I have seen several early Jewish sources (e.g. Midrash Tanhuma, Beshalah 18) refer to the idea that a snake can kill a bird by just looking at its shadow. Has this ancient belief been documented elsewhere and what other sources are there to such an idea?
I think this is a really really great find! I did some research and found nothing. South American myths contains a lot of kinds of Snakes, but this quite new for me. I think we will be waiting for someone reveal some other source.
But here is why makes sense to me: I think it's old knowledge for the universal and ancient questions of the "opposites". You can find this duality - snake and birds, skane and eagles - in many works like the Nietzsche's Zaratustra and Marriage of Havean and Hell from William Blake. In both cases you can see this transcended duality, with the junction of opposites represented as the eagle and the snake. In Blake's work the snake can see better been carrying by the eagle. In Zaratustra, Nietzsche claims in the beginning of the work the friendship of the eagle that carries the snake in its neck. Again, the opposites are together. The bird and snakes are symbols to represent the opposites, the most earthly animal and the most aerial animal.
I will make a guess, using a alchemical proposition: so above, as below. the most earthly animal (or the Devil, as judaic representation) can be view as the "Shadow" in some cases pointed in Carl Jung studies. So, taken this representation, the Devil is a fallen angel, he knows very well the "Shadow" of the higher - higher as the spirit. So anyhow, he is the shadow, he has control of the shadow, the animal instinct, he knows the dark side, so in this case, he knows the weakness of a higher being, like birds. Because he once was a like aerial being. It makes sense? lol
Hope it helps someshow.