The bizarre behaviour of a troop of 'hysterical' baboons at a Dutch zoo has been blamed on everything from an earthquake to a UFO.

Ordinarily seen scampering around on their island at the Emmen Dierenpark in the northern Netherlands, the gang of 112 monkeys have been sitting frozen on the ground and turning their backs on visitors this week.

The baboons have even lost their appetites, say baffled zoologists at the park, who have heard various theories as to what may be behind the animals' strange behaviour.

Maybe they're sick and tired of being held in captivity by humans? To read more and view the video, click here.