These little machines were an early investigation of "Artificial Life".
They were phototropic — i.e. they would notice any moderate light
source in their vicinity and move toward it. Brighter lights they would avoid
— until their batteries were running low, at which point they would find
the brighter light on their 'feeding hutch' suddenly attractive!
The University of the West of England used to have much more about the creatures
on its website, but that page has gone. Fortunately the Wayback Machine has
preserved it here:
Another link I used to have on this page has also died, but I suggest a google search for "Grey-Walter Tortoise" or some such to find some of the interesting stuff on the creatures currently available on the web.