Third, anyone who has ever dismembered a chicken for cooking purposes will seriously doubt that a bird's head is less dense or rigid than a battery
I have carved a fair number of turkeys and have help lift a fair number of batteries out of holds and can conclusively state that batteries are far more rigid and dense than birds heads. Seriously, looks are deceptive. Try picking up a li-ion bike battery sometime, you will be surprised by the weight versus its size. I have some telecom style batteries that are the size of a very small briefcase, and it takes two burley men to pick them up safely. That said, neither birds nor batteries are good things to have impacting jets or helicopters, but we have more ability to control drones than we do birds. In my view the drone hobby craze will soon pass, but commercial use of drones is expanding exponentially and will continue to do so, making it prudent for regulators to consider this issue and take early action to ensure that the skies remain as safe as possible.