I got it now that makes sense to me.
Todd,
What you need is a transformer from a Neon sign. They run in the 12KV range with very low amperage, however enough to quite handily ‘toast’ your rats. Place an alternating set of parallel bare plus and minus wires. Place them far enough apart so the birds cannot be on both at the same time and the birds are safe. Generally speaking a rat is long enough to pretty much assure the voltage/current will traverse the length of his body and through the heart. All said with the largest dose of caution. I would not operate this unless you can SEE the device clearly before turning on the power. The principal here is the same as that used in electrostatic precipitation, just scaled down a bit, as an ESP uses typical 70KV and up.
I would also leave the first one or two laying for a day or two. Most animals will not frequent an area where their ‘kin’ have expired. I did that years ago with a wild dog pack in Tennessee. However my source of expiration was lead poisoning. Todd, you will need to determine what method to use, I only offer another path. Rats (unless controlled by natural predators) can be very problematic to get rid of. As for the glue trap, depending on how often you check it or how loud the rat is, death can be quite quick and painless. Been there done that.