Birds:
Light, squidgy and mostly feathers. When they impact the airframe they usually just go "splat!" They rarely cause any damage. We hit them regularly. I fly about 800 shorthaul hours per year and report bird strikes on average twice per. Most recently were five sparrows on departure from Athens. Most spectacular was a pigeon directly into the centre of the FO's windshield. If they hit a pitot tube then it's a bit more serious, as the gore can block the tube and cause our airspeed indicators to fail.
just a snippit quote from a post above.
But way off the mark!!
Nobody worries much about bird feathers .... it's what holds the feathers together that causes all the bird damage problems.
At least drones aren't expected to come in flocks and take out all your engines at once.
Summary
some birds cause damage and are a lot more populated than drones.
drones are expected to cause damage and are extremely rare to be hit
We need data to sort this out.
anybody willing to fly a four engine B747 into a flock of two drones and document the effects?