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Osprey recovery in SouthEastern SD

Background 1

The Osprey is a fish-eating bird of prey that is listed as a state threatened species in South Dakota. A small population nests in the Black Hills, but Ospreys are very rare elsewhere in the state. Although historically documented in southeastern South Dakota, the first known successful nest in the state in recent times wasn't documented until 1991 at Pactola Reservoir in the Black Hills. Ospreys range throughout much of the world and are common in many parts of North America. This species responded well to the ban on DDT, which had caused eggshell thinning and led to population declines.

Ospreys tend to be poor nesting pioneers, meaning they don't typically nest in new areas far from an existing population. In contrast, Bald Eagles may nest in a completely new area where they find favorable nesting and foraging sites, helping them to expand more quickly than Ospreys.

To help recover the Osprey in South Dakota, South Dakota Game, Fish and Parks (GFP) spearheaded a reintroduction effort. New funding sources allowed the agency to focus on fulfilling its legal responsibility to recover species that are threatened or endangered in the state.

About the bird

Ospreys live in both freshwater and saltwater areas, including coastlines, inland lakes, and rivers. They prey on fish that they capture in shallow water or near the surface. Ospreys select nest sites that are safe from predators and in areas open enough to allow this large raptor (wingspan is more than 60") to maneuver.

Ospreys traditionally used large trees on or near water bodies as nest sites. As these sites declined and potential predators increased, many birds adapted to artificial sites, such as powerlines, channel markers, and nesting platforms erected specifically for them. Ospreys favor nest sites that are higher than surrounding vegetation and relatively free of threats from predators. Platforms are often fitted with predator guards to discourage mammalian predators from reaching the nest.

A male selects a nesting area, usually near the area from which he fledged. Birds are 2-3 years old, or older, when they begin nesting. The nest tree or artificial structure must be strong enough to support a large stick nest. After attracting a mate, the male brings sticks to the nest for the female to arrange. The pair may build a new nest or spruce up a used nest. The male feeds his mate at the nest from the time of courtship through the time the young fledge. The female usually lays 3 eggs, which she incubates for 5-7 weeks. Eggs hatch in the order they were laid, 4-5 days apart, giving the oldest chicks a survival advantage if times are tough. The female also broods the chicks, keeping them warm or shaded as needed, for the next several weeks.

Young birds try their first flight at 7-8 weeks of age. Even after learning to fly, parents continue to feed them for several weeks as they learn to fish for themselves. The adult female may begin her fall migration sooner than the male, which may stay behind to continue caring for the young birds.

Ospreys eat fish almost exclusively, with more than 80 fish species documented. They hunt by flapping or gliding 50-100 feet above the water's surface looking downward in search of prey and dive feet-first to snatch a fish. Strong wings help the bird gain altitude as it adjusts the fish to face head forward on the way to a feeding perch. Ospreys are well adapted for capturing fish, with relatively long legs, a reversible outer toe to better grasp prey, raspy structures called spicules on the bottom of the foot to help grasp slippery fish, long curved claws, and valves that keep water out of the nostrils.

Osprey presence indicates that a wetland ecosystem is healthy and able to support this unique bird of prey. They're also beautiful and interesting birds to see.5

What's involved with Osprey reintroduction?

Reintroduction may be needed to restore or enhance wildlife or plant populations. With birds of prey, reintroduction is often called hacking, a technique that benefited greatly from the expertise of falconers.

Osprey reintroduction makes use of some kind of elevated platform (hack tower) situated in areas that seem suitable for Osprey nesting. Prior to reaching fledging age, chicks are taken from a nest in an area with a stable or increasing Osprey population. At least one chick is always left in the nest. Chicks are placed at the hack site, fed, and monitored for health or safety problems. They are banded with metal U.S. Geological Survey bands and possibly another identifying marker or band. Chicks may be vaccinated against preventable diseases. Chicks are fed fish while in the hacking tower until they start showing signs that they are ready to test their wings and take flight. Even after they take some test flights, food is provided until they can reliably catch their own fish.

Three facets of Osprey biology make reintroduction feasible. Ospreys can learn to fish without their parents. They can migrate on their own without parents. And once mature, males, in particular, tend to select a nesting area near the area from which they fledged. Unfortunately, only a small percentage survives to reach even one year of age, making it critical that enough birds are reintroduced to result in enough survivors that live long enough to nest.

The numbers

A small number of Ospreys were brought from Minnesota in 2003. Beginning in 2004, Idaho became the source of young birds released in South Dakota.

Year # Reintroduced Chicks Source Markers
2003 9 Minnesota Temporary color tape and paint; USGS metal band
2004 20 Idaho Temporary color tape and paint; USGS metal band
2005 20 Idaho Blue metal band on right leg; USGS metal band on left leg
2006 12 Idaho Blue metal band on left leg; USGS metal band on right leg
2007 no releases
2008 20 Idaho Green metal band on left leg; USGS metal band on right leg
2009 20 Idaho Green metal band on right leg; USGS metal band on left leg
2010 19 Idaho

Orange metal band on left leg; USGS metal band on right leg

Tracking the birds

All reintroduced birds were banded with a uniquely-numbered metal identification band. In addition, birds released since 2005 had a color leg band on one leg, with the "silver" metal band on the other.

A tool used during some years of the project is a small radio transmitter to track them near the hack site. These help in finding and retrieving birds that might get in trouble during some of their first flights. The transmitter is attached to a tail feather. When the tail feathers are molted, the transmitter drops off as well.

A more ambitious tracking system makes use of satellite technology. Platform telemetry transmitters, PTTs, are being used on a wide variety of wildlife species to track long-distance movements. We added this feature to our project to learn more about migration movements and wintering habits of reintroduced birds. Ospreys are 2-3 years old before their first nesting attempt. Young birds remain in the wintering area until they are approximately 22 months old before returning to a potential nesting area.

The released Ospreys initiate migration from the hack site during September, with departure ranging from early to late September. The young Ospreys tend to follow the Missouri and Mississippi River drainages during migration. Migration to the Gulf of Mexico is typically rapid with the birds often reaching the coast within a week. Early departing youngsters have reached the Gulf before others have left the hack site.

The birds appear to go east or west once they reach the Gulf, although some may fly directly across the Gulf to the Yucatan in Mexico and continue on to Central America. Birds turning east have the option of flying down the coast through Florida and on to Cuba and the chain of islands to South America. Those that turn west or cross the Gulf could end up in Mexico and Central America. Satellite telemetry has revealed considerable variation in where the young Ospreys released in South Dakota winter. Our birds have ended up wintering in Costa Rica, Cuba, and several locations along the Gulf of Mexico. One bird wintered along the Gulf in Mexico, south of the Texas border. Another bird wintered in the Louisiana delta. Yet another followed the Gulf to the end of the Florida Keys, but returned to the Everglades area, where it wintered.

Read the final report for this project
The story in pictures

Download this form to report a banded Osprey
More about funding for projects like this



For more information

Contact Eileen Dowd Stukel, SDGFP, or Silka Kempema, SDGFP,