Icing is a huge concern. On a drone it just adds weight but it can add up.
Don't fly through clouds.
Flying near waterfalls is where you could find freezing mist. That can accumulate very fast.
I know, FOR A FACT, that you can't hear drones 4-500 feet up.
I know most drugs are widely available in Portland but that doesn't mean you have to partake. Just sayin'
Unfortunately, the video is not conclusive, even if enlarged. I have to vote with the bird group.
Despite the fuzziness of the picture, I don't see any arms with props, but several 'blobs' do appear to be extended wings.
No, there isn't.
What purpose do you imagine those things could have been following where you saw them?
What's bonkers is seeing a few birds, flying the way birds fly, in that environment and thinking ... those can't be birds, they must be some...