Question for the Experts

[Linda954]

How is this frigin weather affecting the incubation period.
I was hoping it won't bother the eagles too much or hurt
the process.

[Jill W]

I hope you get an answer, Linda.  I was thinking about the same thing.
Jill

[NewMexiKen]

Don't mistake me for an expert, but the eagles (like most birds) are well-equipped to heat and also cool their eggs as needed. Both male and female develop brood patches to keep the eggs warm. Even up north, the eagles nest quite early in the year, and they often must protect their eggs against sub-freezing temperatures. I do not think that the expected 35 day incubation time would be significantly affected by the cold weather.

I found this on the Journey North page-- lots more interesting information there:
Bald Eagle Nesting Phenology

Incubating Eggs: 35 days
As soon as the first egg is laid, the female and the male take turns incubating. Both male and female eagles form a brood patch--a bare spot on their tummy where they can press their hot skin directly against the eggs or chicks to keep them warm. The female's brood patch is a little bigger and more feather-free than the male's. And the female incubates the eggs more often than the male does.

One study showed that the female was responsible for 72% of the incubation. (How much was the male responsible for?)

Eagles sit on their eggs most of the time--one study showed that the eggs were incubated 98% of the time! But when the temperature is warm and there is little wind, the parents incubate less often. Sometimes when the parents leave the eggs, they cover them with feathers and nesting materials. Scientists don't know for sure whether they do this to keep the eggs warm or to hide the eggs so predators don't steal them.

Eagles have VERY sharp claws on their powerful talons. When the incubating parent is moving about the nest, it often clenches its talons so the sharp claws can't hurt the eggs or babies by accident. The parents are also very careful to step around the eggs to avoid crushing them. Parents probably turn the eggs at least once a day, but scientists aren't sure how often this happens or which parent does it.

[NewMexiKen]

On a related subject, Barbara Walker forwarded this item. We observed the same thing after the eggs hatched last year-- the female suddenly began sitting up higher in the nest.

Here is a description/definition of brooding which Lynda wrote.  I thought it would be helpful for those who are watching nests.

From Lynda White:

Brooding occurs when one of the eggs has hatched and the chick is still young enough that it has to be kept warm... The adult sits higher in the nest, keeping both the chick and any unhatched eggs warm. By the time they are 10-12 days old and developing the secondary down, they can regulate their own body temperature.

Thanks,

Barb Walker

Palm Harbor, FL

[Linda954]

thanks.    I'm glad they have a few more weeks; clearly they wouldn't want to have to enter the world tomorrow morning in these temperatures.   brrrrrrrrrrrrrrr  

[Trisha]

Thanks for the great info....really interesting! I was wondering about the warmth of the eggs with the duration and "severity" of our cold weather!

Jill posted her photo of the adult bringing fresh straw recently so I assume that would be good insulation also.

[Mike Fossler]

Just remember, eagles are sitting on eggs much further north than here - now and in the past.

[NewMexiKen]

Yes, Mike. Great Horned Owls also nest very early in the season. Growing up in New Jersey, I observed one sitting on eggs in a nest atop the broken-off trunk of a tree. It was February and it had been snowing. The owl was itself covered with snow while it sat close to the eggs.

Like eagles, Great Horned Owls have quite a prolonged nesting and breeding season. Their young require tending into late summer-- for about 5 months after leaving the nest (which is even longer than our local eaglets appeared to be dependent upon their parents for food). For the owl, the early nesting appears to be an adaptation to the timing of the reproductive cycle of its principal prey species-- mostly rabbits. Young rabbits are produced early in the spring, just when the young owls are growing most rapidly and need the extra nutrition.

On that subject, we should be keeping a watch out for Great Horned Owls on their nests. One did nest last year about a mile north of the eagle nest, off Sheridan near the entrance to the landfill next to the prison.

[Trisha]

Oh ....I agree!  I think maybe those eagles are more experienced with
cold weather though. Ours are so accustomed to it always being warm
that as the article stated, they can, and even did leave the eggs for
periods of time. It's a good debate I guess and I'm sure that they
have a sense of the air temperature and don't leave the eggs alone or
uncovered long enough for them to be harmed.

On Thu, Jan 7, 2010 at 8:20 AM, Mike Fossler [via Bald Eagles of
Broward County, Florida] <[hidden email]>
wrote:
> Just remember, eagles are sitting on eggs much further north than here - now
> and in the past.
>
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[NewMexiKen]

I forgot to mention another interesting observation about owls in cold weather. While I was leading a winter bird walk at Rio Grande Nature Center in Albuquerque, we came upon a Great Horned owl that was roosting quite near the trail. We did not see it until it flushed. As it flew off its perch, something dropped to the ground. It was the hindquarters of a Cottontail Rabbit, frozen hard as a rock. Apparently the owl had cached it somewhere and intended to eat it, but it would have been very difficult for it to break off a piece.

Checking the literature, I discovered that these owls are known to store frozen prey in their nests, and actually may "incubate" the food to defrost it. No need for a microwave!