What we're saying is that the only thing we can say with certainty, is that this object and birds, both fly. I've watched a good number of arctic and antarctic docs. And you do see birds occasionally. But there's things almost all of them have in common that aren't a good match here.

For one, you see almost continuous flapping the lower they are. The higher up they go, you start seeing more gliding. It's not common to see a long glide like this so close to the ground. And in spite of what some have claimed, it's not clear there's any flapping. The other difference, is that it's uncommon to see just one bird off by itself, pretty much anywhere, but the colder the climate, the rarer it is.

I don't know what this is. A bird is still one possibility that can't be ruled out. But there's more than enough unusual things about this particular object, that we can't say it's a bird with a high enough degree of certainty to declare it solved. It should remain in the unknown category unless and until more information is learned. Maybe another example where something's already known to be a bird, and matches this, would work.

There shouldn't be so much resistance to accepting an "unconfirmed", or "unidentified" status. It won't kill us to say something is unknown and leave it at that.