HOW DO ZOO ANIMALS EXPERIENCE US?
What decades of research on the “visitor effect” tell us about animal welfare, noise, choice and control
When people visit a zoo, attention naturally focuses on the animals. But animal-welfare science asks us to consider the encounter from the opposite direction: How do the animals experience us?
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Zoo visitors are part of the environment in which captive animals live. They move past enclosures, gather in groups, talk, shout, point, photograph, tap on glass and sometimes participate in close encounters. For the animals, that human presence may occur for hours every day.
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Scientists refer to the ways visitors can influence zoo animals as the “visitor effect.” Research stretching across decades has examined changes in animal behavior, physiology and use of space associated with the presence and behavior of visitors. The evidence tells a more complicated story than simply saying that visitors are either “good” or “bad” for zoo animals.
THE VISITOR EFFECT IS NOT THE SAME FOR EVERY ANIMAL:
A major 2019 scientific review by Sally Sherwen and Paul Hemsworth concluded that visitors can have negative, neutral or positive effects on zoo-animal behavior and welfare. Species characteristics matter, but so can an individual animal's temperament, previous experiences with people, social environment and enclosure design. The number of visitors, their proximity, their behavior and the amount of noise surrounding an exhibit may also influence an animal's response.
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Research has documented increased vigilance, avoidance, aggression, altered activity and changes in enclosure use associated with visitor presence in some animals. But researchers caution against interpreting any single behavioral change as definitive evidence of poor welfare. Understanding welfare may require behavioral observations alongside physiological measures and consideration of the animal's health, environment and opportunities to respond to what is happening around it.
SOMETIMES THE ENCLOSURE MATTERS AS MUCH AS THE CROWD
One of the most important lessons from visitor-effect research is that the question isn't simply how many visitors are present. It is also what options the animal has when visitors are present.
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Research reviewed by Sherwen and Hemsworth found associations between environmental features and physiological measures of stress in several species. In one multi-zoo study, black rhinoceroses housed in exhibits where a greater proportion of the enclosure perimeter was exposed to the public had higher average measures of glucocorticoid metabolites. Research involving pileated gibbons found lower average glucocorticoid metabolite concentrations where animals had greater visual protection from visitors, while another study found higher average glucocorticoid concentrations among clouded leopards housed on public display than among animals housed off display.
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These findings do not establish one universal enclosure formula for every species. They do illustrate why visual protection, enclosure design and opportunities to regulate exposure to people deserve serious consideration in animal-welfare assessments.
VISITORS ARE ALSO SOMETHING ANIMALS HEAR
Human presence is not merely visual. Zoo animals may also experience voices, shouting, children, crowds and other human-generated sounds throughout the day.
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A recent scientific review examining anthropogenic noise in zoological settings found that increased vigilance was the most commonly documented behavioral response among the studies evaluated. Thirteen publications included in the review suspected negative welfare effects, while others found no substantial effect, could not determine the welfare implications or did not directly evaluate welfare.
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The researchers identified significant gaps in the evidence, particularly for some groups of animals, and cautioned against assuming that all species respond similarly. Nevertheless, recommendations across the literature included improved visitor education, sound barriers and giving animals greater ability to choose another location when exposed to unwanted noise.
WHEN AN ANIMAL CAN WALK AWAY:
A 2022 study involving two pied tamarins provides a useful example. The animals lived near a loud waterfall feature but had access to quieter off-exhibit areas. When the waterfall was operating and those quieter areas were available, both tamarins frequently used the off-exhibit spaces. When sound levels were experimentally made more similar across the available spaces, their patterns of space use changed.
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The researchers did not find significant changes in fecal glucocorticoid metabolites and concluded that the overall welfare impact of the noise appeared limited in these individuals. But the study demonstrated something important: the animals used the options available to them to alter their exposure to their environment. The researchers described quiet off-exhibit areas as potentially valuable refuges from noise.
CHOICE AND CONTROL MATTER—BUT THE SCIENCE REQUIRES PRECISION:
The idea of giving captive animals greater choice and control has become increasingly prominent in animal-welfare science. A 2024 scoping review examined experimental studies that directly compared conditions in which animals had choices with conditions in which they did not.
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Only 13 studies met the review's inclusion criteria. Most involved mammals, many in zoological settings, and frequently examined choices involving enclosure access, food or enrichment. Most reported improvements in behavioral or physiological welfare indicators under choice conditions, although some effects were unclear or neutral.
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That is encouraging, but it is also a reason not to overstate the evidence. The scientific literature supports continued investigation of choice as an important welfare tool. It does not establish that every opportunity to choose automatically produces better welfare, nor that every captive animal experiences meaningful control simply because some choices are available. The quality and significance of the choices matter.
HABITUATION IS NOT THE SAME AS POSITIVE WELFARE:
An animal may become less visibly reactive to visitors over time, but reduced reaction should be interpreted carefully. Habituation means that an animal's response to a repeated stimulus decreases. It does not, by itself, tell us that the animal is experiencing good welfare.
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An animal that no longer retreats when people approach is not necessarily demonstrating that it enjoys their presence. This is one reason modern welfare assessment increasingly considers multiple measures rather than relying on a single behavior or observation.
WHAT HAS THE NEWER RESEARCH FOUND?
The field has expanded substantially since the original 2017 ZAWEC review. A 2025 systematic review examined 157 publications comprising 314 studies of animal-visitor interactions in zoos and aquariums. Historically, much of the research focused on primates and potential negative visitor effects. More recent research has expanded to additional species and increasingly considers neutral and positive interactions as well.
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Yet the review found that, after neutral findings were excluded, more visitor-effect studies still measured outcomes associated with negative welfare impacts than positive ones. The authors also identified continuing limitations, including the need for standardized welfare assessments, stronger experimental controls and research that considers both visitor education and animal welfare.
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In other words, decades of research have established that visitors can matter. Science is still working to understand when, how much, for which animals and under what circumstances.
PERHAPS THE QUESTION SHOULD CHANGE:
Zoos understandably devote enormous attention to the visitor experience: whether people can see the animal, whether an exhibit is engaging and whether visitors remain long enough to learn something. Animal-welfare science invites us to consider the other side of that experience.
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Can the animal avoid being seen? Can it move away from noise or crowds? Does it have visual barriers, retreat areas or off-exhibit spaces? Can it exercise meaningful choice over its exposure to people?
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Those questions do not assume that every visitor is harmful or that every animal wants to avoid people. They recognize something more fundamental: an interaction involves two sides.
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If modern zoos ask millions of people to observe wild animals, animal welfare requires us to consider what that observation means for the animals being watched.
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Understanding wildlife involves more than observing animal behavior. It also requires asking how our behavior shapes their lives.
SOURCES & FURTHER READING
Salas, M. & Manteca, X. (2017). Visitor Effect on Zoo Animals. Zoo Animal Welfare Education Centre, Technical Sheet No. 5.
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Sherwen, S. L. & Hemsworth, P. H. (2019). The Visitor Effect on Zoo Animals: Implications and Opportunities for Zoo Animal Welfare. Animals, 9(6), 366.
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Rust, K., Clegg, I. & Fernandez, E. J. (2024). The Voice of Choice: A Scoping Review of Choice-Based Animal Welfare Studies. Applied Animal Behaviour Science, 275, 106270.
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Animal–Visitor Interactions in Zoos and Aquariums: A Systematic Review. Animals (2025), 15(13), 1924.
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Do Zoo Animals Use Off-Exhibit Areas to Avoid Noise? A Case Study Exploring the Influence of Sound on the Behavior, Physiology, and Space Use of Two Pied Tamarins. (2022).
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A Scoping Review: The Effect of Anthropogenic Noise on Animal Welfare in Zoological Settings. (2026).
Related Reading:
Choice Within Captivity: Who Really Has Control?
What science tells us about choice, control and autonomy for animals living in zoos.
KeepingWildlifeWild.org
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