The Overlooked Dimension of Ecosystem Restoration

Rewilding projects have gained momentum worldwide as a means to restore degraded landscapes, reintroduce native species, and re-establish self-sustaining ecosystems. While most efforts focus on physical elements — soil health, vegetation structure, water flow, and wildlife corridors — one critical component often remains absent from planning: sound. The acoustic environment, or soundscape, is more than a background ambience; it is an active force in shaping ecological processes. Recognizing and intentionally managing sound can transform rewilding outcomes, accelerating recovery and enhancing biodiversity. This article explores how sound functions within ecosystems, the tools used to measure and interpret acoustic data, and practical strategies for incorporating sound into restoration projects. As rewilding matures from a niche concept to a mainstream conservation tool, integrating acoustics will separate projects that merely survive from those that truly thrive.

Why Sound Matters in Ecological Systems

The Acoustic Niche Hypothesis

Every species that produces sound occupies a specific frequency range and temporal pattern in the acoustic environment. This concept, known as the acoustic niche hypothesis, proposes that animals evolve to communicate within distinct sound windows to avoid interference. Birds call in one frequency band, insects in another, and mammals in yet another. A healthy ecosystem exhibits a rich, structured soundscape where all available acoustical space is filled in a complementary way. When a habitat is degraded, many of those niches fall silent, leaving gaps that further disrupt communication, mating, and predator-prey interactions. The result is a cascading effect: fewer vocalizations mean less information transfer, which reduces the ability of species to find mates, defend territories, or detect predators, leading to further population declines.

For example, in a tropical rainforest, the dawn chorus involves multiple bird species singing at different pitches and times to minimize competition for acoustic space. If a key species is lost, its niche remains empty, and the entire soundscape becomes less efficient. Rewilding efforts that reintroduce vocal species help restore these missing layers, reconnecting the acoustic web. But the hypothesis extends beyond animals: plants may also respond to sound, with some studies showing that certain frequencies can influence seed germination and root growth, suggesting that the acoustic environment shapes ecosystems from the ground up.

Sound as an Indicator and Driver of Ecosystem Health

Ecologists use sound as a proxy for biodiversity and habitat condition. A vibrant soundscape correlates with high species richness and functional diversity. Conversely, silent or monotonous soundscapes indicate stress, fragmentation, or invasion. Sound also drives behavior: the presence of certain calls can attract or repel other species. For instance, the territorial song of a bird may signal to prospective mates that a suitable territory exists, encouraging colonization. Similarly, the reverberation of a healthy frog chorus can indicate water quality to dispersing amphibians. The absence of such cues can create a "silent trap" where animals avoid otherwise suitable habitat because the soundscape tells them it is empty or dangerous.

Research has shown that playback of natural sounds — such as bird song — can reduce stress in humans and wildlife alike. This "acoustic enrichment" effect suggests that sound has the power to influence physiological states across taxa, making it a potent variable in restoration. Recent experiments in rewilded grasslands have demonstrated that playing healthy prairie soundscapes (crickets, meadowlarks, wind through grasses) can reduce cortisol levels in reintroduced bison and increase foraging efficiency, highlighting the direct physiological link between sound and animal behavior.

Bioacoustics and Ecoacoustics: Tools for Monitoring Rewilding Progress

Passive Acoustic Monitoring

Modern conservation relies heavily on technology, and sound recording devices have become indispensable. Automated recording units (ARUs) can be deployed in remote areas to capture hours of audio data without human presence. These recordings are then analyzed using software that identifies species-specific calls, measures acoustic diversity indices, and detects changes over time. This approach, called passive acoustic monitoring (PAM), allows researchers to track the return of vocal fauna, detect invasive species, and assess noise pollution without invasive sampling. ARUs have become smaller, cheaper, and more rugged; units like the AudioMoth cost under $100 and can run for months on a few batteries, democratizing acoustic monitoring for community-led rewilding projects.

For example, the Ecoacoustics monitoring network used in Australian rewilding projects has helped document the recovery of bird communities after feral cat removal. By analyzing soundscapes every month, managers could pinpoint when certain species resumed breeding and when new species arrived. In one project at Mount Rothwell, acoustic monitoring revealed that Eastern bristlebirds returned to vocalize within three months of cat removal, a recovery that would have been missed by conventional bird surveys requiring trained observers on the ground.

Acoustic Indices for Rapid Assessment

Several indices have been developed to summarize acoustic complexity. The Acoustic Complexity Index (ACI), Bioacoustic Index, and Normalized Difference Soundscape Index (NDSI) each capture different aspects of the sound environment — from the diversity of frequency bands to the ratio of biological versus anthropogenic sounds. These indices serve as early warning systems: a drop in acoustic diversity often precedes visible declines in vegetation or animal counts. Using these metrics, rewilding practitioners can evaluate interventions quickly and adaptively. For instance, a rising NDSI (more biological sound relative to anthropogenic noise) can confirm that noise reduction strategies are working before a single new bird species appears in visual surveys. Advanced machine learning tools, such as BirdNET and Arbimon, now enable real-time classification of calls, allowing managers to receive daily summaries of species activity without manual listening.

Soundscape Restoration: Strategies for Rewilding Practitioners

Reintroducing Vocal Species

The most direct way to restore natural soundscapes is to reintroduce species that produce characteristic sounds. This goes beyond simply bringing back animals — it involves selecting species that fill empty acoustic niches. In European rewilding projects, the return of the Eurasian wolf (Canis lupus) not only restored trophic cascades but also reintroduced howling as a long-distance acoustic signal that influences ungulate behavior and scavenger movement. Similarly, the reintroduction of the kākāpō in New Zealand brings a unique low-frequency boom that once dominated nocturnal forests. The timing of reintroductions matters: releasing animals during their natural vocalization periods (e.g., breeding season) can maximize the immediate acoustic impact and attract conspecifics from surrounding areas.

In many cases, practitioners use acoustic lures — playback of calls — to attract target species to restored habitats. This technique has been successful in seabird colony restoration: playing recordings of breeding pairs encourages prospecting birds to land and settle. Over time, their calls become part of the soundscape and attract further colonization. The same approach has been applied to bats, with playback of social calls increasing roost occupancy in restored woodland patches. However, care must be taken to avoid habituation or attraction of predators; lures should be used as temporary tools during the initial colonization phase.

Reducing Anthropogenic Noise

Noise pollution is a major barrier to rewilding. Road traffic, industrial activities, and even recreational human presence create chronic low-frequency noise that masks animal communication. Studies show that birds sing at higher frequencies in noisy areas, expending extra energy, and many species avoid noisy patches altogether. Rewilding projects must therefore include noise mitigation strategies, such as rerouting trails, scheduling work during non-breeding seasons, or creating buffer zones. Quiet Parks International advocates for preserving acoustic refuges, and several rewilding sites now designate "quiet zones" where motorized access is limited. In practice, this often means closing old logging roads and replacing them with narrow footpaths, limiting mountain biking during dawn and dusk, and establishing "quiet hours" during peak breeding seasons.

Urban rewilding projects, in particular, benefit from noise reduction. For example, removing roads and replacing them with pedestrian paths near restored wetlands in cities has led to the return of breeding amphibians and marsh birds previously absent due to traffic noise. The London Wetland Centre, a rewilded site on former reservoir land, used earthen berms and dense vegetation to buffer noise from nearby highways, resulting in a measurable increase in acoustic diversity within two years. Restoration ecologists are now incorporating sound modeling into site design, predicting how noise propagates through restored landscapes and adjusting topography and planting to create quiet pockets.

Acoustic Enrichment: Actively Enhancing Soundscapes

In severely degraded habitats where animal populations are too low to naturally produce diverse sounds, practitioners may use acoustic enrichment — the deliberate addition of natural sounds to encourage wildlife recovery. Playback of healthy soundscapes (e.g., a coral reef or forest dawn chorus) can trigger settling behaviors in larvae, attract dispersing individuals, and even reduce stress in captive animals being released. This approach is still experimental but promising. Research on oyster reef restoration found that playing recordings of snapping shrimp sounds attracted more oyster larvae to settle. Similarly, playing bird song in reforested patches speeds up colonization by other birds. A recent study in Costa Rica demonstrated that playing forest soundscapes in active pastureland increased seed dispersal by birds and bats, as animals were drawn to the sound and deposited seeds from nearby forest fragments.

Acoustic enrichment should be used carefully to avoid attracting predators or creating unrealistic expectations. However, when combined with habitat structural improvements, it can accelerate the assembly of biological communities. Practitioners recommend using enrichment for short durations (e.g., 2-4 weeks during peak dispersal seasons) and varying the playback content to prevent habituation. The ultimate goal is to jump-start natural acoustic processes so that enrichment can be phased out as animal populations recover.

Case Studies: Sound in Action

The Scottish Rewilding of the Caledonian Forest

In the Scottish Highlands, Trees for Life and other organizations are working to restore the ancient Caledonian pine forest. As part of this effort, they have reintroduced the capercaillie (Tetrao urogallus) — a large grouse known for its elaborate courtship calls. The return of capercaillie not only restored a charismatic species but also reestablished a distinct sound element in the forest understory. Monitoring using acoustic recorders has shown that areas with capercaillie have higher overall bird acoustic diversity, likely because the birds' presence signals safe habitat for other species. This example illustrates how one vocal species can serve as an acoustic keystone, facilitating broader ecosystem recovery. The project also uses soundscapes to monitor pine marten recolonization, as their scuffling and vocalizations provide early evidence of returning predators that are notoriously difficult to trap on camera.

Rewilding Soundscapes in the Ocean

Sound restoration is not limited to terrestrial ecosystems. In marine environments, the soundscape is critical for larval settlement, communication, and navigation. Coral reef restoration projects increasingly include acoustic enrichment. A landmark study published in Nature Communications demonstrated that playing healthy reef sounds on degraded coral patches doubled the number of fish larvae that settled. The sound of snapping shrimp, fish calls, and wave action provided a "homing signal" for young fish. This approach has been tested in the Great Barrier Reef and the Caribbean, showing that sound restoration can complement coral outplanting efforts. More recently, researchers at the University of Exeter found that playing seagrass meadow sounds (crackling of snapping shrimp, fish grunts) attracted fish to barren areas, which in turn facilitated seagrass recovery by reducing algal overgrowth.

Further reading: Acoustic enrichment can enhance fish community development on degraded coral reef habitats (Nature Communications, 2019).

Grassland Rewilding in the American Prairie

In the Northern Great Plains, the American Prairie Reserve uses acoustic monitoring to track the return of grassland birds like the greater sage-grouse and Burrowing Owl. Their distinctive vocalizations were absent for decades due to agriculture and cattle grazing. After removing fences and restoring native grasses, managers deployed ARUs and observed that the first breeding calls of sage-grouse appeared within 18 months — a faster recovery than any vegetation-based indicator. The soundscape data also revealed the arrival of Sprague's pipit, a species that is almost never detected visually because it sings only during high-altitude flights. Acoustic monitoring proved essential for documenting its return, guiding land managers to protect additional buffer areas around lekking sites.

Designing Soundscapes into Restoration Planning

Mapping Acoustic Zones

Just as restoration ecologists create vegetation or hydrology maps, they can now generate soundscape maps that show areas of acoustic diversity, noise pollution, and quiet refuge. Using portable recorders and spatial interpolation, teams can identify where to focus noise reduction efforts and where to prioritize species reintroductions for maximum acoustic impact. For example, a rewilding project in the Danube Delta mapped sound levels across 500 hectares and discovered that a single gravel road was suppressing bird song within a 300-meter corridor. By rerouting the road and planting a dense hedge barrier, the project restored acoustic connectivity between two remaining wetland patches.

Acoustic Corridors

Sound can travel through landscapes and connect populations via acoustic corridors — continuous bands of suitable habitat where animals can hear each other. Rewilding projects can intentionally design these corridors by ensuring that vegetation structure supports sound transmission (e.g., open understory for low-frequency calls, dense canopy for high-frequency songs). This is particularly important for species that rely on long-distance vocal communication, such as howler monkeys or bitterns. In the Brazilian Atlantic Forest, reintroduction of the red-handed howler monkey involved mapping "auditory bridges" — areas where howls could carry between forest fragments — and prioritizing reforestation in those gaps. The result was faster establishment of new troops and reduced inbreeding compared to reintroductions that ignored acoustic connectivity.

Human Dimensions: Sound as a Tool for Connection

Visitor Experience and Environmental Education

Rewilding projects often rely on public support and visitor engagement. The soundscape is a powerful medium for connecting people with nature. Restored natural sounds — bird song, rustling leaves, flowing water — evoke feelings of tranquility and awe. Many rewilded sites now incorporate "listening trails" where visitors are encouraged to stop and absorb the sound environment. This practice, known as soundwalking, can deepen appreciation for biodiversity and foster stewardship.

For instance, the Knepp estate in England — a pioneering rewilding project — offers guided soundwalks that highlight the return of turtle doves, nightingales, and other rare bird species. These experiences have been shown to increase willingness to donate to conservation and reduce support for intensive land management. Sound, in this sense, becomes a bridge between ecological function and human emotion. Some projects have even developed "soundscape apps" that allow visitors to listen to live audio feeds from ARUs installed around the site, turning a hike into an interactive acoustic exploration. The Soundtank initiative provides open-source resources for creating such experiences, helping rewilding sites engage new audiences.

Cultural Reverberations

Many Indigenous and traditional communities have long recognized the importance of sound in ecosystems. For them, a "healing land" is one that sings with the voices of its original inhabitants. Incorporating local knowledge about sound — such as the calls of indicator species or the significance of certain vocalizations in folklore — enriches rewilding projects with cultural depth. Collaborative projects in Patagonia and the Pacific Northwest have used acoustic monitoring to co-manage rewilding with Indigenous partners, blending scientific sound analysis with oral traditions. In the Gila National Forest, the Apache community has worked with ecologists to record and restore the "song of the land" — a mix of elk bugles, canyon wren calls, and wind through ponderosa pines that had been silenced by fire suppression and livestock grazing. Their restoration plan includes cultural soundwalks and protocols for ensuring that acoustic monitoring respects sacred sites where certain sounds should not be recorded.

Challenges and Considerations

Technical Limitations

Acoustic monitoring requires hardware, data storage, and expertise. Analyzing recordings can be time-consuming, and automated species identification software is still imperfect, especially in noisy urban or windy environments. Additionally, sound propagation varies with terrain, vegetation, and weather, complicating comparisons across sites. To overcome these challenges, many projects use open-source software like AudioMoth or BirdNET, which lower the barrier to entry. Cloud-based platforms such as Arbimon now offer automated processing pipelines that can handle terabytes of data, making large-scale acoustic analysis feasible for even small NGOs. However, internet connectivity in remote rewilding sites remains a bottleneck; solar-powered offline recorders with local storage and periodic manual retrieval are still the norm.

Unintended Consequences

Playing recorded sounds may attract predators or cause habituation. If not carefully managed, acoustic enrichment could skew natural behavior. For example, broadcasting predator calls might deter prey species from using habitat. Therefore, any acoustic intervention should be part of a monitoring plan that tracks both intended and unintended effects. In one Australian trial, playing dingo howls to deter kangaroos from restored grasslands also caused a nearby population of bilbies to abandon their burrows, counteracting conservation goals. Learning from such cases, researchers now recommend a precautionary principle: start with low-intensity, short-duration playback, and monitor behavioral responses of multiple taxa before scaling up.

Integrating Sound into Policy

Currently, rewilding guidelines rarely mention soundscape targets. Conservation authorities typically focus on species presence, vegetation cover, or water quality. To mainstream acoustic restoration, a shift in policy is needed. Several initiatives, such as the Soundscape Ecology Congress, are working to develop standards for soundscape metrics in restoration certifications. The IUCN's Rewilding Thematic Commission has debated including acoustic health as a key performance indicator for rewilding projects. The next decade will likely see acoustic indicators become standard in rewilding project evaluations, alongside metrics like number of keystone species, habitat connectivity, and carbon sequestration. Early adopters are already including "soundscape condition" in their annual reporting, giving investors and donors a new dimension of accountability.

Future Directions: Sonic Rewilding

The emerging field of sonic rewilding positions sound as a central component, not an afterthought. New tools, such as real-time acoustic dashboards and AI-based species identification, will allow managers to see the soundscape evolve. Projects might intentionally design sound corridors to connect isolated populations or use sound to deter invasive species while attracting natives. Moreover, soundscape restoration could play a role in climate change adaptation: as species shift their ranges, acoustic monitoring can reveal new arrivals and help guide assisted colonization. For example, a network of ARUs across the Rocky Mountains is already detecting northward shifts in the vocalizations of montane birds, providing early warnings that can be used to prioritize habitat corridors for future rewilding.

Research at the Ecoacoustics International network is exploring how sound influences seed dispersal, pollination networks, and nutrient cycling. For instance, the noise of bat echolocation may affect insect behavior, which in turn affects herbivory rates. Understanding these cascades will help refine sound-based interventions. The concept of "acoustic keystone species" — those whose sounds disproportionately influence the structure of ecological communities — is gaining traction. Identifying and prioritizing such species for reintroduction could yield outsized benefits for whole ecosystems. The next frontier involves combining acoustic enrichment with other sensory restoration — such as olfactory cues (pheromones, plant volatiles) — to create multisensory rewilding that more fully resembles natural conditions.

Conclusion

Sound is not merely a byproduct of a healthy ecosystem — it is an active force that shapes ecological dynamics and accelerates recovery. Rewilding projects that incorporate acoustic considerations, from monitoring to active restoration, can achieve more resilient and biodiverse outcomes. By listening to the land and strategically reintroducing missing voices, conservationists can restore the full symphony of nature. As we move forward, the sound of rewilding will become as important as the sight of a forest or the feel of clean water. The tools are available, the science is advancing, and the benefits — for biodiversity, for ecosystem function, and for human connection — are too significant to ignore. It is time to turn up the volume on rewilding.