We saw two eagles on N2B this morning. The female is around four years old and the male is an adult. This makes multiple nest building even more interesting: It’s one thing to build a nest for yourself and another entirely to let someone else take over! Well, we built N2B, but the concept is the same.
If these eagles move in, we’ll get to see how two eagle power couples respond to one another. We hadn’t considered multiple nests as a factor in eagle population expansion, but perhaps they play an important role in building populations. Nest site availability is a key factor in establishing and retaining birds, so surely the same is true of an entire pre-built nest!
We know that Bald Eagles are quite social away from their breeding grounds. They congregate in large mixed-age groups, roost together, squabble and chase over food, and sometimes hunt cooperatively. Even breeding eagles occasionally accept migrants and wanderers, especially in late summer and early fall. Food attracts eagles, eagles attract eagles, and eagles tend to return to nest in their region of origin, so it isn’t surprising that we’re seeing more eagles in and around Decorah and at N2B.
Do multiple nests play a role in building eagle populations? It seems like an odd question, since nesting eagles don’t welcome other eagles on their home range. But they will tolerate other eagles fairly nearby, assuming a plentiful food supply. In suitable territory, Mark Stalmaster found that the average distance between bald eagle nests was between one and three kilometers (Mark Stalmaster, The Bald Eagle, page 52). Mom and DM2 took advantage of the nest we built for them, so why wouldn’t another eagle couple do the same?
Food attracts eagles and eagles attract eagles, but there may be further advantages to concentrating in a territory. Maybe fledglings have higher survival rates if they can form a post-dispersal crèche. Or maybe a large eagle presence deters (non-eagle) competitors and predators, benefitting the population as a whole. It’s something we’ll be looking into!
Did you know?
We know that modern birds descended from a group of two-legged dinosaurs known as theropods. What did dinosaur social behavior look like? Much of the behavior observed in reptiles seems specific to the ecological setting within which they live. For all those territorial species studied, crowding results in increased social interaction, increased aggression, and a switch to hierarchical behavior. Dinosaur and reptile social behavior might provide an interesting model for bald eagles and other birds: https://academic.oup.com/icb/article/14/1/35/2066806.
Eagle intelligence? Thoughts here: https://www.raptorresource.org/2020/03/27/musings-place-stories-and-eagle-intelligence/.