Anyone know how to keep rats out of a bird feeder? We have the squirrel-proof kind that's suspended from a branch and closes under a squirrel's weight, but apparently the rats aren't as heavy. Plus they love to eat the seeds and shells that fall on the ground. I've sprinkled cayenne pepper all over the area which they don't seem to notice. When they started chasing birds and even squirrels away from the feeder, I finally removed it. But now I miss seeing all the birds in our yard. Any suggestions?