Historically, zoos have assessed animal welfare by evaluating how closely a captive animal’s behavior resembles that of their wild counterparts, assuming more “natural” behavior indicates better well-being. Today, most zoos integrate what’s known about a species’ natural ecology into enclosure designs and daily husbandry. Still, some traits, like migration, are difficult to simulate, and not all animals uniformly respond to captivity.

Behavioral flexibility, as defined by the authors of this study, refers to an animal’s ability to cope with changing environmental conditions. More flexible species often adjust to zoo life, sometimes substituting wild behaviors with enrichment like puzzle feeders. Meanwhile, less flexible animals may exhibit stress or abnormal behaviors like pacing, feather-plucking, or social withdrawal — signals of compromised welfare.

While previous research has helped improve zoo practices, the authors point out that it’s still unclear which behaviors are essential for well-being or which species adapt without suffering. This paper aims to address these knowledge gaps by examining how different taxa (animal groups) respond to captive environments and identifying behaviors most associated with positive welfare outcomes.

To compare how animals behave in zoos versus in the wild, researchers reviewed studies reporting detailed time-activity budgets. These budgets record how animals divide their time among key behaviors. They only included studies with percentage-based data on fully wild or zoo-housed adults, excluding juveniles and semi-wild animals.

Between December 2021 and July 2023, the researchers screened 1,042 papers and selected 104 activity budgets from 72 studies. The main analysis included 94 species with comparable data from both settings across five major Orders: Testudines (turtles and tortoises), Primates, Artiodactyla (hoofed mammals), Psittaciformes (parrots), and Carnivora (meat-eating mammals).

For species that didn’t have enough data for direct comparison, the authors used them in a secondary analysis that grouped animals by migration patterns, activity cycles, social structure, and diet breadth to explore how these ecological traits might predict adaptability to captivity.

Diverse Responses To Captivity

The study found wide variation in how animals respond to captivity. Across nearly all groups, zoo-housed animals spent less time foraging and reproducing — two behaviors closely tied to welfare in the wild. In many cases, abnormal behaviors replaced these natural activities.

Each species was placed into one of three categories based on how closely zoo behavior matched wild activity patterns: behaviorally inflexible (deviating from wild behaviors leads to poor welfare), partially behaviorally flexible (as long as some key behaviors are provided for, deviating from wild behaviors doesn’t reduce welfare), and fully behaviorally flexible (welfare isn’t negatively impacted by large deviations from wild behaviors).

Overall, the five Orders could be categorized as follows:

• Testudines (fully flexible): No apparent signs of poor welfare.
• Artiodactyla (fully flexible): Some aggression, but little abnormal behavior. Enrichment and behavior substitutions increase their ability to cope, though outcomes vary by species.
• Primates (inflexible): Increased aggression and abnormal behavior. Poor fit without intensive enrichment.
• Psittaciformes (inflexible): Reduced foraging and high rates of abnormal behavior. Enrichment and human interaction rarely replace lost natural behaviors.
• Carnivora (partially flexible): Reduced reproductive behavior and some stress indicators. Some species adapt by substituting behaviors.

The authors note that animals with high cognitive or social demands, like primates and parrots, had the most difficulty adjusting to zoo life. These species often require more stimulation and complex habitats to maintain well-being, making many species possibly incompatible with the limitations of human care.

The authors found consistent patterns between species’ ecological traits and how well they adapted to captivity:

• Migratory species often adapted better, possibly because they’re accustomed to changing environments.
• Generalists (animals with flexible diets or wide habitat tolerance) tended to cope more easily than specialists, who evolved to rely on specific foods and conditions.
• Solitary and highly social species both showed increased aggression in zoos, likely due to groups mismatching their natural social configurations.

The authors caution that ecological traits alone don’t determine a species’ response to captivity. Individual personality, cognitive capacity, and context are also important considerations. Some generalist species, like the European starling, still struggle in captivity, while a few specialists, like the chisel-toothed kangaroo rat, adapt well.

Limitations

One major challenge for this study was data availability. Most published studies have a strong research bias toward mammals, meaning data for reptiles, fishes, and birds were sparse. As a result, the team had to group many animals by broad taxonomic Orders or ecological traits, which limited their ability to make species-specific conclusions.

Behavioral visibility also affected findings. In zoo settings, researchers often couldn’t observe animals for long periods or track them when they were “out of sight.” This made it hard to capture full behavioral repertoires and may have underestimated welfare concerns in some cases. This uncertainty limits how confidently welfare can be assessed based solely on activity budgets.

The authors emphasize the need for more behavioral research on underrepresented species, particularly reptiles, amphibians, fishes, and birds, who constitute a significant portion of zoo populations, to help zoos make evidence-based decisions to support welfare across all animals.

Time Budgets Are Telling

This research accents an uncomfortable truth: not all species are suited to captivity. But for the animals who are still housed in zoos, advocates can push for research-based enrichment that supports natural behaviors, especially in species with high cognitive demands. Further, we can advocate for greater transparency and welfare assessments (particularly for underrepresented species), and support policies that consider ecological traits when determining whether a species should be housed in captivity at all.

Ultimately, the authors argue that good welfare in zoos requires more than just preventing harm. It demands thoughtful, tailored environments that give animals the opportunity to thrive, not just survive.