Buddy, aged six, is an eagle owl, one of the world’s largest species, standing at two-feet tall with a wingspan of five feet.
Sally Buckland runs West Sussex Falconry in Compton, near Chichester.
She said she found his enclosure empty on Monday morning, November 17, and believes he escaped between then and Sunday night.
Ms Buckland fears he kicked the door of his aviary, which he does when pigeons are nearby, breaking the bolt and enabling his escape.
Ms Buckland thinks he may have kicked open the door to his aviary (Image: West Sussex Falconry)
She said: “The bolt has come off and the door has come open.
“I went out to look for him. It’s soul destroying going out looking.
“It’s very, very rural here. You could be going in one direction and he could be going another way.
“He’s obviously quite large and distinctive.”
Buddy is described as having ear tufts and orange eyes. He also has leather anklets, flying jesses and a red identity ring.
Ms Buckland has asked members of the public not to approach him if spotted due to the risk of him being spooked and flying off.
Anyone who spots him should instead call the falconry on 02392 631820 or 07796 472716.
“I’m sitting here hoping someone will spot him,” Ms Buckland added.
She has also reported his disappearance to the Independent Bird Registry.