A hungry slug can shear off a new dahlia overnight, speaking from experience. Deer? Rabbits? chipmunks? hedgehogs? ( LOL do they have hedgehogs in Oregon?) I just googled and found an entry that complained hedgehogs had eaten the dahlias.....

Could be a rabbit, they have found mine this year. Can't eat from a nice lettuce patch, have to eat dahlias, must be dessert for them. Also all my cucumbers and beets. My pellet gun is loaded and waiting by the back door. A couple of years ago, I shot 13, and I live in town.

Well well! Here is South GA I was happy to start some lovely dahlias. and the plants grew sturdy and all had two or more huge buds. When they should have opened, the dogs (Irish Setter and Golden Recliner) and I had been away for a week. Instead of flowers the plants had been eaten off from the top down, just stalks and a few leaves at the bottom. Today before writing I looked again and found deer tracks! First time they have come this close to the house. Maybe that is also where my beans went. Drought must have brought them.