I'm using raised bridges to completely wall of the edge of my map so only sea creatures can spawn. Its quite a project, but if it works, and I can club some baby seals, then it will be worth it. However, I just noticed some giant thrips flying over my raised bridge. I'm not sure whether they had spawned there or whether they spawned nearby and then flew over there.
I guess, what I'm asking is, do flying creatures always spawn at ground level? Or can they spawn above the bridges, making this whole project almost worthless?