Are you referring to thermal imaging?
In addition to that birds don't tend to emit much RF. And spectroscopy of the visible light from the materials comprising the body should be quite different unless the drones are covered in harvested genuine feathers.
alt Hacker News
In addition to that birds don't tend to emit much RF. And spectroscopy of the visible light from the materials comprising the body should be quite different unless the drones are covered in harvested genuine feathers.