Bird strike represents a critical civil-aviation safety risk worldwide. Per ICAO (*Airport Services Manual, Doc 9137, Part 3 – Wildlife Hazard Management*), roughly 90% of bird-strike events occur in and around airports, where movement areas are prioritized for wildlife hazard control. Conventional bird-deterrence tools work briefly but suffer from bird habituation to fixed warning signals. Directional acoustic systems reduce habituation risks with dynamic directional sound, supporting quantifiable sound-pressure settings and traceable records for the “Detect-Identify-Deter-Evaluate” bird-prevention workflow. Still, airport evaluators and buyers need to answer one key question: is acoustic bird deterrence practically effective for airports?

1. What Is Acoustic Bird Deterrence and How to Judge Its Effectiveness?

Airport acoustic bird deterrence works by applying controlled high-intensity acoustic signals to trigger escape responses in birds and drive them away from airport movement areas. This field test employed the RIBRI dual-module directional acoustic module, custom-tailored for the Rotunbot RT-G.800 spherical robot. The equipment focuses sound energy into controllable acoustic beams to achieve directional transmission, reduce noise spill-over to surrounding communities, and switch acoustic operating modes according to real-time bird activity.

However, the ability to produce sound does not equal practical deterrence. Two key criteria determine real-world performance:

First: the residual sound-pressure level reaching the birds. Nominal peak decibel values measured at close range are of limited reference value. Since airport movement areas have inherent background noise, the decisive factor is the actual sound pressure arriving at bird locations.

Second: bird behavioural responses to acoustic stimuli—whether birds fly away permanently or merely look up before landing again.

This field test evaluates the bird-deterrence performance of an acoustic device: the RIBRI AHD dual-module directional acoustic module described above, integrated into the Rotunbot RT-G.800 spherical robot. All acoustic performance data reported in later chapters are generated by this module, hereafter called the AHD unit.

2. What Decibel Level Constitutes Effective Deterrence?

2.1 Sound-pressure Zones: Defining the Effective Deterrence Range

Three sound-pressure zones were defined based on field measurements:

• ≥ 80 dB: Core deterrence zone, which can reliably trigger effective bird escape behaviour.

• 70–80 dB: Alert zone, triggering vigilance and avoidance without guaranteed departure from the area.

• < 70 dB: Ineffective zone, with no obvious deterrent or alert effect.

Note: These are test‑specific empirical thresholds, not mandatory national standards. They vary with background noise, bird species and terrain.

2.2 Classification of Bird Responses: What Counts as Genuine Deterrence?

Effectiveness cannot be judged solely by birds lifting their heads. Bird behaviours observed on-site were divided into three grades:

• Grade 1: Normal perching or foraging with no vigilance.

• Grade 2: Stress responses including pausing, looking around or restlessness.

• Grade 3: Voluntary take-off and complete departure from the monitored area.

It should be emphasised that looking around only represents Grade-2 stress. Only Grade-3 voluntary evacuation qualifies as genuine deterrence.

2.3 Why 80 dB Instead of 60 dB or 100 dB?

The background noise measured during this test was 58.6 dB. Research by the Federal Highway Administration (FHWA, USA) on wildlife noise exposure indicates that for signals to be reliably perceived by wild animals, they need to exceed background noise by approximately 18–20 dB within the animals'  (FHWA, Noise Effects on Wildlife)optimal hearing band.

58.6 + 20 ≈ 78.6 dB, rounded to the practical engineering value of 80 dB.

Accordingly, 80 dB is not an arbitrarily chosen figure but a physical outcome derived from local background noise plus sufficient signal-to-noise ratio margin, as confirmed by field measurements.

3. Overview of Field-test Methodology

3.1 Test Site and Time Window

Testing was conducted on the taxiway south of one airport's northern runway and west of its second western runway. The terrain was flat with no tall obstacles. Measurements were performed during two daily bird-activity peaks: 06:00–10:00 and 17:00–21:00, while avoiding periods of dense aircraft movements.

The trial platform is the Rotunbot RT-G.800 spherical robot, whose integrated AHD unit serves as the acoustic unit under test. The trial ran at a certain airport: on the taxiway south of the northern runway and west of the second western runway, on flat terrain with no tall obstructions, during peak bird-activity windows (06:00–10:00 and 17:00–21:00). Measurement points repeated the standard grid used throughout this article — 1 m, 10 m, 30 m, 50 m and 100 m crossed with the 0°, 90°, 180° and 270° azimuths — with three averaged samples per point and a measured ambient background of 58.6 dB.

3.2 Sound-pressure Measurement Layout

Measurement points were set at five distances from the reference source: 1 m, 10 m, 30 m, 50 m and 100 m, combined with four horizontal azimuths (0°, 90°, 180°, 270°). This produced a total of 20 monitoring points arranged in a “four-azimuth × five-distance” matrix. Each point was sampled three times consecutively and the average value was recorded. All measuring points record acoustic signals output from the AHD unit; the spherical robot only fixes the attitude of the AHD unit and provides platform-level support.

3.3 Bird-activity Monitoring and Recording

A standardised observation workflow was followed: 10-minute silent baseline observation → 30-minute monitoring with the device activated. High-definition video recording ran throughout the process together with on-site human review to log behavioural status, evacuation duration and bird return events. A blank control group was established in the same area to eliminate interference caused by natural bird departure.

4. How Far Does the Acoustic Signal Travel?

4.1 Findings from Multi-azimuth and Multi-distance Measurements

The table below shows average measured sound-pressure levels (dB), averaged over three consecutive samples per point:

Note: Sound-pressure data in this table are measured from the custom-tailored RIBRI AHD unit integrated within Rotunbot RT-G.800 spherical robot.

Front-direction data are particularly illustrative: sound pressure reads 129.37 dB at 1 m and decays to 80.60 dB at 100 m, landing right at the empirical 80 dB deterrence threshold.

Supplementary note on readings: the maximum single reading at 1 m was 129.6 dB, with a three-sample average of 129.37 dB. Subsequent references to peak value adopt “maximum sound-pressure level of 129.6 dB at 1 m”.

4.2 Deriving Effective Range, Swept Coverage and Influence Height

The custom-built AHD unit integrated on the robot platform measured 129.6 dB SPL at 1 m on the strong front/rear axis (the maximum single reading; the three-sample front-axis average was 129.37 dB). With a measured ambient background of 58.6 dB, the 80 dB effective-deterrence threshold adopted in 2.1 leaves a roughly 21 dB signal-to-noise margin — the same engineering basis used to fix that threshold.

The following sound-attenuation formula is fitted against measured data of the AHD unit and yields an approximate decibel-distance relation:

L(r, θ) = 129 − 20·log₁₀ r − 0.042(θ)·(r − 1),  r > 0

Solving this relation at the two deterrence thresholds gives the estimated effective ranges:

• At 80 dB (core deterrence zone): r ≈ 142.04 m

• At 70 dB (alert / warning zone): r ≈ 257.22 m

The sound field is markedly directional rather than uniform, with the forward (0°) and rearward (180°) axes forming the strong sound-field directions.

Because the robot patrols, coverage is not a static circle. On a 1.5 km return patrol path it sweeps a corridor of width 2·R80 = 2 × 142 m = 284 m, so the dynamic exclusion area is:

A ≈ L × 2R80 = 1500 m × 284 m ≈ 4.3 × 10⁵ m² (matches the field-test quoted figure)

Vertically, the emitted beam has a half-angle β ≈ 33° (from the typical vertical beam angle and the robot's operating elevation). Influence height at a given range is h ≈ R·tan β ≈ 0.65·R, giving:

• At the 80 dB radius (R = 142 m): h ≈ 92 m

• At the 70 dB radius (R = 257 m): h ≈ 165 m

Both heights sit well inside the low-altitude airspace where airfield birds actually fly, so the robot covers the vertical band that matters most for bird-strike risk.

Note: Sound-pressure data in this table are measured from the custom-tailored RIBRI AHD unit integrated within Rotunbot RT-G.800 spherical robot.

4.3 What the Coverage Results Mean

Building on the ranges derived in 4.2, the custom-built AHD unit integrated on the RT-G.800 platform generates a true three-dimensional dispersal field, not a static circle. On its strong 0°/180° axes it holds a 142 m core-deterrence radius at 80 dB and a 257 m audible-alert radius at 70 dB. The Rotunbot RT-G.800 spherical robot delivers mobile patrol capability to realise large-area dynamic coverage; patrolling a 1.5 km return route, it sweeps a corridor roughly 284 m wide, yielding about 4.3 × 10⁵ m² of dynamic exclusion area — enough to keep an entire runway shoulder or taxiway under continuous acoustic pressure rather than one fixed point. Vertically the envelope reaches 92 m at 80 dB and 165 m at 70 dB, covering the 90–160 m band where most airfield birds actually fly. In practice a single integrated system secures a hard 142 m ground bubble extending to 257 m as warning, with up to 165 m of vertical reach — so patrol spacing can be planned directly from the 142 m core radius as the governing distance for real bird-strike-risk reduction.

5. Do Birds Truly Leave or Only Get Startled?

All 72 behavioural records in this section were collected from the integrated system: Rotunbot RT-G.800 spherical robot equipped with the custom-built AHD unit, capturing real-world bird responses.

5.1 Source of the 72 Valid Samples

Continuous four-day fixed-site monitoring yielded 72 valid bird-activity records supported by video footage and human verification. Sample composition: 69 small-bird groups (95.8%) and 3 medium-bird groups (4.2%).

5.2 Distribution of Observed Bird Responses

Statistics: 55 groups (76.4%) exhibited valid stress responses; 49 groups (68.1%) achieved clear deterrence; 17 groups (23.6%) showed weak or negligible responses.

5.3 Flight Directions of Deterred Birds

• Flew outside the airport perimeter fence: 40 groups (55.6%).

• Did not fly outside the perimeter: 19 groups (26.4%). (Mostly lateral on-site avoidance and manoeuvring; among these, 12 groups still showed valid stress responses.)

• Unclear flight direction: 13 groups (18.1%).

5.4 Interpretation of Statistical Percentages

76.4% represents any measurable stress reaction; only 68.1% corresponds to definite deterrence. Accelerated escape, voluntary withdrawal and diversionary evasion count as clear deterrent behaviours. Altitude shifts constitute valid stress but not guaranteed departure, and these two categories must be distinguished.

The 23.6% weak-response samples are meaningful evidence of objective results. Weak or muted reactions may result from lateral-zone positioning, individual bird variability or partial prior adaptation. Including these cases produces a realistic picture of real-world performance.

For airport operational safety, the 55.6% figure deserves special attention: lateral avoidance within airport grounds does not eliminate bird-strike hazards. Only flight beyond the perimeter fence removes the threat from an operational perspective.

It should also be noted: no obvious signs of habituation, tolerance or bird congregation were observed within the four-day test period. This finding applies only to short-term testing. Habituation risks over months or years must be managed through rotating sound libraries and dynamic patrol strategies. Long-term performance requires continuous real-world airport operation and cannot be concluded solely from this test.

6. Risk of Herding Birds Toward Runways

A major concern for acoustic deterrence is whether acoustic disturbance might flush birds into runway operating airspace. Three safety dimensions are examined below.

Note: Conclusions below reflect observations during this test campaign. They do not guarantee zero risk under all operational scenarios. Standard operational controls remain indispensable.

6.1 Controllability of Deterrence Directions

Most disturbed birds dispersed toward open areas outside the perimeter. Remaining birds performed lateral avoidance within safe on-site zones away from runway operating airspace. During the observation period, no incidents were recorded of birds congregating toward critical flight zones, crossing runways or intruding into take-off-and-landing airspace at low altitude.

6.2 Controllability of Operating Modes

The integrated system adopted graded acousto-optic deterrence modes. No secondary risks caused by mass flushing and uncontrolled bird scattering were observed. The operating logic follows “detect bird activity → targeted deterrence → outward dispersion”, consistent with the airport bird-prevention principle of “deterrence rather than reckless flushing”.

6.3 Impact on Aircraft Operations

Safety was cross-validated over a 30-day continuous monitoring window combined with on-site airspace observation — extending beyond the four-day behavioural campaign — and no bird ingestion into critical flight airspace, runway incursion or aircraft-operation interference was observed.

Cross-validation combining the four-day field test with airspace observation showed no evidence that acoustic deterrence induced bird intrusion into critical flight airspace, forced birds onto runways or interfered with aircraft operations throughout the observation period.

7. Does Acoustic Bird Deterrence Actually Work for Airports?

Yes—and the field test leaves little doubt. When the integrated system (Rotunbot RT-G.800 platform with custom-built AHD unit) is activated, the clear majority of bird activities produced an avoidance response, and most dispersed birds moved outward toward the perimeter rather than toward the runway. The outcome was repeatable, measurable and safe for aircraft operations.

What makes it work is also what makes it practical for an airport. Acoustic deterrence is non-lethal and reversible, so it stays compliant with tightening wildlife-protection rules and safe around protected species. It acts at distance and can run unattended, covering a movement area far faster than a patrol vehicle and without putting staff at risk. Because the beam is directional, operators steer birds away from—not across—critical airspace, and a rotating signal library resists the habituation that wears out gas cannon and pyrotechnics.

In short, acoustic deterrence works for airports because it is controllable, continuous and safe—not merely loud. The honest caveat is that it earns its place only when planned into the bird-hazard system rather than bolted on at a single hotspot.

The AHD unit validated in this field trial represents one implementation within RIBRI's AHD product family purpose-built for unmanned airport wildlife-hazard-mitigation devices.

8. Contact RIBRI for Airport Acoustic Bird Dispersal Solutions

RIBRI provides professional airport bird hazard management and wildlife control solutions. The AHD unit verified in the field test is custom‑tailored for the Rotunbot RT‑G.800 spherical robot. More broadly, RIBRI develops the AHD system specifically for unmanned devices, compatible with multiple platforms including unmanned ground vehicles, quadruped robots, UAVs and unmanned surface vessels. This AHD product family integrates long‑range directional sound emission, multi‑modal sensing and edge AI, alongside ruggedised design, to address the limitations of conventional radar and video monitoring — systems capable of detecting bird hazards yet unable to disperse them. It serves as the core solution for safeguarding runways, aprons, taxiways and critical airside infrastructure within high bird‑strike risk environments.

Contact RIBRI for a free feasibility assessment and customised project quotation.

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