Stakeholder Perspectives on Zoo Sound Environments and Associated Impacts on Captive Animal Behaviour, Management and Welfare

Abstract

Although long neglected, sound is now an increasing topic of interest in zoo and aquarium science. Research has examined the impact of sounds, from various sources, on zoo-housed species, noting that the influence of sound is varied and very context specific. The zoo’s sound environment is influenced by the animals, the built environment, vegetation, climatic, temporal and seasonal factors, equipment use, husbandry practices, and human presence. Different sounds can dominate an enclosure at certain times. This article discusses a workshop involving 12 zoo professionals, held in March 2020, that explored how sound is considered or overlooked in zoo animal management. Although insights are based on a small group, limiting generalisability, the findings highlight areas where further understanding is required and should encourage research extension to other groups of stakeholders. Delegates emphasised that the auditory needs of animals are often underappreciated and that the influence of sound depends on the species involved and how the sound may be perceived. Delegates highlighted the importance of species- and individual-specific approaches, predictability, and how animals have (any) control over sounds experienced in their enclosure. Routine operational sounds, such as closing gates or doors, may inadvertently stress animals, suggesting the need to consider sound in enclosure design and husbandry schedules. Outputs also stated that sound, when carefully managed, can act as enrichment through (for example) structured auditory cues or naturalistic sounds if ecologically relevant. Overall, our findings support integrating sound measurement into broader welfare assessment frameworks and enclosure planning, and they identify practical applications including sound mitigation, enrichment strategies, and staff training. Future research should include a wider range of species (especially understudied taxa), consider the experiences of a wider stakeholder demographic, and evaluate how sound is management in complex or high-traffic areas of the zoo.

1. Introduction

Animals under human care in zoos and aquariums (hereafter “zoos”) are exposed to a range of stimuli that are often outside their control (and, sometimes, that of their caregivers). If animals cannot cope with extraneous stimuli that infiltrate the environment of their enclosures, their abilities to experience positive welfare states will be diminished [1]. To provide their animals with agency, i.e., the ability to engage with their environment and surroundings to meet their fullest potential [2], caregivers in zoos need to consider how to manage, manipulate or mitigate any effect of such extraneous stimuli. Sound from within and outside of an enclosure is one example of a stimulus potentially beyond an animal’s control. The sound environment within the zoo is influenced by many factors, some biotic (e.g., humans, animals) and others abiotic (e.g., weather), some mechanical or technological (e.g., machinery, life support systems, vehicular traffic). Directly anthropogenically created sound, including the voices of zoo visitors, may dominate the sound environment around or in an enclosure at certain times of the day [3,4] and animals may alter their behaviour in response, in an attempt to control the situation and manage their welfare state [5,6]. Such alterations to the sound environment of the zoo are often termed “noise,” but defining what constitutes “noise” is complex, as perceptions of sound are inherently subjective and depend on the sensory abilities and prior experiences of the listener, whether human or non-human. Consequently, we refer to the sound environment, and changes to it, throughout this paper.

The need for evidence to advance husbandry practice, specifically centred on the impacts of zoo sounds on animal welfare, is championed by several authors [5,7]. As many species communicate with sound or use sound to decipher the world around them [8], disruption to sensory modalities that occur from an unnatural or unwanted sound environment in the zoo may be detrimental to how a species can function [9], as well as to their development and health [10], and it can have negative impacts on behaviour [11]. Presumably because of the similarities between their own auditory systems and those of humans, primates tend to dominate the literature focussing on animal responses to zoo sound, (for instance in relation to enclosure design and acoustic enrichment) [12,13,14,15], though studies into the impacts of sound on zoo animal behaviour and welfare are becoming more species diverse [16,17,18,19].

The Economic & Social Research Council (ESRC) funded “Listening to the Zoo” project (LTZP) set out to generate knowledge of how sounds are woven into the experience of zoos for zoo staff, visitors and people who live near zoos. The project also set out to deepen understanding of how certain species experience zoo sound environments, with a specific focus on birds. Data were collected at two zoos in the UK: Paignton Zoo Environmental Park and Bristol Zoo Gardens (at its now closed Clifton site), to assess and evaluate relationships between enclosure usage and changes to the sound environment in two walk-through enclosures. Subsequent published papers suggest a complex relationship between animal behaviours (where birds chose to be within their enclosure), relative to the presence of visitors, the time of day and prevailing weather conditions [6,20]. Change to the sound environment at selected enclosures showed a strong relationship with visitor presence, and animals may be responding to the visual presence of visitors or to associated sounds or to both. Some species of birds housed in walk-through enclosures seemed to ignore changes to the sound environment whilst others became more vocal or more alert, or more inconspicuous by hiding away [20]. These findings highlight the complex nature of what we might think of as a sonic “visitor effect” at an enclosure, and also underscores the methodological complexity of making reliable assessments of the sound environment and properly understanding the animals’ acoustic perspective [21,22].

An additional aim of LTZP was to garner information on where zoo staff perceive areas of strength and weakness to lie in relation to sound and the practices of their own zoos. This paper describes the process of information gathering and summarises the main findings from a workshop run specifically to collect evidence for how staff consider sound in zoo animal management. We evaluate the outputs produced from this workshop in the context of animal welfare states generally and across the husbandry needs of taxa specifically. We hope that our paper sparks future research into key areas of zoo animal husbandry, behaviour and welfare that may benefit from a greater appreciation of how sound could impact on the quality of life a species experiences in the zoo. We aimed to capture workshop delegates’ perceptions of sound impacts as the baseline for future evidence-gathering activities—if zoo care professionals believe a taxonomic group is particularly impacted by changes to the sound environment, yet empirical evidence on whether this is indeed the case is lacking, the workshop outputs can provide the call to action for this species or area of zoo operations.

This workshop took place in March 2020. To ensure the relevance of our work, the outputs from discussion groups, and the validity of our conclusions, we have also performed a short review of the literature on zoo/aquarium sound and welfare (in April 2025) for papers up to the end of 2024 to see what, if any, progress had been made on the issues raised by delegates.

2. Materials and Methods

A key element of the ESRC funded LTZP was to engage stakeholders in the research process. As part of this endeavour, a workshop was held in March 2020 to gain information on how a range of staff at several UK zoos consider the sound environment in their work and take account of potential impacts from sound on animals. Delegates were invited based on their specific experiences and subject specialism and to represent different stakeholders and invested parties from zoos and aquariums across the UK. Delegates (N = 12) were one zoo enclosure designer, two zookeepers, one animal welfare officer, one zoo membership organisation manager, three zoo research officers, one zoo veterinary surgeon and three university academics with specialism in applied animal behaviour and welfare that focussed on zoo and aquarium species. Overall, there was a high level of sonic awareness in the group. For example, the two zookeepers invited worked with what are recognised to be sound sensitive species or species in whom sonic communication is notable, the animal welfare officer and several of the zoo research officers had experience in measuring sound at the zoo during public engagement events, and the zoo enclosure designer had experience in mitigating the impact of unwanted sound during the design, build, and completion of zoo exhibits. The academic delegates were chosen based on their considerable experience of working with/in the zoo and aquarium community (i.e., over a decade’s worth of involvement). Eight different zoos and zoo organisations from the UK and Ireland were represented. The original invitation was sent out to 20 subject experts, but due to individual untoward circumstances on the day or clashes with work obligations, not all were able to attend. The UK was not yet under any form of mandated COVID-19 restriction, although hand sanitiser gel was provided in the meeting room, and no delegates declined from attending due to COVID-19 related reasons.

Five members of the LTZP team assisted with workshops and information gathering during the work. These members included the LTZP’s Principal Investigator (second author of this paper), one post-doctoral researcher with expertise in animal behaviour (first author of this paper), and two academics and a post-doctoral researcher all with expertise in human–animal relations. The workshop was hosted at the University of Exeter on Friday 6th March 2020 from 10:00 to 16:15.

Prior to the activities which yielded the data explored here, delegates were provided with introductory talks into the aims and approach of LTZP and were given a guided soundwalk around a section of the University of Exeter that demonstrated some of the methods used within the project to document how zoo staff and visitors engage with the sound environment. For information gathered from Activities 1 and 2 (detailed in Section 2.1 and Section 2.2 below), the first author of this paper reviewed all raw outputs to identify and then summarise the key terms, phrases and words used. Then, the second author reviewed the same raw workshop outputs alongside of the summarised outputs to check that no salient points had been overlooked or misinterpreted. Any questions or queries from the second author were emailed to the first author for review, explanation or inclusion in the final summarised output. After final discussion between both authors, the finalised summarised outputs were tabulated. Keywords (technical and subject-specific terms) identified from the delegate outputs produced from Activities 1 and 2 were listed and word clouds created using text analysis software [23] via the prompt “Please can you draw a word cloud that includes all technical and subject-specific keywords from this document that has focussed the importance of considering sound in [name of topic].” These word clouds were included as overall summaries to set the scene for the paper’s discussion. As the aim of this paper is to outline and illustrate delegate perspectives on the sound environment of the zoo, and its importance to animal behaviour, management and welfare, no further inferential analyses were conducted. The research on which this paper was based was approved by the College of Social Sciences and International Studies Research Ethics Committee at the University of Exeter (October 2018).

2.1. Activity 1: Where Do We and Where Should We Consider Sound in Zoo Animal Husbandry?

Delegates first participated in a mind mapping exercise for 60 min on a specific taxonomic group, based on their professional expertise and self-reported experience with sound at the zoo. Taxonomic groups included mammals, birds, reptiles and amphibians, fish and invertebrates. They were given pens and A3 paper and asked to identify current zoo animal husbandry practices that consider sound in a positive, negative, or neutral manner for the taxonomic group to which they were assigned. After an initial period of discussion and idea generation, delegates were then requested to pinpoint key areas where sound should be a consideration, and where there are gaps in our knowledge of the potential impact of sound on zoo animal management. Each group then presented their key thoughts and ideas back to the whole audience for comment and discussion. Coverage across the specified taxonomic groups was important to the workshop’s final outputs because some taxa (e.g., herptiles, fish and invertebrates) can be less represented in zoo-focussed literature [24,25], and we hoped to be inclusive of often over-looked species. However, due to budgetary and logistical constraints, we were unable to have discussion groups dedicated to reptiles, amphibians, fish and invertebrates separately and this would be a recommended improvement for any future event of this nature. The wider qualitative dataset for the LTZP is available via the UK Data Service Reshare at https://reshare.ukdataservice.ac.uk/855383/ (accessed on 1 September 2025) (Folder 5 contains the materials pertinent to this paper).

2.2. Activity 2: What Are the Welfare Considerations of Sound at the Zoo?

Delegates also participated in a group discussion activity for 70 min where they considered the importance of sound to specific activities or elements of the zoo environment that relate, or potentially relate, to animal welfare states. The categories for this activity were: environmental enrichment and providing positive challenge, population and individual welfare measures, visitor effects and special events in the zoo and promoting good welfare across the course of an individual animal’s life. The rationale for the topic choice in each case was as follows: auditory enrichment is sometimes practiced but is rarely discussed and is less well considered than other forms of enrichment, for instance nutritional enrichment [26,27]; group-level assessment of welfare is important alongside of monitoring individual responses [28,29] as each animal in a group may respond to stimuli differently and therefore experience welfare states in a manner dissimilar to conspecifics; zoos increasingly run special events (e.g., evening activities or festivals) within their grounds [16,18,30] and the impacts on animals can be unclear; because zoo animals are often held in enclosures for many years they may experience negative stimuli long term.

2.3. Brief Review of Literature Pertaining to Zoos, Sound, and Animal Welfare

The rationale for this brief literature review was to evidence a growing awareness of sound as a concern in zoos, from a welfare, animal management and visitor perception aspect. We also hoped to show what taxa are focussed upon in the existing literature and identify gaps to be filled moving forwards. Using the search terms “zoo sound welfare” and “zoo sound behaviour” and “aquarium sound welfare” and “aquarium sound behaviour”, we looked at the number of papers published pre-2020 on the Web of Science database (webofscience.com) and then counted the increase in sound focussed papers to the end of 2024. Academic papers, theses and dissertations and publicly available research reports and conference proceedings (when the full text could be located) were included in this search. Peer-reviewed concept or review papers where sound was a focus were also included. Papers written by “Listening to the Zoo” researchers were included in the post-2020 catchment but the number of these papers is given in parentheses. Descriptions of grants, where no available research output could be identified, were not included. The papers found in this brief literature search will be provided upon request from the corresponding author.

3. Results

3.1. Husbandry-Focussed Discussion Outputs

Table S1 (Supplementary Information) summarises workshop delegates’ own views and opinions on how sound is currently considered (“DO”) and how it should be further integrated (“SHOULD”) into zoo animal husbandry across taxa. For mammals, sound is already managed to some extent, for example, through visitor signage, the use of background radio or masking sounds, and providing information around sound-sensitive events (e.g., births). However, delegates highlighted the need for more research into the welfare effects of routine husbandry and visitor sounds (e.g., doors, gates, crowd sounds) and the provision of biologically relevant acoustic enrichment. For birds, delegates struggled to identify consistent current practices, though some signage and enrichment are used. Delegates emphasised that the biological relevance of such enrichment remains uncertain and that more evidence is needed on the welfare and behavioural impacts of sound. For reptiles and amphibians, current practices largely involve signage to minimise sudden loud sounds. Future priorities include better enclosure sound insulation, particularly through the use of materials such as plants and soft substrates that can help muffle sound. For fish and invertebrates, sound and vibration are recognised as important, and some facilities take sound readings and use signage to influence visitor behaviour (to reduce and reduced unwanted sound). However, delegates noted that decibel readings are often of limited value and called for improved technology and validated welfare indicators to better understand how acoustic disturbance affects these species. Overall, while some intentional sound management (most notably for mammals) is noted, delegates identified major gaps in knowledge and practice across birds, reptiles, amphibians, fish, and invertebrates. Priorities include improved enclosure design, better sound insulation, the development of species-specific welfare indicators, and further research into biologically relevant sound enrichment.

Table S2 expands upon the findings available in Table S1, outlining the taxa-specific considerations from delegates on how sound affects specific zoo and aquarium taxonomic groups. For mammals, their well-studied but highly variable auditory capacities were noted as both a strength and challenge for welfare management. Some species, such as elephants (Proboscidea) and bats (Chiroptera), have specialised auditory systems that are only partially understood. Loud or unpredictable sounds, whether from visitors or routine husbandry (e.g., metal gates, hosing), can cause chronic stress and abnormal behaviours. Delegates noted that while predictable cues (e.g., feeding bells) may have positive effects, acoustic enrichment must be carefully tailored to the species, using music, natural sounds, or conspecific calls to support welfare. For birds, their high auditory sensitivity means they can detect a wide frequency range and are particularly affected by sudden or high-pitched sounds. Human-created sounds in the zoo can disrupt essential vocalisations used for mating, territory defence, and parent–offspring communication, which in turn can reduce breeding success. Chronic stress may also result from human-generated sounds such as radios, public address systems, keeper activities, and visitor presence. Delegates highlighted the need for improved acoustic buffering and sound-absorbing enclosure design. While issues such as vocal disruption, breeding interference, and a lack of buffering are prevalent, positive uses of sound (such as conspecific call playbacks or natural ambient sounds) may offer enrichment if used carefully. For reptiles and amphibians, there is a major research gap. Reptiles may have poor airborne hearing but are sensitive to ground vibrations, while amphibians rely on both airborne and substrate-borne sound. Artificial sound can suppress natural behaviours, including reproduction in amphibians, as vocalisations may be masked by background sounds. Enclosures and cage furniture can unintentionally amplify sound from equipment, cleaning, or visitors. Stress may result in inactivity or hiding, which can be mistaken as normal cryptic behaviour, leading to undetected welfare compromise. Delegates suggested using vibration-dampening materials under tanks and installing quieter equipment as simple but effective mitigation strategies. For fish and invertebrates, delegates stressed that these groups remain underrepresented in acoustic welfare discussions despite their sensitivity to vibration and low-frequency sound. Fish detect pressure waves and vibrations through their lateral line, while invertebrates use body hairs or surfaces. Continuous equipment sounds (e.g., pumps, filters, chillers) may disrupt behaviour and interfere with reproduction, yet enclosure design rarely accounts for insulation, even though sound travels differently in water. More technological development and empirical data are needed to understand and manage these impacts.

3.2. Welfare-Focussed Discussion Outputs

Table S3 synthesises the implications of sound for zoo animal welfare across key operational areas. Regarding visitor impact and events, delegates emphasised that unpredictable or high-volume sounds (e.g., music, shouting, outputs from large crowds) can trigger stress responses, yet acoustic planning is rarely included in event management. The absence of acoustic refuges in many enclosures forces animals to remain exposed to unwanted sound without the option of retreat, particularly during busy periods when they are expected to be on display. Welfare audits were recommended to help anticipate species- and individual-level responses to such disruption. When considering welfare across the lifespan, sound was identified as a critically underdeveloped area. Delegates highlighted that auditory needs change with age: young and old animals may be more sensitive to sound, and life transitions such as weaning can heighten vulnerability. Chronic exposure to unwanted sound can have cumulative effects, leading to long-term stress or behavioural suppression. Early acoustic experiences may also shape an individual’s resilience and coping ability later in life. In terms of auditory enrichment, sound was seen as a tool with strong potential to enhance welfare if applied in an ecologically relevant way. Natural ambient sounds or conspecific calls may support cognition and positive challenge, particularly in intelligent or vocally active species. Delegates stressed, however, that enrichment must be species-specific and individually tailored, as what benefits one animal may distress another. Enrichment is most effective when sounds are predictable, controllable, or triggered by the animal itself, supporting agency and engagement. Finally, sound in welfare assessment was highlighted as an area requiring integration. Subtle behavioural indicators of sound-induced stress (such as posture shifts, altered vocalisations, or minor changes in activity) are often overlooked. Population-level assessments risk masking individual suffering, since responses to sound vary widely. A lack of validated physiological measures (e.g., cortisol metabolites) further limits the ability to detect acoustic stress. Delegates called for welfare tools to be updated to include acoustic parameters and to evaluate the extent to which animals can control their sound environment.

3.3. Key Themes from Across All Discussion Groups

Table 1. The overall themes across taxonomic orders for husbandry considerations involving sound.

Theme	Cross-Taxonomic Trends and Key Considerations
Under-recognition of sound impacts	Sound is frequently overlooked in husbandry planning, enclosure design, and daily zoo operations, but especially for fish, invertebrates, reptiles, and amphibians. Even for mammals and birds (that are more studied in acoustic-focussed research), the influence of sound is often under-integrated into daily husbandry, zoo operational decisions and routine welfare assessments.
Species- and individual-specific sensitivities	Across these taxonomic groups, species have highly variable sensitivities to sound, within and across species. Based on sensory perception and modalities, certain species are likely to be particularly vulnerable to specific sound types. A “one-size-fits-all” approach is likely to be ineffective when considering sound mitigation approaches.
Impacts on natural behaviours	Across taxa, sound can disrupt the performance of key state and event behaviours. In some cases, these disruptions are chronic and thus linked to long-term welfare issues (manifesting as abnormal repetitive behaviours, or limited use of enclosure space).
Influence of husbandry routines and infrastructure	Equipment (in or around an enclosure) and daily tasks performed by keepers for husbandry purposes often produce sounds and vibrations that can affect animals. These are seldom acoustically managed or shielded and taken as “par for the course”.
Lack of acoustic refuge or control	Many zoo enclosures do not provide animals with ways to escape or control unwanted sounds. Providing quieter zones or options for retreat is rarely implemented but could be a crucial improvement for welfare (especially for species housed in busy areas of zoo grounds).
Potential for positive use of sound	Sound has potential as enrichment, from natural soundscapes to conspecific calls or even to use of music. However, this is underutilised, and its impact may not be always robustly evaluated. Such use of auditory enrichment requires careful tailoring to animals and situations and careful appraisal.
Behavioural and welfare implications go unnoticed	Animals may suppress vocalisations, hide, or freeze in response to unwanted sound. Such responses can be misinterpreted as normal or cryptic behavioural types, especially in reptiles, amphibians, and invertebrates where the knowledge base for behavioural normality is limited.
Need for more research, awareness, and application	Across all taxonomic groups, more research is needed into how sound and vibrations affect zoo-housed animals, especially in non-mammal groups that may experience sounds in ways we find hard to perceive or identify. Research should include a mix of physiological measures, behavioural responses, and long-term outcomes (e.g., use of zoo records on longevity, health status, reproductive viability).

summarises key cross-taxa themes in husbandry discussions. Delegates emphasised the diversity in species and individual auditory sensitivities and the potential for widespread disruption of natural behaviours by unwanted sound. A recurring concern was the acoustic effect of husbandry routines and infrastructure, with little mitigation typically in place. Enclosures often lacked acoustic refuge areas. There was consensus that sound could be used positively (e.g., as enrichment) if well-targeted and informed by valid evidence.

Table 2. The overall themes across welfare-focussed themes in zoo operations.

Theme	Cross-Concept Trends and Considerations
Sound is overlooked in welfare planning	Across all areas, from enrichment to welfare assessment, sound is not routinely included in welfare frameworks. Planning around sound tends to be reactive, not proactive.
Individual variation is critical	Whether in response to enrichment, visitor presence, or environmental change, animals show wide individual differences in how they respond to sound. Welfare strategies must move beyond species-level generalisations yet be species-focussed with the ability to record and respond to individual variations.
Control and predictability shape outcomes	Sound experiences are perceived differently depending on whether animals have control over them (e.g., can avoid or trigger sounds) and whether the sounds are predictable. This is a major differentiator between stress and positive challenge. Understanding whether an animal has demonstrated control is likely easier in some species (e.g., mammals) than others (e.g., invertebrates).
Subtle behavioural and physiological impacts	Sound-related welfare issues are often hard to detect and can manifest as minor changes in posture, suppression of behaviour (e.g., increased hiding and lack of positive activity), or elevated physiological responses (if measurable and valid for a species). These may go unnoticed unless assessments are fine-grained for the individual and species.
Poor sound environments undermine attempts at providing for good welfare	Even when housing, husbandry and social needs are met, unmanaged sounds (from infrastructure, unmanaged visitor groups, inappropriate enclosure location in the zoo) can diminish welfare and quality of life over time.
Sound can be both a risk and a resource	Sound has the potential to cause stress or to enrich; the difference depends on how, when, and by whom (or by what) it is delivered. Acoustic enrichment needs to be researched, planned and a risk-reward analysis conducted before it is implemented.
Welfare is cumulative and context-dependent	The impact of sound is shaped by life stage, previous experiences, and co-occurring stressors. For example, a sound that is tolerable to an adult animal may be distressing to a juvenile or an elderly individual. These factors need to be recorded and documented and described in species-specific husbandry guidelines.
Current assessment tools may not capture sound impacts	Welfare audits and assessments often focus on visual and spatial factors, with little attention to acoustic environments. This can lead to underestimation of welfare challenges linked to unwanted sound. Further research is needed on sound perception on the species level to provide a basis for welfare assessment protocols.

compiles overarching themes from the welfare-focused activities. A major finding was the omission of sound considerations from formal welfare planning frameworks. Delegates stressed the importance of individual variation in responses to sound and the central role of control and predictability in shaping whether sound is enriching or aversive. Behavioural indicators of acoustic stress were noted to be subtle and potentially misinterpreted, while poor sound environments were seen to undermine otherwise adequate welfare provisions. Importantly, participants identified sound as both a risk and a resource, depending on its implementation, and highlighted the need for more refined assessment tools that include acoustic quality and animal agency.

3.4. State of the Zoo Sound and Animal Welfare Literature to the End of 2024

Table 3. The number of publicly available articles (peer reviewed papers and dissertations) that have investigated impacts or influences of sound on zoo and aquarium animal welfare up to the end of 2024. (2) refers to the number of papers produced on this topic from LTZP.

Period	Number of Papers (Zoo/Aquarium, Sound, Welfare)	Most Studied Taxonomic Order *	Unstudied Taxonomic Orders
Up to and including 2019	25	Mammals (64%)	Amphibians (0), Invertebrates (0), reptiles (0)
2020–2024	37 (2)	Mammals (54%)	Amphibians (1) Fish (1) Invertebrates (1)

* Where papers focussed on mammals and birds, these were counted once for each category.

provides a review of the scientific literature up to 2024 that focussed on zoo/aquarium sound and welfare. Although the number of publications increased from 25 pre-2020 to 37 by the end of 2024, mammals remained the most studied group (54% of articles). For multi-taxa papers, mammals and birds were the most common subjects. Amphibians, reptiles, and invertebrates continued to receive little attention, echoing the knowledge gaps identified during the workshop. The lack of taxonomic breadth in the literature reinforces the workshop’s call for more inclusive and diversified research into the role of sound as a potential impact on animal welfare for individual under human care. Of the papers noted in the 2020–2024 sample, six (16%) were review or concept papers applicable to sound research across all zoo-housed taxonomic orders. Of the species focus in the 2020–2024 sample, the following were the focal subjects: cetaceans (six papers, with three on bottlenose dolphins, Tursiops truncatus), primates (five papers in total; four on monkeys, one on apes), meerkats, Suricata suricatta (one paper), collared peccaries, Dicotyles tajacu (one paper), big cats (two focal papers, one where they were included with other species of mammals and birds), two-toed sloths, Choloepus didactylus (one paper), manatees, Trichechus sp. (two papers), penguins (two paper), kiwis, Apteryx sp. (one paper), and flamingos (one feature paper, one included amongst other bird species), frogs, Galapagos giant tortoises (Chelonoidis niger), crocodiles, fish, and three species of cephalopod all featured in one paper each. Ten cross-taxonomic papers were located (27% of the sample). Two papers focussed on multiple bird species in different aviaries. Species diversity is high when multiple animal responses to sound are recorded. For example, the mammal and bird study by Harley et al. [18] included 22 species from reindeer (Rangifer tarandus), to eagle owls (Bubo bubo), Asian short-clawed otters (Aonyx cinereus) to red-crowned cranes (Grus japonensis), to the big cats already mentioned previously.

Between 2020 and 2024, research on sound in zoos and aquaria has focused on the following topics, remembering that multiple topics can appear within a paper. The largest focus was on animal welfare and stress (16 papers), particularly the impacts of visitor “noise”, sound from routine husbandry, and environmental sound on behaviour and welfare. Sound-based enrichment (13 papers), involving music, natural playbacks, and acoustic stimuli, were also common, although the biological relevance and long-term impact of such enrichment remain uncertain. Visitor effects (13 papers) also emerged as a major theme, with work documenting how crowds and human activity can disturb animals. Research on zoo soundscapes (10 papers) has characterised environmental “noise” patterns across facilities, while far fewer studies addressed animal communication (two papers) in captive contexts, despite the importance of vocalisation as a stimulus for further social and reproductive behaviours. Marine mammals (six papers) and primates (five papers) appear disproportionately represented across this sample of articles. Overall, these post-2020 publication trends indicate that progress is being made in recognising alteration of the sound environment as a welfare issue, but significant gaps remain in long-term monitoring, the exploration of positive and biologically relevant soundscapes, and the inclusion of a wider range of taxa in such research questions.

Up to 2019, most research was also centred on welfare/stress (14 papers), with scientists examining behavioural or physiological impacts from changes to the sound environment. Other research strands in this period addressed communication (6), soundscape measurement (6), hearing and perception (6), and auditory enrichment (6). Visitor effects (4) appeared less frequently than in the 2020–2024 dataset, and marine mammals/aquatic systems (1) were rarely the focus in this earlier set. These patterns suggest early recognition of unwanted sound as a welfare concern, with foundational measurement and perception studies in place, but limited application to visitor management strategies or longer-term implications of a changed sound environment across taxa.

4. Discussion

We can summarise our workshop outputs in the word clouds below (Figure 1 and Figure 2). Figure 1, derived from delegate responses about how sound is or should be considered in husbandry practices across taxa, reveals several notable patterns. Dominant terms such as “enclosure,” “design,” “species,” “noise,” and “behaviour” highlight that delegates were primarily concerned with the physical environment and how it amplifies or modulates sound exposure. The frequent appearance of “sensitive,” “relevant,” and “natural” suggests an awareness that acoustic interventions must be tailored to the biological and ecological needs of individual species. The prominence of words such as “research,” “impact,” and “stress” implies a strong recognition that current practices may be insufficiently informed by evidence, particularly around sound as a welfare-relevant stimulus. Repeated mentions of “reptiles,” “amphibians,” “fish,” and “invertebrates” emphasise the taxonomic disparity in current husbandry approaches and the lack of inclusion of ectotherms in sound-related welfare planning. Together, these insights suggest that delegates viewed sound as an underappreciated but critical factor in husbandry and expressed a need for more evidence-based, species-specific guidance—particularly in enclosure design and routine zoo practices.

Figure 2 captures language from responses relating to welfare assessment, enrichment usage, and visitor interaction. It reinforces and extends the findings from the taxonomic-focussed output in Figure 1. Core words like “stress,” “enrichment,” “individual,” “control,” “predictability,” and “response” suggest that delegates conceptualised sound through its potential to challenge or compromise welfare, depending on how it is managed. However, the inclusion of “positive,” “agency,” “engagement,” and “interactive” points to a growing interest in the opportunities for sound as enrichment, especially when animals are given choice and control over their acoustic environments. Such control can come from enabling quiet areas of an enclosure, retreat spaces, or use of cladding or other soundproof or sound-reducing materials within and around an enclosure. The high visibility of “noise,” “visitors,” and “events” reflects a shared concern over anthropogenic sound and the unplanned or unpredictable nature of many zoo soundscapes. The terms “planning,” “assessments,” and “consideration” imply that delegates saw the current lack of acoustic strategy or inclusion in welfare frameworks as a key oversight in operational zoo management. This word cloud suggests that delegates see sound as a cross-cutting issue, one that not only affects animal welfare directly in a given moment, but that also has relevance for the ways in which welfare is measured, planned for, and delivered across an animal’s life in captivity.

Ultimately, when taken together, Figure 1 and Figure 2 suggest that

• Sound is acknowledged to be an overlooked but pervasive influence in zoo environments.
• There is a growing recognition of both the risks and potential benefits of sound in animal care.
• Delegates prioritised species-specific sensitivity, the importance of enclosure design, and the value of predictability and control where possible for animals exposed to what we might consider ‘human-generated’ sound.
• A need for better integration of sound considerations into welfare assessments, enrichment protocols, and zoo event planning is required.

We hope that other researchers will use the knowledge gaps and priorities identified by this group of zoo professionals as the basis for future investigations. Especially for understudied taxa, or areas of zoo operations that generated more questions than answers, our paper clearly identifies a future direction for sound research in zoos and aquariums and why a multi-stakeholder, collaborative approach is beneficial in addressing such challenges. The delegates in the workshop discussed the importance of control and predictability in the sound environment around them, and this has been noted in the available literature. For instance, research on captive squirrel monkeys identified that animals become more anxious and display more behaviours associated with negative welfare when unplanned sounds occurred, e.g., banging of doors and sounds associated with keeper entry into an enclosure [11]. Inadvertent sounds such as these may leverage an individual affective state (and thus experience of welfare) differently at different times and during different days and thus should be researched across a wider range of taxa.

The outputs from our workshop show that further discussion around specific taxa would be extremely useful. For species that are less commonly the subject of sound, behaviour and welfare research in zoos, such as birds, vigilance (as a behavioural state), alert (as discrete counts of an individual responding to a stimulus around it) and preening (as a comfort behaviour) may be relevant measures of individual welfare for future research to focus on [20]. We also have some degree of taxonomic bias here as we grouped fish and invertebrates, and reptiles and amphibians but we included mammals and birds in their own groups. This was not because of any perceived lack of importance for ectotherms, but rather to promote the skills, expertise and background of this ground of delegates. However, we acknowledge the limitations that have resulted from this unavoidable grouping of these taxa. Although the relevance of sound to fish and invertebrate communication [31,32] and life history [33,34], and indeed how anthropogenically altered environments negatively impact on sound-focussed behaviours [35,36], is researched, there are likely barriers to the uptake and application of such studies. For example, accessibility of this published information, and this could be improved by further zoo and academic collaboration. We hope that if we were to run this workshop in 2029 or 2039, we could have separate groups for marine and freshwater fish, terrestrial and aquatic invertebrates, reptiles and amphibians. We encourage zoo-focussed (sound) researchers to seek out the available information on anatomy and physiology pertaining to auditory perception and processing of these species, to provide this important information on how they interact with the world around them to those who care for them in zoos. A development of this workshop would be to broaden the list of invitations to in situ biologists who were currently investigating sound and auditory communication to enhance and decipher some of the ideas and conundrums presented by the ex situ experts that attended. The addition of such delegates would also improve the generalisability of our findings by expanding the number of voices in the workshop and thus robustness of any consensus.

Furthermore, development of baseline ethograms of behavioural inventories of how these species behave in the zoo is required so that others can determine what responses are normal, natural, or species typical for the individuals housed in their zoo. This approach likely requires wild behavioural ecology information to ensure a valid and relevant analysis of in-zoo behavioural responses, which further strengthens the case for academic-zoo collaboration. Advertisement of current peer-reviewed papers, such as the “Flash Newsletter” from the World Association of Zoos & Aquariums (WAZA) or the Association of Zoos & Aquariums (AZA) “What’s New in Zoo and Aquarium Animal Welfare Research” email circular, help improve accessibility to science and signpost where to find such evidence.

As control and choice are key elements for enabling positive affective states [37], research into both population level responses to sound (i.e., for that species) as well as focussing on individual animal responses is required. Especially for animal populations where group data collection is likely easier (e.g., in fish and invertebrate), individual differences from a group norm may help determine responses to specific sound environments and thus feed into welfare assessments. However, it is likely demanding to connect individual level as well group-level research because of animal preferences, behavioural syndromes and past experiences. Comparison between zoos (even for the same or similar species) can also produce different behavioural responses to sound [6], highlighting the care that needs to be taken with cross-establishment generalisations. Furthermore, acting in the best interests of four animals (for example) in the same enclosure where one individual is sound enrichment aversive, one responded positively to acoustic enrichment positive, and two individuals appear indifferent. We encourage further collaboration between animal management experts and academic researchers with expertise in acoustic recording or acoustic biology to help develop protocols that can capture such variation accordingly.

Delegates noted that there could be associative learning occurring between the sound experienced and the animal’s interpretation of the environment around them as inferred from the animal’s response to the sound. For example, acoustic cues linked to feeding or husbandry events can provide predictability and could be enriching, whereas poorly managed associations (e.g., abrupt mechanical sound paired with stressful handling) may exacerbate fear or anxiety. The perceptual abilities of a species set fundamental limits on the detection and processing of sound. Differences in auditory range and the sensitivity to specific sound characteristics can mean that a sound could be benign to one taxon yet highly aversive or disruptive to another. Consequently, this emphasises the need for species-specific assessment of acoustic environments in the zoo, especially pertaining to enclosure design and furnishings. In particular, choice of access to acoustic refuges and the ability to retreat from unwanted sound, would offer animals agency in managing their own welfare [5]. Providing opportunities to disengage from uncontrollable or aversive auditory stimuli would not only mitigate stress but also align with broader positive welfare principles related to autonomy and agency [37,38]. Considering associative learning, perceptual abilities, and choice alongside control and predictability therefore presents a more comprehensive framework for evaluating how zoo sound environments shape animal behaviour and wellbeing.

Given the aversive impact that unwanted and artificial sound can have on conservation efforts and breeding programme viability [10], we need to conduct more research into the impact of life support systems and other equipment that is placed directly in, or attached to, enclosures as the vibrations and/or sound produced may have long term, unwanted influences across generations. Unwanted, or artificial or anthropogenic sounds at, around and in the zoo can be sources of stress to the animals that reside there [1]. We believe that it is important to consider what we mean by noise? Several texts state they have discussed the impact of noise on zoo animal behaviour [3,4,5,7,10,17,39,40], but this is a subjective expression and one that does not consider the animal’s sensory modalities and perception of stimuli. What is noise to one observer may be different for another. Also, repetitive natural sounds may become noisy over time. Defining noise, then, is a very complex task [41], and is highly dependent on the particular positionally of the listener/hearer whether they be human or non-human. We were not prescriptive in the sessions about what did or did not count as noise, so we can take the sound sources identified by participants as giving some indication of what they considered to be potentially problematic sound sources. Equally we recognise that some loud and persistent sounds might be beneficial or have positive impacts on some species (for example repetitive vocalisations associated with courtship or group cohesion). Overall, it may be a challenge for zoo scientists and other invested parties to agree an operationalised definition of noise in relation to zoo/aquarium animal behaviour and welfare.

Main Outputs from Expert Discussion Activities

When considering the summaries of each discussion activity (Table 1 and Table 2), several key themes emerged, reflecting consistent concerns and priorities among workshop delegates:

• Sound is under-recognised across zoo operations; in both husbandry and welfare contexts, sound was frequently described as a neglected factor, rarely integrated into planning, enclosure design, or welfare assessments, despite its clear potential to influence animal behaviour and wellbeing.
• Individual and species-specific sensitivities matter; both groups involved in this exercise emphasised the importance of tailoring sound management to species and individual animals. Delegates noted that animals vary in how they perceive and respond to sound, making one-size-fits-all solutions ineffective.
• Control and predictability influence outcomes; whether in daily care routines or welfare assessments, the ability of animals to predict or control sound exposure was consistently linked to better welfare outcomes. Unpredictable or uncontrollable sounds were seen as key welfare risks.
• Behavioural responses to sound are subtle and often misinterpreted; across both domains, delegates highlighted that animals may suppress behaviours or retreat in response to sound, which can be misread as normal or cryptic behaviour, especially in less-studied taxa like reptiles or fish.
• Sound can be both a risk and a resource; there was a shared recognition that sound is not inherently negative. It can be enriching when ecologically relevant and controllable but damaging when unregulated or intrusive. Care must be taken to distinguish between the two.

Our research has identified areas of zoo operations where the perceptions of zoo professionals and academics can be supported or nuanced with empirical evidence from research at the zoo. For example, where delegates suggest in Table S2 that the high audio sensitivity of many bird species may mean they are a prime candidate for welfare compromise in a “noisy” environment. Research shows that anthropogenic sound can impact on key facets of wild bird behaviour [42,43], and therefore this may form the basis for this perception (of birds as being especially sound sensitive) by zoo professionals. However, the literature on zoo birds of different species and their responses to the sound environment of the zoo paints a more mixed picture [6,20,39,44]. Ultimately, this highlights the need for nuanced, species-specific research within zoos to ensure that management decisions, which aim to deal with such “noise” or are considering the wider sound environment, be guided by evidence collected widely across establishments. Similar principles are being recognised in other managed animal industries, such as domestic rabbit (Oryctolagus cuniculus domesticus) farming, where environmental enrichment and the control of sensory stimuli are highlighted as central to improved welfare outputs [45]. This cross-sector evidence reinforces the idea that managing sensory environments is a universal challenge, but that animal welfare can be strengthened when opportunities for predictability and control are enabled through enhancement of housing and environmental furnishings.

Further discussion amongst zoo professionals and academics who research sound-focussed questions involving captive wild animals will no doubt continue. Especially given that zoo membership and accreditation organisations are actively promoting the relevance and importance of sound regarding animal management and animal welfare. For example, the British Association of Zoos & Aquariums (BIAZA)’s 2023 Animal Welfare Policy specifically refers to “noise and acoustics” [46] and the organisation also has a Sound Focus Group as part of its Research Committee to generate sound-centred research outputs useful to member establishments [47]. This growing emphasis on sound within professional zoo networks reflects a positive shift towards evidence-based practices (i.e., where study of how animals respond to noise is then applied to husbandry change and development) that can directly enhance animal welfare.

5. Conclusions

This research highlights the complex and under-explored role of sound in shaping the behaviour and welfare of zoo-housed animals. Through interdisciplinary workshop discussions, a group of zoo professionals identified consistent gaps in current husbandry and welfare practices across taxa, particularly for reptiles, amphibians, fish, and invertebrates. Delegates agreed that sound is often overlooked in enclosure design, daily operations, and welfare assessments, despite evidence that artificial and unpredictable sounds can disrupt natural behaviours and contribute to long-term stress. Conversely, when appropriately managed, sound environments can potentially act as valuable enrichment tools that supports animal agency, cognitive stimulation, and positive welfare outcomes. Key themes across all discussion activities pointed to the need for species- and individual-specific approaches, improvements in enclosure acoustics, and a better understanding of the behavioural and physiological impacts of sound. Importantly, this project calls for sound to be formally integrated into zoo welfare planning and monitoring frameworks. Our findings are relevant beyond the zoo’s perimeter, applying to other managed animal industries where control over sensory environments is equally critical (e.g., in laboratories, pet shops or in farmyards). By elevating sound as a central consideration in animal care, this research promotes holistic and evidence-informed approaches to welfare and supports the development of environments that promote health and resilience across taxa.