Tag Archives: Incubation

What Makes Bald Eagles Incubate?

February 21, 2022: North Nestoration Follies!

We wrote this blog to describe events at the North Nest back in 2023, when Mr. North and DNF were coping with a lot of intruders. Instead of perching near the nest, packing in food, and developing the reserves she needed to lay eggs, DNF guarded her nest, egg, and mate from potential rivals. After egg number one, her testosterone and progesterone should rapidly decrease, while prolactin, a hormone that induces incubation and brood patch swelling, should rapidly increase. But intruder-related

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Bald Eagles, Eggs and Cold Weather

The eggs are warmed and protected by their parents’ bodies and the insulation beneath and around them.

Cold weather often raises concerns among Bald Eagle watchers. Will their favorite eagles keep their eggs warm and dry in sub-zero temperatures and snow? Eagles don’t have central heating or electric blankets, but they have everything they need to incubate their eggs through the worst a Midwestern winter can throw at them: meticulously built nests that aid incubation and withstand winter’s chill, highly vascularized brood patches that transfer body heat directly to their eggs, and remarkably robust eggs.  In short:

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What is a brood patch?

March 30, 2018: Mrs. North's brood patch

Daylight length, or photoperiod, strongly influences hormone production in birds. In the northern hemisphere, our story begins shortly after the winter solstice in December. As daylight length increases, a cascade of hormones causes birds’ gonads to swell in preparation for reproduction, egg-laying, and incubation. In this blog, we’ll discuss the role the brood patch plays in incubation and determining clutch size. How do bald eagles keep their eggs warm in subzero temperatures? They apply heat via a special area of

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Do bald eagles delay incubation?

February 14, 2019: FSV

This blog was first published on Tuesday, March 29, 2016. It has been updated to reflect new knowledge and events. Do bald eagles delay incubation? It wasn’t an a question we’ve thought about much, since bald eagles in Iowa usually lay eggs in temperatures under – sometimes well under – freezing! However, 2016 was quite a bit warmer, and the eagles in Decorah and Fort St. Vrain seemed to spend more time off the first two eggs than we are used

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