We saw a once-in-a-nest event at Xcel Energy Fort St. Vrain last night! Ma FSV has been a three-egg layer for most of her laying career, and we had no reason to think this year would be any different until she laid egg #4 at 6:32 MT last night. Congratulations, Ma and Pa – we’re so egg-cited for you! Watch live here: https://www.raptorresource.org/birdcams/xcel-energy-cams/.
How common are four-egg nests? Will all the eggs hatch? How likely are any hatchlings to survive? I turned to classic Bald Eagle research and academic databases, but really couldn’t find an answer other than a: uncommon, and b: four eggs might be the result of two female eagles laying eggs in the same nest. But Ma FSV is banded, so we know that she laid all four eggs, and I learned nothing about rarity or survival rates.
March 4, 2025: Four eggs for Ma FSV!
I ended up talking with Elfruler (https://www.elfruler.com), who has been documenting Bald Eagle nests since 2006. In a extensive dataset published on her website, she documented nesting activities at 401 nests between 2006 and 2020.
| Nest Type |
Number of Nests |
Number of Eggs |
% of Eggs Hatched |
% of Eaglets Fledged |
| One Egg |
27 |
27 |
44.4% |
67% |
| Two Eggs |
244 |
488 |
78.9% |
80% |
Three Eggs |
126 |
378 |
83.3% |
79% |
Four Eggs |
3 |
12 |
75% |
78% |
Five Eggs |
1 |
5 |
0% |
0% |
Elf’s data opens up several fascinating avenues for exploration and research. Could behavioral differences or inexperience explain why one-egg clutches tend to fare poorly? Do female eagles that lay a single egg one year increase their egg production in subsequent years? While the number of eggs laid fluctuates annually, the percentages of eagles laying one, two, or three eggs remain remarkably consistent when viewed over a five-year period. So what might cause an eagle that has been laying since 2007 to suddenly produce four eggs?
Good News!
Whatever led Ma to lay four eggs, I was thrilled to learn that four-egg nests tend to do quite well! According to Elf, of the five four-egg nests she knows of, 16 out of 20 eggs hatched (80%), and 14 of those hatchlings survived to fledge (87.5%). While anything can happen in the wild, these hatchlings have a much better than even chance of making it. Talons crossed for Ma, Pa, and their brood!
While eagles don’t truly delay incubation, they will stay off their eggs a little more often if weather allows. On March 3, we noted that Ma and Pa had been spending a fair amount of time off and hovering over their eggs. In hindsight, this might have been a sign that another egg was coming. We’re looking forward to documenting whatever this nest brings and wish nothing but the best for the FSV eagles.
The Raptor Resource Project