Monday, November 1, 2010

Bald Eagle

On Friday, Erika and I birded locally.  We flushed this Bald Eagle as we drove around a corner on the north edge of the Carleton College Arboretum along Little Canada Road.  The eagle briefly perched atop a nearby pine, but then flew away. 

"That would have made a good blog entry," remarked Erika.  "Not without a photograph." I replied.  About 20 minutes later, we returned to the same spot.  We found the eagle perched in a large oak and I was able to take one photograph before the bird again flew. 

Bald Eagles require four years to obtain their striking adult plumage. During these years, the eagles continually molt, and so continually change their appearance. According to the description is the Peterson Field Guide Series, Hawks, our bird is probably a second-year bird. This book is a decent field guide to birds of prey and can be obtained through the accompanying link at bargain prices. (Two volumes by Brian Wheeler may be better, Raptors of Western and Eastern North America, but they are expensive.  Minnesota is covered in the Western volume.)
The eagle was feeding on an opossum carcass. I assume the opossum was road-kill and that the eagle was scavenging. A cursory search of the literature finds no mention of Bald Eagles consuming opossums.  Eagles are primarily fish-eaters, but are known to take a wide variety of prey when fish are not available.  Arthur C. Bent, in his monumental masterpiece Life Histories of North American Birds of Prey, wrote, "As eagles do not disdain carrion, they may often be seen...feeding on the carcasses of any animals they can find.." This 26-volume set of books is now somewhat dated, but still contains a wealth of information.  The books were first published by the Smithsonian and then reissued as Dover reprints. Prices for these books vary greatly, so some research is advised if you are interested in obtaining them.

If you are interested in up-to-date life histories of birds, the American Ornithologists' Union's Birds of North America is now a continually evolving, on-line resource.  Subscriptions to the series are pricey, but free to AOU members!  Some libraries have copies of the print version of Birds of North America, but they do not appear to be available through Amazon.

1 comment:

  1. An adult Bald Eagle enjoyed the 4-day-cured road-kill opossum on the gravel road in front of our house in Chisago county one February. Soon about 30 crows were on the ground, harassing the eagle at a distance. I was able to film it but do not know where the tape is at this time (had it online for a bit) The eagle made a few charges at the crows - pretty neat to watch. The eagle left after about an hour, and the crows immediately afterward, paying little attention to the opossum itself. Within 30 minutes, a red-tailed hawk came and alternated eating it and sitting on a pole. As to other carrion and eagles, when I lived in Wisconsin, pig farmers would mix their still-born pigs with their manure and eagles would pick at this when it was spread on fields in late winter.