Song Intensity Research Articles

Environmental conditions and marine heatwaves influence blue whale foraging and reproductive effort.

Animal behavior is motivated by the fundamental need to feed and reproduce, and these behaviors can be inferred from spatiotemporal variations in biological signals such as vocalizations. Yet, linking foraging and reproductive effort to environmental drivers can be challenging for wide-ranging predator species. Blue whales are acoustically active marine predators that produce two distinct vocalizations: song and D calls. We examined environmental correlates of these vocalizations using continuous recordings from five hydrophones in the South Taranaki Bight region of Aotearoa New Zealand to investigate call behavior relative to ocean conditions and infer life history patterns. D calls were strongly correlated with oceanographic drivers of upwelling in spring and summer, indicating associations with foraging effort. In contrast, song displayed a highly seasonal pattern with peak intensity in fall, which aligned with the timing of conception inferred from whaling records. Finally, during a marine heatwave, reduced foraging (inferred from D calls) was followed by lower reproductive effort (inferred from song intensity).

Shaken, not stirred: blue whales show no acoustic response to earthquake events.

Quantifying how animals respond to disturbance events bears relevance for understanding consequences to population health. We investigate whether blue whales respond acoustically to naturally occurring episodic noise by examining calling before and after earthquakes (27 040 calls, 32 earthquakes; 27 January–29 June 2016). Two vocalization types were evaluated: New Zealand blue whale song and downswept vocalizations ('D calls'). Blue whales did not alter the number of D calls, D call received level or song intensity following earthquakes (paired t-tests, p > 0.7 for all). Linear models accounting for earthquake strength and proximity revealed significant relationships between change in calling activity surrounding earthquakes and prior calling activity (D calls: R2 = 0.277, p < 0.0001; song: R2 = 0.080, p = 0.028); however, these same relationships were true for ‘null’ periods without earthquakes (D calls: R2 = 0.262, p < 0.0001; song: R2 = 0.149, p = 0.0002), indicating that the pattern is driven by blue whale calling context regardless of earthquake presence. Our findings that blue whales do not respond to episodic natural noise provide context for interpreting documented acoustic responses to anthropogenic noise sources, including shipping traffic and petroleum development, indicating that they potentially evolved tolerance for natural noise sources but not novel noise from anthropogenic origins.

Anthropogenic noise and atmospheric absorption of sound induce amplitude shifts in the songs of Southern House Wren (Troglodytes aedon musculus)

Birdsong is an important feature that mediates several aspects of bird reproduction, such as mate choice, territory defense, and individual recognition. Any factor that impairs vocal transmission through the environment may also impair conspecific recognition and thus reduce the effectiveness of reproduction. In this scenario, birds inhabiting urban environments might be subject to different selective pressures on their vocal amplitude due to acoustic barriers in the song transmission, such as excessive background noise and abnormal atmospheric absorption of sound. Therefore, we measured the amplitude of the song of the Southern House Wren (Troglodytes aedon musculus), to determine the relationships between the variation in vocal intensity and the environmental features. We expect divergence in vocal amplitude according to the noise levels, with song intensity responding to the increasing noise. We found that birds sang with higher amplitude in areas where traffic noise is elevated. Multiple linear regression showed a positive relationship between song amplitude and background noise and a negative relationship between vocal intensity and atmospheric attenuation. Our findings suggest a direct influence of urban environmental structures on the vocal behavior of wrens, which may challenge the effectiveness of communication between subjects and affect the behavioral ecology of the species.

A comparison of humpback whale singing and ambient noise cycles in the Gulf of Tribugá, Chocó, Colombia

To monitor potential changes in the humpback whale (Megaptera novaeangliae) singing cycle, typical singing intensities, and acoustic behaviors requires a baseline understanding of singing activity in the context of an acoustic environment that is minimally disturbed. The Gulf of Tribugá in the Colombian Pacific (the breeding ground for Stock G) was named a Hope Spot in June 2019 as a local conservation campaign against the Colombian government’s plans to build an international port here. To document this minimally disturbed acoustic ecosystem, data were recorded at Morro Mico from October to November 2018. An Ecological Acoustic Recorder (EAR) collected data on a 33.3% duty cycle at a 15 kHz sampling rate. Power spectral densities were explored across several bands up to 6250 Hz and were used to rank sound source influence and to detect diel and lunar cycles. Spectrograms in Raven Pro 1.5 were used to manually classify sounds into six groups: dolphins, humpback whales, fish, wind and rain, snapping shrimp, and boats. These sound source time series combined with power spectral density and humpback whale song intensity cycles now serves as the first year of a baseline study in preparation to document the effects of a pending major construction project.

Sensorimotor Transformations Underlying Variability in Song Intensity during Drosophila Courtship

Diverse animal species, from insects to humans, utilize acoustic signals for communication. Studies of the neural basis for song or speech production have focused almost exclusively on the generation of spectral and temporal patterns, but animals can also adjust acoustic signal intensity when communicating. For example, humans naturally regulate the loudness of speech in accord with a visual estimate of receiver distance. The underlying mechanisms for this ability remain uncharacterized in any system. Here, we show that Drosophila males modulate courtship song amplitude with female distance, and we investigate each stage of the sensorimotor transformation underlying this behavior, from the detection of particular visual stimulus features and the timescales of sensory processing to the modulation of neural and muscle activity that generates song. Our results demonstrate an unanticipated level of control in insect acoustic communication and uncover novel computations and mechanisms underlying the regulation of acoustic signal intensity.

Connecting soundscape to landscape: Which acoustic index best describes landscape configuration?

Soundscape assessment has been proposed as a remote ecological monitoring tool for measuring biodiversity, but few studies have examined how soundscape patterns vary with landscape configuration and condition. The goal of our study was to examine a suite of published acoustic indices to determine whether they provide comparable results relative to varying levels of landscape fragmentation and ecological condition in nineteen forest sites in eastern Australia. Our comparison of six acoustic indices according to time of day revealed that two indices, the acoustic complexity and the bioacoustic index, presented a similar pattern that was linked to avian song intensity, but was not related to landscape and biodiversity attributes. The diversity indices, acoustic entropy and acoustic diversity, and the normalized difference soundscape index revealed high nighttime sound, as well as a dawn and dusk chorus. These indices appear to be sensitive to nocturnal biodiversity which is abundant at night in warm, subtropical environments. We argue that there is need to better understand temporal partitioning of the soundscape by specific taxonomic groups, and this should involve integrated research on amphibians, insects and birds during a 24h cycle. The three indices that best connected the soundscape with landscape characteristics, ecological condition and bird species richness were acoustic entropy, acoustic evenness and the normalized difference soundscape index. This study has demonstrated that remote soundscape assessment can be implemented as an ecological monitoring tool in fragmented Australian forest landscapes. However, further investigation should be dedicated to refining and/or combining existing acoustic indices and also to determine if these indices are appropriate in other landscapes and for other survey purposes.

True katydids (Pseudophyllinae) from Guadeloupe: acoustic signals and functional considerations of song production.

Guadeloupe, the largest of the Leeward Islands, harbors three species of Pseudophyllinae (Orthoptera: Tettigoniidae) belonging to distinct tribes. This study examined the basic aspects of sound production and acousto-vibratory behavior of these species. As the songs of many Pseudophyllinae are complex and peak at high frequencies, they require high quality recordings. Wild specimens were therefore recorded ex situ. Collected specimens were used in structure-function experiments. Karukerana aguilari Bonfils (Pterophyllini) is a large species with a mirror in each tegmen and conspicuous folds over the mirror. It sings 4–6 syllables, each comprising 10–20 pulses, with several peaks in the frequency spectrum between 4 and 20 kHz. The song is among the loudest in Orthoptera (> 125 dB SPL in 10 cm distance). The folds are protective and have no function in song production. Both mirrors may work independently in sound radiation. Nesonotus reticulatus (Fabricius) (Cocconotini) produces verses from two syllables at irregular intervals. The song peaks around 20 kHz. While singing, the males often produce a tremulation signal with the abdomen at about 8–10 Hz. To our knowledge, it is the first record of simultaneous calling song and tremulation in Orthoptera. Other males reply to the tremulation with their own tremulation. Xerophyllopteryx fumosa (Brunner von Wattenwyl) (Pleminiini) is a large, bark-like species, producing a syllable of around 20 pulses. The syllables are produced with irregular rhythms (often two with shorter intervals). The song peaks around 2–3 kHz and 10 kHz. The hind wings are relatively thick and are held between the half opened tegmina during singing. Removal of the hind wings reduces song intensity by about 5 dB, especially of the low frequency component, suggesting that the hind wings have a role in amplifying the song.

The effect of courtship song components in Drosophila melanogaster

Courtship between male and female Drosophila melanogaster involves a complex emission of sounds produced by the male. This song comprises two aspects: a low‐frequency sine song followed by a series of intense pulses. These songs increase the chances of the female accepting the male. However, the reason for the complexity of the song, and the effect on the female of the song's components, is poorly understood. Using measurements of the male courtship song for a canonical stimulus, we investigate the importance of the sine song on both the mechanical and electrophysiological responses of the female antenna: the nonlinear auditory sensor. While stimulating the antenna with modified courtship songs, antennal motion was measured using laser Doppler vibrometry, and compound potentials were simultaneously measured from the auditory neurones. Results show that, even at the periphery, there exists a significant change in the way the antenna responds to the pulses as a function of the sine song intensity, most emphatically through the neurophysiological signals. Results indicate that the sine song is an advantageous trait used to increase the female perception of the pulses in both time and amplitude sensitivity, and therefore improve the male's chance of successfully courting a female.

Female weight predicts the timing of forced copulation attempts in stitchbirds, Notiomystis cincta

Male birds can often accurately gauge the fertile status of females. As is found in other species, the stitchbird manifests this ability through increased mate guarding and attempted extrapair copulations centred on the female's peak fertile period. Males are thought to use various behavioural cues to assess female fertility, including (1) within-pair copulation, (2) mate-guarding intensity, (3) female solicitation, (4) female flight behaviour, (5) nest building, (6) egg laying and (7) paired male song intensity. Using a correlational approach, I examined which behavioural cues were closely linked with the fertile status of the female stitchbird, as well as which cues accounted for patterns of extrapair male behaviour. Female stitchbirds increased their body weight by an average of 31% (maximum 43%) in the 3 weeks before laying. Extrapair male interest rose sharply as the female's weight increased from 31 g to a peak weight of approximately 41 g, 2 days before the first egg was laid. Thus, increasing female weight appears to be the primary fertility indicator in this species, and it is likely that males evaluate this through changes in her flight behaviour. Because of potential costs associated with forced copulation, female stitchbirds may attempt to limit the availability of information regarding their fertile state by burying eggs within the lining of their nest.

Male–male vocal interactions and the adjustment of song amplitude in a territorial bird

Recent studies have shown that territorial songbirds do not maximize vocal amplitude. Instead, song intensity appears to be a flexible trait that is individually regulated. Given the benefits of singing loudly with regard to signal transmission in the context of territory defence and mate attraction, we investigated whether songbirds adjust the sound level of their territorial songs depending on social influences. While interacting with the playback of a simulated conspecific rival, seven male nightingales, Luscinia megarhynchos, increased the sound level of their songs, on average, by more than 5 dB. The nightingales increased their song level to significantly lower values (about 1 dB) in response to control songs of other species, so the revealed increase in vocal intensity during interactions cannot be fully explained by the acoustical masking of the interfering conspecific songs. Thus, the birds improved signal transmission to a higher degree during conspecific male–male interactions.

Pattern amplitude is related to pattern imitation during the song development of nightingales

Song intensity has been neglected in studies on the song development of oscine birds. We analysed this ontogenetic trajectory in the singing of hand-reared nightingales, Luscinia megarhynchos, from their earliest song vocalizations (subsong) through plastic singing, to their adult full song. Embedded in an age-dependent increase in overall sound level, nightingales showed systematic amplitude differences within their song performances. Episodes of song performance containing many imitations of acquired model songs (IPA phases) were produced with a higher amplitude than episodes with only few or no imitations (UPA phases). Further analysis of song patterns revealed that this difference was mainly due to the high number of imitations occurring during the IPA phases. However, unidentified patterns (UPA) that were vocalized during IPA phases had a significantly higher vocal amplitude than UPAs vocalized during UPA phases. This finding indicates that, besides pattern-related amplitude differences, performance phases as a whole also differed in amplitude. The consistent pattern- and phase-related differences in sound level indicate that the control of vocal amplitude should be viewed as an integrative part of the vocal learning process.

Body temperature and the acoustic behavior of the cicadaTibicen winnemanna (Homoptera: Cicadidae)

Tibicen winnemanna (Davis) produces a broad-band frequency- and amplitude-modulated advertisement call. Observations of the animals in the field show that the cicadas produce varied acoustic output. This work investigates the connection between the acoustic behavior of the cicada and the body temperature of the calling animal. The results show there is strong evidence to support the hypothesis that both acoustic output and song intensity are highly dependent on body temperature.

Song Rate Correlates With Paternal Care and Survival in Willow Tits: Advertisement of Male Quality?

Abstract Dawn song in birds may advertise male quality in terms of parental care and/or survival. Males who sing most may also be the best parents, and eager singing may also reflect good chances of a male's or his mate's survival. These relationships were studied in the willow tit Parus montanus, a species with a simple and relatively non-variant song. Song output was expressed as the proportion of time a male spent singing at dawn. Later in the breeding season, two aspects of parental care, nest defence and feeding effort, were measured in the same males. High song output was associated with more intense nest defence behaviour (eager singers attacked the predator model more often and approached closer to it) and high nestling feeding effort. However, reproductive success was not associated with song output, although males with high song rates tended to be more likely to produce recruits. Males who survived to the next year had higher song intensity than males who did not survive, while female survival was not correlated with song output of her mate. The results suggest that dawn song in the willow tit advertises male quality. Some aspects of honest advertisement and female choice are discussed.

Information cues used in male competition by Tettigonia cantans (Orthoptera: Tettigoniidae)

Males of the bush cricket Tettigonia cantans often occur in dense populations in which agonistic, competitive behaviour between singing males is frequently seen. Some of the informational cues that might be used to resolve these competitive interactions have been examined here, the results being drawn from studies of field behaviour and laboratory observations. The cues examined were song frequency (carrier frequency), song intensity, body weight, prior occupation of ‘territory’ and onset of singing activity. Of these the most reliable cue was song frequency; dominant males have songs pitched almost 1 kHz (on average) lower than subordinate males. Song frequency was not related to body size. No consistent relationship was found between song intensity (of the carrier frequency) and body weight, or intensity and dominance, though 63% of dominant males had a louder high-frequency component in their songs. Body size was not related to status though the heaviest males in the population had a higher probability of becoming dominant. Generally dominant males initiated acoustic interactions. The independence of the carrier frequency and body weight, and the relatively low song frequency of T. cantans (compared to other tettigoniid speices of similar size) suggest that sexual selection has acted to depress song frequency in this species.

Phonotaxis in flying crickets

The effects of two-tone stimuli on the high frequency bat-avoidance steering behavior of flying crickets (Teleogryllus oceanicus) were studied during tethered flight. Similarly, the effects of two-tone stimuli on the ultrasound sensitive auditory interneuron, Int-1, which elicits this behavior, were studied using intracellular staining and recording techniques. When a low frequency tone (3-8 kHz) was presented simultaneously with an aversive high frequency tone (in a two-tone stimulus paradigm), the high frequency avoidance steering behavior was suppressed. Suppression was optimal when the low frequency tone was between 4 and 5 kHz and about 10-15 dB louder than the high frequency tone (Figs. 2, 3). Best suppression occurred when the low frequency tone-pulse just preceded or overlapped the high frequency tone-pulse, indicating that the suppressive effects of 5 kHz could last for up to 70 ms (Fig. 4). The threshold for avoidance of the bat-like stimulus was elevated when model bat biosonar (30 kHz) was presented while the animal was performing positive phonotaxis toward 5 kHz model calling song, but only if the calling song intensity was relatively high (greater than 70-80 dB SPL) (Fig. 1). However, avoidance steering could always be elicited as long as the calling song was not more than 10 dB louder than the ultrasound (Fig. 1). This suppressive effect did not require performance of positive phonotaxis to the calling song (Fig. 2) and was probably due to the persistence of the suppressive effects of the 5 kHz model calling song (Fig. 4). The requirement for relatively high intensities of calling song suggest that the suppression of bat-avoidance by the calling song is not likely to be of great significance in nature. The high frequency harmonics of the male cricket's natural calling song overlap the lower frequency range used by insectivorous bats (10-20 kHz) and are loud enough to elicit avoidance behavior in a flying female as she closely approaches a singing male (Fig. 5). The high frequency 'harmonics' of a model calling song were aversive even if presented with a normally attractive temporal pattern (pulse repetition rate of 16 pps) (Fig. 6A). When the 5 kHz 'fundamental' was added to one of the high frequency 'harmonics', in a two-tone stimulus paradigm, this complex model calling song was attractive; the high frequency 'harmonic' no longer elicited the avoidance behavior (Fig. 6) and the animals steered toward the model CS. Thus, addition of 5 kHz to a high frequency harmonic of the calling song 'masked' the aversive nature of this stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Phonotaxis inGryllus campestris L. (Orthoptera, Gryllidae)

Phonotaxis of receptive female field crickets (Gryllus campestris L.) towards a taped model of the species-specific calling song (Fig. 1) presented azimuthally at 12 different sound pressure levels, ranging from 39 to 106.5 dB, is investigated using a locomotion compensator. The orientational performance of the crickets is analysed in the intact state (1.), as well as after occlusion of both prothoracic spiracles (2.), both posterior tympana (3.), both prothoracic spiracles and both posterior tympana (4.), one posterior tympanum and one prothoracic spiracle at a time (5.). 1. In intact female crickets acoustic orientation on average starts at 44 dB. The orientational performance improves steadily up to 79.5 dB, deteriorates slightly at 86 and 91.5 dB and remarkably at 106.5 dB calling song intensity (Figs. 3, 4 and 11). 2. Following wax occlusion of both prothoracic spiracles (Figs. 5 and 6) behavioural threshold of phonotaxis is raised by on average 5 dB to 49 dB. The course of the intensity curve is similar to that evaluated for intact crickets, the orientational performance at a given intensity being merely slightly reduced (Fig. 11). 3. Occlusion of both posterior tympana (Figs. 7 and 8) does not abolish the capability of acoustic orientation. Compared to intact animals the behavioural threshold is only raised by on average 17.5 dB to 61.5 dB (Fig. 11). Orientational performance at suprathreshold intensities improves with increasing song intensity, but remains inferior to that of intact crickets unless a 106.5 dB calling song is presented. 4. Phonotaxis is even evident after occlusion of the posterior tympana and the prothoracic spiracles with wax (Figs. 9 and 10). This operation results in an effective attenuation of on average 30 dB, the behavioural threshold being raised to 74 dB (Fig. 11). At suprathreshold intensities orientational performance is further reduced compared to that of crickets after occlusion of the posterior tympana only. 5. Occlusion of a posterior tympanum and a prothoracic spiracle on opposite sides results in a stable course deviation of on average 49 ° towards the side of the intact posterior tympanum at 61.5 to 91.5 dB (Figs. 13, 14A and B). This demonstrates that the effect of an occluded posterior tympanum overrides that of an occluded prothoracic spiracle. Occlusion of these sound entrances on the same side results in strong turning tendencies towards the intact side, which increase with calling song intensity (Fig. 14C and D). Except in a single cricket's run performed at 106.5 dB, stable courses are no longer found (Fig. 15). Thus, phonotaxis is more strongly impaired than after occlusion of these sound entrances on opposite sides.

Visual and Auditory Conspicuousness in a Woodland Bird Community: a Quantitative Analysis.

Summary.1. Quantitative observations were made in a Berkshire copse throughout a breeding season. Monthly coefficients of relative conspicuousness are given for each species, together with the coefficients for the previous year's study; it is therefore possible to present a mean coefficient from two seasons' work in the same habitat.2. The counts from which the coefficients are computed have been subjected to analysis and give the relative position of each species in the woodland stratum, being illustrated by a diagram showing the vertical graduation of the different niches. Closely related species obtain their food from different strata; the male inhabits a higher stratum than the female.3. It is shown how a coefficient of sexual conspicuousness can be obtained from the observed sex ratio.4. Song lends itself to quantitative treatment. Persistency varies less than might be expected, among the few examples given. A direct relation between song intensity and size of territory in monogamous territorial birds is suggested. It is shown how population density can affect conspicuousness.5. No attempt is made to ascribe a function to each aspect of coloration. It is suggested that birds are conspicuous in the spring rather than inconspicuous in the summer,