Question: If they bond, can Pride and the new female nest later?

[NewMexiKen]

I received a good question and am not able to give a definite answer.

If it takes more time for Pride and the new female to bond, can they just nest later than normal?  We know time will tell all!

My best respose is:

I know that for many bird species, songbirds in particular, that their reproductive system goes through an annual cycle. The ovaries enlarge as breeding season approaches and regress afterward for the rest of the year.

Raptors' cycles are typically synchronized with availability of prey so that when young are growing fastest prey is most plentiful. Great Horned Owls have greatest need when baby rabbits are most plentiful.

Bald Eagles in the northern part of North America must finish breeding in time to fly south to find open water or, in the case of our South Florida eagles, north, to find fish closer to the surface in the cooler water.

So my guess is that there may be a window of opportunity after which breeding would be unlikely. Make sense?

[KellyHeffernan Proj Perch]

Ken -

Thank you for that answer.

We were forgetting that the eagles are migratory, moving north in summer
and have a serious annual timing to their breeding and movements.  We're
watching these resident Burrowing owls and Cooper's Hawks that are not as
scheduled, but they also don't need to get anywhere far in summer, so
being late is not a big deal.  Our resident species may also rely on more
urban food sources.

So now your answer left us asking this:  If most birds fly north to nest
and south to winter, it seems these Florida eagles are south for the
winter, but nesting?  Are we confused or are eagles different?

Regards - Kelly



Kelly Heffernan
SFAS's Project Perch
[phone]

>
>
> /I received a good question and am not able to give a definite answer.
> /
> *If it takes more time for Pride and the new female to bond, can they just
> nest later than normal?  We know time will tell all!
> *
> /My best respose is:
> /
> *I know that for many bird species, songbirds in particular, that their
> reproductive system goes through an annual cycle. The ovaries enlarge as
> breeding season approaches and regress afterward for the rest of the year.
>
> Raptors' cycles are typically synchronized with availability of prey so
> that
> when young are growing fastest prey is most plentiful. Great Horned Owls
> have greatest need when baby rabbits are most plentiful.
>
> Bald Eagles in the northern part of North America must finish breeding in
> time to fly south to find open water or, in the case of our South Florida
> eagles, north, to find fish closer to the surface in the cooler water.
>
> So my guess is that there may be a window of opportunity after which
> breeding would be unlikely. Make sense?*
>
>
>
> -----
> Ken Schneider
> Web site: http://rosyfinch.com
> Blog: http://rosy-finch.blogspot.com
>
>
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[NewMexiKen]

Our southern eagles are also smaller, and this pair had adapted to a diet that included many birds. Not sure whether they were a more important protein source than fish, but the Bald Eagles up north, especially Alaska subsist almost entirely on fish.

I think this proves they are adaptable creatures, just as they have adjusted to the urban environment and the presence of humans. My guess is that the northern range was the norm earlier in time but that breeding to the south conferred certain advantages to those who wandered there to breed a long time ago, particularly a longer breeding season and food availability during the winter. Their smaller size provides relatively more surface area to cool them, while the northern eagles can better conserve heat because of a lower surface/mass ratio. This latter trait is common in many species. Those in the northern part of their ranges tend to be heavier and also often have darker plumage.

Of course my theory may be upside-down, but I am not familiar with the fossil record of eagles. My guess is that they moved north as the glaciers retreated until about 14,000 years ago, but where did they move FROM? Maybe they started as smaller eagles in the south and their range slowly moved northward. They may have adapted in the opposite direction, becoming bigger and heavier up north. Need Help from a Paleontologist!!