It all depends on how you place the animated birds in the landscape.
If you simply place them and have to go looking for such a small assets group, such as a few birds, when free roaming or other driver views it is probably pointless.
However, if you place them in front of a trackside camera they can be seen for as long as the train remains in camera range.
Here I’ve placed neoklai’s ravens above the train. They may not be too obvious in this still shot, but against a sky background, flapping their wings, moving around, and audibly squawking, they make a great addition to the atmosphere as the Orient Express moves through the shot.
They work well in a multitude of environments, all IMHO of course!