Your kingsnake is looking for small mammals or birds. While they are known to eat other snakes, they love mice. I kept a prairie kingsnake in the dorm room while in college and fed him pinkie mice.
How large is it? Young black rat snakes look almost the same when young, they darken with age and turn black. If I remember right, you have to look at the pattern on the belly scales to determine which is which. Adult black rat snakes have a pattern on their back if you look close enough.
Feral cats carry all kinds of disease, and are hell on baby rabbits, birds, and other critters in your yard that are more fun to watch. I am blessed with 2 nesting pairs of doves, several robin nests, bluejay, and even a cardinal in the pines by the swing. My trees I planted 16 years ago are making nice nesting sites. Probably some hummingbirds too, nests are too small to find in the foliage.