The witch uses the whistle and sends out a call to all small animals within approximately 400 paces. The animals do not need to hear the physical whistle, as the call is carried by the wind, the grass, the trees and bramble. The animals will rush to the witch, with intent to help them with whatever they need.
Exactly what kind of animals are called is down to the mentality of the witch. An evil, mean-spirited witch will attract bats, flies, spiders and other vermin, while a good natured witch will attract rabbits, mice and other friendlier animals.