When people see the large nest inside the Dickinson County Nature Center and the big raptors on the outdoor nest during the summer, they often think they are bald eagles.
Many people don’t realize that after being extirpated in Iowa, osprey populations have started to make a comeback in the 2000s. Each summer, osprey come to Kenue Park to nest and raise their chicks before heading south for the winter.
Even after learning about osprey, people have trouble telling the difference between them and bald eagles. Other than their coloring being different, there are seven other key differences between osprey (Pandion haliaetus) and bald eagles (Haliaeetus leucocephalus).
1. Size: Osprey have an average 59- to 70-inch wingspan and weigh 3-4 pounds. They have long, narrow wings with a marked kink that makes them look like an M-shape from below.
The bald eagle is one of the largest birds in North America, with an average 80-inch wingspan and weighing 6.5 to almost 14 pounds.
2. Diet: Osprey eat a diet of about 99 percent fish, usually 4-12 inches long. The type of fish varies depending on where in the world the osprey lives, but the osprey in Okoboji seem to enjoy panfish and the occasional koi from a local water feature.
Bald eagles love fish as well, and sometimes rather than doing their own hunting they will harass osprey, making them drop their fish or even steal their fish right out of their talons.
Bald eagles also eat birds, reptiles, amphibians, rabbits and muskrat, both live or as carrion. They sometimes gorge on food and digest it over several days, and they can also survive fasting for many days or even weeks.
Beak: An osprey’s beak is black, short and has a sharp hook that helps it tear into fish to eat.
Bald eagles have a yellow beak which is also hooked for tearing into flesh.
Talons: Osprey have extremely long, curved and sharp talons that help them grip the fish they catch. Their white feet have spiny scales, and they also have four equal toes. The outer toe is reversible, allowing the osprey to hold its fish aerodynamically when it flies.
Eagles have giant talons on their first and second toes that give them a secure grip on struggling game. They also have yellow feet.
Special abilities: Osprey can dive about three feet into the water to catch fish, and they can dive both head and feet first. They also have the ability to take off straight from the water instead of having to swim to shore.
Sometimes bald eagles hunt cooperatively, with one individual flushing prey toward another.
Nest: Osprey nests are built of sticks and lined with bark, sod, grasses, corn stalks and other softer materials. Most nesting platforms are about 5 feet wide and a foot deep. However, it has been seen that osprey who nest in the same place year after year have ended up with nests 10-13 feet deep and 3-6 feet in diameter.
Osprey also like to nest in open areas, usually built on snags, treetops, cliffs or human-built platforms, cell phone towers or light towers.
Bald eagles nest in trees, usually conifers, and create huge nests — 5-6 feet wide and 2-4 feet deep — out of sticks lined with grass, moss or corn stalks. Nests can take up to three months to build. Bald eagles typically build near the trunk of a tree, high but not at the crown like osprey. Some eagles also nest on the ground when necessary, using kelp or driftwood for construction near coastal shorelines.
Chicks: Osprey typically lay 1-4 eggs once per season. Eggs are cream-colored and spotted with reddish brown dots. The incubation period is 36-42 days, and the chicks usually fledge within 55 days.
Bald eagles lay 1-3 eggs once per season. Eggs are dull white, usually without markings. The incubation period is 34-36 days, and chicks stay in the nest 56-98 days.