Ground squirrels, and the name is key. I haven't researched, but I know that often such animals eat small insects. And worms. Insects are meat, too.
So if there is a vole population explosion, and voles live underground, and are hungry, a ground squirrels den is going to get invaded, with the voles trying to steal food. And the ground squirrel will of course attack and kill intruders. Especially if they have young in that underground nest.
So it's not a far stretch for them to get used to the taste. I think they prefer nuts, because they can store nuts, but on that front they also eat berries and really anything they find, so storage isn't a diet limiter. And after killing a vole, why waste it?
So if there is a vole population explosion, and voles live underground, and are hungry, a ground squirrels den is going to get invaded, with the voles trying to steal food. And the ground squirrel will of course attack and kill intruders. Especially if they have young in that underground nest.
So it's not a far stretch for them to get used to the taste. I think they prefer nuts, because they can store nuts, but on that front they also eat berries and really anything they find, so storage isn't a diet limiter. And after killing a vole, why waste it?