Song Frequency Research Articles

Tenors Not Sopranos: Bio-Mechanical Constraints on Calling Song Frequencies in the Mediterranean Field-Cricket

Male crickets and their close relatives bush-crickets (Gryllidae and Tettigoniidae, respectively; Orthoptera and Ensifera) attract distant females by producing loud calling songs. In both families, sound is produced by stridulation, the rubbing together of their forewings, whereby the plectrum of one wing is rapidly passed over a serrated file on the opposite wing. The resulting oscillations are amplified by resonating wing regions. A striking difference between Gryllids and Tettigoniids lies in wing morphology and composition of song frequency: Crickets produce mostly low-frequency (2–8 kHz), pure tone signals with highly bilaterally symmetric wings, while bush-crickets use asymmetric wings for high-frequency (10–150 kHz) calls. The evolutionary reasons for this acoustic divergence are unknown. Here, we study the wings of actively stridulating male field-crickets (Gryllus bimaculatus) and present vibro-acoustic data suggesting a biophysical restriction to low-frequency song. Using laser Doppler vibrometry (LDV) and brain-injections of the neuroactivator eserine to elicit singing, we recorded the topography of wing vibrations during active sound production. In freely vibrating wings, each wing region resonated differently. When wings coupled during stridulation, these differences vanished and all wing regions resonated at an identical frequency, that of the narrow-band song (∼5 kHz). However, imperfections in wing-coupling caused phase shifts between both resonators, introducing destructive interference with increasing phase differences. The effect of destructive interference (amplitude reduction) was observed to be minimal at the typical low frequency calls of crickets, and by maintaining the vibration phase difference below 80°. We show that, with the imperfect coupling observed, cricket song production with two symmetric resonators becomes acoustically inefficient above ∼8 kHz. This evidence reveals a bio-mechanical constraint on the production of high-frequency song whilst using two coupled resonators and provides an explanation as to why crickets, unlike bush-crickets, have not evolved to exploit ultrasonic calling songs.

Impacts of the COVID-19 pandemic on human-nature interactions: Pathways, evidence and implications.

The coronavirus (COVID‐19) pandemic and the global response have dramatically changed people's lifestyles in much of the world. These major changes, as well as the associated changes in impacts on the environment, can alter the dynamics of the direct interactions between humans and nature (hereafter human–nature interactions) far beyond those concerned with animals as sources of novel human coronavirus infections. There may be a variety of consequences for both people and nature.Here, we suggest a conceptual framework for understanding how the COVID‐19 pandemic might affect the dynamics of human–nature interactions. This highlights three different, but not mutually exclusive, pathways: changes in (a) opportunity, (b) capability and (c) motivation.Through this framework, we also suggest that there are several feedback loops by which changes in human–nature interactions induced by the COVID‐19 pandemic can lead to further changes in these interactions such that the impacts of the pandemic could persist over the long term, including after it has ended.The COVID‐19 pandemic, which has had the most tragic consequences, can also be viewed as a ‘global natural experiment’ in human–nature interactions that can provide unprecedented mechanistic insights into the complex processes and dynamics of these interactions and into possible strategies to manage them to best effect. A free Plain Language Summary can be found within the Supporting Information of this article.

The Allometry of Sound Frequency Bandwidth in Songbirds.

AbstractTheory predicts that allometric constraints on sound production should be stronger for the lower frequencies of vocalizations than for the higher frequencies, which could originate from an allometry for sound frequency bandwidth. Using song recordings of approximately 1,000 passerine species (from >75% passerine genera), we show a significantly steeper allometry for the lower song frequencies than for the higher song frequencies, resulting in a positive allometry of frequency bandwidth: larger species can use wider bandwidths than smaller species. The bandwidth allometry exists in songbirds (oscines) but not in nonoscine passerines, indicating that it emerges from a combination of constraints to sound frequency production or transmission and the evolved behavior of oscines: unlike the narrow bandwidths of most nonoscine songs, the learned songs of oscines often use wide bandwidths that can be limited by both lower and upper constraints to sound frequency. This bandwidth allometry has implications for several research topics in acoustic communication.

Does anthropogenic noise affect the acoustic courtship interactions of Gryllus bimaculatus?

Acoustic courtship displays are ubiquitous among animals. Signallers use these acoustics to advertise their willingness to mate, while receivers may be able to infer something of the signaller's quality from them. However, increases in anthropogenic noise may reduce the production, transmission and reception of these signals, leading to consequences for reproductive success. In this study, we conducted behavioural observations of courtship interactions of the Mediterranean field cricket, Gryllus bimaculatus , under anthropogenic noise conditions. We found that the presence of traffic noise had no effect on the outcome courtship interactions in this species, and their behaviour during courtship did not appear to be altered either. However, we found that the presence of white noise led to a reduction in male signal production, resulting in fewer successful matings. Males that did signal under white noise conditions had altered signal characteristics, including increased song frequency and reduced tick rate. Mate-guarding behaviour was also found to differ between individuals that courted and those that did not. The use of typical anthropogenic noise and white noise in this experiment allows us to consider the importance of specific characteristics of the acoustic pollutant in causing this disruption. • Human-generated acoustics can have a significant impact on the behaviour of animals. • We observed the courtship of field crickets under anthropogenic noise conditions. • Traffic noise did not affect the mating behaviour or acoustics of these crickets. • White noise affected male signalling behaviour, but not female response behaviour.

Which Traits Influence Bird Survival in the City? A Review

Urbanization poses a major threat to biodiversity worldwide. We focused on birds as a well-studied taxon of interest, in order to review literature on traits that influence responses to urbanization. We review 226 papers that were published between 1979 and 2020, and aggregate information on five major groups of traits that have been widely studied: ecological traits, life history, physiology, behavior and genetic traits. Some robust findings on trait changes in individual species as well as bird communities emerge. A lack of specific food and shelter resources has led to the urban bird community being dominated by generalist species, while specialist species show decline. Urbanized birds differ in the behavioral traits, showing an increase in song frequency and amplitude, and bolder behavior, as compared to rural populations of the same species. Differential food resources and predatory pressure results in changes in life history traits, including prolonged breeding duration, and increases in clutch and brood size to compensate for lower survival. Other species-specific changes include changes in hormonal state, body state, and genetic differences from rural populations. We identify gaps in research, with a paucity of studies in tropical cities and a need for greater examination of traits that influence persistence and success in native vs. introduced populations.

Contributions to the study of the grasshopper (Orthoptera: Acrididae: Gomphocerinae) courtship songs from Kazakhstan and adjacent territories.

Male courtship songs of 9 grasshopper species of Gomphocerinae from Kazakhstan and Orenburg region and Altai Republic of Russia were studied. We analyzed not only the sound, but also the stridulatory movements of the hind legs to more entirely describe the songs. We also analyze the frequency spectra of the songs and the whole visual display during courtship. The courtship songs of three species, Stenobothrus miramae, Chorthippus dubius and Ch. angulatus, were studied for the first time. In four species, Omocestus haemorrhoidalis, O. petraeus, Myrmeleotettix pallidus, Ch.karelini, we found certain differences in temporal pattern of the courtship songs in comparison with the previous data on the respective species from other regions. In five species, O. viridulus, S. miramae, M. pallidus, Ch. dubius and Ch. karelini, various parts of elaborate courtship songs differed in the carrier frequency. In four species, O. haemorrhoidalis, O. petraeus, M. pallidus and Ch. dubius, the dominant frequencies of the courtship song were shown to lie in the range higher than 20 kHz. The conspicuous movements of antennae and legs during courtship were studied in M. pallidus, S. miramae and Gomphocerus sibiricus.

A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection

AbstractAnimals use acoustic signals for communication, implying that the properties of these signals can be under strong selection. The acoustic adaptation hypothesis predicts that species in dense habitats emit lower‐frequency sounds than those in open areas because low‐frequency sounds propagate further in dense vegetation than high‐frequency sounds. Signal frequency may also be under sexual selection because it correlates with body size and lower‐frequency sounds are perceived as more intimidating. Here, we evaluate these hypotheses by analysing variation in peak song frequency across 5,085 passerine species (Passeriformes). A phylogenetically informed analysis revealed that song frequency decreases with increasing body mass and with male‐biased sexual size dimorphism. However, we found no support for the predicted relationship between frequency and habitat. Our results suggest that the global variation in passerine song frequency is mostly driven by natural and sexual selection causing evolutionary shifts in body size rather than by habitat‐related selection on sound propagation.

Chronic exposure to urban noise during the vocal learning period does not lead to increased song frequencies in zebra finches

It has often been observed that birds sing at a higher pitch in cities and other areas that are polluted with intense low-frequency noise. How this pattern arises remains unclear though. One prevailing idea is that songbirds adjust song frequencies to environmental noise profiles through developmental plasticity via vocal learning. However, the conclusions of previous studies testing this hypothesis are inconsistent. Here we report the findings from two song learning experiments with zebra finches (Taenopygia guttata), in which we exposed young birds to anthropogenic noise during their sensitive vocal learning period. Unlike previous studies that addressed this issue, we did not use constant synthetic noise but natural urban noise with its typical amplitude fluctuations that was broadcast at realistic sound levels. We found that noise-exposed males in neither experiment developed higher pitched songs compared to control males. This suggests that the natural fluctuations between higher and lower noise levels in cities may allow young birds to exploit relatively quiet moments to hear their tutors and themselves, permitting them to make accurate copies of even low-frequency song elements.Significance statementIf animals are to persist in urban habitats, they often must adjust their behavior to the altered conditions. Birds in cities are often observed to sing at a higher pitch, but we are largely ignorant of how this phenomenon arises. We investigated whether low-frequency traffic noise interferes with the song learning of birds so that they develop higher pitched songs. Accordingly, we played back natural traffic noise from urban bird habitats to young birds during their learning period and then analyzed their adult songs. We found that birds that learned their songs in noise did not sing at higher frequencies compared to control males that learned their song with no noise exposure. Our results show that typical traffic noise in cities may not be sufficient to interfere with vocal learning in a way that birds develop higher-pitched songs.

Senescence of song revealed by a long-term study of the Seychelles warbler (Acrocephalus sechellensis)

Senescence is widespread in nature, often resulting in diminishing survival or reproduction with age, but its role in age-dependent variation in sexual traits is often poorly understood. One reason is that few studies of sexual traits consider non-linear relationships with age, or only consider a narrow range of years relative to the life span of the species. Birdsong has evolved to allow assessment of conspecific quality in numerous bird species. Whilst theory and empirical work suggests that song may become more elaborate with age, there are a paucity of long-term studies testing whether song is associated with age or longevity. In particular, the occurrence of song senescence has rarely been demonstrated. Using an exceptional long-term dataset for the Seychelles warbler (Acrocephalus sechellensis), we analysed relationships between male song, age, survival, and longevity. This species is a long-lived songbird with early life increases, followed by senescent declines, in survival and reproduction. The study population (Cousin Island, Seychelles) is a closed population, with no depredation of adults, providing an excellent opportunity to study senescence in free-living animals. We tested whether song traits were related to age at recording, future survival, longevity, and territory quality. We found age-dependent changes in five song traits (duration, maximum frequency, peak frequency of songs, and duration and frequency bandwidth of trills). Relationships with age were quadratic, indicating reversal in the expression of song coinciding with the onset of senescence in reproduction and survival in this species. One song trait (trill bandwidth) had a quadratic relationship with future survival, but no song traits were related to longevity, suggesting age-related patterns were not the result of selective disappearance. Our study provides one of the first examples of functional senescence in song, offering new insights into avian senescence. Late-life declines in avian song, and possibly other sexual traits, may be more common than currently known, and may play a fundamental role in age-dependent changes in reproductive success.

The effect of noise variation over time and between populations on the fine spectrotemporal characteristics of different vocalization types

Noise affects the recognition of acoustic signals by masking information. To compensate for increased noise, individuals often increase the minimum frequency of their vocalization to reduce noise interference. Our goal was to analyze the effect of noise on the characteristics of different bird vocalizations, through a comparative study of vocalizations on the same bird species. We analyzed the effects of noise variation on the fine spectrotemporal characteristics of calls, songs, and duets of White-eared Ground-sparrows (Melozone leucotis) across three populations over a three-year period. We recorded vocalizations and noise levels simultaneously from 41 territories between 2012 and 2014. We measured the duration, minimum, maximum, and maximum amplitude frequency, and counted the number of songs elements for each vocalization recorded. As we predicted, noise influences the minimum frequency of song, but did not have an effect on the fine spectrotemporal characteristics for calls and duets. We did, however, find that low and high frequency of calls and duets increased with noise-population-year interaction. Our results suggest that differences in noise values at each population were inadequate to observe changes in vocalization characteristics. In conclusion, evaluating responses to different noise levels on different vocalization types for the same species expands our understanding of the flexibility of birds to adjust vocalizations in response to anthropogenic noise.

Urban birdsongs: higher minimum song frequency of an urban colonist persists in a common garden experiment

Environmental changes caused by urbanization and noise pollution can have profound effects on acoustic communication. Many organisms use higher sound frequencies in urban environments with low-frequency noise, but the developmental and evolutionary mechanisms underlying these shifts are generally unknown. We used a common garden experiment to ask whether changes in minimum song frequency observed 30 years after a songbird colonized an urban environment are a consequence of behavioural flexibility. We captured male juvenile dark-eyed juncos, Junco hyemalis thurberi, from two populations (urban and mountain) soon after they reached independence (aged 25-40 days), raised them in identical indoor aviaries and studied their songs at an age of 3 years. We found that the large population difference in minimum frequency observed in the field persisted undiminished in the common garden despite the absence of noise. We also found some song sharing between the common garden and natal field populations, indicating that early song memorization before capture could contribute to the persistent song differences in adulthood. These results are the first to show that frequency shifts in urban birdsong are maintained in the absence of noise by genetic evolution and/or early life experiences.

Songbirds reclaim favored frequencies

Pandemic Pause When severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic lockdowns were instituted across entire countries, human activities ceased in an unprecedented way. Derryberry et al. found that the reduction in traffic sound in the San Francisco Bay Area of California to levels not seen for half a century led to a shift in song frequency in white-crowned sparrows (see the Perspective by Halfwerk). This shift was especially notable because the frequency of human-produced traffic noise occurs within a range that interferes with the highest performance and most effective song. Thus, our “quiet” allowed the birds to quickly fill the most effective song space. Science , this issue p. [575][1]; see also p. [523][2] [1]: /lookup/doi/10.1126/science.abd5777 [2]: /lookup/doi/10.1126/science.abe8026

Black-capped chickadees (Poecile atricapillus) alter alarm call duration and peak frequency in response to traffic noise.

Anthropogenic noise is an often-overlooked byproduct of urbanization and affects the soundscape in which birds communicate. Previous studies assessing the impact of traffic noise have focused on bird song, with many studies demonstrating the ability of birds to raise song frequency in the presence of low-frequency traffic noise to avoid masking. Less is known about the impact of traffic noise on avian alarm calls, which is surprising given the degree to which predator information within alarm calls may impact fitness. The objective of this study was to assess the impacts of traffic noise on the Black-capped Chickadees (Poecile atricapillus), a small non-migratory songbird with a well-studied and information-rich alarm call. We studied birds at eight locations in Stark County, Ohio, from 15 January to 7 March 2016, and used a taxidermic mount of an Eastern Screech-Owl to elicit alarm calls. In half of the trials, a pre-recorded traffic noise track was also broadcasted at 50 decibels. In noise trials, chickadee calls contained more introductory notes (P < 0.001), more total notes (P < 0.001), were of longer duration (P < 0.001), and had lower introductory and D-note peak frequencies (P = 0.032 and P = 0.041, respectively). No differences were noted in the number of D-notes per call between noise and control trials. Modifying alarm call duration and frequency, without changing the number of D-notes, may be a strategy that chickadees use to convey predator information and to coordinate a threat-appropriate mobbing response when it is not possible to change call type. Our results add to the small, but growing, literature documenting the effects of anthropogenic noise on avian alarm calls, demonstrate the flexibility and complexity of chickadee calls given in response to predators, and may partially explain why chickadees adapt well to urban areas.

On the tympanic membrane impedance of the katydid Copiphora gorgonensis (Insecta: Orthoptera: Tettigoniidae).

Katydids (bush-crickets) are endowed with tympanal ears located in their forelegs' tibiae. The tympana are backed by an air-filled tube, the acoustic trachea, which transfers the sound stimulus from a spiracular opening on the thorax to the internal side of the tympanic membranes (TM). In katydids the sound stimulus reaches both the external and internal side of the membranes, and the tympanal vibrations are then transferred to the hearing organ crista acustica (CA) that contains the fluid-immersed mechanoreceptors. Hence the tympana are principally involved in transmitting and converting airborne sound into fluid vibrations that stimulate the auditory sensilla. Consequently, what is the transmission power to the CA? Are the TM tuned to a certain frequency? To investigate this, the surface normal acoustic impedance of the TM is calculated using finite-element analysis in the katydid Copiphora gorgonensis. From this, the reflectance and transmittance are obtained at the TM. Based on the impedance results obtained from the pressure recordings at TM and the velocity field calculations in the AT, in the frequency range 5-40 kHz, it is concluded that the tympana have considerably higher transmission around 23 kHz, corresponding to the dominant frequency of the male pure-tone calling song in this species.

Singing in a silent spring: Birds respond to a half-century soundscape reversion during the COVID-19 shutdown.

Actions taken to control the coronavirus disease 2019 (COVID-19) pandemic have conspicuously reduced motor vehicle traffic, potentially alleviating auditory pressures on animals that rely on sound for survival and reproduction. Here, by comparing soundscapes and songs across the San Francisco Bay Area before and during the recent statewide shutdown, we evaluated whether a common songbird responsively exploited newly emptied acoustic space. We show that noise levels in urban areas were substantially lower during the shutdown, characteristic of traffic in the mid-1950s. We also show that birds responded by producing higher performance songs at lower amplitudes, effectively maximizing communication distance and salience. These findings illustrate that behavioral traits can change rapidly in response to newly favorable conditions, indicating an inherent resilience to long-standing anthropogenic pressures such as noise pollution.

Mainstream Technology as Basic Support for Individuals with Extensive Neuro-Motor Impairments and Absence of Verbal Skills

The present study was aimed at assessing a simplified technology-aided program to allow eight participants with extensive neuro-motor impairments and absence of verbal skills to access preferred leisure events and call the caregiver independently. The technology included mainstream commercial components such as an Echo Dot© with Amazon Alexa©, a Samsung smartphone, and two voice recording devices. Each voice recording device served to record and produce a verbal message, that is, “Alexa music” and “Alexa call the caregiver (NAME)” during the intervention phase of the study. The devices were displayed in front of the participants and could be activated by a simple hand-pressure response. Activation of the devices led the Alexa application of the Echo Dot to deliver a song and call the caregiver, respectively. During the baseline sessions (without the support of the voice recording devices), the participants failed to access songs or to call the caregiver. During the intervention phase (with the support of the voice recording devices), all participants managed to access songs and to call the caregiver independently. The cumulative mean frequency of songs accessed and calls made per 10-min session varied between slightly above 4 and nearly 6. The mean frequency of songs accessed tended to be predominant for all participants. The new technology-aided program may be a useful resource for supporting individuals like the participants of this study.

Social context and noise affect within and between male song adjustments in a common passerine

AbstractAcross populations, animals that inhabit areas with high anthropogenic noise produce vocalizations that differ from those inhabiting less noisy environments. Such patterns may be due to individuals rapidly adjusting their songs in response to changing noise, but individual variation is seldom explored. Therefore, we tested the hypothesis that male house wrens (Troglodytes aedon) immediately adjust their songs according to changing noise and that social context further modifies responses. We recorded songs, quantified noise, and defined social context within pairs as female fertile status and between males as number of conspecific neighbors. We used a reaction-norm approach to compare song trait intercepts (between-male effects) and slopes (within-male effects) as a function of noise. Individuals immediately adjusted song duration in response to changing noise. How they achieved adjustments varied: some sang shorter and others longer songs with greater noise, and individuals varied in the extent to which they adjusted song duration. Variation in song duration could be affected by competition as between-male noise levels interacted with number of neighbors to affect syllable duration. Neither within- nor between-male noise effects were detected for frequency traits. Rather, males with fertile mates sang lower-frequency songs and increased peak frequency with more neighbors. Among males, social context but not noise affected song frequency, whereas temporal structure varied between and within individuals depending on noise and social factors. Not all males adjusted signals the same way in response to noise, and selection could favor different levels of variation according to noise.

Lack of consistent responses to aircraft noise in dawn song timing of bird populations near tropical airports

Abstract: Birds living near airports can reduce the noise interference by advancing their dawn chorus timing and avoiding the start of airport operations. Data supporting this finding come from temperate areas, but little is known from tropical environments, where seasonal variation is lower and biodiversity is higher. Here, we investigated whether 15 tropical bird species are able to advance their dawn song and avoid aircraft noise interference. We sampled dawn song in three airports and three control sites in Brazil, using automated recording units. We found that dawn song times were not globally affected by the exposure to airport noise. Instead, changes were highly variable and species-specific, as dawn song onset was significantly advanced in two and delayed in four species. This large variation in responses was surprising given patterns found in previous studies. Indeed, this is the first time that a significant delay is reported for bird’s dawn song. We explored whether between-species differences in this response could be explained by additional variables (song frequency, degree of urbanity, and noise release), but none of them explained the direction or the strength of the changes. We suggest that earlier airport activity and shorter variations in day length and in twilight duration of tropical areas may be restricting birds’ ability to change dawn song timing. Further studies should consider these differences and analyze to what extent populational declines in noisy areas and the resultant reduced competition for acoustic space may be affecting the changes in dawn chorus onset time. Significance statement: Birds have been shown to advance the timing of their song at dawn to avoid airport noise in Europe. However, we did not find a similar pattern in the birds near three Brazilian airport-affected sites, where the tropical environment can be a key factor (higher biodiversity and lower seasonal variation). We found that of the 15 studied species, only two followed this pattern, 9 species showed no changes in their timing, and 4 species showed the opposite trend, delaying their dawn song in an apparently non-adaptive manner. Neither differences in the birds’ song frequencies and degree of urbanity nor the noise release could account for delays in dawn song. We suggest that the birds’ ability to change their song timing may be limited by shorter seasonal light variations in tropical areas and by earlier airport activity in studied sites.

Bioacoustic variation in Wren Troglodytes troglodytes populations on Welsh islands

ABSTRACT Capsule: Duration and peak frequency of Wren Troglodytes troglodytes songs differ between Welsh islands (Skokholm, Flat Holm, and Sully Island) and a mainland site, suggesting random or cultural divergence. Aims: The study tests for differences in bioacoustic traits in Wren song between four breeding sites. Methods: Songs from breeding male Wrens were recorded from three Welsh islands and a representative location on the local mainland. Each sonogram was measured for six variables from the whole song and two distinct phrases from the beginning and middle. The variables were measured manually using an open source acoustic tool and compared between sites using generalized linear mixed-effects models. Results: There was significant variation in song variables between island sites and the mainland. Skokholm Wren songs were significantly longer in duration than all other sites by up to 66%. Peak frequency was significantly different across all sites with Sully Island having the highest peak frequency and Skokholm the lowest. Conclusion: The differences in song duration and frequency do not directly suggest a trend associated with selective pressures such as habitat or noise, but instead may be explained by non-selective drivers such as cultural drift or local dialect formation.

Exposure to noise pollution across North American passerines supports the noise filter hypothesis

AbstractThe noise filter hypothesis predicts that species using higher sound frequencies should be more tolerant of noise pollution, because anthropogenic noise is more intense at low frequencies. Recent work analysed continental‐scale data on anthropogenic noise across the USA and found that passerine species inhabiting more noise‐polluted areas do not have higher peak song frequency but have more complex songs. However, this metric of song complexity is of ambiguous interpretation, because it can indicate either diverse syllables or a larger frequency bandwidth. In the latter case, the finding would support the noise filter hypothesis, because larger frequency bandwidths mean that more sound energy spreads to frequencies that are less masked by anthropogenic noise. We reanalysed how passerine song predicts exposure to noise using a more thorough dataset of acoustic song measurements, and showed that it is large frequency bandwidths, rather than diverse syllables, that predict the exposure of species to noise pollution. Given that larger bandwidths often encompass higher maximum frequencies, which are less masked by anthropogenic noise, our result suggests that tolerance to noise pollution might depend mostly on having the high‐frequency parts of song little masked by noise, thus preventing acoustic communication from going entirely unnoticed at long distances.