The return of the ern

StoryImage( ‘/Images/Story//img-CgkEyBJNem.jpg’, ‘Photo by Dr. Robert Hedeen’, ‘An osprey or ern leaves its nest on a navigation light to search for food.’);

The shrill, piercing scream made by the bald eagle startled me. I glanced upward to see a bald eagle make a pass at an osprey carrying something in its talons. The smaller bird disengaged its claws from the object, and it fell toward the surface of the river with the eagle in hot pursuit. The eagle grabbed it just before it hit the surface of the water, but discarded it when he determined it was a stick and not a fish. The disgruntled bully then flew away toward a line of trees on the shore while emitting another scream in an attempt to intimidate the osprey further.

The osprey (sometimes called the erne, ern, sea eagle, or fish hawk) did not seem to be overly perturbed by or particularly impressed by the attack of the overpowering symbol of the United Sates. The ern had probably been subjected to such degradation many times in the past. He had learned that when a “true” eagle demanded something he possessed, the prudent thing to do was to let him have it and entertain no thought of resistance.

I observed this scenario last summer as it took place on the Illinois River as it flows through Starved Rock State Park. It is highly unlikely I would have witnessed this drama 30 or so years ago, as the numbers of the magnificent participants had fallen to dangerously low levels.

The year 1969 marked the low point in population numbers of ospreys, eagles, and other birds of prey. 1969 also marks the date when these birds started on the long road of recovery from being threatened species to the adequate population numbers we see today.

Shortly after the end of World War II, the insecticide DDT was broadcast over our landscape for almost 25 years, and the primary blame for the rapid decline in numbers of birds like the osprey and eagle can be laid squarely at the door of this chlorinated hydrocarbon pesticide.

There is no question DDT and other long-lasting, broad-spectrum insecticides contributed great benefits to mankind in the fields of agriculture and disease control, but there were also serious negative aspects to their widespread use. These silent killers amass in the tissues of fish, and ospreys and eagles were loaded up with these poisons when they dined on their favorite food item. Many were killed outright when they ingested a lethal concentration, but others were subjected to a more subtle type of annihilation.

When eaten in sublethal concentrations, DDT built up in the bird’s tissues and adversely affected the reproductive system. Researchers noted that ospreys with a high level of DDT in their bodies laid eggs that were frequently infertile. In addition, the chemical was found to cause a malfunction of the shell gland so that the egg covering at the time of laying was abnormally thin.

Eggs in museum collections that were collected prior to the advent of DDT were found to have significantly thicker shells than those laid after the use of DDT became widespread. A large number of these emaciated eggs (even though they might be fertile when laid) were accidentally crushed in the nest by the weight of the parents during the month of incubation.

Fortunately for wildlife (and non-wildlife also), DDT and its relatives (dieldrin, lindane, aldrin, endrin, and others) were banned for general use in the United States in 1969, and the increase in numbers of these splendid birds of prey in subsequent years has been nothing short of miraculous.

Other factors played a part in the decline of ospreys prior to 1969, one of which was the routine destruction of nests constructed on aids to navigation. The U. S. Coast Guard took a dim view of any bird that would have the nerve to build a nest on government property, and crews routinely removed any nest they found that might hinder navigation. The Fish and Wildlife agency pointed out to the Coast Guard the error of its ways, and the practice of destroying nesting sites ceased about the same time as DDT was discontinued.

Today, we can be glad that we are still able to witness one of the most spine-tingling thrills to be seen in the natural world. This occurs when a soaring osprey suddenly folds back its wings and goes into a power dive straight into the water and disappears for a few seconds. We hold our breath until it reappears with a fish impaled in its steel-like claws and flies away to eat the fish or feed its young in the nest (unless an eagle hijacks it for its own use).

Ben Franklin had the eagle’s number when he protested its adoption as our national symbol, mainly on the grounds that it was a bully and frequently steals food from others. If the osprey had been able, it surely would have endorsed Franklin’s position.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system.

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