.The text description of the bird ("X") is from about 3 weeks ago.
3 weeks ago, X was 90% white with dark grey spots.
Each spot was the size a 5p coin. Each spot was about 2 inches from any neighbouring spot. So the bird was about 90% white.
When the wings were folded, the trailing edge of each wing was the same dark grey as the spots.
Today: The spots are disappearing, so I'm assuming that X will eventually be all-white.
The length and height of X has always been similar to its friend, which is a normal UK grey town pigeon. But the pigeon is more sleek.
By "sleek" I mean that that the largest measurement round the body is smaller for the pigeon than for X.
When both birds are together, and the pigeon is startled, both birds fly off in unison.
But if X is alone, I can gradually edge to within half of the distance that would startle the pigeon. I keep my eyes averted, and I walk only sideways or backwards, at about 2 inches per second.
I would be grateful if someone could identify this bird.
Thanks
Footnote: The spell-checker is based on US spelling. So "neighbouring" was marked as incorrect. Removing the "u" removed the red underline..
Pity you haven't a photo of the bird in question, or even both.
Often birds of different species if spooked will alarm other birds when they fly off, the others taking the safe option and flying off as well. it could be they are family, and the demise of the spots may be a normal plumage change, either winter to summer, juvenile to adult.
But I am guessing, and hopefully someone may be able to give you more info.
As for the spell check, don't worry too much, we're not going to insist on perfect spelling, but you should be able to change from English US to English GB by looking in the browser settings.
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Thanks for all responses.
Here's the photo.
It took me a while to figure out how to zoom out on a photo, then save the new photo. (Spoiler: Duplicate, Crop, Save)
The discrete spots of a few weeks ago have gradually blurred, and have almost disappeared. The tips of the folded wings still show a hint of dark grey/black.