Northern Prairie Wildlife Research Center
Originally published in:
North Dakota Outdoors
Official Publication of the
State Game and Fish Department
100 North Bismarck Expressway
Bismarck, North Dakota 58501-5095
Gomes, Scott. 1998. A closer look: The osprey. North Dakota Outdoors 60(7):16-17.This resource should be cited as:
Gomes, Scott. 1998. A closer look: The osprey. North Dakota Outdoors 60(7):16-17. Jamestown, ND: Northern Prairie Wildlife Research Center Online. http://www.npwrc.usgs.gov/resource/wildlife/closlook/osprey.htm (Version 15MAY98).
With spring just around the corner, migration will soon begin. North Dakota is a main stopover for many bird species whose final destination is Alaska or the arctic tundra. Among them, raptors are some of the first species to make the move north from southern wintering grounds.
One species, the osprey, begins this trek as early as mid-February. The osprey is a type of hawk that followed a different evolutionary path than other hawks typically found on North Dakota's prairies. In fact, the osprey is in a family all by itself, scientifically placed somewhere between hawks and falcons.
While other hawks feed mainly on ground animals, the osprey is adapted to catch and survive almost exclusively on fish. Its legs and feet are notably different from other hawks - they have a reversible outer toe. With this adaptation, the osprey can rotate its outer front toe, which enables it to grasp prey with two toes in front and two in back. All other hawks have three toes in front and one in back. The toe configuration makes it easier for osprey to carry tubular-shaped fish, and also allows them to carry fish head-first during flight. The underside of the toes, covered with spicules or tiny projections, also aid in holding slippery fish.
|Other hawks and falcons have feet with three toes in front and one in back. |
The ospreys can move the outer toe on each foot interchangeably from front
Ospreys have dense feathers, which helps absorb impact and reduces wetting when they dive into water.
In North America, ospreys nest from Alaska to Nova Scotia, south to the Great Lakes and coastal regions of the United States. They do not nest in North Dakota, but migrate through the state along the Missouri River System, starting in late February, with the best chance for viewing in March and April.
The last documented observation of a pair of ospreys trying to nest in North Dakota was in 1973. From May 2 to May 9, John Martinson and Frank A. Splendoria observed a pair of ospreys constructing a nest on a power transmission line tower near Garrison Dam. However, the nest was blown down by strong winds on May 9.
Ospreys are fairly easy to recognize in the field. They are large, almost the size of an eagle, with a wingspan of 54-72 inches. Plumage is largely solid brown above and white below. The head is entirely white, much like a bald eagle, but with a broad black band that extends from behind each eye to the nape of the neck. The female often has dark streaks that form a "necklace" across the upper chest. In flight, the osprey is distinguished by white underparts, narrow-shaped wings like a falcon, and a black patch at the bend or "wrist" of the wing. The osprey flies with slow deliberate strokes, alternating with short glides during which the wings are held above the body.
Having made a capture, an osprey rises from the water with the fish locked in both feet. While in flight, the osprey arranges the fish so it will point head-first, reducing resistance to airflow.
Catching a fish, however, doesn't always guarantee a meal. Bald eagles often key in on fishing ospreys. If a bald eagle sees an osprey make a catch, it will dive upon the osprey and try to force it to drop the fish.
How did this happen? DDT would wash from surrounding soils into rivers and lakes. Since DDT was not water soluble it would accumulate in the food chain. If an osprey would take a fish from a contaminated river, DDT would enter the osprey's tissue via the contaminated fish. DDT would then interfere with calcium production necessary for eggshell strength. DDT is now banned in the United States, but unfortunately not worldwide.
If you would like to learn more about raptors, the North Dakota Game and Fish Department's Nongame Wildlife Program has colored brochures entitled "Hawks, Eagles, and Falcons of North Dakota" and "Owls of North Dakota." They are available free of charge by calling 328-6224 or 328-6612.