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Ospreys - Unique Birds of Prey (May 2005) In the March issue of Montana Best Times, the discussion centered on the ubiquitous Bald Eagle and the current status of this species since the times of Lewis and Clark. In this month's column we will learn about Ospreys and Osprey ecology. Ospreys are some of the easiest species of birds of prey or raptors to identify. Their coloration is simple chocolate and white, with a dark stripe through the eye, and they are quite large. Their flight is unique for they are some of the largest raptors able to hover, and their prey is almost exclusively fish. Nearly every person who has ever carried a fishing rod, or stopped to rest at a fishing access site, or boated on a lake or river knows how to identify Ospreys. What I am about to present is additional information on Ospreys and Osprey ecology, so that your next encounter with this bird will be filled with careful study, enlightenment, and amazement.
Scientific classification Contrary to popular belief however, Ospreys can kill and eat prey other than fish. During the 1988 Yellowstone wildfires, I personally witnessed them feeding on mammals such as yellow pine chipmunks and red squirrels, and amphibians such as frogs and salamanders. But I must add these are atypical occurrences. Ospreys are unique birds of prey in that they are currently classified under the Order Falconiformes or grouped into a family all by themselves called Pandionidae. Hence, the scientific name of the Osprey is Pandion haliaetus. The genus for the Osprey comes from Greek mythology: Pandion the King of Attica, had two daughters (Philomela and Procne) in which one was metamorphosed into a nightingale and the other one into a swallow. The specific epithet "haliaetus" refers to fish eagles. Ospreys not only belong in a family all by themselves, but are also represented by a single genus and species.
Different from other raptors Ospreys are unique in that they have: long, rounded, sharply curved claws or talons; a reversible outer toe and spiny foot pads or spicules for handling slimy fish; a very elongated small intestine used to digest fish - bones and all; dense, compact oily plumage; valves in the nostrils that close and shut out water when the bird dives; narrow head that lacks a bony ridge above the eyes, streamlined for diving; the ability to hover, soar, and hunt from a perch; long, narrow, pointed wings, making it an excellent flier under many different conditions and a superb migrant; mostly large, long, narrow wings with a surprisingly small body for the size of the bird. Worldwide, Ospreys can be broken down into four subspecies based on coloration and size. Two of the races found in the Caribbean and Indo-Australia regions are both non-migratory and small in size, the former being very bleached in the head almost Bald Eagle-looking, with a faint eye stripe, the latter being the smallest of them all and possessing a dark breast band. The other two races are from North America and Eurasia and are larger and darker, the North American race being the darkest and largest of the two. But both are classified as migrants, even though in the extreme southern end of their range some of these birds do not migrate to any extent.
Other identifying features Ospreys have bodies that are chocolate in coloration, with dark stripes through the eyes and a dark hind neck. Young birds near or post-fledging possess beautiful white scalloping on each feather, particularly on the back. Osprey feet are always pale blue-gray, and their bills are one color: black. They have very long legs for a raptor. These legs are used to reach out to capture and carry fish. Besides having the ability to hover, they fly with a distinct flight. Their cross-section when flying to or away nearly always possesses this "^^" silhouette, whereas when they fly over they have a pronounced point or "crook" midway in the front of the wing at an area called the wrists or carpal joints.
Osprey nests and nesting characteristics Osprey nests are typically situated on the very top of the substrate and have a shape that is referred to as "telescoping" - in other words, the nest is bigger at the bottom and slightly smaller at the top. Osprey nests occur in a wide variety of places in North America. The classic cases in Montana are in the top of a dead tree, a telephone pole, or on a pinnacle such as those found in Yellowstone National Park. But in some areas they can nest on the ground on open islands, sea stacks, rock outcrops, bridges, smokestacks, duck blinds, mangroves, channel markers, and in the Mediterranean, only on cliffs on steep rocky islands. Most Ospreys are solitary nesters, but there are some places where they nest in colonies. Such is the case of Frank Island on Yellowstone Lake. In addition in these colonies, one often finds polygyny occurring, i.e. one male mated with more than one nesting female. Osprey nests measure 2 to 4 feet in diameter and are composed mainly of sticks they break off from a dead tree or shrub and carry to the nest. Along many rivers in Montana, especially near ranchlands, you can find Ospreys nests made out of sticks and orange bailing twine. The Ospreys have learned this bailing twine is easy to come by in hay meadows, and makes excellent construction material for a nest. Other important things to know about Ospreys are that they lay two to three eggs. The eggs are camouflaged a cream with chestnut swirls and dots so that they are concealed from predators. It takes 40 days for the eggs to hatch, and 50 days for the young to fledge from the nest. They typically begin nesting in April and May in Montana. It is important not to disturb nesting Ospreys during egg-laying or incubation or to keep them off the nest for any length of time. If kept off the nest in the middle of the day, the eggs or young can easily die from cold exposure or heat prostration. So it is important to realize it is not a good idea to spend a lot of time near an Osprey nest.
Capturing fish Ospreys feed on almost exclusively medium-sized live fish. They typically do not dive deeper than 3 feet below the water's surface. When they do dive, they dive feet first. When they capture the prey, they come catapulting out of the water, shake off the water and carry the fish head-first, with one foot in back of the other. Bald Eagles have learned to be "kleptoparasitic" in that they steal recently caught fish from Ospreys in the air and get rewarded with a quick meal.
Migrants They arrive in March in western Montana, and usually April in places like Yellowstone and areas east of the Continental Divide.
Osprey's status The Osprey is currently classified as a migratory bird, protected under the Migratory Bird Treaty Act of 1918. Population-wise, it once was dangerously low due to egg collectors in the late 19th and early 20th centuries, and dangerously high levels of DDT in New England and the Midwestern United States from 1950 to 1970. Today Ospreys are thriving in numbers due to the cleaning up of DDT and a vastly improved fish management program, coupled with catch-and-release fishing. There are currently hundreds of pairs of nesting Ospreys in Montana, and their numbers keep going up.
Coming next Enjoy! And the Best of Big Sky Birding to you!
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