Stanley the white-tailed eagle flew off during a show in September and despite a number of sightings handlers were unable to catch him.
He was first spotted in Leamington and was later seen in a tree in Preston Capes, Northamptonshire, in October.
A Warwick Castle spokesman said staff had not given up hope of him returning but admitted it was unlikely.
'Coast hope'
The general manager of the tourist attraction, Tim Harrison-Jones, said: "We had a few sightings over in Northamptonshire and we sent our falconers out to go and see if they could find him.
"We located him to a tree but he was feeding quite well on what we think were dead rabbits so the falconers have decided to leave him.
"What we hope is he'll make it to the coast. If he can make it to the coast he'll have a really good life."
Stanley, who is aged over 10, has a wingspan of more than 6ft (1.82m). He is named after Kazakhstan, where he is originally from, and had been flying at the castle for more than eight years.
For more on this story see the article on the BBC web-site here.
