I did a quick check of food lists for Robins in A.C. Bent's Life Histories of
Birds. I was surprised to see a couple mentions of Robins taking small fish.
But no mention of snakes.
I think that with a few exceptions (osprey, Limpkins, Snail Kites, etc.) many
species will feed themselves with food that they can get as they can.
Opportunistic is a big word in the animal world.

Jim Rosso
Sammamish
jrosso at aol.com