Tuesday, May 28, 2013

Elegant Eagles

There are more than 60 species of eagles, and in all known species, females are larger than the males!  You're familiar, of course, with our national symbol, the Bald Eagle...


and you may know about the only other eagle species found in the United States, the Golden Eagle.


The Bald Eagle may be the most recognized, but in fact, the Golden Eagle is the slightly larger bird.  There are two subspecies of Bald Eagles and while this raptor is the only one endemic to North America and can be found throughout the U.S., the birds living in Alaska, upper U.S.and Canada are larger than the ones living in the southern U.S. and Baja California. The majority of Bald Eagles live in the north and migrate south for the winter when coastal waters and rivers freeze as their diet is mainly fish.. Besides North America, the Golden Eagle is also found in Eurasia and parts of Africa.  There are six subspecies of Golden Eagles, the largest living in southwest China, northern Pakistan and southern Kazakhstan.  The largest female Golden Eagles can have a wingspan of just over 9 feet and weigh up to 27 pounds, while the largest Bald Eagles can weigh up to 17 pounds and a wingspan of up to 8 feet across.  However, a Bald Eagle holds the record of the largest verified load carried in flight of a 15-pound mule deer fawn.  Larger eagles will kill prey that weigh much more than they do, but will eat on the ground and then carry off pieces of its kill. 

The width of wingspan depends on the environment in which the eagles live.  Those that prefer a forest home have smaller wingspans so they can navigate through the trees more effectively.  Eagles that live in open country have larger wingspans.  Eagles are known for riding the thermal air currents rather than actually flapping their wings. Eagles have much better eyesight than humans allowing them to see prey from long distances.  Not only do eagles' eyes have retinas more densely coated with light-detecting cells called cones than human retinas, but they have a much deeper fovea than humans.  A fovea is a cone-rich structure in the backs of the eyes that detects light from the center of the visual field.  Some investigators think this deeper fovea allows their eyes to act like a telephoto lens, giving them extra magnification in the center of their field of vision.  They also see colors more vividly,can discriminate between more shades, and are able to see ultraviolet light — an ability that evolved to help them detect the UV-reflecting urine trails of small prey.

Based on median measurements, the largest eagle by weight is the Stellar's Sea Eagle which lives along coastal northeast Asia...


the largest by body length is the critically endangered Philippine Eagle...




and by wingspan, the White-Tailed Eagle from Eurasia, which is also known as the Sea Eagle and a close cousin to the Bald Eagle.


Other large species include the Wedge-tailed Eagle from Australia and southern New Guinea...



and the Harpy Eagle from Central and South America.


However, it is the Wedge-tailed Eagle that has the longest wingspan ever recorded of 9 feet, 4 inches.

Among the smallest eagles are the Booted Eagle from Europe, southern Africa and Asia weighing only a couple of pounds and a wingspan of under 50 inches...


and the Great Nicobar Serpent Eagle.

Photo by A P Zaibin   Source:  Oriental Bird Club

Some of the more unusual looking members of the eagle family are the Changeable Hawk-Eagle, also known as the Crested Hawk-Eagle from India and Sri Lanka...


from Africa, the Long-crested Eagle...


the flashy Bateleur from Africa and southwest Arabia...


and from Asia Blyth's Hawk-eagle


The larger eagles are considered apex predators in the areas where they live.  Besides fish, prey of various eagle species includes monkeys, sloths, foxes, and small deer and goats, snakes and lizards, rabbits and hare, other birds, and carrion.

By the way, I recently passed 160,000 views on my blog.  Thanks everybody for your interest in my nature musings.

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