Is birds nest soup vegan?
Would it be vegan if instead of swiftlet saliva it was just a nest made of twigs and pine straw and stuff like a robin makes?
I'd argue yes, if it's been abandoned for sufficient time that you're sure it won't be revisited.
I'd not recommend eating it, especially if it's not something you've eaten before, you have no idea what kind of parasite eggs or diseases may have been left behind in that nest.
Probably not. Many people consider honey to not be vegan - I think that could be extended to other products that animals produce, including your speculative bird twig soup.
It’s not speculation, they made one under an awning and it’s all twigs and pine needles and trash.
I guess if the bird had already vacated the nest and wasn't likely to return it would be fine?