2-3-2025 Delayed Incubation - What Is It?

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During the week when Jackie was laying her 3 precious eggs, we received a lot of questions about delayed incubation.

Many bald eagles do not incubate the first egg right away, delaying development so that their chicks hatch closer together. The main idea behind this evolutionary adaptation is to ensure that younger chicks have a higher chance of survival while competing with their older siblings for food and shelter.

Individual pairs may have their own preferred “recipe”: some may delay a lot, some not at all.

It works primarily because freshly laid eggs do not need to be incubated right away. They can be suspended or stored in a state of “suspended development” for days and even weeks. The ideal storage temperature is about 50F, but some research suggests it may be as low as 28F.

You may have heard about folks who hatched store bought or refrigerated chicken eggs in incubators - suspended development works with chickens too!

Once the clutch is complete, Jackie and Shadow usually start incubating full time. Their high body temperature of 105F allows them to keep their eggs toasty warm, at the incubation temperature of about 98F. The difference between internal body temperature and incubation temperature allows for some heat loss while incubating in colder climates.

Here is the most fascinating thing we observed: Jackie appears to “know” how many eggs she is about to lay, because she does noticeably more delayed incubation with 3-egg clutches compared to 2-egg clutches. Isn’t it neat?

Now that Jackie appears to be done with laying eggs, our Pip Watch will begin on 3/1. Our eggs historically hatched around 38-39 days, but with 3 eggs it could be a bit longer.

We hope you will enjoy this video of Shadow whacking Jackie on the head with a big stick. To get on the eggs of course!

Cali

P.S. You can find detailed information about incubation behavior in our Activity Log. The data was meticulously collected by our dedicated volunteers, who have been observing and documenting eagle activities around the clock for many years. Thank you!♥️




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