As we come to appreciate more about the habits and behaviour of animals, the enclosures that we consider suitable at zoos become both larger and less intrusive. The forerunner of such projects was London Zoo's Snowden Aviary, but there have been great advances in both technology and behaviour studies since then. One of the latest schemes is at Burger's Zoo in Arnheim, The Netherlands, where architect Officium Design Engineering of Stuttgart, Germany, has designed an enclosure for leopards and jackals. A total of 700m2 have been allocated to the leopards and 230m2 to the jackals, where they can live among a wood of American oaks. The effect is as if the architect, working with structural engineer IPL, has thrown a net over both the existing trees and new artificial steel 'trees'. Seemingly casual and unobtrusive, the structure is in fact very carefully considered since it is crucial that there can be no prospect of escape or even of biting the public.Mesh, cables and assembly are by Carl Stahl.