Raven

The raven was a variety of bird native to Earth. (TV: The Stones of Blood, et al)

Actual ravens
During the Middle Ages, Merlin had a raven familiar. (COMIC: Dr. Who's Time Tales)

In the 12th century, when walking through a forest that had been infiltrated by Krynoids, Osbert and Alfred noted that the ravens seemed scared. They were soon attacked by a Krynoid themselves. (AUDIO: The Green Man)

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)

Raven-like beings
UNIT kept ravens of death in the Tower of London. (TV: The Power of Three) Kate Stewart revealed that they ran on batteries. (TV: The Day of the Doctor) When the Faction Paradox moved into the shadow-London of the Eleven-Day Empire, they discovered the Unkindnesses, giant raven-like creatures, who seemed to be the "shadows" of the Tower of London's ravens from normal reality, were already living there. (PROSE: Interference - Book One) During her time as Mayor of the Trap Street, Me made a contract with a Quantum Shade which frequently took the form of a raven, and was referred to as "the Raven". (TV: Face the Raven)

Other references
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)