[Thamnophis]

I believe that the amount of rodents that are eaten in the wild by Thamnophis is very low.
Cannot prove that, but that is what I believe.
I think the chance that they find (accidentally) a nest with pinkies is not that great. But when they do, they probably will eat them.
I doubt if a gartersnake easily can catch an adult mouse. Catching a live, wild mouse looks like a big risk for a garter snake getting injured. Fish, amphibians and worms are much easier.
When they find a dead mouse, maybe they will eat it.

Every specimen that I take care of gets every feeding:

1 pinky
Smelt
Some pieces of chickenheart
These items are all dusted with some Minerall indoor, Gistocal and Carmix.

When available they get every now and then one or two worms.

My snakes are all juveniles. When they grow bigger I will change the pinky for a bigger mouse.