From the internet or any other medium of information I came to know that some cutting edge stealth aircraft have radar cross sections of a bird (or something similarly small).
I don't have the in depth technical know how of how modern radars, air surveillance and detection systems work (obviously). But judging from what they are required to be, here is my conclusive query:
If you want to detect an enemy aircraft (either using a centralized monitoring system or in an anti aircraft missile), you want the detection in the 3D cartesian (x, y, z) axis location of it. If that is possible, and an aircraft with a bird size of RCS, is seen as a bird or small object on radar, still a small object at heights of 30,000 - 40,000 feet moving at a speed of near Mach 1 or higher Mach numbers, would not that be something very obviously alarming?