The ospreys are back in the forest preserves around Palos Park. A pair has been resident there the past two summers, but they didn’t seem to lay any eggs in the nest they built; ospreys typically spend a few years building a nest before they use it. One of the birds I saw last Sunday was perched in a tree next to the snag that supports the nest. Back in 1854 Robert Kennicott reported that this species was known to nest in Cook County. There are no records since that time, so if these birds were to nest they would represent the return to this county of a species that has been absent for nearly a century and a half.
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Ospreys are fish eaters. “Fish hawk” is the most descriptive of the common names for the species. Although ospreys have gone their own evolutionary way in the direction of a specialization in catching fish, there is no doubt of their close relationship to hawks and eagles. Their scientific name, Pandion haliaetus, combines a name from Greek mythology with the Latin for sea eagle. According to some sources, Pandion was the father of Procne and Philomela. These sisters are major characters in the sort of story the founders of our civilization used to explain the world. This particular tale involves rape, mutilation, and a mother murdering her only son, cooking him, and feeding him to his father for dinner. The outcome was that Procne became a swallow (hence the genus of the purple martin, Progne), and Philomela became a nightingale. Apparently whoever named the osprey thought Pandion became a fish hawk.
Although ospreys got less publicity than bald eagles, they suffered as badly from the effects of DDT. The two birds have similar diets, but ospreys tend to concentrate more on live food and less on carrion. Bald eagles commonly watch ospreys hunt. If the fish hawk captures a fish, the larger bald eagle dives on the osprey and forces it to drop its prey. Often the eagle plucks the falling fish from the air. This habit of thievery was one of the objections that Benjamin Franklin raised to the selection of the bald eagle as our national bird.
The usual nesting location for the species is on standing dead trees–snags–near water, but the species will quite happily use nesting platforms built by humans. Such platforms once lined the Atlantic coast, from Connecticut south. In the DDT era the platforms were almost all empty; now those that remain have begun to fill up again, and new platforms are under construction. The birds seem to tolerate considerable human presence around their nests, and some lucky shoreline property owners can watch the growth of nestlings from their living room windows.
The birds now taking up residence in Palos are benefiting from improved water quality in the lakes scattered around the preserves and in the Des Plaines River. And they are probably helped by the fact that the Forest Preserve District and the state of Illinois are stocking fish in the lakes for the benefit of anglers. Hatchery fish are famous for being easier to catch than truly wild fish, and ospreys are likely to be as eager to grab an easy meal as the rest of us.
