Love is in the nest! This is a traditional Valentines Day post for us, but after HD and HM copulated this morning, we thought we would post it in celebration.
Bald eagle courtship
Bald eagles are famous for their whirling nuptial flight, but eagle courtship includes any activities that establish a new pair bond or renew an existing one. At our Decorah, Decorah North, and Fort St. Vrain nests, courtship usually begins in early October. Bonded pairs start working on their nests by bringing in sticks, large branches, and soft materials to replenish and rebuild them.
As courtship deepens in December and January, eagles ramp up their nestwork, burying last year’s nestorations under piles of new sticks and heaps of corn husks, corn stalks, and fluffy grass. Male eagles bring food gifts to their mates, eagle couples perch and vocalize together, and eagles prepare their nest bowls for eggs by digging, scraping, and molding multiple layers of soft stuff to the nest’s floor. Couples move from working and perching together to pecking, footing, body brushing, and displaying as they signal their growing interest in bonding.
Male eagles, like most male birds, lack an external phallus. Eagle mating goes something like this. An eagle (usually but not always the male) approaches its partner, vocalizing, swishing its tail, and leaning into or looming over its object of desire. An uninterested female (not now, dear!) might respond by standing up and starting what looks like a breast-bumping competition. An amorous female tilts forward, allowing her mate to land with his curled feet lodged on her back. She twists and moves her tail feathers to one side so he can press and twist his cloacal opening around her cloaca, passing sperm from his cloaca to hers. Intense, rapid vocalizations often precede and accompany mating, which takes seven to twelve seconds.
Female eagles also approach and mount their mates, letting them know in no uncertain terms that they are receptive and ready for copulation. This behavior varies widely from nest to nest and eagle to eagle. Mom Decorah took the lead on a fairly regular basis, but it’s rare for DNF and Ma FSV to do so. HD appears to need a lot of encouragement from HM, but they are new mates and this could change.
Why are nestorations part of bonding?
Why are nestorations part of bonding? It goes something like this: birds that build awesome nests relative to other members of their species must be healthy, high-quality mates. Think about bald eagles! As we’ve seen at Decorah and Decorah North, eagles spend a lot of time procuring and hauling wood and soft materials into the nest. This is an energetically costly activity that requires them to be in good shape: well-fed, skilled at flying, and relatively parasite-free. While different things indicate quality to different species of birds, large nests appear to signify quality to bald eagles.
Besties or Beakersons? HD and HM work on N1 together.
Both bald eagle parents build and maintain their nest, but males tend to spend more time getting sticks just right, preparing the nest bowl, and building the egg cup. What’s going on? Many female birds adjust their reproductive efforts in relation to their mate’s nest-building activities. The more time he spends working on the nest, the more time and energy she puts toward reproductive processes, including copulation. The end result? A higher chance of reproductive success for both of them!
Bald eagle mating – not as straightforward as we once thought!
HD and HM copulated on N1 this morning. At 25 seconds, HM drops into the nest and makes it very clear she is feeling amorous – look at her swishing tail and looming position, and listen to her voice. I’m not an eagle, but even I know she’s interested! After a little beaking, he gets on top. I’m not really sure how to describe what happens next. I feel uncomfortable using human terms, but it’s hard not to think of terms like ‘afterglow’. I’ve seen a whole lot of eagle copulation in our years documenting eagle life and this is the first time I would use the word ‘cute’ to describe it.
Why do some male eagles seem timid? Why do some couples bond more often than others? Mr. North and DNF bonded frequently in their first year together, DM2 needed a lot of encouragement to approach Mom, and HD also seems a little timid – although he’s getting less so, just in time for eggs! Sex, age, relationship status, and eagle personalities all influence bonding behavior. Look for them at every nest you watch – and read more about the difference between the two Decorah nests here: https://www.raptorresource.org/2019/12/31/whatta-year-a-tale-of-two-nests/
We know a lot more about eagle bonding than we did back in 2011! At the time, people believed that eagles didn’t bond very often outside their fertile periods. While female eagles were receptive to bonding, they seldom initiated it and always assumed a submissive role during copulation. But bird cams revealed a whole new world! Couples bond well outside their egg-laying period, although bonding becomes more frequent and intense when eagles are at or near peak fertility. Both male and female eagles initiate bonding and either one may assume a dominant role during copulation. Territorial eagle couples are usually monogamous and are not known to participate in extra-pair bonding, but mating systems can include thruples instead of couples. Whatever an eagle’s inner landscape looks like, their pair behaviors are richer and more complex than we once believed. The more we learn, the more questions we have!