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Tag Archives: Incubation

What is a brood patch?

March 4, 2024 RaptorResource

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

What Makes Bald Eagles Incubate?

March 2, 2023 RaptorResource

We wrote this blog a year ago. I wanted to revisit it given the events at the North nest this year. Mr. North and DNF have been dealing with intruders for a couple of weeks. Instead of perching near the nest, packing in food, and developing the reserves she needs to lay eggs, DNF is guarding her nest, egg, and mate from potential rivals. After egg number one, her testosterone and progesterone should rapidly decrease, while prolactin, a hormone that

What Makes Bald Eagles Incubate?

February 23, 2022 RaptorResource

I loved watching Mr. North incubate eggs through today’s snowy weather. He turned his head out of the wind, closed his eyes to protect them from the blowing snow, and fell asleep as the nest rocked gently back and forth. What makes normally active birds like hawks, falcons, and eagles spend so much time sitting on eggs? Hormones, egg production, and broodiness As daylight length increases, birds’ gonads swell. Both sexes produce testosterone, although male birds produce more than female

Eggs and cold weather

February 20, 2019 RaptorResource

This blog was first published on Wednesday, February 26, 2014. It has been updated to reflect Mom’s new mate and includes some information about the Fort St. Vrain eagles as well. Everyone was worried about the eggs in Decorah back in 2014. Iowa was facing a polar vortex while Mom was laying and incubating eggs. While there have been other cold years, 2014 was one for the record books, with windchills of -50F when Mom laid egg #2. Given that 2019

Do bald eagles delay incubation?

February 15, 2019 RaptorResource

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