People are curious whether the warm weather this winter and spring has affected eagles’ behavior. In fact, eagles aren’t too concerned about the weather in terms of when they lay eggs. The main cue for eagles to begin courtship and breeding is the photo period.
The photo period is the amount of daylight hours. This period changes throughout the year. March 21 is the vernal equinox, which means that there is equal hours of daylight and night. As we move toward June 21 the summer solstice, the daylight hours are increasing. A particular photo period will trigger hormones in eagle to initiate courtship and breeding. In our area, we usually see that beginning in February. Interestingly, the photo period in February is similar to that in October and November. We can sometimes see eagles engaging in courtship and nest building in the fall when the photo period triggers those same hormones.
Courtship for eagles can look a lot like fighting. Eagles will fly together and sometimes lock their talons together in mid-air. Sometimes they will stop flying and tumble together, gripping each other’s talons. They will also perform aerial acrobatics. All of this in an effort to assess each other’s strength and impress their potential mate.
Nest building is also a part of courtship and bonding. Eagles continue to use the same nest year after year. Each spring they will add up to a foot in diameter and height to the nest. This process of adding to the nest is part of their bonding to one another, but also to that territory. Eagles exhibit what is called nest-site fidelity. They seem to be bonded to the nest territory, so that if one of the pair fails to return in the spring, the other eagle will try to find a new mate and continue to use that nest and territory.
Because eagles use the same nest year after year and add to it each and every year, after many years of use eagles nests can be up to ten feet across!
With this camera view right into the nest, you can see that there’s more than just sticks in an eagle’s nest. The pair also brings back grassy materials or lines the bowl with their own down to get the nest ready for eggs. They want to create a nice soft spot for those eggs and young eaglets.