April 28, 2013

Birding: The graceful osprey is a remarkable raptor

By Herb Wilson

For birders, one of the joys of April is the arrival of the ospreys. We'll look at this remarkable raptor today and in the next column.

click image to enlarge

Ospreys, which return to Maine in April, sometimes fly as high as 200 yards above the water before making their dive and grabbing a fish with razor-sharp talons.

John Ewing/Telegram File

Let's start with the scientific name of osprey -- pandion haliaetus. The genus name pandion comes from a king of Athens in Greek mythology. Unfortunately, the scientist Savigny -- who established the genus name -- did not know his mythology very well. According to the myth, Pandion had two daughters. A man named Tereus married one of the daughters and later forsook her for her sister. The Greek gods transformed the sisters into a nightingale and a swallow, and Tereus into a hawk, and Tereus spent eternity chasing the swallow and the nightingale. Thus, Tereus would be a much better genus name for the osprey.

But pandion does have the prefix "pan" -- meaning all, an appropriate meaning here as ospreys have a nearly worldwide distribution. They occur on all of the continents with the exception of Antarctica, as well as many oceanic islands, including such far-flung locales as the Lesser Sunda Islands in the South Pacific.

The specific name haliaetus is the genus of the bald eagle, so there is a bit of similarity there.

The common name turns out to be a misnomer as well. This word comes from Latin roots, meaning bone-breaker. This name is appropriate for the Lammergeier, an Old World vulture that drops bones onto rocks to crack them and expose the marrow.

I think fish hawk would be a much more appropriate common name for the osprey. Fish make up at least 99 percent of the diet. Other animals that are rarely taken include salamanders, birds, snakes, voles, squirrels and even a small alligator. Finally, it must be been mind-boggling for observers to see osprey tearing flesh from the carcass of a white-tailed deer but also competing with turkey vultures for access to a road-kill opossum.

Access to fish is a strong determinant of the distribution of ospreys. In North America, a look at the distribution map of breeding sites reveals they nest broadly in Florida but are restricted to the coastal plain along the rest of the East coast until they reach Maine. Ospreys nest commonly throughout most of our state. They also breed across Canada, extending south into many of the northernmost states with breeding populations extending along the Pacific coast to central California.

Over much of their breeding range, winters are cold enough to cause lakes and rivers to freeze, denying ospreys access to fish. Hence the majority of ospreys breeding in North America are migratory, spending the winter either along the coast or rivers in Central and South America. Unlike many migratory hawks, ospreys readily migrate over broad expanses of water.

We have all thrilled at the sight of an osprey diving for fish. An osprey may fly as high as 200 yards above the water to seek a fish near the surface. Sometimes they hover as they scope the scene. The dive is made feet first and is usually no deeper than three feet.

The feet of osprey are marvelous tools. Their talons are long and razor sharp. The base of the foot pad and toes are covered with short spines that aid in gripping a slippery fish. The outer toe is flexible and can reverse its orientation so that the foot of an osprey can have two toes pointing forward and two backward to grip a fish firmly.

An osprey can fly with a fish weighing half its body weight, as long wings and powerful wing muscles allow them to generate enough lift to rise off the water. Then, once aloft, the osprey will orient the fish parallel to its own body to reduce air resistance.

 

Herb Wilson teaches ornithology and other biology courses at Colby College and perches in South China. He welcomes reader comments and questions at:

whwilson@colby.edu

 

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