known object or measurement. FindPet Care
Simply looking at a bird overhead is not enough.
A bird flying closer to the observer will naturally appear much larger than the same bird at a greater distance.
Without knowing the distance, apparent size cannot reliably be converted into actual size.
This is why scientists generally place much more weight on photographs with recognizable scale, physical specimens, measurements, or repeated observations by trained observers.
Without those things, a reported ten-foot wingspan remains an estimate—not a measurement.
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