The consensus at the co-op was that this was the work of bunnies and you have tulips coming up. We didn't CSI it or anything, but that's our best guess.
What to do about the little critters? Here is what the co-op Board's President has done in past years to prevent this: Buy some "Liquid Fence" spray. It is petrified eggs and smells terrible initially but works! Spray it on the leaves and buds. You may need to reapply if it rains heavily and do this weekly. It will deter the bunnies and is non-toxic. I know that there are other non-toxic sprays too but I personally have had luck with this one.