A combination of nest timing and behaviors made us consider the likelihood that Mrs. T could have a new Mr. for the second year in a row. Read on to learn more!
Nesting records: A new mate (usually) equals later eggs
In general, eagles tend to lay eggs later during their first season with a new mate and move laying earlier in the years that follow. Here’s what our records show:
Mom and Dad Decorah
1st egg: March 5, 2008
1st egg: March 3, 2009
1st egg: February 25, 2010
1st egg: February 23, 2011
1st egg: February 17, 2012
No data for 2013 *
1st egg: February 23, 2014
1st egg: February 18, 2015
1st egg: February 18, 2016
1st egg: February 20, 2017
1st egg: February 21, 2018
* Mom and Dad built a new nest in 2013
Mom Decorah and DM2
1st egg: February 22, 2019
1st egg: February 26, 2020
Mr. and Mrs. T
1st egg: February 25, 2024
1st egg: March 4, 2025 *
* 2024 was a leap year, which means the T’s fell back 8 days
Ma and Pa FSV
1st egg: March 3, 2007
1st egg: February 27, 2008
1st egg: February 17, 2009
1st egg: February 14, 2010
1st egg: February 16, 2011
1st egg: February 16, 2012
1st egg: February 17, 2013
1st egg: February 21, 2014
1st egg: February 14, 2015
1st egg: February 16, 2016
1st egg: February 14, 2017
1st egg: February 12, 2018
1st egg: February 13, 2019
1st egg: February 14, 2020
Ma and New Pa
1st egg: March 4, 2021
1st egg: March 3, 2022
1st egg: March 2, 2023
1st egg: February 29, 2024
1st egg: February 22, 2025
Mr. North and Mrs. North
1st egg: March 11, 2016
1st egg: February 19, 2017
1st egg: February 25, 2018 *
*Mrs. North laid just one egg, which broke.
Mr. North and DNF
1st egg: February 21, 2020
1st egg: February 16, 2021
1st egg: February 16, 2022
1st egg: February 20, 2023 *
1st egg: February 15, 2024
1st egg: February 11, 2025
*DNF laid just one egg, which broke.
Egg-laying is influenced by individual, social, and environmental stressors, including competition, weather, and nest availability. Having said that, egg-laying dates usually move earlier and stabilize over time. In five of the six eagle pairs we’ve tracked to date, female eagles moved laying earlier after their first year with a new mate. We don’t know why Mom Decorah laid four days later in her second year with DM2, but she was an outlier.
We thought that the T’s would maintain their previous timing or shift slightly earlier this year, but theirs was the only nest to shift later. Ma and Pa FSV shifted seven days earlier and DNF and Mr. North shifted four days earlier.
Nesting records: a brand new layer (often) lays fewer eggs
Back in March, I wondered if we had a new Mrs. T because she started laying later and produced three eggs instead of two. But when I dived into our records, I found that female eagles who increased the number of eggs they laid did so after the first year they laid. New male mates were not correlated with an increase or decrease in the number of eggs that females laid. From our records:
- Mom Decorah laid two eggs in 2008 and three eggs every year thereafter.
- Ma FSV laid two eggs in 2008 and three eggs every year thereafter, with the exception of 2010 (two) and 2024 (four).
- Mrs. T laid two eggs in 2024 and three eggs in 2025.
- DNF laid two eggs in 2019 and two eggs every year thereafter, with the exception of 2023 (one).
Although eagles have nested in Trempealeau since 2017, we didn’t install cameras until 2024. Based on her egg-laying pattern, Mrs. T was likely a new nester that year, though we lack biometric data to confirm it. However, nesting history and the images we’ve collected since 2024 suggest that the current female is the same Mrs. T who nested here last year. The 2024 image was enlarged from video footage, but her eye flecks appear strikingly similar in both years.
Behavior: a new parent has a lot to learn!
Again, we thought that the T’s would maintain their previous timing or shift slightly earlier this year, but theirs was the only nest to shift later – and they did so by eight days. The female eagles we’ve tracked haven’t tended to shift later by more than four days with two exceptions: Mrs. North in 2018, when she laid just one egg, and Mom Decorah in 2013 or 2014.
We don’t know why Mom Decorah shifted six days later in 2013 or 2014 – new nest, perhaps? – but Mrs. North’s egg-laying pattern in 2018 indicates that she was under stress. It influenced the number of eggs she laid (one), when she laid it (later), and quite possibly egg-formation itself (the egg broke during incubation). We saw a similar pattern at the North Nest in 2023, when DNF was continuously harassed by adult female eagles as she was laying.
In short, our records show that a new mate is far and away the most likely cause of a dramatic shift to later laying.
So Mrs. T could have shifted later due to an unknown stressor, but Mr. T’s behavior is also more typical of first-time eagle fathers. He vanished during incubation and has a very mixed record of brooding and feeding, by which we mean he’s been as likely or more likely to take fish for himself instead of feeding his young. It sometimes feels like Mrs. T is feeding the whole family! Based on behavior alone, I’d suspect Mr. T is a new mate. Our nesting records support that conclusion.
Mr. T’s instincts finally seem to be kicking in, but he still has a lot to learn about sharing food!
Biometric data: Are those eye flecks the same?
How about biometric data? While Mrs. T’s eye flecks are quite similar, Mr. T’s are less so…
One fleck is very similar, but two others are missing. We’re not yet prepared to say that we know Mr. T is a new male eagle: our lone camera in 2024 was lower resolution and not positioned especially well for close-ups, which means we couldn’t get the high resolution photos we usually use to identify eagles based on biometric data like eye flecks. But nesting chronology, behavior, and what biometric data we have all make a pretty persuasive case for a new Mr. T.
The Raptor Resource Project