Chickens gang up on fox, “attacked him with their beaks”.
The unusual incident in Brittany took place after the fox entered the coop with 3,000 hens through an automatic hatch door which closed immediately.
“There was a herd instinct and they attacked him with their beaks,” said Pascal Daniel, head of farming at the agricultural school Gros-Chêne.
The body of the small fox was found the following day in a corner of the coop.
“It had blows to its neck, blows from beaks,” Mr Daniel told AFP news agency.
The farm is home to up to 6,000 free-range chickens who are kept in a five-acre site.
The coop is kept open during day and most of the hens spend the daytime outside, AFP adds.
When the automatic door closed, the fox – thought to be around five or six months old – became trapped inside.
“They can be quite tenacious when they are in a pack”.