Kites had the gift of song but were enchanted by the neigh of a Horse. In trying to imitate that the Kites lost their ability to sing.
The desire for imaginary benefits often involves the loss of present blessings.
Townsend version
The kites of olden times, as well as the Swans, had the privilege of song. But having heard the neigh of the horse, they were so enchanted with the sound, that they tried to imitate it; and, in trying to neigh, they forgot how to sing.
Moral
The desire for imaginary benefits often involves the loss of present blessings.
Perry #396