Maybe a bit of both? I mean, you were attached to the bird, even if for just a short while. Death affects people, hence burials and their cultures and traditions. That stuff I would say is cultural, although they are effects of something much more instinctive. Covering the bird so you don’t see it, I would say is part of that. But would it have been the same, if you found a dead bird in your yard? One you never got attached to? You might just dispose of it for the sake of sanitation, and then you’d never think of it again. THIS bird though, in 10 years, you’ll still remember it.
But say you find an animal carcass on the ground, you’re not going to want to touch it, and the smell will keep you away. That is, obviously, instinctual, and has its reasons for happening. You could get sick if you fucked around with the carcass. touched a dead fish when I was small and got horribly sick, guess I should consider myself lucky to have been born in a modern age haha
And yeah, animals do act up around carcasses. Animals are way more in touch with their instinct obviously, and as survivors, they have to know to recognize death. This will often show, but I don’t believe that however they act is ritualistic in any way. Whether they run off or start munching out, it’s their instinct acting up and making them do whatever that animal is meant to do in that situation. We humans created the entire idea of burial and all, which is secondary when it comes to the natural instinct which spawns the need to justify, for lack of better word.