For most of zoo history, enclosure design was driven by visitor viewing convenience, not animal needs. The science of zoo design has transformed over the past 40 years: evidence-based naturalistic enclosures, behavioral enrichment integrated into design, and animal agency as a core design principle have produced measurable welfare improvements. Yet the gap between leading practice and average zoo remains large.
The shift from traditional zoo design to welfare-centered design reflects a fundamental change in how zoos understand their purpose. Traditional zoo enclosures — concrete floors, metal bars, minimal space — were designed around three priorities: animal containment, keeper access, and visitor viewing. Animal welfare was not a design criterion.
Beginning in the 1970s-80s, influenced by Heini Hediger's work on animal psychology and growing evidence of stereotypic behaviors and poor welfare in traditional enclosures, a new generation of zoo designers began applying behavioral ecology to enclosure design: asking not "can the animal fit in this space?" but "what does this animal need to behave normally?"
Good zoo design begins with a behavioral analysis of the target species: What behaviors do they perform in the wild? How much space do they range over? What substrates do they interact with? What social structures do they form? The enclosure is then designed to support these behavioral needs, not simply contain the animal.
A key insight from welfare science is that the ability to exercise choice and control over one's environment is itself an important welfare factor — independent of specific resource provision. Animals with more choices show lower stress, better immune function, and higher positive welfare indicators. Design should maximize animal agency: ability to approach or avoid conspecifics, humans, and stimuli; ability to access different microhabitats and substrates; ability to control their own feeding timing and effort.
Off-exhibit areas — keeper areas, indoor dens, training areas — are as important as public-facing exhibits. Animals must be able to retreat from public view. Off-exhibit complexity, social management in off-exhibit areas, and keeper relationship quality all contribute significantly to welfare outcomes.
Philadelphia Zoo's "Zoo 360" network of aerial trails allows great apes, big cats, and other species to travel above visitors' heads across large areas of the zoo grounds. This dramatically increases the available territory for exhibit animals, provides enriching new environments, and gives animals agency to choose their location — including away from public viewing areas. This design innovation has been adopted and adapted by several other zoos and represents a creative approach to expanding animal choice within limited urban zoo footprints.
Zoo welfare science now uses multiple tools to assess whether design changes actually improve welfare:
Despite significant progress in zoo design science, important challenges remain: