Hans Slabbekoorn

Anthropogenic noise pollution induces changes in the behavior of wild animals. Birds exhibit a well-characterized response to noise pollution: by vocalizing at higher frequencies, birds can escape the masking effects of low-frequency anthropogenic sounds. Although Paris ranks among the world’s largest and most densely populated cities, in recent years Parisians have piloted a multi-faceted effort to reduce anthropogenic noise. Are the city’s noise reduction efforts sufficient to affect the frequency characteristics of city-dwelling birds? We used directional microphones to collect field recordings of Parus major (Great Tit) in noisy urban sites within Paris and quiet forest sites outside of Paris in Fontainebleau. We recorded birds at both sites during two time periods, separated by two decades, in 2003 and 2023. We collected field measurements of ambient noise using a calibrated sound level meter and we evaluated long-term noise monitoring data collected by the French government. We predicted that birds would sing higher frequency songs in noisy urban Paris compared to quiet natural areas, and we predicted that the magnitude of these differences would diminish in 2023 compared to 2003 given the city’s recent noise reduction efforts. We show that urban birds sing at higher frequencies when noise levels increase, matching previous findings from across Europe. Long term data reveal a decline in anthropogenic noise in Paris over the past decades, with average noise levels in 2023 reaching half of their previous intensity. Despite noise reduction efforts, urban birds continue to sing with higher frequencies compared to non-urban birds, and those frequencies have not declined over two decades. We conclude that the noise reduction efforts in Paris have decreased anthropogenic noise levels, but that birds maintain songs with higher minimum frequencies in spite of this change.

The marine world is an acoustic world that has become noisier with the increasing diversity and intensity of human activities at sea. The harbour porpoise ( Phocoena phocoena ) is one of the best-studied cetaceans regarding hearing and responses to human-made underwater sound. The species is most sensitive to high frequencies, yet most impact studies have focused on relatively low-frequency sources. As such, the effects of high frequency sonar – including echosounders – remain largely unstudied, despite their widespread use on vessels for depth sounding, fish or object detection, and seabed mapping. We investigated the effects of scientific echosounder use on harbour porpoise occurrence using 13 multi-sensor mooring deployments in the southern part of the North Sea. Moorings operated for an average of 57 days, with split-beam scientific echosounders active for an average of 51 days, for 10 minutes every hour (5 min at 70 kHz, followed by 5 min at either 185–255 kHz or 70 kHz again). Porpoise acoustic presence was continuously monitored with C/F-PODs and additionally validated with hydrophone detections at four of the locations. Across all 13 sites, detections declined by 65– 79% during echosounder transmissions and returned to typical levels within ∼30 minutes after the echosounder stopped pinging. Despite this relatively quick recovery, there was no indication of habituation, as responses did not diminish across observation periods over six weeks of hourly exposure. Spatial effects appeared local, as no deterrent effect was observed at 2.5 km from the source. We believe that our findings have important implications for studies that investigate both harbour porpoise and fish presence to understand predator-prey interactions, but they should also raise concern about the potentially cumulative impact on sensitive cetaceans from the wide use of relatively high frequency sonar in offshore practices.

Anthropogenic sounds increasingly contribute to the underwater soundscape and can have negative consequences for aquatic animals. High-amplitude, impulsive sounds, such as from seismic surveys and pile driving, can be especially harmful to nearby marine mammals and fishes. However, with acoustic deterrent devices, sound may be used as a mitigation measure. These devices play back specific sounds intended to drive animals away from a potentially dangerous site. Previous studies have explored the efficacy of several sound stimuli in guiding marine mammals at sea and fishes in rivers and estuaries. However, there is still little insight into what type of sounds would be most efficient to deter pelagic fishes at sea. In the current study, we played back a set of eight pulse train sound stimuli, varying in amplitude and temporal pattern, to test for response triggering potential in Atlantic herring ( Clupea harengus ) in captive conditions. We expected pulse trains with a fade in amplitude and an accelerating pulse rate to elicit stronger behavioural responses, as this may be perceived as looming and the approach of a potential threat. Groups of four herring clearly responded to the sound exposures by turning. However, other short- and long-term behavioural changes were absent or subtle, and did not reveal significant responsiveness to pulse train variation. Consequently, we found no evidence for specific variants to have potential to improve an acoustic deterrent device for herring. However, our results in captivity with limited effect sizes can also not exclude a horizontal fleeing response in free-ranging conditions. Nevertheless, a follow-up sound exposure study at sea has confirmed limited spatial responsiveness to sound also in free-ranging pelagic fish. Further studies are needed to test whether acoustic features of a looming stimulus can affect response strength in other fish species or in other conditions.

Noise pollution is on the rise worldwide. An unresolved issue regarding the mitigation of noise pollution is whether and at which timescales animals may adapt to noise pollution. Here, we tested whether continuous highway noise exposure perinatally and during juvenile development increased noise tolerance in a songbird, the zebra finch ( Taeniopygia castanotis ). Breeding pairs were exposed to highway noise recordings from pre-egg-laying until their offspring reached subadulthood. Subsequently, offspring were tested for noise tolerance both as subadults and adults in a spatial preference test, where birds could choose to enter aviaries with different levels of highway noise. Unlike control birds that preferentially chose the quiet aviaries, noise-reared birds exhibited no spatial preferences for quiet in the first test. However, when the experimental birds were retested after two months without noise exposure, they now avoided the previously tolerated noise levels and preferred the quieter aviary. The increased noise tolerance observed directly after the release from the noise treatment was thus only transient. Growing up with chronic highway noise exposure did thus not increase subjects’ noise tolerance, meaning that at least in this songbird species, adaptation to noise pollution is unlikely to arise on a developmental time scale.

In this paper, six different acoustic environments with different loudness and sharpness levels were reproduced to two groups of listeners—control and experimental. The difference between the groups was achieved by adding different melodious singing bird sounds to the original recording of a children’s park. Therefore, the recording of the children’s park represents the recording listened to by the control group, while the experimental groups listened to the recordings of a children’s park mixed with different types of bird species. The questionnaire used in this research relies on the semantic differential method implemented by defining bipolar adjective pairs, which are selected in a way that they can significantly describe an auditory and emotional human response to a certain soundscape recording. In analyzing the results, psychological research methodology was used to determine the statistical significance of obtained human feedback, which enabled us to evaluate different acoustic environments appropriately. The calculation and correlation between the objective acoustic parameters (loudness, sharpness, roughness, and fluctuation strength) and subjective questionnaire parameters were carried out. The aim of this paper was to investigate the influence of different singing bird species, which are typical for Eastern Europe in terms of human appraisal and overall well-being, especially for participants residing in urban areas where the decline of biodiversity is already present. The results of this type of study could serve as a guideline for restoring and recovering biodiversity in urban areas across Europe; furthermore, it could benefit residents’ mood and overall health.