Habitat Acoustics Research Articles

Auditory discrimination of natural soundscapes.

A previous modelling study reported that spectro-temporal cues perceptually relevant to humans provide enough information to accurately classify "natural soundscapes" recorded in four distinct temperate habitats of a biosphere reserve [Thoret, Varnet, Boubenec, Ferriere, Le Tourneau, Krause, and Lorenzi (2020). J. Acoust. Soc. Am. 147, 3260]. The goal of the present study was to assess this prediction for humans using 2 s samples taken from the same soundscape recordings. Thirty-one listeners were asked to discriminate these recordings based on differences in habitat, season, or period of the day using an oddity task. Listeners' performance was well above chance, demonstrating effective processing of these differences and suggesting a general high sensitivity for natural soundscape discrimination. This performance did not improve with training up to 10 h. Additional results obtained for habitat discrimination indicate that temporal cues play only a minor role; instead, listeners appear to base their decisions primarily on gross spectral cues related to biological sound sources and habitat acoustics. Convolutional neural networks were trained to perform a similar task using spectro-temporal cues extracted by an auditory model as input. The results are consistent with the idea that humans exclude the available temporal information when discriminating short samples of habitats, implying a form of a sub-optimality.

Cryptic Communication in a Montane Nocturnal Haplorhine, Tarsius pumilus

Crypsis, including visual and auditory concealment, usually manifests in primates as an antipredator strategy. Other factors may also influence cryptic communication style, including habitat structure and phylogenetic history. Compared to less cryptic lowland Sulawesian tarsiers, montane pygmy tarsiers (Tarsius pumilus) exhibit a communication style that lacks scent marks and lower-frequency vocalisations. This study examines why auditory crypsis occurs in montane tarsiers more so than in larger tarsier species and presents the only known spectrograms of T. pumilus in the field. T. pumilus regularly exhibited calls with a dominant frequency of 60–80 kHz (n = 4) in both social situations (duet calls) and stressed contexts. These results indicate that highland, smaller-bodied tarsiers habitually communicate at high frequencies in contexts where Sulawesian and Philippine tarsiers use lower frequencies. While predation threats and habitat acoustics may influence the use of high-frequency vocalisations, this study found that T. pumilus shows an expected relationship between vocal frequency and body mass. These traits may represent a retention of primitive haplorhine traits rather than derived adaptations to a montane environment.

Duetting Patterns of Titi Monkeys (Primates, Pitheciidae: Callicebinae) and Relationships with Phylogeny.

Simple SummaryTiti monkeys—a diversified group of pair-bonded, territorial neotropical primates exhibiting biparental care—produce elaborate, powerful vocal duets used for long-range communication. While the callicebine taxonomy has been centered mainly on the biogeography, morphology, anatomy, and genetics of titi populations, vocal attributes have received little attention as potentially informative markers of phylogenetic relationships. We conducted acoustic analysis of callicebine loud calls recorded from ten species of titis at sites in Bolivia, Peru, and Ecuador and found four distinct patterns of duetting that only partially match three major clades identified in recent molecular genetic studies. In particular, we found that the loud calls of the San Martin titi monkey, P. oenanthe, and the Urubamba brown titi, P. urubambensis, strikingly differ from putative relatives within the donacophilus lineage. Our findings highlight interplay between genes and environment on the expression of vocal behavior and suggest that closer interaction between taxonomists, ethologists, and molecular biologists should be rewarding in resolving the callicebine phylogeny. Such concerted efforts, in turn, will most likely generate valuable recommendations for the conservation of some endangered populations of titi monkeys, such as the vocally distinctive San Martin titi.Long-range vocal communication in socially monogamous titi monkeys is mediated by the production of loud, advertising calls in the form of solos, duets, and choruses. We conducted a power spectral analysis of duets and choruses (simply “duets” hereafter) followed by linear discriminant analysis using three acoustic parameters—dominant frequency of the combined signal, duet sequence duration, and pant call rate—comparing the coordinated vocalizations recorded from 36 family groups at 18 sites in Bolivia, Peru and Ecuador. Our analysis identified four distinct duetting patterns: (1) a donacophilus pattern, sensu stricto, characteristic of P. donacophilus, P. pallescens, P. olallae, and P. modestus; (2) a moloch pattern comprising P. discolor, P. toppini, P. aureipalatii, and P. urubambensis; (3) a torquatus pattern exemplified by the duet of Cheracebus lucifer; and (4) the distinctive duet of P. oenanthe, a putative member of the donacophilus group, which is characterized by a mix of broadband and narrowband syllables, many of which are unique to this species. We also document a sex-related difference in the bellow-pant phrase combination among the three taxa sampled from the moloch lineage. Our data reveal a presumptive taxonomic incoherence illustrated by the distinctive loud calls of both P. urubambensis and P. oenanthe within the donacophilus lineage, sensu largo. The results are discussed in light of recent reassessments of the callicebine phylogeny, based on a suite of genetic studies, and the potential contribution of environmental influences, including habitat acoustics and social learning. A better knowledge of callicebine loud calls may also impact the conservation of critically endangered populations, such as the vocally distinctive Peruvian endemic, the San Martin titi, P. oenanthe.

The effect of habitat acoustics on common marmoset vocal signal transmission.

Noisy acoustic environments present several challenges for the evolution of acoustic communication systems. Among the most significant is the need to limit degradation of spectro-temporal signal structure in order to maintain communicative efficacy. This can be achieved by selecting for several potentially complementary processes. Selection can act on behavioral mechanisms permitting signalers to control the timing and occurrence of signal production to avoid acoustic interference. Likewise, the signal itself may be the target of selection, biasing the evolution of its structure to comprise acoustic features that avoid interference from ambient noise or degrade minimally in the habitat. Here, we address the latter topic for common marmoset (Callithrix jacchus) long-distance contact vocalizations, known as phee calls. Our aim was to test whether this vocalization is specifically adapted for transmission in a species-typical forest habitat, the Atlantic forests of northeastern Brazil. We combined seasonal analyses of ambient habitat acoustics with experiments in which pure tones, clicks, and vocalizations were broadcast and rerecorded at different distances to characterize signal degradation in the habitat. Ambient sound was analyzed from intervals throughout the day and over rainy and dry seasons, showing temporal regularities across varied timescales. Broadcast experiment results indicated that the tone and click stimuli showed the typically inverse relationship between frequency and signaling efficacy. Although marmoset phee calls degraded over distance with marked predictability compared with artificial sounds, they did not otherwise appear to be specially designed for increased transmission efficacy or minimal interference in this habitat. We discuss these data in the context of other similar studies and evidence of potential behavioral mechanisms for avoiding acoustic interference in order to maintain effective vocal communication in common marmosets.

Does acoustic adaptation drive vertical stratification? A test in a tropical cricket assemblage

In species-rich assemblages, differential utilization of vertical space can be driven by resource availability. For animals that communicate acoustically over long distances under habitat-induced constraints, access to an effective transmission channel is a valuable resource. The acoustic adaptation hypothesis suggests that habitat acoustics imposes a selective pressure that drives the evolution of both signal structure and choice of calling sites by signalers. This predicts that species-specific signals transmit best in native habitats. In this study, we have tested the hypothesis that vertical stratification of calling heights of acoustically communicating species is driven by acoustic adaptation. This was tested in an assemblage of 12 coexisting species of crickets and katydids in a tropical wet evergreen forest. We carried out transmission experiments using natural calls at different heights from the forest floor to the canopy. We measured signal degradation using 3 different measures: total attenuation, signal-to-noise ratio (SNR), and envelope distortion. Different sets of species supported the hypothesis depending on which attribute of signal degradation was examined. The hypothesis was upheld by 5 species for attenuation and by 3 species each for SNR and envelope distortion. Only 1 species of 12 provided support for the hypothesis by all 3 measures of signal degradation. The results thus provided no overall support for acoustic adaptation as a driver of vertical stratification of coexisting cricket and katydid species.

Structural Adaptations to Local Habitat Acoustics in Carolina Wren Songs

Recordings of Carolina wren songs were played back and re-recorded through 50 m of habitat. A new method for quantifying degradation using differences in sound energy distribution was utilized to compare songs before and after playback. Songs that were native to the test habitat retained more of their original physical characteristics after 50 m than did songs foreign to that habitat. Songs of Carolina wrens seem to be designed to retain their source characteristics for as great a distance as possible. Zusammenfassung Ob Vogeldialekte Habitat-Anpassungen sind, wurde am Beispiel des Carolina-Zaunkonigs Thryothorus ludovicianus auf folgende Weise gepruft: 50 Gesange, die von zwei okologisch sehr verschiedenen Orten stammten, wurden vom Band gespielt und jeweils 50 m vom Lautsprecher entfernt wieder aufgenommen; und zwar an den ursprunglichen Aufnahmeorten (woher die einen Gesange stammten, die anderen aber nicht) und in neutraler Gegend. Im Frequenzbereich und in der mittleren Hauptfrequenz waren alle Gesange gleich. Berechnet wurde deshalb ein entfernungsbezogener „Anderungs-Index” in der Verteilung der Ton-Amplituden (in dB). Entscheidend scheint die Starke der Frequenzanderung pro Zeit in den Gesangselementen. Am Herkunftsort veranderten sich die Gesange mit der Entfernung am wenigsten; die starksten Anderungen ergaben sich, wenn man die Gesange ortsvertauscht abspielte. Offenbar sind die Gesange den ortstypischen oko-physikalischen Gegeben-heiten so angepast, das sie moglichst weit reichen.

Year-round variability of ambient noise in temperate freshwater habitats and its implications for fishes

Changes in habitat acoustics over the year can potentially affect fish hearing and orientation to sound, especially in temperate climates. This is the first study where year-round changes in ambient noise in aquatic habitats were assessed. Seven different European fresh-water habitats were chosen for this study. Sound pressure level (SPL) and spectral composition of the ambient noise varied in both quiet stagnant habitats (lakes, backwaters) and in flowing habitats (streams, rivers). Linear equivalent SPL (L(Leq, 60s)) tended to be lower in stagnant habitats (means: 91.6-111.7 dB) than in flowing habitats (means: 111.2-133.4 dB). The changes in SPL were smallest in the river (means: 4.2-4.4 dB, maxima: 8.5-10.1 dB), whereas significantly higher values were measured in stagnant habitats and the stream (means: 9.9-14.9 dB, maxima: 25.1-30.9 dB). The spectral compositions of the ambient noise determined at different times of the year were highly correlated to each other at the river sites (mean cross-correlation coefficients: 0.85 and 0.94) and were weaker or not correlated at the other study sites (means: 0.24-0.76). The changes in ambient noise spectra were negatively correlated to changes in SPL, indicating that large changes in SPLs were accompanied by large changes in spectral composition and vice versa. Comparison of these ecoacoustical data with a preceding study (Amoser and Ladich in J Exp Biol 208:3533-3542, 2005) indicates that the auditory sensitivity in hearing specialists is affected by changes in ambient noise levels and spectra throughout a year and that this effect tends to be more pronounced in stagnant waters and the stream than at river sites. On the other hand, absolute noise levels result in a higher degree of masking in flowing waters.

Communication in Noisy Environments i: Acoustic Signals of Staurois Latopalmatus Boulenger 1887

Physical aspects of anurans constrain sound production, and noisy habitats pose a challenge to signal recognition and detection. Habitat acoustics impose selection on anuran calls within the phylogenetic and morphological constraints of the vocal apparatus of senders and the auditory system of receivers. Visual displays and alerting calls can be used as alternative or additional signal strategies to overcome these problems. In this study, we investigated sound pressure levels and spectral features of calls of the ranid rock-skipper frog Staurois latopalmatus, exclusively found at waterfalls of Bornean streams. A total of 176 calls and waterfall recordings were analyzed to characterize acoustic signals and environmental noise. To obtain information on possible signal adaptations, dominant frequency and snout–vent length of 75 ranid species were collected from the literature and compared to our findings. Distributions along acoustically characterized rapids and waterfalls within a 1-km long river transect showed that S. latopalmatus exclusively occurs in noisy habitats. Two different call types could be distinguished in S. latopalmatus: a short, single-note call and a long, multi-note call. Both calls had a lower sound pressure than the noise produced by waterfalls. The dominant frequency analyses revealed that the signal-to-noise ratio can be maximized within high frequency bands around 5 kHz. Correlations of frequency versus body size in ranids indicated that S. latopalmatus has higher call frequencies than predicted by body size, suggesting acoustic adaptation to environmental noise. We conclude that acoustic signal efficiency in environments with low-frequency dominated noise can only be attained through high frequency calls. The single-note call is interpreted as an alerting signal directing the receiver's attention to a subsequent visual signal. The multi-note call is interpreted as a graded aggressive call. We suggest that microhabitat characteristics represent strong selective pressures on the form of acoustic signals. Short calls with a narrow frequency band could reflect a trade-off among detectabilty, sound propagation and discrimination between individuals.

Dialects in pygmy marmosets? Population variation in call structure

Population variation in primate vocal structure has been rarely observed. Here, we report significant population differences in the structure of two vocalizations in wild pygmy marmosets (Trills and J calls). We studied 14 groups of pygmy marmosets Callithrix (Cebuella) pygmaea pygmaea from five populations in northeastern Ecuador. We analyzed the acoustic structure of Trills and J calls recorded from two adult animals in each group through focal samples. Although individuals and groups within a population differed in call structure, we found consistent structural differences at a population level for Trills and J calls. Pair-wise comparisons for the two call types point to San Pablo and Amazoonico as the populations that differed the most, whereas Hormiga and Zancudococha showed the least differences. Discriminant function analysis indicates that calls from each population could be classified accurately at rates significantly above chance. Habitat acoustics, social factors and genetic drift may explain interpopulation vocal differences. This is the first evidence of within-subspecies vocal differences, or dialects, in wild populations of a neotropical primate species.

Sound transmission in the habitats of Japanese macaques and its possible effect on population differences in coo calls

AbstractRecently, the acoustic features of coo calls were reported to differ between two populations of Japanese macaques (Macaca fuscata yakui), namely the Ohirayama and Yakushima populations. We hypothesized that this difference may arise through differences in the acoustic environments of the two habitats, and measured the degrees of transmission of pure tones (250-8000 Hz) and the coo calls of the two populations in each habitat. In the Ohirayama habitat, lower frequencies were transmitted more efficiently, and the low-pitched coo calls of the Ohirayama population showed significantly better transmission than the high-pitched calls of the Yakushima population. In the Yakushima habitat, the degrees of transmission of the calls of the two populations did not differ significantly. Therefore, the calls of the Ohirayama population possess acoustic features that allow better transmission in their own habitat, suggesting that the habitat acoustics may be a factor contributing to the population difference between the calls.

Are frog calls modulated by the environment? An analysis with anuran species from Bolivia

Studies have shown that long-range songs of birds and primates are structurally adapted to local habitat acoustics. The evolution of frog calls, however, seems to be less influenced by habitat. Frogs are extremely dependent on energetically costly acoustic signals, which frequently have to be transmitted over large distances to elicit an encounter with the opposite sex. Different acoustic properties of advertisement calls from 95 Bolivian anuran species were analyzed according to their taxonomic position and the habitat characteristics where each species occurred. The majority of call characteristics, such as diversity of notes, number of pulses per note, or dominant frequency, appear strongly related to taxonomic position. Large-scale habitat characteristics (ecoregion and macrohabitat type) were not related to call characteristics, whereas small-scale habitat (microhabitat) complexity appeared to explain some of the variation in dominant frequency modulation. Species that call in closed microhabitats are more likely to use frequency-modulated calls, which may allow for more efficient sound transmission. To further the understanding of frog-call evolution in response to habitat selection, this and other studies have indicated that studies at finer spatial scales are needed, as well as additional studies restricted to the genus or species level.

Degradation of Great Tit (Parus Major) Song Before And After Foliation: Implications for Vocal Communication in a Deciduous Forest

AbstractSongbirds living in temperate forests experience great seasonal changes in habitat acoustics during the part of the breeding season when singing activity is high. These changes, which are brought about by accelerated vegetation growth and leaf burst in spring, affect sound propagation and potentially render vocal communication more difficult as the total number of scattering and absorbing obstacles increases. We investigated this in a sound transmission experiment in which representative great tit (Parus major) songs were broadcast in a typical forest habitat before and after foliation. Speaker and microphone were placed at natural separation distances and in typical sender and receiver positions. For each song note we quantified several aspects of sound degradation and found that they all increased considerably when leaves were present. Before foliation the same amount of degradation would only be obtained by doubling the transmission distance, i.e. foliage shortens the active space of great tit song. This inevitably alters distance information, provided that distance-dependent, structural changes of received songs are used as ranging cues. Moreover, sender and receiver positions within the canopy become unfavourable compared to heights just below the canopy when the aim is to maximise song propagation distances. Altogether, the presence of foliage greatly affects the potential for vocal information transfer in great tits and requires behavioural and/or perceptual adjustment of the communicating individuals to counteract or reduce the impact of foliage on signal degradation.

Environmental correlates of vocal communication of wild pygmy marmosets, Cebuella pygmaea

We quantified the acoustic characteristics of the habitats of two wild populations of pygmy marmosets, in Amazonian Ecuador to evaluate their effects on vocal signal structure. We obtained measures of ambient noise, sound attenuation and reverberation through recordings and broadcasts of exemplars of two short-range vocalizations and one long-range vocalization of the marmosets. Ambient noise levels differed among habitats. The calls of pygmy marmosets had frequencies that coincided with relatively quiet regions of the ambient noise spectra of the habitats. The three vocalization types were degraded similarly in all habitats. The two short-range signals, with a pulsatile structure, were more affected by reverberation than was the long-range, less pulsatile vocalization. This degradation could be used by the marmosets to estimate the distance of the caller animals. We obtained data on context of vocalizations from six groups of pygmy marmosets, three from each population, in both the dry and rainy seasons. The use of Trills, J calls and Long calls was related to the distance between the calling animal and the potential receivers suggesting that marmosets are using the calls in a way appropriate to the effects of habitat acoustics. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Geographic variation in the calls of wild chimpanzees: a reassessment.

Male chimpanzees produce a species-typical call, the pant hoot, to communicate to conspecifics over long-distances. Calls given by males from the well-known Gombe and Mahale populations typically consist of four different phases: an introduction, build-up, climax, and let-down. Recent observations suggest that chimpanzees living in the Kibale National Park, Uganda, consistently give calls that lack a build-up and are thus qualitatively distinguishable acoustically from those made by other East African conspecifics. We analyzed additional recordings from Mahale and Kibale to re-examine geographic variation in chimpanzee calls. Results indicate that males from both sites produce pant hoots containing all four parts of the call. Calls made by chimpanzees from the two populations, however, differ in quantitative acoustic measures. Specifically, males at Kibale initiate their calls with significantly longer elements and build-up over briefer periods at slower rates than individuals from Mahale. Kibale males also deliver acoustically less variable calls than chimpanzees at Mahale. Although climax elements do not differ between populations in any single acoustic feature, discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct population at rates higher than that expected by chance. Ecological factors related to differences in habitat acoustics, the sound environment of the local biota, and body size are likely to account for these observed macrogeographic variations in chimpanzee calls.

Inter‐ and Intraspecific Variation in the Acoustic Habitats of Three Marmot Species

AbstractClosely related species often have remarkably different vocalizations. Some of the variation in acoustic structure may result from species adapting their calls to maximize transmission through their acoustic environments. We document the relative magnitude of inter‐ and intraspecific variation in acoustic transmission properties of the habitats of three closely related marmot species to study the relative importance that the acoustic environment may have played in selecting for species‐specific marmot alarm calls. We used spectrogram correlation to quantify the degree to which pure tones and alarm calls changed as they were broadcast through marmot home ranges to describe the acoustic habitats of golden (M. candata aurea), yellow‐bellied (M. flaviventris), and alpine (M. marmota L.) marmots. Species lived in quantifiably different acoustic habitats. One analysis partitioned variation between species and between marmot social groups (nested within species). We found significant interspecific variation in the acoustic transmission fidelity of the three species' habitats and insignificant intraspecific variation between social groups. Further analysis of a larger sample of alarm calls broadcast through golden marmot social groups found significant intraspecific variation. Interspecific variation greater than intraspecific variation suggests that variable acoustic habitats may be responsible for at least some of the interspecific variation in alarm call structure. This is the first study to use spectrogram correlation to describe habitat acoustics. We discuss aspects of the method that may be useful for others seeking to quantify habitat acoustics.

Dialect Differences in the Song of Zonotrichia capensis in the Southern Pampas: A Test of the Acoustic Adaptation Hypothesis

Journal Article Dialect Differences in the Song of Zonotrichia capensis in the Southern Pampas: A Test of the Acoustic Adaptation Hypothesis Get access Pablo L. Tubaro, Pablo L. Tubaro Laboratorio de Biologia del Comportamiento, Institute de Biologia y Medicina Experimental, Obligado 2490-1428 Buenos Aires, Argentina Search for other works by this author on: Oxford Academic Google Scholar Enrique T. Segura Enrique T. Segura Laboratorio de Biologia del Comportamiento, Institute de Biologia y Medicina Experimental, Obligado 2490-1428 Buenos Aires, Argentina Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 96, Issue 4, 1 November 1994, Pages 1084–1088, https://doi.org/10.2307/1369117 Published: 01 November 1994 Article history Received: 11 January 1994 Accepted: 18 July 1994 Published: 01 November 1994

Evolution of intraspecific variation in the advertisement call of a cricket frog (Acris crepitans, Hylidae)

Advertisement calls of the cricket frog, Acris crepitans, show statistically significant variation among populations in all call variables measured. Call variables show strong clinal variation resulting in calls of lower frequency, longer duration and slower call rates produced by A. c. blanchardi in open habitat in the west of the range, and calls of higher frequency, shorter calls and faster call rates produced by A. c. crepitans in the pine forests in the eastern part of the range. This clinal variation does not result from pleiotropic effects of body size or any other morphological characters we measured. The two subspecies usually reside in different habitats, but some A. c. blanchardi reside in an isolated pine forest in central Texas. By comparing the calls of this subspecies in open and forest habitat, and by statistically removing the effects of clinal variation for all populations, we determined that habitat explains some of the variation in call structure; this is not true of subspecies. Our data reject several hypotheses that purport to explain the evolution of mate recognition signals. (1) We reject the notion of Paterson and others that there is strong stabilizing selection on species-specific mate recognition signals. (2) There is no support for the hypothesis that call variation is primarily due to pleiotropic effects of body size or other morphological characters over the geographic range we examined. (3) There is no evidence for reproductive character displacement. (4) Our data, as well as experimental studies of habitat acoustics, support the hypothesis that some differences in calls among habitats result from environmental selection on call structure to enhance call transmission. We suggest that the latter hypothesis does not explain the strong clinal component of call variation. This might result from the passive effects of gene flow between populations at the extremes of the range under selection generated by habitat acoustics.

Habitat acoustics and primate communication.

The acoustic characteristics of three tropical habitats were investigated to determine how they might constrain the structure of primate signals. Ambient noise was measured, along with signal attenuation and aspects of signal degradation (reverberation, amplitude fluctuations, and pulse train modulation depth). These measures allowed estimation of the effects of habitat acoustics on the distances over which calls would be audible (the "active space") and over which primates could reliably transmit amplitude-modulated or pulse-coded information.

Is there a ?sound window? for primate communication?

It has long been asserted that habitat acoustics can determine the frequency band bestadapted for long-range communication, but the generality and validity of measurements claiming to demonstrate a “window” of best frequencies have recently been questioned. We report the discovery of a prominent sound window in Kenyan rain forest in a study that is free of methodological difficulties. Our results allow us to calculate the range advantage attained by an animal vocalizing within the sound window, and show that sound windows can be a potent factor for the evolution of primate communication.

Ecological Sources of Selection on Avian Sounds

This study describes selection derived from habitat acoustics on the physical structure of avian sounds. Sound propagation tests were made in forest, edge, and grassland habitats in Panama to quantify pure tone and random noise band sound transmission levels. The sounds of bird species in each habitat were analyzed to determine the emphasized frequency, frequency range, and sound type (whether pure tonelike or highly modulated). Forest habitats differ from grass and edge in that a narrow range of frequencies (1,585-2,500 Hz) has lower sound attenuation than lower or higher frequencies. Attenuation increases rapidly above 2,500 Hz. Bird sounds from species occurring at the lower forest levels were found to be predominantly pure tonelike with a frequency emphasized averaging 2,200 Hz, conforming to the predictions based on sound propagation tests. The edge habitat is characterized by a wide range of frequencies having a generally similar attenuation rate. Pure tone and random noise band sounds did not differ in attenuation rates. The sounds of edge birds have high variance in the frequency-emphasized component, and more are composed of both modulated and pure tone elements to a greater extent than forest or grassland species. It is suggested that this variance is a reflection of a relative lack of selection pressure from habitat acoustics. Grassland propagation tests showed a positive correlation between increasing frequency and increasing attenuation. It is hypothesized that information transfer may be based on temporal aspects of the signal since these are less distorted in temperature- and wind-speed-stratified open environments.