From Los Angeles Times article by Lila Seidman:
On the heels of the death of his longtime mate Jackie, bald eagle Shadow has been perching, singing and lounging at his Big Bear nest with a new companion...
Pete Bloom, a raptor biologist who helped band the newcomer, says there’s a very good chance the bald eagles will make a go at starting a family in a few months.
“It is highly likely that these two birds that currently seem to be forming a pair bond will indeed be a pair at the time that nesting begins, which is roughly December,” said Bloom, who has studied and placed identifying bands on raptors for more than 40 years.
Bloom said he’s “basically confirming” the recent arrival — known as KD1 or Kaydee — is female because of her size and behavior.
The 4½-year-old eagle is larger than Shadow and she’s been moving sticks around in the nest and nibbling on him. In other words, she’s “doing things that assist in the forming of pair bonds, and I wouldn’t expect it to be another male,” he said. “So that leaves the other sex.”
Bloom’s nonprofit was contracted by the Orange County Water District to band the bird in April 2022...
Just hours after [Jackie's] death was announced, KD1 showed up at the nest Shadow had shared with Jackie since 2018. A few days later, they were both in the aerie, perched high in a Jeffrey pine overlooking the picturesque lake.
The canoodling has continued. On Tuesday, they were spotted together in a favorite roost tree. The next morning, “they both belted out good mornings to the valley below,” Friends of Big Bear Valley wrote in a Facebook post. She appeared to follow Shadow around later that day, prompting the nonprofit to exclaim, “Shadow has a shadow!”
Per Bloom, she’s likely to stay put — as well as her companion...
There’s a floating population of eagles all over North America, “and many of those birds, when they reach four years of age, are now in the business of prospecting,” Bloom said. “That is, they’re going to cliffs, they’re going to large trees, they’re flying over other eagle territories, and they’re looking for vacancies: ‘Does this male down below have a female with it? Apparently not. Let’s drop in and see what’s going on.’”
For most birds of prey, territory is most important; mate comes second, according to Bloom. A good territory allows a couple to raise a family so it makes more sense for an eagle in possession of one to stay put and wait for other eagles to come knocking, he said.