Teratsutsuki is an ominous bird which is a specter described in "Konjaku Gazu Zoku Hyakki" (Continued Illustrations of the Many Demons Past and Present), a collection of specters' illustrations by Sekien TORIYAMA, and which looks like a peckerwood.
It is said to appear in Shitenno-ji Temple and Horyu-ji Temple trying to destroy the temples by pecking all over the temples with its beak.
It is said that MONONOBE no Moriya, who had a faith in deities from ancient times, turned in to a vengeful ghost in the form of Teratsutsuki after he was subdued by Prince Shotoku and SOGA no Umako; Teratsutsuki is said to be trying to cause an obstacle to Buddhism by destroying the temples that were built by Prince Shotoku.
According to "Genpei Seisui Ki" (Rise and Fall of the Minamoto and the Taira clans), a tale of military affairs during the Kamakura period, Prince Shotoku changed into a hawk to fight the Teratsutsuki, and since then Teratsutsuki no longer made its appearance.
The identity of Teratsutsuki is said to be akagera (great spotted woodpecker).