An 18-second clip of a Silverback gorilla walking upright on his hind legs like a human has become a YouTube sensation.

Almost 150,000 people have viewed the clip in just a few days and the number is rising.

The 21-year-old named Ambam is part of a group of critically endangered Western lowland gorillas at Port Lympne Wild Animal Park near Hythe.

The footage was filmed by animal researcher Johanna Watson as she worked on a project on great apes.

But as gorilla keeper Phil Ridges explains, walking on hind legs is not a new phenomenon: "Ambam was hand raised for a few months when he was a year old because he became very ill and as a last resort he had to be taken away from his mother Shumba.

"He came over to Port Lympne when he was seven or eight years old. He is our biggest gorilla at around 220kg.

"Ambam's father Bitam used to display the same behaviour if he had handfuls of food to carry.

Video: The YouTube footage of Ambam

"Ambam also has a full sister, Tamba, and a half sister at Howletts, who also sometimes stand and walk in the same way. All gorillas can do it to some extent but we haven't got any who do it like Ambam and he is quite a celebrity at the park."

He said he thought Ambam might do it to get a height advantage to look over the wall at feeding time.

Ambam was born at Port Lympne's sister park, Howletts, in 1990.

Both parks are dedicated to protecting rare species and are managed by an international conservation charity called The Aspinall Foundation (TAF).