Raven

The Raven was a variety of bird native to Earth. Druids believed that ravens acted as the eyes of Cailleach. Leonard De Vries of the British Institute of Druidic Studies, a modern day worshipper of Cailleach, kept a raven in his home.

Cessair, who impersonated Cailleach during her time on Earth, had an affinity with ravens, many of whom perched ominously on the TARDIS after it had landed there. (DW: The Stones of Blood)