Ravens guarded their food caches when they had reason to believe another raven could see through a peephole into the caching room. The experiment tested whether ravens responded only to an actually visible competitor or also to the possibility of being watched.
Researchers used connected compartments with a covered window and small peepholes. In the peephole condition, a raven cached food while sounds suggested that another bird was nearby, but the potential observer was not visibly present in the same room. After familiarization with the setup, the caching birds behaved more cautiously, finishing caches more quickly and revisiting them to improve concealment, patterns resembling behavior in the openly observed condition.
The result supports the idea that ravens can use information about visual access when protecting stored food from competitors. It does not prove that ravens possess a fully human-like theory of mind. In particular, the group did not reliably place caches outside the specific viewing angle of the open peephole.
The birds in this work were common ravens, Corvus corax. “Crows” is a frequent but imprecise substitute: ravens and crows are close relatives, but they are different species.