One of our rat baiters offers this advice to those whose bait-stations are visited by slugs and snails, and bodies need to be disposed of.
“Kill all slugs and snails that have ingested the rat bait and leave them in the box; the rat will then eat them.
If you discard the slugs / snails on the open ground, you negate the objective of protecting birds etc. - you risk killing them as well!
Same goes for cleaning out the trap with rat bait crumbs that accumulate in the trap.”
He offers a photo showing the dye from the bait in a slug cleared from a bait station.