Having looked at the Bird Forum for a while, I joined on 27 Oct 2017, and have gone back and read all of the posts on this subject, and almost all of the attachments.
I am stopping now.
There is opinion, hearsay and possible evidence, but a lot is from shaky sources to support the supposition that birds disappear due to mobile phones (I know I have grossly oversimplified it) and, other than Nohatch and a few others, little to support the scientific method; even though it may be the case that results could support the supposition.
I have been worn down, and will not follow nor post here further.
I wish you well, Joost, along with your reasoned responses, and to all the others that have maintained their dignified positions.
I also wish you well Diane, for your determined and usually well presented posts.
My conclusion is that this will end in an inconclusive stalemate, even if Joost is able to bring evidence to show the original supposition was wrong.
Following other posts today about greenfinches etc, could disease have caused the loss of sparrows in your area? Just a thought.
Thank you for the ride