Detection and discrimination of natural calls in masking noise by birds: estimating the active space of a signal

We tested the ability of birds to detect and discriminate natural vocal signals in the presence of masking noise using operant conditioning. Masked thresholds were measured for budgerigars, Melopsittacus undulatus, and zebra finches, Taeniopygia guttata, on natural contact calls of budgerigars, zebra finches and canaries, Serinus canaria. Thresholds increased with increasing call bandwidth, the presence of amplitude modulation and high rates of frequency modulation in calls. As expected, detection thresholds increased monotonically with background noise level. Call detection thresholds varied with the spectral shape of noise. Vocal signals were masked predominantly by noise energy in the spectral region of the signals and not by energy at spectral regions remote from the signals. In all cases, thresholds for discrimination between calls of the same species were higher than thresholds for detection of those calls. Our data provide the first opportunity to estimate distances over which specific communication signals may be effective (i.e. their ‘active space’) using masked thresholds for the signals themselves. Our results suggest that measures of peak sound pressure level, combined with the spectrum level of noise within the frequency channel having the greatest signal power relative to background noise, give the most similar results for estimating a signal's maximum communication distance across a variety of sounds. We provide a simple model for estimating likely detection and discrimination distances for the signals tested here. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

Estimating density of calling male Eleutherodactylus coqui in Hawaii from audio recordings of the nighttime frog chorus

Analysis of sound pressure data obtained from audio recordings of night-time Eleutherodactylus coqui chorusing was used to estimate population density of calling male coqui frogs in the major Hawaiian island populations. Study plots 400 m² in size (20 by 20 m; n = 32) were established on the islands of Hawaii and Maui to provide venues for field counting calling male frogs to investigate the ground truth relationship with the recorded sound pressure data. Male coqui frogs emit a two-note ‘co-qui’ advertisement call at regular intervals. Exploiting the temperature-related and relatively consistent male coqui call repetition rate and the average emitted ‘co’ call sound pressure level (70.4 dB at 1 m), cue counts obtained from a correlation process available in the program Raven were also used to estimate the density of calling male coqui. The study methodology included comparing linear regression results between the field-counted frogs and the number of frogs obtained from the cue count method. Both methods revealed a linear relationship between calling male population density and associated average sound pressure of the resulting chorus.     

Change of the heterogametic sex from male to female in the frog

Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.     

Female frog auditory sensitivity,male calls,and background noise: potential influences on the evolution of a peculiar matched filter

The matched filter hypothesis proposes that the tuning of females' auditory sensitivity matches the spectral energy distribution of males' signals. Such correspondence is expected to arise over evolutionary time, as it promotes conspecific information transfer and reduces interference from other sound sources. Our main objective was to determine the correspondence between the acoustic sensitivity of female frogs of Eupsophus roseus and the spectral characteristics of advertisement vocalizations produced by conspecific males. We also aimed to determine how auditory sensitivity is related to the characteristics of background noise. We analysed data on the auditory sensitivity of E. roseus females, and recordings of conspecific male vocalizations and of the acoustic environment during the breeding period of this species. Our results indicate a concordance between the auditory sensitivity of females and call spectra that would provide an appropriate detection of these signals. In addition, this matching is large relative to the correspondence between auditory sensitivity with the spectra of the abiotic and biotic background noise, with the last component being associated with calls of the related species Eupsophus vertebralis. This may be an adaptation of receivers confronting sound interference, which improves the capability of E. roseus to communicate sexually by means of acoustic signals. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 814–827.     

Real estate ads in Emei music frog vocalizations: female preference for calls emanating from burrows

During female mate choice, both the male's phenotype and resources (e.g. his nest) contribute to the chooser's fitness. Animals other than humans are not known to advertise resource characteristics to potential mates through vocal communication; although in some species of anurans and birds, females do evaluate male qualities through vocal communication. Here, we demonstrate that calls of the male Emei music frog (Babina dauchina), vocalizing from male-built nests, reflect nest structure information that can be recognized by females. Inside-nest calls consisted of notes with energy concentrated at lower frequency ranges and longer note durations when compared with outside-nest calls. Centre frequencies and note durations of the inside calls positively correlate with the area of the burrow entrance and the depth of the burrow, respectively. When given a choice between outside and inside calls played back alternately, more than 70 per cent of the females (33/47) chose inside calls. These results demonstrate that males of this species faithfully advertise whether or not they possess a nest to potential mates by vocal communication, which probably facilitates optimal mate selection by females. These results revealed a novel function of advertisement calls, which is consistent with the wide variation in both call complexity and social behaviour within amphibians.     

Context-dependent reproductive site choice in a Neotropical frog

In organisms whose offspring develop in discrete habitat patchessuch as pools, studies have frequently shown that adults avoidsites based on a single risk factor facing offspring. However,natural reproductive sites often vary in multiple risk factorsin both space and time. In this study, I used choice tests amongfield mesocosms to determine whether adults of a Neotropicalanuran, Edalorhina perezi, select the safest pools for offspringbased on two biotic risks of different magnitude: insect predatorsand conspecific competitors. I also investigated whether adultsite-choice was context dependent (i.e., whether it varied bysex or by season or whether it was based on local pool quality).I found that both sexes avoided pools containing predatory insects,but only females significantly avoided those containing conspecifictadpoles. When offered two risky options, both sexes favoredpools with competitors over those with predators. Site-choicebehavior also varied depending on the temporal and spatial context.Female sensitivity to insect predators decreased late in theseason. In addition, both sexes exhibited dampened reproductiveactivity when only risky sites were available locally. Thisstudy emphasizes that social and environmental factors simultaneouslyimpact reproductive site choice. Whether a site is acceptedultimately depends not only on the assessment of mortality risksto offspring but also on the sex and spatiotemporal contextof the decision maker.     

Nightly calling patterns in a Neotropical gladiator frog

In anurans, vocalization is the primary communication form and acoustic parameters are influenced by climatic conditions, but also by social contexts. We investigated calling site use and within-individual variation of acoustic parameters throughout the night in the gladiator-frog Hypsiboas goianus. We expected that large males would call closer to the water and at higher perches to avoid dehydration and maximize sound propagation. Furthermore, we tested the prediction that males would emit more aggressive calls early in the night and more advertisement calls late at night. Male size was not correlated with either distance from the water or perch height. However, as expected, males of H. goianus adopted a calling strategy that consisted of emitting more aggressive calls early in the night and more advertisement calls later in the night. Furthermore, repetition rate and interval between notes of the aggressive calls and repetition rate of the advertisement calls showed within-individual variation throughout the night that agreed with our expectations. The calling strategy of H. goianus is probably related to the establishment of calling sites early in the night and an investment in female attraction in the middle of the night when males’ aggressive interactions have faded away, or due to habituation increasing the males’ aggressive thresholds. This is the first study investigating within-individual patterns of acoustic parameters of calls throughout the night for anurans.     

Kin‐bias,breeding site selection and female fitness in a cannibalistic Neotropical frog

Resource availability influences sexual selection within populations and determines whether behaviours such as territoriality or resource sharing are adaptive. In Thoropa taophora, a frog endemic to the Atlantic Coastal Rainforest of Brazil, males compete for and defend limited breeding sites while females often share breeding sites with other females; however, sharing breeding sites may involve costs due to cannibalism by conspecific tadpoles. We studied a breeding population of T. taophora to determine (i) whether this species exhibits polygynous mating involving female choice for territorial males and limited breeding resources; (ii) whether limited breeding resources create the potential for male–male cooperation in defence of neighbouring territories; and (iii) whether females sharing breeding sites exhibit kin‐biased breeding site choice, possibly driven by fitness losses due to cannibalism among offspring of females sharing sites. We used microsatellites to reconstruct parentage and quantify relatedness at eight breeding sites in our focal population, where these sites are scarce, and in a second population, where sites are abundant. We found that at localities where the appropriate sites for reproduction are spatially limited, the mating system for this species is polygynous, with typically two females sharing a breeding site with a male. We also found that females exhibit negative kin‐bias in their choice of breeding sites, potentially to maximize their inclusive fitness by avoiding tadpole cannibalism of highly related kin. Our results indicate that male territorial defence and female site sharing are likely important components of this mating system, and we propose that kinship‐dependent avoidance in mating strategies may be more general than previously realized.     

Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication

Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.     

Bioacoustic analysis of frog calls from northeast India

Mating calls of three frog species abundant in northeast IndiaRana tigerina,Rana cyanophlyctis andRana limnocharis were recorded in the fields of Assam and Meghalaya during their breeding season (July-August, 1991). The calls were analysed for their temporal and spectral characters. They were species specific, with distinct call duration and call period, number of pulses per call and interpulse interval, and dominant frequency and frequency domain. A comparison of the mating calls ofRana cyanophlyctis with those of the siblingRana ehrenbergi from Yemen showed differences in their temporal and spectral characters, supporting the suggestion that these two species are distinct species, rather than subspecies of the same species. Differences in the temporal and spectral pattern were found in the mating calls of morphologically alike specimens ofRana limnocharis, indicating that the present morphotypeRana limnocharis in northeast India is composed of several species.     

Spatial and temporal patterns of phenotypic variation in a Neotropical frog

Aim Studies of the spatial and temporal patterns of phenotypic diversity help to elucidate the fine‐scale evolutionary and ecological mechanisms underlying geographical differentiation. The red‐eyed tree frog, Agalychnis callidryas, is a widespread Neotropical frog that exhibits a broad range of polymorphism of coloration and flank‐stripe pattern. The goal of this study was two‐fold: first, to investigate the stability of polymorphisms over a 38‐year period; and second, to evaluate biogeographical hypotheses of diversification between lower Central American populations through quantification of phenotypic diversity on a fine geographical scale. Location This study was conducted at 12 sites across four biogeographical regions in Costa Rica and Panama. Methods We quantified colour, categorized flank‐stripe pattern from digital photos taken during field sampling, and measured body size for each individual. We compared the regional frequency of each flank‐stripe pattern in 2005 with the frequency distribution from a previous study of the same sites in 1967 using logistic regression analyses. We determined the geographical signal of leg coloration by employing linear discriminant function analyses to generate a classification matrix based on covariance similarities, and by comparison of the average hue values within and between regions. Results We found a temporal shift in the frequency of flank‐stripe patterns in three of four regions over 38 years. Based on measures of leg coloration, the frequency distribution of flank‐stripe patterns and body size, we conclude that A. callidryas populations are easily distinguishable at a regional scale. Main conclusions Agalychnis callidryas exhibits regional differentiation in all phenotypic traits measured in this study, supporting the role of three major biogeographical barriers to gene exchange. We found evidence of a putative contact zone between polytypic regions in Costa Rica. In addition, we report temporal instability of the relative frequency of stripe patterns located on the flanks. The ecological and evolutionary mechanisms that may underlie this variation include sexual selection and avoidance of predators.     

Frequency modulated calls and species recognition in a neotropical frog

Summary The neotropical frogPhysalaemus pustulosus (Leptodactylidae) has a complex advertisement call and different call components perform different functions. The whine is a necessary and sufficient stimulus for species recognition. The chuck provides information about male body size that is used by females in mate choice (Ryan 1980, 1983), but the chuck must be combined with the species-identifying whine to elicit maximum behavioral responses from males and females. One of the important features of the whine in eliciting behavioral responses from both sexes is the direction of frequency modulation. This suggests that current models of species recognition in anurans based on a frequency filtering mechanism of the peripheral auditory system and selective responses to combinations of frequencies in the central nervous system are not sufficient to explain species recognition inP. pustulosus. Recent neurophysiological studies of the anuran torus semicircularis are discussed in terms of a mechanism for decoding frequency sweeps.     

Acoustic interference limits call detection in a Neotropical frog Hyla ebraccata

Problems1999 The Association for the Study of Animal Behaviourassociated with communication in noisy environments include detection, discrimination, and localization of appropriate signals. I investigated the effects of broadband background noise on call detection by female Copyright 1999 The Association for the Study of Animal Behaviour.     

Construction of natural appearing female genitalia in the male transsexual.

A surgical technique is presented which gives an excellent appearance and functional result in male-to-female transsexual conversion of genitalia. The complications have been few, and the conversion is done in one operation.