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Bald Eagles

March 3, 2012
Kevin Williams - Grundy County Conservation Director , Reinbeck Courier

I have my son and daughter-in-law to thank for the news column inspiration this week. Sean and Heidi were over for supper the other night and Heidi mentioned that she had listened to a radio show that week where the Decorah Eagle cam and Bald Eagles in general were discussed. A caller was surprised to find out that even a single Bald Eagle feather was illegal to possess. We talked about how Eagles, like every other healthy bird, molt some of their feathers continually and molt in large numbers a couple of times per year. And while a possessing a single, solitary molted feather may not seem like a big deal to most folks, it is a law enforcement nightmare to begin to determine and prove whether the feather was obtained by picking it up off the ground or by killing the bird. That is the reason for being so strict. By the way, it is not just Eagles, possession of any migratory songbird parts (including feathers) without the proper federal permit is illegal.

Sean then mentioned that he had observed a Bald Eagle soaring high (way high) in the air the other day. This led to discussing how high they can fly and why in the world they would fly that high in the first place. I told him that they can see something a mile away. It was a good discussion maybe not a common after dinner discussion topic for most households, but not an uncommon type of one for ours.

Well, when I returned to the office the next day, I decided to put together some information that you could use for an Eagle discussion at your table sometime. So, here is some Bald Eagle to get you started:

Eagles, like all birds, have color vision. And while an Eagle's eye is physically almost as large as ours, the sharpness is at least four times that of a person with perfect vision. The Eagle can likely identify a rabbit moving almost a mile away. That means that an Eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles!

But before I leave the height topic, let me add that Eagles during migration can fly to an altitude of 10,000 feet. Eagles use thermals, which are rising currents of warm air, and updrafts generated by terrain. Soaring is then accomplished with very little wing-flapping, enabling them to conserve energy. Long-distance migration flights are accomplished by climbing high in a thermal, then gliding downward to catch the next thermal, where the process is repeated. But during active flapping flight, a Bald Eagle can achieve speeds of about 30 to 35 mph.

The female Bald Eagle is larger than the male. Northern birds are significantly larger than their southern relatives. An Eagle's average weight is ten to fourteen pounds. Of that, their complete skeleton weighs only about half a pound. Their feathers weigh twice that much. A Bald Eagle's lifting power is about 4 pounds.

Shrill, high pitched, and twittering are common descriptions used for Bald Eagle vocalizations. Eagles do not have vocal cords. Sound is produced in the syrinx, a bony chamber located where the trachea divides to go to the lungs. Bald Eagle calls are a way of reinforcing the bond between the male and female, and to warn other Eagles and predators that an area is defended.

Once paired, Bald Eagles remain together for life. Although, if one dies, the survivor will not hesitate to accept a new mate.

And while our body temperature is normal at 98 degrees Fahrenheit, an eagle is about 106 degrees.

The Bald Eagle was de-listed from the Endangered Species list in 2007. One of only a very few species to achieve numbers that warranted that. The number of nesting pairs in the lower 48 United States increased 10-fold, from less than 450 in the early 1960s, to more than 4,500 adult Bald Eagle nesting pairs in the 1990s. Today, there are an estimated 9,789 nesting pairs of Bald Eagles!

Alaska is still the place for Bald Eagles. About half of the world's 70,000 Bald Eagles live in Alaska and another 20,000 in British Columbia.



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