Unknown individuals or a single person transported the chickens in cardboard boxes and abandoned them in the woods near Happerswil, a village in the canton of Thurgau, cantonal police said in a news release.
The hens were released either on Sunday night or early Monday morning, Thurgau police said.
A car was seen in the area and investigators are seeking witnesses who may be able to provide further information.
Police officers were able to corral the birds, with help from the Thurgau cantonal veterinary office and the animal protection association from the nearby town of Kreuzlingen.
The hens have “housed humanely”, said police, without going into details.
Police did not say whether the birds were stolen or simply abandoned by their owners.
Anyone with details that could shed light on the incident is asked to contact cantonal police in Weinfelden on 071 221 45 00.