Remember January and February of 2025? Bald Eagle Mr. T was attentive, his mate Mrs. T laid three eggs, and both eagles actively tended their nest. But after March 19, he began spending less time there. He disappeared entirely between March 27 and April 5, and when he returned, his visits were brief and infrequent. Mrs. T was left to manage the nest mostly on her own – although Mr. T brought in a few fish, he took more than he gave. We’ve watched seven eagle pairs since 2011 and we’ve never seen anything like it.
April 20, 2025: Mr. T’s other nest and mate.
On Sunday April 20th, our camera operators documented Mr. T flying to a bald eagle nest roughly 1700 feet west of the nest he shared with Mrs. T. As of this writing, Mrs. T is caring for the couple’s lone remaining eaglet while Mr. T cares for two eaglets – presumably his – on what we’re calling the MN Island nest. So what’s going on and how common is it? I’m still looking for documentation and reaching out to our Eagle Council, but former RRP lead mod Elfruler recorded just two cases of cooperative breeding captured on streaming cameras and seven cases of more than two eagles at a nest or of one eagle attending two different nests during the breeding season. Check it out: https://www.elfruler.com/?page_id=910.
Eagle triads are rare. This is only the second polygynous trio streamed online.
What is Cooperative Breeding?
Cooperative breeding occurs when more than two birds of the same species attend a nest during the breeding season. It typically involves a mated male-female pair and one or more caregivers who help incubate, brood, feed, defend the nest, or otherwise assist in raising young. Pair-nesting describes a system in which helpers provide alloparental care but do not contribute genetically to the brood: cooperative polygamy describes a system in which helpers also engage in mating, leading to the possibility of shared parentage among group members.
Cooperative polygamy can be further broken down into cooperative polyandry, or one female with multiple males, and cooperative polygyny (also described as ‘traditional polygamy‘), or one male with multiple females. Polyandry is an alloparental care system that revolves around one nest, but females in a polygynous system often maintain separate nests and may not cooperate at all. Trempealeau is a great example of the latter, since neither nest has more than two eagles in attendance and – as far as we know – no eagle is caring for offspring that aren’t its own. But Fulton – remember the Fulton triad? – is an excellent example of the former. Male eagles Valor and Valor II both mated with Star and all three cared for young in one nest.
Polygynous Bald Eagle Triads: Not Very Cooperative!
April 25, 2025: Mrs. T opens her mombrella to protect TE3 from a chilly April rain.
As far as we know, raptors are usually monogamous; that is, they engage in a single, exclusive relationship for at least one breeding season and usually more. While recent studies cast some doubt on exclusivity, it is rare for raptors to engage in polygamy. When they do, it usually looks like this:
- Polygyny appears to be more common than polyandry or polygynandry (what some of you might call a free-for-all). One male mates with multiple females and provides care (or not) for multiple broods.
- Each female tends her own brood in her own nest. Although nests are within sight of one another, they aren’t clustered together.
- Males often invest unequally in their nests, typically providing more care to the primary female’s brood.
Sound familiar? Mr. T has two mates who each tend their own brood, in their own nest, across about 1700 feet of open water. And although we’re somewhat confused about the nuts and bolts of his unequal nest investment – it sure seemed like Mrs. T was his one and only earlier this year! – he is clearly putting more into the MNI nest right now. Was the MNI eagle his primary all along? Did she lose her mate, giving Mr. T a chance to move in? Was he doing this last year, too? We don’t know, but what we’re seeing fits the textbook definition of polygyny.
Why is it considered cooperative if each female tends her own brood in a separate nest and no one is sharing care? Technically, the two are sharing Mr. T and they aren’t fighting over territory or resources. But it’s hard to argue that the group is nesting cooperatively given what we’re seeing. Similar behavior was documented in a polygynous trio in Erie, Colorado beginning in 2018: https://frontrangeeagles.org/our-eagles/the-erie-nest/ and another in New York State (documented in an abstract for the Raptor Research Foundation in 1994).
In short: based on what little documentation we have, polygynous Bald Eagle triads don’t appear to involve alloparenting and aren’t especially cooperative.
Polyandrous Bald Eagle Triads: Very Cooperative!
Female Eagle Starr and her Valors. The Valors recruited her into their triad after Hope was killed. Photo credit Stewards of The Upper Mississippi webcam.
The Fulton case might be the most famous example of Bald Eagle polyandry. In 2012, resident female Hope and new mate Valor produced two eggs. Valor – who was believed to be a first-time father – provided inconsistent care and the nest failed. In 2013, a new breeding male (Valor II) entered the scene. He and Hope produced two eggs, although Valor remained on site. The three eventually formed a triad in which Valor and Valor II copulated with Hope; after Hope was killed by intruding eagles in 2017, the two males raised their young and recruited a new female for their triad. This is a textbook example of cooperative nesting: all three eagles inhabited the same nest, all three engaged in copulation, and all three raised their young together. While the two Valors were never documented having sex with one another, they formed a bond that outlasted Hope.
In short, documented polyandrous Bald Eagle triads tend to be highly cooperative and involve alloparenting. While often grouped together, Bald Eagle polygyny functions more like a mating system, whereas polyandry seems rooted in shared parental care.
So Many Questions!
This case raises so many questions. We don’t know why Mr. T’s ‘wives’ haven’t engaged in aggressive activity, why Mr. T left a nest he seemed invested in, or why Mrs. T let Mr. T take fish from her nest to another nest. We don’t know why territorial, monogamous birds sometimes decide to form a triad. And we don’t know what influences polyandry versus polygyny, especially since eagles do both.
April 14, 2025: TE3 lunges for a bone.
It’s only recently that we’ve deployed the technology for 24×7 monitoring of eagles, which happened right as their numbers began booming. Are eagles as flexible about mating choice as they are about food and landscapes? If so, we might start to see more triads, especially where eagles are crowded in close together. Is this another resumption of an old behavior that might have occurred when eagles were more numerous? As we’ve written before, they are social during some periods of their lives: https://www.raptorresource.org/2023/12/07/bald-eagles-a-fission-fusion-species/. So. Many. Questions!
Perhaps Bald Eagle triads are more common than we thought, but this was only the third polygynous case I could find reference to. We’re reaching out to our Eagle Council to learn more and we’ll share their ideas with you soon!
A lot of you are angry with Mr. T. I get it. It was heartbreaking to watch TE4 and TE5 die. Still, Mr. T isn’t a deadbeat dad, and he didn’t deliberately harm his young. We know that eagles have internal lives and emotions, but that doesn’t mean they think like us or share our motivations. We may never know why the three eagles formed a triad, but this is where they have brought us. So let’s trust the eagles, stay curious, and keep watching, sharing, learning and especially caring – together.
Things that helped me learn and write about this topic
The Raptor Resource Project