Korreds, also known as korrigans, rutterkins, rumpelsticks, or mesmers, are creatures described as being from the family Strigiformes, which would suggest they are owl-like. However, in the novels they are described more as "family monsters" typically found in basements, where they hibernate.
They are described in the "Physiologus". Geralt meets one in the basement of the Pomerol estate in Toussaint.