by meg macdonald wildbirdsjax@comcast.net
For most birds, the annual task of nest building, laying of eggs, and rearing young is complete. Cooler temperatures herald the change of season and southward migrations. While Jacksonville is still welcoming many of the standard fall migratory birds, Goldfinch, Warbler, Baltimore Oriole, etc. there is one bird that will migrate in all other locations across North America except Florida. The Bald Eagle. Our national bird. Second in size only to the California Condor. They were almost extinct due to the use of DDT and other pesticides in the 1950’s and 60’s and placed on the Endangered Species list in 1978.
The typical seasonal behavior of the Bald Eagle is reversed for the eagles of Florida, Texas and Mexico. For the eagles of these states, courtship begins in earnest in the fall. Although mated pairs of bald eagles court throughout the year, this time of year brings them in closer proximity to their nests and they spend increasing time together as a pair. Much of their courting rituals take place in the air. They ride updrafts, circle, dive, and chase their mates. One of these flight rituals is also when one mate will roll on his/her back under it’s mate then the two will extend their talons and touch while rolling and changing places. The pair will also perch side by side for hours and touch often with their beaks.
The nest is the center of an eagle’s life for a large part of each year. Eagles will return to the same nest each year and continue to add new sticks to continuously augment the structure. While first year nests may measure three feet across and one foot from top to bottom, mature nests often measure five or six feet across and three to four feet tall. There are documented nests that measured nine feet across and 20 feet tall from base to top. It is estimated these nests are the result of more than 100 years of use by eagles. Eventually, the weight of those nests causes the tree or tree limbs to break.
After mating, the female eagle usually will lay two eggs, the appearance of each egg separated by two to three days. Although both parents share responsibility, the female spends the majority of time incubating the eggs, keeping the eggs warm. Incubation averages 35 days. The thick and insulating feathers that work so well keeping adult eagles warm is a detriment in sharing body heat with the incubating eggs. But as in the way of nature overcoming other obstacles, both parent eagles lose an area of feathers from their breasts, forming a skin patch to bare against their eggs. This bare spot is called a “brood patch”. This same patch does occur in other wild birds, but typically this occurs only in the female.
If Jacksonville has successful courting this month, there should be some eagle hatchlings coming in with the new year.
Hatchlings weigh just three to four ounces at birth yet will grow to nine to fifteen pounds in three months. By the age of 10 to 12 weeks, eagle chicks have increased to full adult size, grow their third layer of feathers, and are eager for flight. For several weeks, the chicks will jump and flap and test their flight feathers. But when the winds are right and the feathers are strong, up they jump and away they will go-although not far at first. The young eagles may only venture a few hundred feet on that first outing. The eagle parent will continue to provide food for the young for several more weeks. But after just ten weeks, the bonds are broken and the young eagles set off on their own.
Notice that the timing of the hatching and the growth spurt of these young, although reversed from our other wild birds, coincides with the abundant food availability. Although the geography of Florida provides for good fishing year round, our spring time is also when young mammals and rodents are in abundance and more vulnerable to predation. Then, by July and August and our searing heat, those first year eagles are fully feathered and already off on their own. Once again, nature and evolution have overcome potential obstacles.
By the way, in 1996, the bald eagle was reclassified as a Threatened species. Then in 2000 it was removed from the Threatened category. Although recovering from pollution and chemical contamination, the greatest threat now is loss of habitat.
Wishing you a Happy and wild Thanksgiving.
|
