Tag Archives: Reproduction

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

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

How long does it take a bald eagle to lay an egg?

An egg in cross section, modified from Romanoff and Romanoff, 1949

This blog was first posted on Thursday, February 22, 2018. While it was written about Mom and Dad Decorah, it applies to all of the eagles we watch. We’ve talked about how long it takes bald eagle eggs to hatch after they are laid (an average of 38 days from first egg to first hatch in Decorah), how long hatch takes once pip starts (it can take upwards of 24 hours), and how long it takes Mom to lay each

When will our eagles lay eggs? Bald eagle breeding in Iowa and Florida

Daylight Length Graph from Fort Meyers Florida

When will the Decorah and Decorah North eagles begin laying eggs? While nest timing can very from region to region (Florida, for example, is quite different from Iowa), mark your calendars as follows! In the nests we watch in Iowa and Colorado, bonding and copulating behaviors become more pronounced and frequent after the winter solstice. Female eagles begin laying eggs 5-10 days after productive copulation begins. This usually happens in mid-February at the Decorah and Fort St. Vrain nests. In