The review, conducted by a single investigator using PubMed and Google Scholar, began with 1,608 publications and, after rigorous screening against modified PRISMA 2020 guidelines, distilled the evidence down to 34 peer-reviewed studies, comprising 31 research papers and three case studies. Nearly all of the included work was published between 2014 and 2025, underscoring how recently the topic has captured scientific attention. The United Kingdom and the United States together produced almost two-thirds of the studies, with additional contributions from Australia, Brazil, New Zealand, China, Pakistan, Portugal and Singapore. Mammals dominated the species roster, with non-human primates studied most often, but birds were also well represented, including flamingos, penguins, hornbills, kiwi and free-flight aviary collections, alongside a handful of reptiles such as an American alligator, a Siamese crocodilian and semi-aquatic turtles. Notably, no study examined teleost fish, and half of all investigations evaluated two or fewer individual animals, a small sample size that limits how broadly the results can be generalized.

Behavioural observation was by far the most common assessment tool, deployed in 28 of the studies through species-specific ethograms that catalogue activities such as resting, foraging, pacing and social interaction. The single most frequently documented response was increased vigilance, reported in ten studies across macaques, gibbons, capuchins, peccaries, orangutans, giraffes, hornbills, cheetahs and mixed aviary species. Vigilance, the scanning behaviour animals use to monitor their environment for threats, is widely interpreted as a sign of heightened arousal or anxiety. Other documented responses included retreating away from visitors or out of sight, decreased rest, increased self- or social grooming, increased pacing, reduced appetite, increased swimming, altered circadian activity patterns, greater time spent underwater in a Siamese crocodile, and even increased protectiveness of infants in orangutans. Importantly, six studies found no statistically significant behavioural change linked to noise, and no publication reported overt abnormalities such as self-inflicted trauma or serious aggression.

Physiological measurement, by contrast, was rare. Only six studies assessed glucocorticoid concentrations, the hormonal fingerprints of activity in the hypothalamic-pituitary-adrenal axis, with five pairing faecal or urinary hormone analysis with behavioural observation. Three of the six reported elevated glucocorticoids: one in okapis attributed to visitor presence, one in orangutans linked to ventilation system noise, and one in a giant panda later attributed to normal physiological variation unrelated to noise. The remaining studies found no elevation or no correlation with behaviour. The review’s authors note that the broader literature increasingly cautions against interpreting glucocorticoids as stand-alone welfare indicators, since levels can fluctuate with reproductive status, circadian rhythms and sampling methods, and argue that pairing hormone data with complementary measures, such as the cognitive bias testing used in one primate study, would produce far more robust welfare conclusions.

Perhaps the most surprising finding concerns the sources of the noise itself. Visitor noise was the focus of 27 studies, but construction noise appeared in five and concerts in two. Yet in two publications, researchers suspected that ventilation systems, not visitors, were the real acoustic culprit, because decibel levels did not rise appreciably when crowds grew. A third study found that behavioural changes tracked a habitat’s waterfall feature more closely than visitor noise. One investigation concluded that reducing visitor numbers or limiting opening hours did not guarantee a quieter environment, highlighting the persistent hum of mechanical infrastructure in zoo soundscapes. At the same time, enclosure acoustics can work in animals’ favour: one study showed that a habitat’s soundscape substantially buffered short-term fluctuations in external noise, suggesting that thoughtful acoustic design can be a protective factor rather than a hazard.

The objective acoustic data gathered across the studies spanned an extraordinary range, from 51.5 decibels to a peak of 122.2 decibels recorded near a sloth habitat in a walk-through enclosure. Concert noise reached a maximum of 88 decibels and construction noise 76 decibels. One study measured construction and non-construction days at different frequencies in hertz, while another compared how A-weighted and C-weighted decibel filters affected penguin species, finding that only southern rockhoppers responded positively to pool use under elevated C-weighted levels. These technical details matter because sound meters positioned on the public-facing side of a habitat may not accurately represent what an animal actually perceives, a limitation the review flags as a significant obstacle to drawing welfare conclusions from sound pressure levels alone.

When it came to characterizing welfare outcomes, the literature revealed a striking inconsistency. Eleven studies suspected a negative welfare impact from anthropogenic noise based on observed behavioural changes, nine could not determine whether welfare was affected, seven reported no substantial impact, and seven did not address welfare as an outcome at all. Welfare assessment protocols were rarely described in a standardized way, and many studies acknowledged confounding factors, including the visual presence of visitors, the sight of construction workers, species-level and individual differences in noise sensitivity, and even the acoustic interference of precipitation. Under the Five Domains model of animal welfare, which integrates nutrition, physical environment, health, behavioural interaction and mental state, these complications underscore that noise cannot be evaluated in isolation. The ventilation system example illustrates the dilemma: mechanical noise may be stressful, yet reducing ventilation could compromise thermal comfort and air quality, producing a net welfare loss across multiple domains.

Fourteen publications offered mitigation recommendations, clustering around three practical strategies. Public education, delivered through signage or trained staff, was the most frequently cited, and one study found that ‘watching eyes’ signage requesting quietness measurably reduced noise levels. The second strategy centred on giving animals choice and control over their location, an established contributor to positive welfare, with several studies documenting animals retreating to indoor or off-exhibit spaces to escape noise. Additional suggestions included controlling visitor numbers and timing, habituation training, adding soothing background sound, increasing vegetation, redesigning enclosures to dampen sound and continuing behavioural monitoring during disruptive periods. Operational planning, such as relocating noise-sensitive species during extended construction, could preserve visitor engagement while protecting animal welfare.

The review concludes that anthropogenic noise alone may not harm welfare in every case, since some studies could not disentangle acoustic from visual disturbances, and that species and individuals differ markedly in their responses. Individual-level welfare assessments, the authors argue, allow institutions to plan more appropriately and may prevent costly habitat reconstruction by identifying minor, targeted modifications before welfare is seriously compromised. As zoo accreditation standards evolve, the authors suggest that noise deserves more formal inclusion in welfare assessment frameworks, and that future research should explore how animals respond to different human-generated frequencies, whether reactions differ between chronic and acute exposure, and which documented behaviours genuinely reflect negative welfare states. For a field barely a decade old, the message is clear: the soundscape of the modern zoo is not just background noise, but a variable that zoological institutions can measure, design around and ultimately manage to the benefit of the animals in their care.

Subject of Research: The effects of anthropogenic noise on animal welfare in zoological settings

Article Title: A Scoping Review: The Effect of Anthropogenic Noise on Animal Welfare in Zoological Settings

Article References: Kruse, T. N., & Flint, M. (2026). A Scoping Review: The Effect of Anthropogenic Noise on Animal Welfare in Zoological Settings. Veterinary Medicine and Science, 12(5), Article e71197. https://doi.org/10.1002/vms3.71197

Image Credits: AI Generated

DOI: 10.1002/vms3.71197

Keywords: anthropogenic noise, zoo animal welfare, animal behaviour, soundscape, glucocorticoids, visitor effects, Five Domains model, noise mitigation, scoping review, captive animals, vigilance, zoo acoustics

The pilot study was conducted during the summer of 2023 at two very different UK institutions: the small Fenn Bell Conservation Project in Kent, where 76 visitors observed a pair of Asian small-clawed otters (Aonyx cinereus), and the much larger Twycross Zoo in the Midlands, where 155 visitors studied two Rothschild giraffe (Giraffa camelopardalis rothschildi). Participants were recruited through posters with QR codes at the enclosures and asked to watch the animals for two minutes before completing an online questionnaire built on a pre-defined ethogram, a structured list of species-typical behaviours including positive, negative and neutral welfare indicators. The questionnaire also invited optional sections on how the animals seemed to be feeling, what animal welfare meant to the visitors themselves, and how they had found the citizen science experience.

Technically, the design was deliberately cautious. Because visitor observations could not be paired with simultaneous video observations from the same individual, and because the two data sources differed in duration, the researchers did not treat the comparison as a validation exercise. Instead, they used systematically coded CCTV footage as a reference dataset, applying instantaneous scan sampling with one-minute intervals between 11am and 3pm, and summarising both datasets as hourly and daily presence or absence records. At the daily level, both data sources captured walking or running in the otters on all study days and chewing the cud, eating and drinking, standing and locomotion in the giraffe, while the largest discrepancies appeared for infrequent or harder-to-identify behaviours such as grooming and social interactions.

The psychological results proved equally instructive. Visitors scored the animals on eight qualitative terms, including content, relaxed, agitated, frustrated, comfortable, wary, confident and distressed, and then gave an overall welfare rating from 1 to 10. Spearman’s rank correlations revealed a coherent pattern at both sites: welfare scores rose alongside positively valenced adjectives such as content, comfortable, confident and lively or engaged, and fell alongside negative terms such as frustrated, agitated and wary. For the otters, the correlation with contentment was particularly strong, while for the giraffe even wary and agitated scores tracked downward with welfare ratings. Although participants were told in advance which terms indicated positive or negative welfare, the authors note these exploratory associations provide preliminary evidence of construct validity in public assessments of animal affective states.

Perhaps the most encouraging finding concerned how visitors conceptualised welfare itself. Asked to define or describe animal welfare, most respondents produced answers that mapped cleanly onto the Five Domains model, the contemporary framework covering nutrition, environment, health, behaviour and mental state. At Fenn Bell, 86 percent referenced physiological welfare, 64 percent mental state and 41 percent behaviour; at Twycross the figures were 93, 54 and 24 percent respectively. Fifteen otter visitors and thirteen giraffe visitors touched on all three broad themes, offering definitions such as meeting an animal’s emotional, physical, mental and health needs as naturally as possible through diet, environment and enrichment. The researchers observed, however, that visitors leaned towards input-based measures such as food and space rather than output-based measures such as behaviour, and that behavioural domains were the hardest for the public to articulate.

Where visitors learned their welfare concepts also carried a clear message for the zoo sector. Zoos themselves ranked among the most frequently cited sources of knowledge, with 45 of the Twycross respondents attributing their understanding to that zoo alone, ahead of television documentaries and educational facilities. The authors interpret this as evidence that educational material provided by zoos is being positively received, and they recommend that zoos place greater emphasis on positive behavioural interactions within their welfare science communication. Given that negative public perceptions of welfare can erode trust in zoos and reduce willingness to engage in conservation efforts, effective communication of welfare science is not a luxury but a strategic necessity for modern institutions.

Engagement levels were striking. At Twycross, where a researcher was present at the enclosure to encourage participation, an average of 27 visitors per day completed the survey; at the smaller Fenn Bell site, where participation was self-directed, the mean was 3.4 per day. Across both sites, 93 to 95 percent of respondents said they would take part in a similar activity again, and 79 percent overall described the process as rewarding. Crucially, the majority of participants were infrequent zoo visitors, with the largest group attending less than once a year, suggesting that citizen science could reach beyond the committed membership base of season-pass holders. Most participants also expressed confidence in their ability to identify the behaviours on the ethogram, which the researchers attribute to the deliberately simple design of the observation task.

The study is candid about the limitations of visitor-generated behavioural data. The otters were out of sight of the cameras for 67 percent of video observations, and both visitors and cameras faced blind spots and varying viewing opportunities. Behaviours that were infrequent or complex, such as positive social interactions in the otters or grooming in the giraffe, showed the greatest divergence between the two datasets. The authors stress that their analyses are exploratory descriptions of behavioural occurrence rather than measures of observer accuracy or reliability, and they call for future studies using time-matched designs, cameras positioned to replicate the visitor’s view, and controlled comparisons with trained observers to enable formal inter-rater reliability assessment. Training, structured prompts and simplified measures such as active versus inactive states are proposed as ways to improve data quality.

Beyond the data, the researchers argue, the process itself may deliver benefits that matter to the mission of the modern zoo. Watching animals closely is known to foster empathy and a sense of connectedness, visiting zoos has been linked to improved human wellbeing, and citizen science participation has been associated with gains in scientific understanding. Longer dwell times at exhibits may not automatically translate into learning, but they can deepen the visitor experience and support lasting connections with nature. As biodiversity losses reach unprecedented levels and conservation science becomes an ever more urgent discipline, the authors conclude that engaging zoo visitors in behavioural citizen science deserves far wider consideration, both as a source of data on how animals spend their opening hours and as a pathway to a more empathetic, conservation-minded public.

The study sits within a broader rethinking of what zoos are for. Traditional frameworks described zoos through four pillars of conservation, education, research and recreation, but more recent models have proposed adding a fifth pillar of wellbeing that applies to both animals and people, alongside a ‘sphere of influence’ recognising that zoos operate at local, national and global scales. Within that framing, communicating welfare science to the public is not peripheral but central, since public trust depends heavily on whether visitors believe the animals they are watching are thriving.

Citizen science itself is usually understood as having two distinct strands. In one, the priority is collecting usable data at scale, as in large wildlife monitoring programmes; in the other, the priority is engaging citizens, with data quality a secondary concern. The zoo project deliberately straddled both, and the tension between them explains much of the authors’ caution about the behavioural records. Previous zoo-based citizen science in the UK, such as campaigns encouraging visitors to log native species seen on site, has built ecological awareness but stopped short of fostering connections with the zoo’s own animals, a gap this study sought to address.

The choice of study species was pragmatic rather than incidental. Asian small-clawed otters and Rothschild giraffe were selected because they were consistently visible from public viewing areas, attracted longer dwell times, and could accommodate camera installations allowing simultaneous remote observation. Behavioural research is already the dominant form of zoo science, valued for capturing real-time information about animal experiences at low cost, yet large-scale data collection can be impractical for busy animal care staff. Distributing observation across millions of annual visitors offers one possible solution, provided questions of validity and reliability are resolved.

Earlier work also suggests the timing matters: visitors report more positive experiences and stronger feelings of connection after watching animals, particularly active ones, meaning the observation task itself may amplify the very engagement the projects aim to cultivate.

Subject of Research: Citizen science engagement of zoo visitors in animal behaviour and welfare assessment

Article Title: Exploring citizen science as a tool for engaging zoo visitors with animal welfare

Article References: Stephens, D., Wright, D., Rowden, L., Frost, N., Carter, A., Ward, S. J., & Williams, E. (2026). Exploring citizen science as a tool for engaging zoo visitors with animal welfare. Discover Animals, 3(1), Article 85. https://doi.org/10.1007/s44338-026-00247-2

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00247-2

Keywords: citizen science, zoos, animal welfare, animal behaviour, Five Domains model, ethogram, visitor engagement, giraffe, Asian small-clawed otter, conservation education, public engagement, affective state