Squirrels will dig up any disturbed soil, spring or fall.
I usually lay chicken wire over newly planted areas, hold it down with bricks or rocks, then remove it after the ground has frozen.
Works anytime.
:-)

I planted a lot of tulips one year, and squirrels dug them all up. But then I planted some species tulips, T. praestans unicum, which are beautiful red with variegated foliage, and found one the squirrels had dug sitting on the top of the ground blooming the next spring. They didn't bother with the rest of them.

They also don't bother my Narcissus and Muscari.

The dig them up regularly when I plant them. Some they will eat, if they like them. Others they just leave lying on the ground. I think they watch me plant and after I step away, they dig them up to see what I buried. Usually I just replant them later and they don't bother them again. They will steal crocus bulbs and as for cyclamen, they eat them on the spot. I find a good spraying of Ropel on the bulbs, helps, and I usually spray it on the ground after I plant them. Just don't get the stuff on your hands!

Mix daffodils and alliums in with the other bulbs. Rocks help, I've also tried mixing up garlic powder, cayenne powder and blood meal and sprinkling that everywhere.

I live in the woods with some very giant squirrels. I planted bulbs, the squirrels dug, I chased them away and then I covered the ground where they were planted with alot of Chilli powder! They havent touched them since!! I learned that from my mom growing up! They won't touch them!!