Get to Know an Osprey

Osprey (Pandion haliaetus)

Osprey are fish-eating hawks found on every continent except Antarctica including all throughout the Great Lakes and increasingly along the Chicago River system.

Fish make up 99% of the osprey’s diet and ospreys are very adept at catching them. Osprey swoop and dive to catch fish with reversible outer talons, closable nostrils to keep out water during dives, sharp spines and backwards-facing scales on the talons that act as barbs to help hold its catch.

Once almost driven to extinction, ospreys all but vanished over 60 years ago due to habitat loss and widespread pollution in the 1950s and ‘60s. DDT (dichloro-diphenyl-trichloroethane), an insecticide banned in 1972, was especially damaging because it impaired ospreys' ability to absorb calcium, resulting in eggshells thinned to the point that they were crushed and the young could not survive. DDT and other contaminants also killed fish, depriving the osprey of food, and fish that did survive passed toxic substances on to the osprey. Today USEPA considers DDT a known carcinogen.

Since the 1990s, the FPCC has installed about 20 constructed osprey nesting platforms, and Friends joined them starting in 2015, installing five more at the river-edge preserves including the Beaubien Woods Boat Launch in 2018. In 2020, an osprey pair successfully fledged two chicks there and in April 2021 returned to the nest site. Osprey will continue to return if they have successfully raised young. As of May 2021, it is unknown whether there are eggs in the nest.

The nesting poles Friends installed weigh approximately 5,200 lbs. and are 80' long with 10' below grade. The nests are six-sided and 40" across with an offset so that a researcher climbing pole can reach into the nest to access eggs and chicks. The installed nests mimic natural habitat towering over the tree line, providing a 360 degree view, and the poles have safeguards at ground level to prevent ground based predators from climbing up.  The principal threat to young osprey is great horned owls.

Another factor in the increasing osprey population locally is the fact that fish and populations are increasing which is helping osprey return to their historic range including in the Chicago area.

Osprey Fun Facts

  • Osprey are unusual among hawks in possessing a reversible outer toe that allows them to grasp with two toes in front and two behind. Barbed pads on the soles of the birds' feet help them grip slippery fish. When flying with prey, an osprey lines up its catch head first for less wind resistance.
  • Osprey eat fish caught in the nearby river in a spectacular hunt that features the birds diving into the water at speeds of nearly 80 miles per hour and snagging prey with their talons. An osprey may log more than 160,000 migration miles during its 15-to-20-year lifetime.
  • When flying with prey, an osprey lines up its catch head first for less wind resistance. Ospreys catch fish on about one in every four dives, and have success rates sometimes as high as 70 percent. The average time they spent hunting before making a catch was about 12 minutes.
  • Osprey eggs do not hatch all at once. They hatch over several days, in a determined sequence. Older hatchlings dominate their younger siblings, and can monopolize the food brought by the parents. If food is abundant, chicks share meals in relative harmony; in times of scarcity, younger ones may starve to death.
  • The name "osprey" literally means “bird of prey” and made its first appearance around 1460, from the Medieval Latin phrase avis prede.
  • The oldest known osprey was 25 years, two months old.

You can help us continue this important wildlife habitat work by symbolically adopting an osprey, one of the many wildlife species that Friends has been working to assist in and along the Chicago River system.