Tulips at risk again!

This morning when we came into class, we were shocked to find that the soil had been knocked out of the plant pot. This was very surprising to us, as we had covered it carefully with a net and wire so that the birds couldn't destroy it.
This couldn't have been a bird, or any other animal so we are asking ourselves, who or what did this to our tulip project?
As for the rest of the plant pots, they are safe and growing well in our greenhouse corridor.