The Yamabiko (山彦) is legendary yokai from Japan. It is said to create echoes when someone sounds towards the slopes of mountains and valleys, the phenomenon of when it comes back echoing with a delay is also called a "yamabiko" when it is thought to be the answering voice of a yamabiko or a phenomenon that a yamabiko caused.
In Tottori, Tottori Prefecture, a yobuko (呼子) or a yobukodori (呼子鳥) that lives in the mountain is thought to give out the yamabiko's voice. In Kusuyama of Hashikami village, Hata District, Kōchi Prefecture (now Sukumo), regardless of whether it was day or night, when a sudden dreadful voice is heard deep in the mountains, this strange phenomenon is called "yamahiko."
They are sometimes seen to be the same as the yamawaro told about in Western Japan, as well as the yamako in the Wakan Sansai Zue, and as it is thought that tree spirits would cause yamabiko to occur, they are also seen to be the same as the yōkai penghou that lives in trees. In collections of yōkai depictions like the Hyakkai Zukan and the Gazu Hyakki Yagyō, the yamabiko that looks like a dog is thought to be based on the yamako or the penghou.
The aforementioned yobukodori of Tottori is said to take the appearance of a bird, and other than that, there is also a small rock mountain in Kitaazumi District, Nagano Prefecture called the "yamabiko rock" (山彦岩) that return people's words, among other appearances of the word "yamabiko," and thus it can be seen that the yamabiko as yōkai are not uniform in either origin or what kind of yōkai they are.