The raven was a variety of bird native to Earth.
Druids believed that ravens acted as the eyes of the Cailleach. Leonard de Vries of the British Institute of Druidic Studies, a modern-day worshipper of the Cailleach, kept a raven in his home.
Cessair, who impersonated the Cailleach during her time on Earth, had an affinity with ravens, many of whom perched ominously on the TARDIS after it had landed there. (TV: The Stones of Blood)
In 1994, the Fifth Doctor and Nyssa saw a raven while visiting Alaska. (AUDIO: The Land of the Dead)
The Tower of London had ravens of death. (TV: The Power of Three) Kate Stewart revealed that they ran on batteries. (TV: The Day of the Doctor)
Stephanie, a resistance fighter on the planet Moldox during the Last Great Time War, had hair matching the colour of a raven. (PROSE: Engines of War)
The Quantum Shade frequently took the form of a raven. (TV: Face the Raven)