A raptor is a raptor is a raptor, right?
Not so fast! While osprey do share a lot of the same behaviors we expect from other birds of prey, there are plenty of traits that make osprey unique and intriguing in their own ways.
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Hi, my name is Pandion haliaetus
What makes the osprey particularly unique among birds of prey is that it is the sole member of the family, Pandionidae. There are four recognized subspecies of osprey, differentiated by geographic region, with very little differences among them.
The genus name, Pandion, comes from the mythical Greek king of the same name, who transformed into an eagle. Haliaetus is derived from the Greek word for sea eagle—even though the osprey is not considered a sea eagle.
The common name, osprey is derived from the Anglo-French word ospriet and the Medieval Latin word avis prede—“bird of prey,” which comes from the Latin avis praedae. There is some noted association to the Latin word ossifraga or “bone breaker.”
Regardless, the osprey has been around for a very long time. Bones belonging to an earlier species of Pandion were found in California and Florida that have been dated back to approximately 13 million years ago.
One of the earlier documentations of modern osprey exists in Carolus Linneaus’ 18th century publication Systema Naturae.
The original snowbirds
Most osprey are known to be migratory, breeding in the north and migrating south for winter. Osprey migrate individually, not in groups.
There are non-migratory populations who breed and winter in the same place because they have a steady food supply, like those in the southern states. Non-migratory populations breed between December and March, while migratory populations (like what we have in Montana) often don’t return to the nest to start breeding until April or May.
Another quality that makes them unique from other raptors is that young migrating osprey from the northern climates of North America will follow the coast south to Central and northern South America in their first fall—and they will stay there when their parents fly back north in the spring. After a year and a half, they will fly north again, to their home territory, to find a mate and build their first nest. Most young osprey pairs will not successfully breed until they are three years old.
Welcome to the nest
Osprey build their nests in the general area of the nest that they fledged from. Often times, the nest was built or used the previous year.
You will find osprey nests on dead trees, buildings, rock outcrops, power poles, buoys, dock pilings, and other manmade platforms—as long as it is near water and has clear visibility with an abundant food supply nearby. A site should be able to support the size of the nest and be well protected from predators, usually up high on a pole or outcrop.
Osprey, at times, form loose colonies in areas where the habitat is ideal, but the density of nests in a given area is determined by the amount of available food.
Both the male and female osprey collect material for the nest, but the female arranges it and puts on the finishing touches, much like other species we know. Osprey nests are quite conspicuous, as they are composed of a mass of sticks and are rather large – usually up to five feet in diameter and two to seven feet thick!
The lining of the nest is typically made of softer material, like grasses or seaweed, and any number of human made materials like cardboard, fishing line, or plastic bags. Unfortunately, they also use bailing twine which can be fatal if they get their talons caught in it. Dunrovin cleans the nest of bailing twine whenever they use a boom truck to access the nest or camera.
Osprey tend to return to the same nest year after year, but they will always update it with the latest and greatest materials, before laying their eggs.
Always faithful (to the nest)
In North America, Osprey breed along rivers, lakes, wetlands and coastal marshes.
The males typically arrive to the nesting territories before the females. There they claim their nest, which is often the same nest they used previously and/or near to the one they fledged from. Hopefully, the nest has not already been claimed by another species, like the great blue herons, eagles, hawks, geese, owls, gulls, or ravens.
The male osprey puts on a graceful aerial display, ostensibly to stake out his claim and advertise for a mate. He flies sharply up, gaining altitude and beating his wings rapidly. Often, he carries a fish or nest material with him. Then, he hovers with his tail fanned, at several hundred feet. Next, he dives down and quickly ascends—repeating the maneuver several times—often singing with a loud “Creeee!”. The male osprey will perform this often in the few days before the female arrives. Once she arrives however, the frequency of his routine dwindles.
While there is evidence that osprey mate for life, it appears that both the male and female returning to the nest has more to do with nest and territory fidelity than pair bonding. However, osprey are typically monogamous, except in the rare case when a male has the agility and ability to defend two nest that are close together.
Makin’ whoopie – and adorable osprey chicks
Once the female arrives, a period of courtship takes place that will last for up to three weeks. The male brings food to the female. In fact, the more food they get, females are more receptive to breeding. In this case, the way to her heart really is through her stomach.
The pair will spend time together on the nest as well. A male will protect his mate from other males and will ensure his own brood by copulating with her frequently.
Copulation is usually preceded by a mating display, from either or both the male and the female. It may occur shortly after the feeding ritual. The female will drop her wings slightly and point her tail up to one side, while the male may spread his wings and depress his tail.
Once the first egg is laid, incubation begins. Eggs are laid from one to three days apart and a clutch usually has two to four eggs. The female osprey is primarily responsible for incubation, leaving the eggs only to feed. The male will take over until her return. After 34-40 days, the eggs will hatch.
To nest or not to nest
The chicks are small enough to be brooded by the female for about ten days. During this time, they are covered in fluffy white down.
After that, she will continue to protect the young by shielding them with her wings, and feathers will slowly replace their down. Once the chicks are three or four weeks old, they will start flapping their wings and will be about 70-80% of the adult size. The mother will then give them room and move to a nearby perch, but continue to guard the nest
The father osprey will be the sole hunter for his family for a time. When he delivers a fish to the nest, the female will tear off a piece and feed the nestlings. When the chicks are about six weeks old, the mother can start hunting again and they will start to feed themselves, when a fish is delivered.
The first chick to hatch usually establishes dominance and if the food supply is low will often commandeer what is food, at the expense of the younger siblings’ survival. This is common among raptors and is called brood reductions. It ensures the survival of at least one chick, in lean years.
Time to fly
Young osprey will take their first flight at seven or eight weeks old. Migratory osprey, like those in the Dunrovin nest, will fledge a little earlier than non-migratory osprey.
They will spend time practicing and resting near the father’s feeding perch, so they can still be fed. Two weeks after fledging, they will begin to follow him on hunting trips. Four to eight weeks after fledging, they will begin hunting on their own. They must be able to take care of themselves for their long, solo flight south.
Talk about a crash course!
Fish, it’s what’s for dinner.
Osprey eat fish, fish and more fish.
In fact, fish make up 99% of the osprey diet. They are not particular about what fish species they eat—generally they will eat what is most easily accessible. If it’s in shallow water or near the surface of deep water, it could be osprey food.
North American Osprey have been known to eat more than 80 different species of fish, but usually there are two or three species that dominate the diet of osprey in a specific area.
Osprey, on occasion, have been known to also prey on rodents, rabbits, hares, other birds, and small amphibians and reptiles.
One might think that all this time around water would mean that osprey drink the stuff, but they don’t, typically. It has been surmised that their diet of fresh fish gives them enough.
Osprey are not known to cache fish as other species do. While they typically catch fish that weigh 5-10 ounces and are about 10-14 inches in length, they don’t always consume it all, in which case it is either discarded, carried around or left in the nest.
The hunt
Osprey hunt in flight, it is rare to see them hunt from a perch.
But osprey don’t just fly, they dive. Gliding 30-100 feet above the water, osprey use their excellent eyesight to look for fish in the water’s surface. Once they’ve spotted their prey, they hover above it then dive towards the water. At the last moment, before hitting the water, the osprey swings its legs forward and bends its wings back, so that its feet hit the water first. There is often a wild display of splashing and struggling as the bird makes contact.
Even though osprey have closable nostrils and thick plumage to protect them during a dive, osprey can’t swim, so they must use their powerful wings to lift out and away from the water with prey in their talons.
If you are lucky enough to see an osprey catch a fish, you will notice that its wing beats are almost horizontal when it is lifting out of the water. This is when some of the greatest acrobatics occur, because once the osprey clears the water with a fish, it may reorient the fish so that it is headfirst—to cut down on wind resistance.
Occasionally, you may witness other acrobatics. Osprey and eagles fish in similar habitats and sometimes an eagle will battle an osprey for its catch—forcing the osprey to drop the fish, then catching it in midair, before it hits the water or the ground.
The range of lucrative dives is rather broad, as hunting success depends on the skill of the individual bird, weather, and water conditions (like the tide in coastal areas). 24%-74% of an osprey’s dives will result in a caught fish. On a rare occasion, an osprey will drown after getting its talons caught in a fish that is too heavy to lift.
Once an osprey succeeds, it takes the fish to their perch, often near the nest, to eat it. Of course, sometimes they bring it to the nest itself, if they are feeding nestlings. An adult bird will start with the head and work towards the tail. Male osprey are known to eat part of the fish before sharing it with their mates during breeding season.
