Mercifully there is yet to be footage of slugs devouring baby birds, but the fact that it happens has been confirmed after years of suspicion.
"The actual moment of slugs predating on nestlings isn't easy to observe," says Katarzyna Turzańska at the University of Wroclaw in Poland. "You are more likely to come across the traces of the 'tragedy': dead or alive nestlings with heavy injuries, covered in slime – and often slugs' droppings found nearby."
She and Justyna Chachulska, a colleague at the University of Zielona Góra in Poland, were studying common whitethroat birds near Wroclaw, in Poland, when they spotted a slug of the Arion genus in a nest with newly hatched chicks. The next day, the slug was gone, and the chicks were dead with severe injuries on their bodies that hinted at the slug as the culprit.
They were gobsmacked. "We couldn't believe that the slug had killed the nestlings," says Turzańska. "We talked to many experienced ornithologists, but none of them had observed slug predatory behaviour towards birds before."
For your enjoyment, the Trailer to Slugs (1988).