Ospreys are high-flying, fish-catching experts
- 11 minutes ago
- 4 min read
What’s the first bird that comes to mind when you think of a large bird soaring over a lake or river? Maybe a bald eagle? How about a hawk? Another likely suspect is an osprey, a raptor that is most at home along the world's shorelines.
Ospreys are widespread, and they live on every continent except Antarctica. Some populations of ospreys migrate, and their journeys can be long. The ospreys that spend the breeding season in North America travel to South America for winter. Over the course of their 15- to 20-year lifespan, the birds may fly as far as 160,000 miles during their migrations.
These birds are dark brown from above with white underparts. They are sometimes called seahawks because they like to be near water and they like to eat fish (more on that later). Look for them soaring above area waterways, chirping and calling in flight.
They are sometimes mistaken for bald eagles
Ospreys are often mistaken for bald eagles. This is especially true of juvenile eagles that do not yet have their trademark appearance: a white head and bold yellow beak and legs. There are some key differences in appearance, however. To start, ospreys are white underneath, whereas eagles are dark colored.
Words to know
Barb: A sharp projection.
Contaminate: To soil, stain, corrupt or infect.
Hazard: A source of danger.
Pesticide: An agent used to destroy pests.
Ospreys are also smaller than bald eagles. Ospreys have a wingspan of about 5 feet to 5 1/2 feet, while a bald eagle's wingspan can be between 6 feet and 7 1/2 feet.
Ospreys hold their wings differently than eagles while in flight. An eagle's wings will be stretched out and appear straight in flight, but ospreys fly with a bend in their wrist. This creates an M shape. This positioning of their wings helps them quickly dive down.
If you're close enough for a good look, their talons can help you tell the difference too. Ospreys' talons are sharply curved to help them catch prey, and their four talons are arranged differently than eagles'. Ospreys have two talons facing front and two facing back. Eagles have three facing front and one facing back.
They are big fish eaters
Ospreys have a one-track mind when it comes to food. They eat fish, fish and more fish. In fact, their diet is about 99% fish. They are quite successful at catching fish too, They come up with a fish on about 75% of their dives.
While they are picky about preferring to eat fish, they aren't that picky about the kind of fish. In North America, ospreys are known to eat about 80 different kinds of fish. Their typical catch is between 6 inches and 13 inches long and weighs between 1/3 pound and 2/3 pound.
In those rare times when they aren't eating fish, they will eat snakes, salamanders, birds, small mammals and fish carcasses.
They are highly skilled fish hunters
A bird that eats a lot of fish has to have the necessary skills to catch fish, and ospreys do. Their toes are key to their hunting ability. The four toes have barbs that help them tightly grasp onto fish, and their outer toes can switch from facing backward to forward for better grip. Once they catch a fish, they will position it so it is facing forward. This allows them to be more aerodynamic in flight.
Ospreys are good at finding fish too. As they soar over water, their good eyesight helps them see fish on the move below. On a dive, they can go up to 3 feet deep to snatch a fish out of the water.
As they enter the water, they close their nostrils to keep water out and close a third eyelid, called a nictitating membrane. This eyelid is translucent, working like goggles as they move underwater.
They nest in wide open spaces
Ospreys like to build their nests in open areas that provide plenty of space for them to approach the nest. Common nesting spots include tree snags and treetops, cliffs and human-built structures and platforms. Males usually pick a nesting site and collect most of the nesting material. The females build the nest.
Manmade structures like utility poles are prime nesting spots for ospreys, but these sites can be problematic. When these poles include power lines, the nests are a fire hazard and can result in power outages. To help protect the birds and prevent outages, electric companies monitor poles and build nesting platforms in hopes that the birds will nest in a safer location.
Like eagles, ospreys add to their nests from year to year, so they get larger over time. At their largest, they can be 10 feet to 13 feet deep and 3 feet to 6 feet wide!
Other birds often use osprey nests too, but at different times of the year. Eagles, great horned owls and even Canada geese may move into an osprey nest in late winter or early spring, then the osprey will take it over during their nesting season later in the year. Some smaller birds like grackles, starlings and house sparrows may even create their own nest in an out-of-the-way spot in an active osprey nest.
Their population remains at risk
The bald eagle population was hurt by the use of the pesticide DDT, but they weren’t the only bird affected. Ospreys also suffered large population declines when the pesticide was widely used to prevent crop damage in the 1950s, '60s and '70s.
The pesticide harmed ospreys, eagles, peregrine falcons and more as it entered the food chain. As the birds ate prey that had become contaminated by DDT, it began to build up in their bodies. Eventually, it hurt their ability to nest successfully because DDT caused their eggs to have thin, weak shells that couldn’t be incubated.
In some areas, ospreys nearly disappeared during the time when DDT was in use. After DDT was banned in 1972, the osprey population slowly began to recover, but they are still listed as endangered or threatened in some states.
In Illinois, ospreys are a threatened species. Their population in the state dropped because of the use of DDT, and they are also affected by poor water quality and human disturbance near waterways. Farther from Illinois, population declines of a fish species called the Atlantic menhaden are affecting ospreys because the fish are one of their main food sources in coastal areas.
