I have no English sources for you, but with some translation app you can probably still check them out. One article that I used is not available online unfortunately.
The Owl Camera(they have other owls and other birds too, as well as some interesting articles. The site is only in Dutch unfortunately).
[Article by NOS](Oehoe bezig aan opmars: 'Mogelijk al boven de honderd' - https://nos.nl/l/2519607), the public broadcasting service. From this article is the ringing video that I talked about in the post.
This German Site which has some numbers about the Eurasian Eagle Owl in Germany. They also have This article that talks about how the Eurasian Eagle Owl was perceived in the past in Germany. It is really interesting, so definitely check it out! They have some more articles that are very interesting too.
Also some random linguistic facts: The Eurasian Eagle Owl is called Oehoe in Dutch and Uhu in German; both pronounced as "oo-hoo". This is the only Dutch owl name that doesn't end in owl; it is also an onomatopeia.