Tag Archives: Reproduction

When will our eagles lay eggs?

January 26, 2025: Mr. North and DNF duetting

When will the Decorah North, Trempealeau, and Fort St. Vrain eagles begin laying eggs? At the nests we monitor in Iowa and Colorado, Bald Eagles typically lay eggs 5-10 days after productive copulation begins. The past six years look like this… In 2025, DNF laid her first egg on February 11, Mrs. T laid her first egg on March 4, and Ma FSV laid her first egg on February 22. Once an egg-laying pattern is established, Bald Eagles tend to

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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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Nest-guarding and intraspecific intrusions

March 16, 2023: Mr. North and his last evening of incubation.

The Decorah North Eagles have been dealing with a lot of intraspecific intrusions this year. Intrusions happen when members of other species encroach on or enter a nest in search of food, nesting materials, or a nest: think squirrels, mice, raccoons, chickadees, woodpeckers, red-tailed hawks, house sparrows, and other animals we’ve seen in and around our nests. Intraspecific intrusions happen when other eagles intrude on daily nest activities in search of food, new mates, or breeding territories. They can lead

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How long do peregrine falcons live?

Peregrine falcon Michelle at fifteen years old

How long do peregrine falcons live and/or reproduce? This question was inspired by a discussion in the Midwest banding group last week. Jackie Fallon of the Midwest Peregrine Society shared a Facebook post about Hunter, a 21-year old male peregrine falcon who was rescued in Toronto, Canada. Hunter is the oldest known wild-producing falcon in North America: https://www.facebook.com/Canadian-Peregrine-Foundation-149280041803853/. The Manitoba Peregrine Falcon Recovery Project followed up with the story of Princess, a 19-year old falcon who was rescued in Winnipeg,

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What is up with our eagle Moms?

05/09/19: Mom and DM2

We first blogged on this subject on April 30, 2014, but we’re asked about Mom’s behavior every spring. Wondering where the love went? This blog is for you! We’ve had several questions and comments about our eagle Moms. Why are they so demanding? Why are they mad at their mates? Why are they so mean? While I can find snippets of behavior that seem loving to human observers – shared incubation duty, mutual nest defense, and tandem feedings, to name

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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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