An acoustic basis for maternal recognition in timber wolves (Canis lupus)?

An in-den recording system was used to monitor the vocalizations and behavior of adult wolves tending to a litter of pups during the first five postnatal weeks. Two female adults, one of them the mother, tended to the pups on nonoverlapping schedules. The distributions of the fundamental frequencies of the adults' squeak vocalizations were largely nonoverlapping, suggesting that this feature may be available as an acoustic cue to individual recognition. Squeaks emitted outside the den, and which were associated with pup exit responses, had fundamental frequencies wholly within the range of the mother's, raising the possibility that the pups used this as a cue for maternal recognition.