Osprey

Appearance

Osprey are a fish-eating migratory raptor found all over the globe. They have largely white feathers with a black eye strip and black wings. From below, look for their dark carpal, or wrist, patch that contrasts the white underside of each wing.  

They are large, with a 6-foot wing span, and weigh between 2.5 and 4.5 lbs. They can spot fish from two hundred feet away and dive feet-first into bodies of water moving as fast as 40 mph and reaching up to three feet deep to capture their prey. 

They are the only raptor with nose flaps that close, so they are able to submerge completely under the surface. Fish taken are generally in the range of 5 – 12 inches in length and Osprey are successful in one out of three tries to catch a fish.

Migration, Nesting & Family

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. Some Ospreys migrate as far as 4,000 miles, and most go from North America to South America for the winter months. The average life expectancy can be fifteen years so an Osprey may migrate over 62,000 miles in a lifetime.

Osprey become sexually mature at age 3 to 4. They build a platform nest of sticks, generally at a high prominent location such as the tallest tree or a human-provided nesting platform, and in Iowa they especially like to nest on communication towers. They lay 3-4 eggs each year, typically in May. After around 53 days, the young are able to fly and they disperse in late August into early September.

When young are produced, the young follow the parents to South America during migration but will then stay in the nonbreeding range for the whole year that follows. This is an evolutionary strategy that benefits the Osprey population. Most mortality occurs during migration. The young will then return to Iowa as two-year olds and will roam around Iowa until choosing a mate and nest site when they are four or five years of age.

Population & Decline

Osprey populations in North America crashed because of the organochlorine chemical DDT in the 1950s. They were exposed to DDT through their prey and the chemical build up in their bodies resulted in eggshell thinning which led to fewer and fewer young to replenish the population. Osprey populations have shown a gradual increase since DDT and similar substances were banned in the United States in 1972.

According to tribal elders of the Omaha nation, accounts of Ospreys nesting along Iowa waterways are included in their oral traditional stories.  However, no successful Osprey nesting had been documented in Iowa since colonial times until Osprey were re-introduced by the DNR in the early 2000s.

• Osprey Status in Iowa Report

Osprey Restoration

Male Osprey show strong fidelity to ancestral breeding areas, preferring to nest within 20 miles of where they were hatched. Due to this very low dispersal tendency by males, young Ospreys are prime candidates for relocation. Projects are designed to spread the young of the population to areas where osprey habitat exists but the birds do not currently nest. This strategy improves nestling survival.

Minnesota and Wisconsin DNR officials suggested that Ospreys do not readily pioneer into new breeding ranges. Instead, they experience suppressed reproduction as density of nesting pairs increases.  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.

Iowa Program & Growth

The Osprey restoration program in Iowa began in 1997 and involved translocating young birds from Minnesota and Wisconsin to strategic locations across Iowa. Juvenile birds were taken from nests just before they could fly and were brought to habitat in Iowa and placed in small groups in hack towers, where they were fed and kept safe for a time so they would imprint on the area and return there in the future to nest. 

The strategy worked, and the first successful nesting since colonial times occurred at Spirit Lake and Iowa City in 2003. Many partners and hundreds of volunteers worked for nearly 20 years to restore Osprey to Iowa. 

The last year that birds were released was 2016 and currently the objective is to monitor nesting activity. There are now three main areas in the state where Osprey have become well established: the Iowa City to Waterloo corridor, Des Moines and vicinity, and Spirit Lake and vicinity. There are also three nesting pairs on the western border of Iowa south of Sioux City.