I couldn't do without it anymore, Jo! Neither with the new transform shader version.
I have to re-title this, as these trees are too old to be present when the first birds were there as well. So I replaced them with a brachiosaurus, found on the internet (credits to the unknown maker), and now wading around in a mud hole, grazing on giant ferns.
Although I liked the white birds, so I might replace all trees by modern trees.