The thought was that a pesticide ingested through eating other critters which had also eaten the poison, was causing them to lay eggs with too thin shells.
This has been questioned..
And the suggestion was raised that people may have been the ones to hurt the population. I don't think this is up for debate.
Public awareness changed the path of their decline, however.
In the USA, they've now been moved from the category of Endangered Species to Protected Species, and they're thriving in my area.
For the first time ever, I've been able to see eagles regularly in wooded areas. I don't think they're thrilled to see me, but they ignore me gracefully. Seriously, if they were as ferocious as they look, I'd not be taking their picture because I'd be cowering from them. They can get angry. I've seen a local video of one of the young ones...maybe one pictured...knocking another eagle for a loop.
I don't expect to see any hatchlings because they'll be hidden. That doesn't disappoint me. The youngest ones aren't cute and cuddly.
Coloration changes on the eagles' head as they mature, and around the age of five years, they become the bald eagles we are more used to seeing in photos.