Bob Pitchford, 67, was on a visit to the city's zoo last week when he spotted the large ape chewing on some grass. He took his camera out to take a photo but when the the mammal caught sight of Mr Pritchard he swiftly made the rude gesture.
'When I saw the pictures, I just thought "you little devil",' he added. 'He really does look a bit cheese off. 'I quite regularly photograph the animals at Bristol, but I've never seen anything like this. 'Gorillas are really good at expressing their feelings. I was just really lucky to capture this.'