Ospreys: Fish Predator Secrets Revealed

Enlarge Image Image Gallery Ospreys prefer high spots for nests, which are always close to water. Gustav W. Verderber

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Few species (except humans and their introductions) can claim a worldwide distribution, but the osprey (Pandion haliaetus) is one feathered exception. Ospreys are found on every continent except Antarctica, near coastal areas, rivers and lakes: anywhere there is a steady supply of finned fare. Since ospreys feed almost exclusively on fish, they are often referred to as fish hawks or fish eagles.

North American ospreys are often found in the same areas as bald eagles (also a fish eater) and often may be confused with them. Like bald eagles, ospreys are large birds. Adult ospreys grow to nearly 2 feet in height and may have a wingspan of almost 6 feet. Their crown, forehead, neck, breast and belly are all white, while their back and wings are black. Ospreys also have a distinctive black eye stripe separating the white feathers on the crown from those on the neck and chest. By contrast, the entire body of a bald eagle is black, with the head and tail feathers a bright white.

Subtle sexual dimorphism exists between male and female ospreys (like many other birds of prey): the female osprey is slightly larger than the male, weighs about 20 percent more and has a larger wingspan. Female ospreys also have darker plumage. 

Home life

Ospreys mate for life. Once they construct a nest, the pair will return to that same nest year after year, continuously building onto it. An older nest can easily reach 4 to 5 feet in diameter and weigh several hundred pounds.

Ospreys are sexually mature at roughly 3 years of age. Males court the females with an aerial display and delivery of food (fish). The more food he brings her, the more receptive she will be to him and less likely to mate with another male. Once the pair bonds, nest construction begins. Both sexes collect nesting materials, although the female generally arranges the materials to her liking, since she is the one that spends most time incubating the eggs. From the time the eggs are laid until the young fledge, the male osprey will spend much of his time hunting for himself, his mate and, eventually, his offspring.

Female ospreys generally lay two or three eggs that are light brown with brown, red and grey speckles. Osprey eggs hatch in about a month in the order they were laid. This gives the oldest hatchling an advantage as it gets to start feeding and growing before its siblings. When there is a shortage of food, the younger birds often do not survive. This is a common occurrence among many raptors and is referred to as “brood reduction.” Osprey chicks are covered with white and brown down, which is soon replaced by a dark gray down.

Both osprey parents help care for the young, and the chicks grow rapidly. Osprey chicks reach more than 70 percent of their adult size in just a month’s time. The juveniles are ready to leave the nest after about two months, but they may return to the nest for several weeks to beg food from their parents until they learn to fish on their own.

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