could be squirrels. i have seen them eating buds on my camellias.
no way to eliminate them (not that you would want to) but maybe next year spray with something that would have an unpleasant taste. have heard of people using cayenne pepper as a deterrent.

It could also be deer. Deer rip the buds off while squirrels chew them off. There are netting products that will keep both deer and squirrels off the plants.

I'm having the same problem. I've used bird netting on my hydrangeas to keep the deer from eating them; it's light weight and doesn't weigh the plant/shrub down.. This is the first year I've had deer eat the buds off my rhodies and camellias. Next year I'm going to have to plan a ahead.