San Franciso Bay's First
Ospreys – sometimes known as “sea hawks” – are magnificent large hawks that evolved to hunt and eat fish. Their vision is over three times better than human vision so they can spot fish swimming below. The dark band around their eyes reduces glare from water. Their feet are unique among North American hawks: Rough pads on the feet help grip slippery fish, while one of their talons rotates to hold fish more aerodynamically in flight.
Ospreys are one of the most widely distributed birds of prey, found on every continent except Antarctica. Ospreys are relatively easy to identify. Look for the white head, white breast, dark back, dark eye patch, and hooked beak. Flying overhead, their wings make a sharp M or W pattern rather than a gentle curve. Hovering over the water, they dive for their prey and then plunge with their head and feet forward, grabbing the fish with their feet. You might spot an Osprey carrying a fish across the water to its chicks, to a mate sitting on the nest, or over to a perch to eat it solo.
We owe an environmental debt to Ospreys: They were one of the bird species that showed us the dangers of DDT, a toxic pesticide common in the 1950s and 60s. DDT washed into our waters and accumulated in fish and then in the Ospreys that ate them. That exposure to DDT caused Ospreys’ egg shells to become thin and break before hatching. The U.S. Environmental Protection Agency helped Ospreys survive by banning DDT in 1972. Since then, their numbers have grown from just 1,500 nesting pairs nationally in the 1970s to over 10,000 pairs today.
Ospreys can live as long as 15 to 20 years. In that time, they may fly 160,000 miles in migration! According to Cornell University’s All About Birds web site, the oldest known Osprey was at least 25 years old and lived in Virginia. It was banded by scientists in 1973 and found again in 1998.
Ospreys build their nests near the water in a wide open space that allows easy access from the air, and is off the ground to deter predators like raccoons. Traditionally they nested in tall trees or on cliffs. Today, with urban development taking over much of their habitat, they may nest on tall artificial structures like utility poles, cranes, or human-made nest platforms. They often return to the same nest site year after year, building on their old nests, which can grow to 10–13 feet deep and 3–6 feet wide.
Ospreys typically raise one brood of chicks each year, laying one to four eggs. The male and female take turns sitting on the nest for 36 to 42 days until hatching. The chicks hatch one at a time, with the last sometimes hatching as many as five days after the first. Then the young spend 50 to 55 days in the nest – being fed by their parents – before they learn to fly.
Length: 21.3 to 22.8 inches
Wingspan: 59.1 to 70.9 inches
Weight: 49.4 to 70. 5 ounces
Egg Length: 2.2 to 2.7 inches
Egg Width: 1.7 to 2 inches
Nest Size: 2.5 ft. to 6 ft. wide.
For More Information:
All About Birds (Cornell Lab of Ornithology)
Guide to North American Birds (National Audubon Society)
Welcome Ospreys to San Francisco Bay (Golden Gate Audubon Society, 2014)
Atop Food Chain, Ospreys Ingest Many Poisons (National Geographic, 2014)