There was a changing of the guard at the eagle nest this weekend while I watched.
When I arrived on this late afternoon, one of the eagles was on the nest engaged in incubation duties. The other eagle was perched on the arm of an adjacent transmission tower keeping watch.
After some time, the eagle on the tower flew over to the nest, and the two big birds traded places. They were effectively taking turns with the egg incubation duties.
The newly relieved eagle wasted no time flying to the top of the tower where she began stretching her wings a preening—behaviors clearly demonstrating her appreciation for getting a brief respite from the tedium of nest sitting.
NOTE: To date I have been referring to the incubating eagle as the female, and the roaming bird as the male. Though, this is clearly not always the case, it is a convention I will probably continue with unless I discover someway to clearly differentiate the gender of the two adult birds.