizen of the World.” Four subspecies are presently recognized, two of which occur in North America; P.h. carolinensus in temperate North America (including Iowa) and P.h. ridgwayi in the Caribbean. The common name Osprey is from ossifragus, a Latin word meaning “bone breaker,” referring to the strong grip of its talons.
Osprey fossils, the bones and other remains of ancient animal life, show that Ospreys have been on earth for 13 million years. An Osprey from the past was smaller, but had a range similar to today’s Ospreys.
People have long admired the Osprey’s fishing skills and strength, incorporating Ospreys into their cultures. Ancient Greeks thought Ospreys could predict lightning. Asian emperors had Osprey pictures woven into palace tapestries. In South America, native people used Osprey feathers and bones in ceremonies to guarantee fishing success. In Canada, a Northwest Coast First Nation legend tells of a marriage between an Osprey and a whale that created the Orca whale. Osprey calls consist of a series of shrill, staccato whistles, gradually rising in pitch, tewp, tewp, teelee, teelee, tewp.
Ospreys are large narrow-winged, fishing raptors, weighing between 2.5 and 4.5 pounds. An Osprey’s six-foot wingspan is so large it is sometimes mistaken for an eagle, but an Osprey’s wing is narrower and curves backward at its wrist, like the wing of a gull. Unlike an eagle’s wing-plane, which is straight, the Osprey needs to rise out of water with a large fish and has a special joint allowing this maneuver. In contrast to the eagle an Osprey’s forehead is smooth. Ospreys don’t fly through trees or tall grass to catch their prey, so they don’t need the bony ridge above their eyes that other raptors have for protection.
Ospreys’ field marks are dark carpal, or wrist, patches on the underside of each wing. The dark spots come in handy when the bird is hunting. From a distance the dark spots look like two small gulls dipping and soaring rather than one large bird about to strike.
An Osprey wears light feathers on the underside of its body and dark feathers on top. The white feathers on its chest look like the light colors of the sky to its prey - any fish swimming below. The dark colors camouflage, or hide, the Osprey from its predators, large owls that attack from above, particularly when they’re on the nest. The brown and white barred, or evenly striped, feathers on the underside of an Osprey’s wings and tail help hide its shape in flight. To camouflage its head, an Osprey wears dark spots on top, and a dark stripe through its eye area, like wraparound sunglasses. This eye stripe, called a malar (MAY-ler) stripe, may reduce sun glare, like the black grease used under the eyes of athletes. An adult Osprey’s eyes are yellow. Its brown hooked beak, its gray legs and feet, and its black talons don’t reflect sunlight, so there’s no glare to give away its position. An Osprey’s talons are made of keratin, the same substance as our fingernails. If part of a talon breaks off it will slowly grow back.
Unlike many raptors, male and female Ospreys are very similar. A female Osprey is slightly larger, and usually wears a darker necklace, or band of speckles, across her white chest that helps her hide while nesting.
While hunting, Ospreys can spot a fish two hundred feet away. An Osprey is a strong flyer, flying with a slightly circular motion at about 25 mph. When diving for its prey, an Osprey enters the water at about 40mph and can catch a fish up to three feet underwater. Studies report a family with two young needs four to five fish per day. Fish like bullheads and carp forage about the bottom and lakesides. With their interests directed downward, they become vulnerable for Ospreys from above. Fish taken are generally in the range of 5 – 12 inches in length. A fish is usually successfully snagged in one out of three tries. Ospreys are known to carry fish upwards of five miles to remote nests.
Nests may be built at varying heights upon any structure, natural or man-made, that provides a platform. Ospreys occasionally nest on or near the ground or upon buoys over water. Nests are usually one foot deep, four to five feet wide, made of sticks and lined with grass. Apparently, visibility is important in nest-site selection; osprey nests provide a commanding view of surroundings. They are usually located on prominent landforms, peninsulas or islands with few, or preferably no, tree branches higher than the nest.
Osprey clutches consist of three or four eggs that are creamy white and heavily spotted brown. Eggs are laid at two-to-three-day intervals in late May. After the first egg is laid, incubation proceeds for 38 days and is dominated by the female. Both parents have “brood patches” to aid incubating eggs. Brood patches are featherless areas on raptors’ abdomens where eggs receive warmth for necessary incubation. The male provides food for the female and brood after hatching. The female remains in constant attendance the first 30 days, providing protection from predators and the elements. Predators include raccoons, gulls, crows and owls. When predators are near, camouflaged nestlings lie outstretched and motionless as a natural defense.
At 42 days, young can tear apart fish provided by parents and around 53 days, first flight occurs. Young of the year quickly acquire fishing skills and gradually expand their range until dispersal in late August. Immature Ospreys spend up to 20 months at their over-wintering areas in Central and South America. Some Ospreys migrate 4,000 miles from the Northern Hemisphere to the Southern Hemisphere. Adults attain sexual maturity when three to four years of age. Researchers estimate first-year bird mortality at 51 - 57% with adult mortality at 16 - 20% annually. Average life expectancy can be fifteen years. So an Osprey may migrate over 62,000 miles in a lifetime. That is about as far as 2 ½ times around the world!
Ospreys were heavily affected by the biocide crash of the 1950s, which was caused by organochlorines like DDT. Organochlorines caused eggshell thinning which led to fewer and fewer young to replenish the population. Numbers were severely reduced throughout their range, but were hardest hit in Great Lakes and Atlantic coast areas. Osprey populations have shown a gradual increase since DDT and similar substances were banned in the United States in 1972. By 1981, 8,000 osprey pairs existed in the continental 48 states, and by 1994 a national survey tallied 14,109 pairs.
According to tribal elders of the Omaha nation, accounts of Ospreys nesting along Iowa waterways are included in their oral traditional stories. These indigenous people have lived throughout northwestern Iowa for thousands of years. However, 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 the addled Osprey egg was not recognized by the Iowa Ornithologists' Union of that time as positive proof of nesting.
Male Ospreys show strong fidelity to ancestral breeding areas, preferring to nest colonially where adults originated. Female ospreys may disperse hundreds of miles from their origin, however males will generally return within about 20 miles of origin. Due to this very low dispersal tendency by males, young Ospreys are prime candidates for relocation. Projects are designed to spread young of the population, geographically, to areas where ospreys do not nest. This strategy will ultimately improve nestling survival and complete continental population distribution.
With construction of lakes and reservoirs by Department of Natural Resources, County conservation boards, private industry, and U.S. Army Corps of Engineers, potential Osprey habitat exists today that was previously not available. Historically, there were numerous Osprey summer sightings in Iowa, but apparently these young, non-breeding Ospreys returned to areas where they were reared for mating and nesting. During the last 20 years, the number of migrants through Iowa has increased as breeding populations to the north have grown. Despite this population growth, Ospreys have demonstrated little breeding range expansion. Minnesota and Wisconsin DNR officials suggested that Ospreys, in our lifetime, do not readily pioneer new breeding ranges. Instead, they experience suppressed reproduction as density of nesting pairs increase. Scientists have determined that a raptor population is in jeopardy of crashing, when the average fledging success of young per nest approaches 0.8 chicks/nest. To address this issue, young Ospreys from Wisconsin and Minnesota began being relocated to areas with suitable habitat in southern Minnesota, Iowa, Kansas, Missouri and Ohio.
Dr. Larry Rymon, noted Pennsylvania ornithologist who initiated Osprey relocations along the eastern seaboard, observes that 45% of the continental Osprey population nest upon manmade structures. Therefore nesting platforms have been placed near all release sites in anticipation of returning Osprey usage. Mr. Bill Fraundorf from ALLETE Energy of Minnesota and Mr. Mark Martell of Minnesota Audubon and Ms. Pat Manthey and Mr. Lowell Tesky of Wisconsin DNR, assisted by The Raptor Center of St. Paul, have provided Ospreys for Iowa releases.
Young Ospreys' availability for potential relocation is evaluated in early July. Approximately 42-day-old Ospreys from Minnesota and Wisconsin are located in nests where more than one young exists. Within hours, The Raptor Center staff members in St. Paul examine the Ospreys for relocation suitability. When approved, birds are driven to release sites and placed in carefully constructed release towers or "hack sites." Hack sites are predator proof 8' x 8' x 8' structures with bars on the front that provide visibility of surroundings. The bars are opened when ospreys are released. Trained volunteers feed the young daily in such a manner that the birds do not imprint on people. By quietly viewing ospreys through one-way mirrored glass or from monitors, detailed observations of each bird's temperament and condition are logged daily.
When Ospreys are approximately 53 days of age, they are full-grown with rapidly developing feathers and are ready to be released. The birds are actually heavier than they will be as adults, due to built-in fat reserves until self-sufficiency is achieved. Great care is exercised to ensure that young are not startled into their first flight - at this stage of the young Ospreys’ development, the less disturbance or drama, the better. Once Ospreys have flown, volunteer spotters monitor the birds' movements the best they can, either from shore or in boats for the first few days. It has been shown that young Ospreys can fly better, the first time out, than they can land upon a perch. As with other raptors, returning to a perch near the hack box can become a fatal learning experience for young flyers. After the Ospreys fledge, volunteers supplement the birds’ diets with fish at the hack site, until birds begin fishing on their own and self-sufficiency is achieved.
These combined activities by volunteers provide tremendous opportunities for outdoor-loving families to connect with a most dynamic raptor. These duties have become great opportunities to establish touchstones with our environment and influence our need to be good stewards of our land and waters. Efforts by these volunteers are moving this project forward. There is empowerment volunteers can build upon in other wildlife and habitat enhancement projects.
The Iowa Department of Natural Resources has assisted conservation partners with technical assistance and providing proper permits to bring Ospreys to Iowa. Encouragement and fish to successfully release Ospreys in Iowa have also been included. Ms. Jodeane Cancilla of the Macbride Raptor Project located near Coralville Reservoir spearheaded this work. Beginning in 1997, four or five young ospreys were released annually at their facility from 1997 until 2002. Since that time, Hartman Reserve Nature Center staff in Cedar Falls released Ospreys at their facility from 1998 - 2005. In succession County Conservation Boards and volunteer groups have placed Ospreys at Jester Park in Polk Co. from 2000 - 2004, Don Williams Lake in Boone Co. from 2003 - 2006, Clear Lake in Cerro Gordo Co. from 2004 - 2008, Wickiup Hill in Linn Co. from 2004 - 2007, Red Rock Reservoir in Marion Co. from 2005 - 2008, White Rock Conservancy by S.O.A.R. from 2006, Spirit Lake in Dickinson Co. from 2007, Mud Lake in Dubuque Co. from 2008, and Annett Nature Center in Warren Co. from 2009. The U.S. Army Corps of Engineers has provided distinguished service for releases at Coralville and Saylorville Reservoir respectively. Assisted by literally hundreds of volunteers, these conservation organizations have devoted their efforts to bring Ospreys to Iowa as a nesting species. Project fundraising is the responsibility of the conservation organizations doing the releases. Ospreys cost about $525 per bird. In Iowa, Ospreys have two bands, a silver U.S. Fish and Wildlife Service band and a numbered, lavender band on separate legs. Wild produced Ospreys from Iowa receive a green USFWS band on their left leg. In 2010 a green banded, F2 generation Osprey fledged three young at Polk City Refuge in Polk County. Also, in 2010 natural reproduction around the state was 21 Ospreys at fourteen successful sites which equaled the number of birds relocated to Iowa at 21 Ospreys.
We can think of Ospreys as "sentinels of clean water." Ospreys rely upon fish for food and fish need clean water. Ospreys also need to be able to see fish in our water, so turbidity and siltation become critical issues. Fish need clean water, ospreys need clean water; we all need clean water. But clean water doesn't just happen. It requires standards of decency that can benefit everyone and everything. Joining Bald Eagles, Trumpeter Swans, Sand-hill Cranes, wetland mammals and our myriad of waterfowl, Ospreys can be appreciated in all water quality endeavors and provide a rewarding environmental connection for all Iowans. Moreover, as a highly desirable watchable wildlife species, it's great to see "fishing perfection" in Iowa.
For more information contact: the Wildlife Diversity Program, 1436 255th St., Boone, IA 50036.
As the osprey flew from sight, we felt privileged to
part the placid pool with our paddles and proceeded onward.
Story by Pat Schlarbaum and photos courtesy of Bill Schuerman
Brochure: Ospreys in Iowa
Map: Ospreys in Iowa 2010 (nests and release sites)