Friday, March 23, 2018

The Broken Egg at the Decorah North Nest

We asked our panel of eagle experts about the broken egg at the Decorah North nest. Could egg viability be determined from the video? Did they have any ideas about egg breakage? Was Mrs. North likely to produce more eggs?

In general, the panel believed that the egg’s viability couldn’t be determined from the video, although two of them commented that a darker patch in the draining egg fluid could have been an embryo. At 19 days old, an embryo would still have been quite small and not especially easy to see given the circumstances. Since we couldn’t come to a definite conclusion, our answer is “No” – we don’t know whether the egg was viable or not. We have some information about embryonic developmental stages here: https://raptorresource.blogspot.com/2017/03/whats-inside-those-bald-eagle-eggs.html

So why did the egg break? Female eagles lay down calcium in their shell gland/uterus, and their large eggs take a lot of calcium. Was she not able to lay down enough calcium to protect her egg from breaking, and if so, why? She may not have had enough calcium available during that stage of egg formation, or something else could be going on with her reproductive system. One member of the panel asked about her age. Female bald eagles and peregrine falcons can experience reduced fertility as they age. They might lay fewer eggs, strangely colored eggs, oddly shaped eggs, ‘smooshy’ eggs, thinly-shelled eggs, or infertile eggs that never hatch. It’s too early to know whether that’s the case, but we will be watching to see if any of those things happen moving forward.

Was she poisoned again? We saw no sign that she was poisoned this year, and the poison from two years ago would not affect her shell deposition now.

Is Mrs. North likely to produce more eggs? The answers were mixed. If she does, it should happen around March 30, or about 14 days after she lost the first one. Other birds of prey, including gyrfalcons and barn owls, take 14 days to recycle after losing a clutch. I really went back and forth about this (19 days is a long time to incubate an egg!) but the answer gave me some hope, especially given that Mr. and Mrs. North are still copulating. We’re crossing our talons, hoping for the best, and keeping a very sharp eye on Mrs. North!

9 comments:

Linda said...

Thank you for that information.

Joan Milley said...

Yes, thanks so much for your comments.

Cornelia S said...

Thank you Amy for that info. Love the blogs.

Judy Jackson said...

Thank you for the explanation.
It was very helpful.

Donna Martini said...

Thank you so much. It was very informative and interesting.

Dino K said...

I was wondering about the "thin shell" being the reason for the loss. At the Sauces nest in California the female laid 8 eggs in two different clutches and every single egg broke in less then 4 days. That was last year and this year the same eagles laid three eggs and now gave 3 thriving eaglets that are approaching 1 week of age. It is hard to understand but a great joy at the same time for the Sauces pair. Hoping for the same outcome for the North's even if it needs to wait until next year. Thank you for the information Amy.

theresa anderson said...

Fingers crossed and thank you! :-)

Rohi Shri said...

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James McKee said...

Thanks for the good explanation! This will liven things up again!