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24 January 2011: First winter wanderings

We are pleased to report that both of the 2010 hatched bald eagle chicks on which we placed GPS, solar-powered transmitters are still alive and well. It is nearly February now, and we are in the full swing of winter with snow on the ground in Oklahoma and nightly temperatures dropping to around zero. As usual, the lows and highs in the Sooner state have a tendency to fluctuate with the arrival of various weather fronts.

It is obvious to viewers by now that the young eagles made repeated excursions for several months away from their fledging site in Sand Springs, OK, gradually wandering all over the state of Oklahoma and into Kansas, and finally ended up in the more southerly (and warmer) climes of Texas where they have been spending the coldest part of the winter so far. This location pretty much insures open water where the eagles can catch fish and waterfowl, and if warm enough, the turtles and snakes that they likely fed on when they first fledged.

Our first year eagles have been learning to deal with competition from their distant relatives that have arrived from far northern locales, many of them older and more experienced at stealing and protecting food than our two youngsters. These two eagles, however, are learning the “ins and outs” of survival too, and for bald eagles, this includes eating carrion and learning to steal meals from other birds. Without being able to examine the health of our two Okie eagles in hand, it is hard to know how strong they are and thus how long they may survive. But, this is one of the reasons we are conducting this study. All indications are that the birds are moving about regularly, are usually in association with small or larger bodies of water at which they can find food, and they are in a relatively warm part of the U.S. These are all good signs, so with any luck from the technological side of things, we hope to keep learning about the movements of these birds for several years to come.

28 September 2010: Independence and Juvenile Wandering by Young Eagles

With the appearance of fall 2010, our young eagles have begun to wander farther from their home parental territory, but they did not head north to Canada as did the young eagles we hacked at Sequoyah in 1987 and that Alan Jenkins tracked by truck that year.  Most of the movements by both the male and female youngsters this year have been for relatively short distances, although some are as far as 110 miles in a week. One has to remember, however, that such movements are probably made up of many short flights summarized on the map. There seems to be a tendency for the eagles to check back to the nesting area from which they first flew, even after making significant sojourns. These youngsters are wandering about in efforts to find good hunting areas where prey is abundant, hunting perches are available, and water is shallow so that prey is visible. Best hunting areas can easily change as the weather turns and as prey types also change. The turtles and snakes that frequented the sand bars in summer will disappear, but new life will arrive too, both as competitors and as prey.

Before long, bald eagles will be entering the state from northern areas such as the Great Lakes and Canada as they make instinctive movements south in anticipation of impending freezing waters in northern realms. Southern areas with open lakes and rivers will provide good fishing for the influx of eagles and great flocks of waterfowl will arrive too.  Bald eagles are efficient at catching waterfowl as they often team up during attacks after a duck on the water, forcing it to dive repeatedly until it becomes exhausted and is snatched from the water’s surface. Then a great chase ensues as the prize winner tries to carry its bounty until exhaustion and another eagle grabs the prey to repeat the process. These chases can go on for as long as an hour, and it is difficult to understand how such chases can pay for themselves in terms of lost energy for all eagles who are not the winner. Bald eagles are scavengers too, and will feed on winter kills of cattle, fish, or other mammals during the winter.  Some bald eagles turn to catching mammals such as rabbits too. And, wintering eagles often roost communally in flocks of a half dozen to perhaps 30 or more. This could be a challenging time for our two youngsters as they learn to compete with the influx of northern visitors, and perhaps learn to switch over to feed on wintering waterfowl and other species of fish that were not near the surface during the summer.

We are watching with interest where these two young eagles go. In some other raptor species such as peregrines and other falcon species, females tend to disperse significantly farther than males. This apparently is behavior that helps encourage genetic diversity by avoiding inbreeding.  To study this behavior will take a much greater sample size and a much longer period of evaluation, but if financial support can be found, we hope to place more satellite transmitters on Oklahoma fledglings during this approaching nesting season.

29 June 2010: Early Post-fledging Movements by Young Eagles

For those viewers who have been watching the mapped movements of the young eagles, it might seem that little has been happening. Actually more is going on than might at first appear. The “transmitterized” male first flew from the nest on June 5 and the female on June 9. These were just short flights, but within a few days the two young eagles (and probably their brother that is not wearing a transmitter) had flown across the Arkansas River and were perching in the trees and other vegetation that provide riparian habitat on either side of the waterway. Just as for humans, these trees provide shade during the hot spell we have been experiencing over the last couple of weeks, and some evaporative cooling is also provided from the green vegetation.

Part of the area they have been frequenting on the river is intermingled with sandbars. These structures provide shallow areas where the birds can bathe and sit next to the water. Bathing provides a cooling effect as the eagles sit and dry their feathers, and sitting next to the water also provides evaporative cooling. Sometimes eagles will sit with their feet in the shallows so that heat is transferred directly to the cooling water and away from the eagles’ bodies.

The shallow depths close to the sand bars also provide habitat for various creatures that can be tasty to the eagles such as turtles, snakes, and frogs as well as fish. (Fish and turtles were found as prey remains from food brought to the nest by the parents before these youngsters took their first flights.) The first step in catching these animals is for young eagles to just get used to watching them as the prey moves about in the water; this is something the eagles do as they sit on the sand bars or in the trees above. Usually the eagles will soon learn to take these types of prey by snatching them from the water with their feet while in flight, but young eagles first exhibit early predatory behavior by grabbing floating leaves and sticks from the river or even footing at branch tops swaying in the wind. Soon they will begin making capture attempts not only after floating debris but after live animals. While their attempts will be playful initially and not “in earnest,” eventually the young eagles will sometimes succeed in catching live prey. During all the playful prey capture attempts the eaglets are learning, and the adults keep the young eagles well fed so they will have plenty of energy to stay on the wing and to keep trying to capture “floating sticks” as well as real prey. Provision of food is the primary role of the adults during this post fledging period; the young are genetically programmed to initiate predatory behavior and do not need parents to teach them to hunt.

These young eagles are building up muscle tone for strength in flight and will become efficient at catching prey so that they can become self sufficient and head north to cooler climes for the rest of the summer.  At least we think that is what will happen, judging from what the young eagles did that we hacked out in Oklahoma 20-some years ago after hatching them from Florida eggs (the grandparents or great grandparents of these “transmitterized” youngsters). We are assuming our radioed eagles will be following in their footsteps. Like other site viewers, we are anxious to see what happens, so we will be watching to see when the mapped arrows (tracking movements of the eaglets) strike out and head north.  Read more about our Bald Eagle reintroduction project here.