How many bald eagles can the North Country support?
“Bald eagles fall in love for life.”
There’s a common statement people like to share with me about birds. I bristle a little bit whenever I hear it. For one thing, bald eagles are more attached to a good territory than each other. For another, if you start looking to nature to confirm your moral guidance, expect to be traumatized.
Case in point is a fascinating trio of bald eagles on a live Internet camera in Illinois. Eagles had been occupying the nest for a while. The pair originally was Hope (the female) and Valor I (the male). In 2013, Hope chose a new mate soon to be called Valor II, but Valor I wasn’t quite ready to part with the territory and stuck around. The new male and Hope tolerated his continued presence and they successfully fledged young that summer as all three birds incubated the eggs and brought food to the young.
In March 2017, Hope was killed by a another eagle, and Valor I and Valor II eventually found a new female, referred to as Starr, and all three remain a family unit in mating, incubating, and raising young. And all three are back at it this year. Murder and an open relationship? That’s not exactly “in love for life.”
As our population of bald eagles recovers in the United States, we are unsure about the carrying capacity of the species. Every time I think we have enough eagle nests where I live, a new one appears. I work for the Mississippi National River and Recreation Area, a 72-mile stretch of the Mississippi River through the Twin Cities metro area in Minnesota. The last time we surveyed bald eagle nests in my corridor, we had 55 active nests, up 35 percent from the last survey in 2011. And we have more nests now. Every time I think we are at capacity, we are not.
We’re starting to see some of the effects of so many eagles as territory battles happen in backyards and on the sides of roads. Perhaps this trio decided not to fight and work together as a means to deal with limited territory. There was an infamous battle between two bald eagles in Florida that resulted in both birds brawling on the ground and then falling into a storm drain. People captured the battle on smartphones and shared it far and wide.
Some birds, however, aren’t fighting to the death for territory but working together to make their nests work. We don’t watch every single eagle nest out there; maybe these trios or cooperative breeding situations happen more often than we realize. It certainly does with other species. Researchers studying the Laysan albatross in Hawaii found that a third of the birds were involved in same-sex pairings. In 2004, 39 of the 125 nests were genetically tested and were found to belong to female-female pairings. One of the females would find a willing male to fertilize her egg and then she and her female mate would raise it.
Bobolinks with good habitat have been documented being polygamous. A study in Wisconsin tracked 62 males, and 36 of them were polygamous. Even that beautiful cardinal in your backyard could be polygamous. Birds do what they have to do to manage territory and raise young.
As we find more intimate ways to track birds with DNA and hidden cameras, who knows what else we will discover about the complex mating dynamics of birds and what exactly is natural.