The design of this piece is usually attributed to Hero of Alexandria, though the web site from which this comes attributes it to another great inventor form antiquity, Philo of
About the owl and bird automaton:
For the operation of the automaton, water from a spring was driven inside the upper airtight container forcing the air to leave through a pipe. Because the pipe-flute led to water, the oscillating wavelength produced a chirp with notes of different frequency. Then when the water level exceeded the curved siphon of the container, it emptied through it to the intermediate container, diverting a yoke to the side. This forced the built-in rotating shaft supporting the owl to turn towards the birds that then stopped chirping. When the water level exceeded the axial siphon of the intermediate container, it emptied through to the lower container, diverting the yoke towards its counterweight, which caused the owl to turn away from the birds that then began to sing again, etc.
This is quite a beautiful reproduction!
See more great inventions on this site about ancient Greek technology.
[ Thanks again, Thomas!]