There are at least two chipmunks that have discovered that the birds are messy eaters and knock a lot of seeds out of the feeder to the ground. There is one of them on the other side of the fence in the middle of this picture, although it's a little hard to see.
I've never been able to get a good photo of the chipmunks, because they startle easily and dash off to hide under the minivan at the slightest sound or movement. That means that they sometimes startle the birds, and sometimes the birds startle the chipmunks. Somewhat foolishly, they jump up into the minivan, which is not going to be good for them if they hide in the engine compartment when I'm getting ready to drive somewhere.