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Bald Eagles Fact of the Day - REBORN!

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We are restarting our Bald Eagles Fact of the Day thread; had some technical issues with it and are hoping to get everything going again.  We are very sorry for the disruption!

With the severe weather and big weather changes, we get a lot of questions about how the eagles manage staying safe and warm (or cool). Stalmaster says that eagles belong to a category of "regulated heterothermy" which allows their temperatures to fluctuate within a narrow range. Body temperatures of bald eagles range from 101.84 degrees Fahrenheit at night to 105.26 degrees Fahrenheit during the day to 106.16 Fahrenheit during flight. With body temperatures lower at night, they can minimize heat loss. Maintaining internal temperature is critical. In hot weather, without sweat glands, they pant to reduce body temperature. In the cold, the base layer of thermal down, which we are seeing come in on DH2 now, insulates the body, but the eaglet must still be protected from wet weather until the waterproof plumage comes in. Once the feathers are present, the eagle can manipulate the feathers to provide an extra level of insulation, by creating a warm air layer between the down and the feathers.

The average rate of weight gain for a nestling prior to fledge varies but may be as much as 1 pound every 5 days. The largest weight gains are early in the nestling period. Between the ages of 18-24 days the eaglet gains about 4 oz. per day, more weight than at any other stage of development. So DH2's fastest rate of weight gain is coming up very soon. Many physical changes will also be taking place. Thermal down will be coming in so he is able to self-regulate his body temperature (thermoregulate), however, he'll not yet be waterproof.

In his book The Bald Eagle - The Improbable Journey of America's Bird - author Jack E.Davis writes about a Fish and Wildlife bald eagle census report completed in 2021. On the basis of aerial surveys from the previous two years, researchers calculated the bald eagle population in the lower 48 states had quadrupled during the previous decade.  Nesting couples totaled more than 71,000 and individual eagles well over 300,000.  Alaska's bald eagle population was put at over a conservative estimate of 70,000.  Canada had approximately the same as Alaska. To quote Davis "It would not be a stretch to say from coast to coast and from northern Canada to northern Mexico, five hundred thousand (bald eagles) occupied their indigenous  lands." 

The comeback of the American Bald Eagle has been truly remarkable.

An eagle can keep its body temperature within certain boundaries, even when the surrounding temperature is very different: thermoregulation!   Thermal down has very good insulating qualities and by 15 days old the chicks are typically able to thermoregulate on their own.  Parent eagles can be absent from the nest for slightly longer periods of time, although they are still close by and protective.

At 2 weeks of age the nestling should instinctively back up to the edge of the nest and defecate over the side.


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