Evolutionary Mobiles

I think it's possible it is a survival instinct. the same can be observed in tons of species.

Not saying it might not have been a survival instinct or be related. But most kids after being quiet for a bit start to laugh or babble and try to grab the mobile. I can't think of how that behavior relates to not being eaten by a bird. If children were terrified, there would also be an increase in heart rate, and the body would go into "fight vs flight" type of response. Which would make them useless in a crib to get a child to sleep. The colors and shapes in mobiles are meant to stimulate the child visually, and the soft music is meant to remind the child of their mothers heartbeat and other sounds they heard while in the womb. So I can see why someone might draw the conclusion stated in the post, a straight line cannot be drawn between the two reactions of animals trying not to be eaten, and how babies react to a mobile.

Salt makes a lot of valid points. Babies are very good at making their needs and emotions known. If they were terrified, it would be obvious.