Hmmmm, what doesn't!

If they are in the open (not under a net) they could be birds such as pigeons. More likely to be a caterpillar or slugs.

Sorry, a bit vague but look for slime trails, slugs/snails being top candidates.

ITS THE SQUIRELL, THIS YEAR THAT LITTLE DEVIL HAS BEEN NIBBLING OF ANY THING HE CAN GET HIS MITS ON, INCLUDING THE NEW RED SHOOTS OF MY ROSES,, EVEN THE TOPS OF MY SNAP DRAGONS, MY MINT. AND HE LEAVES THEM ON THE FLOOR FOR SPITE,, A FEW YEARS AGO ,HE REMOVED THE WHOLE SUNFLOWER HEAD, IT WAS IN FULL BLOOM, I WENT OUT ONE MORNING TO TAKE IT IN TO MY AVAIRY, IT WAS GONE?? I LOOKED OVER MY NEXT DOOR NEIGHBORS GARDEN THERE HE WAS YELLOW SUN FLOWER PETALS EVERYWHER,,