Apparently the F-22 Raptor has the radar signature of a bird. Wouldn’t a bird traveling 700 km/hr be suspicious, so what’s stopping radar operators from detecting an F-22?
The now sadly retired Nimrod anti-sub plane
Could detect a metal biscuit tin floating in the North Atlantic from a hundred miles away. The problem is that the North Atlantic is full of bits of floating junk. If you looked at a radar screen with the sensitivity turned to that setting all you’d see would be the noise of hundreds of contacts.
Anything displayed on a radar screen has been filtered by computers to eliminate “junk” returns. You’re entirely right: a bird sized return travelling at 15 knots will not be displayed. A bird sized return travelling at 700 knots WILL be flagged up. The F22 is low profile but its not invisible, especially to powerful AWACS level radars.