The word fischio (whistle) in Italian refers to any kind of high-pitched sound emitted by blowing through the teeth and lips, in addition to a similar range of sounds emitted by birds, animals or objects.
In order to say to whistle, you have the option of using either the single verb fischiare or the verbs fare (to make) / emettere (to emit) / mandare (to send) placed in front of un fischio.