This is difficult to say. It is possible that that an animal such as a squirrel or a raccoon did it; however, there are a couple of other scenarios to consider.
If you are finding bits or pieces of shingles on your lawn, these may be loose remnants from the roofing job that the wind and rain is now moving around. It could also be leftover material from when your roof was redone that is now making an appearance, or it could be a shingle that has come loose. If the latter is the case, then you could ask the people who did your roof to return to do the necessary repairs.
I hope that helps!