Quick concept sketch that I took to a semi finish of a creature for the Aerie: The Ichneumon.
In medieval zoology the Ichneumon (in actuality the Egyptian mongoose) is the enemy and killer of dragons, as well as serpents and crocodiles. Dragons in ye olden times were interchangeable with snakes, and anything that could kill serpents was treated as the enemy of the dragon in myth.
In thinking for the Aerie, these will be large creatures; lion-sized, fearless, and coated with porcupine-like quills. They're not capable of tangling with adult dragons, but will sneak into dragon dens and kill hatchlings. If the Ichneumon should happen upon a young drakling out on its own, it may also try to ambush it; savaging the drakling with bites to the neck before its prey can fight back.