Second nature : environmental enrichment for captive animals /
Shepherdson, David.
Mellen, Jill D.
Hutchins, Michael.
Conference on Environmental Enrichment(1st :1993 :Metro Washington Park Zoo)
Washington ; London : Smithsonian Institution Press,
c1998.
An outcome of the First Conference on Environmental Enrichment held at the Metro Washington Park Zoo, Portland, Or., July 16-20, 1993.
Includes bibliographical references and index.
Captive wild animals
Environmental enrichment (Animal culture)