The Owl physical qualities are that he is quite large and he have five talons an inch long. His beak was curved and sharp and cruel with yellow eyes. 

He have helped Mrs.Frisby to transfer her house from the garden patch to the lee of the stone when he knew that she's Jonathan's wife by telling her to go and talk to the rats therefor they can move her house and save them from the Moving Day. Moreover the Owl have helped Nicodemus when he wwanted to gain other home for themselves. The Owl told Nicodemus to go to the Thorn Valley.

The Source

Brien, Robert c. o .New York, 1971. Mrs.Frisby and the rats of NIMH.