They supply high voltage but limit the current to a non-lethal level. Cattle hide is high resistance, like your bird's feet, and high voltage is needed to overcome it. A fence transformer will help keep you from electrocuting yourself if you make a mistake.
Wire the output of the transformer to the wires on the feeder, and plug in an extension cord at the house end to activate it for the nuisance bird, deactivate for desired birds, reactivate for squirrels.
“Cattle hide is high resistance...”
That’s for sure. I had a cattle rancher friend in SE Idaho who I asked for advice on setting up an electric horse fence. He told me about his horse fence setup but advised that it didn’t work for cows. His cows would get under the wire and scratch their heads on it until their hair was smoking.