Why could continuous partnership in monogamous species be worth to the individual when reproduction is not restricted to the pair-bond? Could the stable pair-bond of flock-forming bird species be considered as a valuable social relationship? Valuable relationships (clear reciprocal friendly behaviours between individuals with none or little agonistic conflict) are widespread in maintaining cohesion in species forming stable social groups. Zebra finches (Taeniopygia guttata) are gregarious songbirds establishing life-long pair-bonds. Using Network theory, we quantify and analyze well-defined behaviours that describe this species’ social links. In a group with balanced sex-ratio, birds form reproductive male-female pair-bonds that also represent real valuable relationships. To test the stability of this pair-based social organization, we study the relationships established in groups of varied sex-ratio: birds form pair-bond with the available partner, regardless of the sex. So, before a reproductive link, zebra finch pair-bond is a real valuable social relationship. Social grooming is the main way to establish and maintain partnerships, but vocal communication could also service group cohesion and should thus reflect zebra finches social network. Using a homemade threshold-based automatic system, we show that pair-bonding affects the group acoustic dynamic: the more paired birds, the less the group vocalizes. To confirm this pair-bond effect, we prevented males from establishing relationships by physical isolation. Isolated males show more burst-like vocal activity and use differently their vocal repertoire. Because zebra finches behaviour and acoustic communication dynamic only depend on pair-bonding regardless of the sex, monogamy could be more a valuable relationships than a reproductive strategy.
As with other African great lakes, Lake Malawi exhibits an explosive radiation of several hundred cichlid species, most of which are endemics. Although visual communication is widely considered the predominant force driving species recognition and mate choice in this radiation, recent studies highlighted a potential role for acoustic signals. To corroborate this proposition, we are analyzing internal and external constraints on acoustic communication in several species from different tribes. Here we focus on the correlation between characteristics of species-specific vocalizations, auditory sensitivity, and eco-acoustical constraints shaping this communication system. Ambient noise in Lake Malawi is characterized by a steep increase to 800 Hz and a slow decline up to several kilohertz. This increase is particularly pronounced during windy conditions creating a low frequency sound window. Interestingly, hearing sensitivity in Melanochromis johanni and Metriaclima callainos revealed by auditory evoked potential measurements, is maximally sensitive at 150-200 Hz and lowest at 800-1000 Hz. Moreover, this is true whether sensitivity is measured in terms of acoustic pressure or particle acceleration. All genera investigated to date produce pulsed sounds during agonistic and reproductive interactions with energies concentrated between 200-300 Hz. Thus, the main frequencies for sound communication are concentrated both at the maximum auditory sensitivity, and within the ambient noise window of the lake. These results indicate that sound communication in Lake Malawi cichlids is facilitated by both internal sensory and eco-acoustical conditions in the lake, and could play a major role in speciation.
Hearing sensitivity and sound characteristics of poikilothermic animals are influenced by ambient temperature. The present study investigates the influence of temperature on the hearing ability and on sound characteristics in the neotropical Raphael catfish Platydoras costatus. Using the auditory evoked potential (AEP) recording technique, the hearing thresholds of eight specimens were tested at six different frequencies from 100 to 4000 Hz. The temporal resolution was determined by analyzing the minimum resolvable click period (0.3 - 5 ms). Hearing sensitivity and sound production were measured after acclimation to 22 °C followed by acclimation to 30 °C for at least three weeks each. Auditory sensitivity increased from 1 to 4 kHz with rising temperature, whereas the temporal resolution showed no change. Catfishes produce stridulation sound by rubbing the pectoral spines in the shoulder girdle during abduction and adduction of pectoral fins. Distress calls were recorded when fish were handheld. The stridulation sounds produced during pectoral fin spine abduction and adduction became shorter at the higher temperature. Maximum and minimum pulse period as well as pulse number did not change with temperature, whereas the dominant frequency of sounds was higher at the higher temperature. Our data indicate that constraints imposed on hearing sensitivity at different temperatures cannot be compensated even by longer acclimation. As sound characteristics also change with temperature, we suggest that the ambient temperature directly affects acoustic communication in the neotropical catfish P. costatus.
Batrachoidids, including the Lusitanian toadfish Halobatrachus didactylus, have become good models for studying acoustic communication as they are unusual strongly vocal species and rely on their hearing abilities to find mates during the breeding season. The major goals of this ongoing study are (1) to verify whether the hearing sensitivity of the Lusitanian toadfish is well adapted to detect its complex acoustic repertoire and (2) to investigate the encoding of conspecific sounds in the toadfish auditory system. Hearing sensitivity was measured based on potentials recorded from the inner ear saccule. Responses to conspecific sounds were evaluated with the auditory evoked potentials (AEP) recording technique. Both experiments were performed in reproductive males and females. Saccular potentials of the toadfish were evoked greatest at twice the stimulus frequency. Saccular hair cells of both males and females were most sensitive at frequencies between 15 Hz (lowest frequency measured) and 205 Hz, where thresholds were below 118 dB re. 1·µPa. Auditory thresholds increased towards higher frequencies. AEP recordings revealed that males and females are capable of resolving temporal patterns, amplitude fluctuations and frequency content of agonistic and mating calls. Our results suggest that the auditory system of the Lusitanian toadfish is well suited to detect fine features of vocalizations which might be important for acoustic communication and orientation, especially during mate attraction and territorial defence. This study was supported by MCTES, Portugal.
Current studies on the ontogenetic development of acoustic communication in the labyrinth fish Trichopsis vittata and the toadfish Halobatrachus didactylus show that the ability to detect conspecific sounds develops during growth. In order to investigate at which stage sound detection starts in an otophysine fish, we investigated the ontogenetic development of auditory sensitivity and vocalizations in the mochokid catfish Synodontis schoutedeni. Mochokids are also called squeakers because they produce broadband stridulation sounds during abduction and adduction of pectoral fin spines. Fish from five different size groups – from 22 mm standard length to 126 mm – were studied. Hearing thresholds were measured between 50 Hz and 6 kHz using the auditory evoked potentials (AEP) recording technique; stridulation sounds were recorded and their sound pressure levels determined. The smallest juveniles showed the poorest hearing abilities of all size groups between 50 Hz and 1000 Hz. At higher frequencies (5 and 6 kHz), hearing sensitivity was lowest in the largest groups. Duration of abduction and adduction sounds, sound pressure level and pulse period increased, while the dominant frequency of sounds decreased with size. Comparisons between audiograms and sound spectra revealed that the most sensitive frequencies correlate with the dominant frequencies of stridulation sounds in all Synodontis size groups and that all specimens are able to detect stridulation sounds. This study demonstrates that the hearing ability in the siluriform S. schoutedeni changes during ontogeny, whereas no changes were observed in two cypriniform species investigated earlier. Furthermore, S. schoutedeni is able to communicate acoustically at all stages of development, which contrasts to prior findings in teleosts.
The British Library Sound Archive has one of the world’s largest and most comprehensive collections of bioacoustic sound recordings. Founded in 1969, the collection now contains more than 160,000 recordings of wildlife and natural soundscape recordings, many of which have never been published. The wildlife collection was originally formed to serve as an international resource for bioacoustics research, providing copies of recordings to researchers and archiving field recordings for future generations to benefit from. Today recordings are also provided for educational projects, exhibitions, private listening, artistic sound installations, musical compositions, broadcasting and commercial publications. SoundServer is an automated service that offers immediate onsite access to a growing number of recordings. Visitors to the British Library’s Reading Rooms can either browse the Sound Archive collections via the Jukebox service or pre-order a personal playlist according to their specific needs. Remote access is available through the Archival Sound Recordings (ASR) website. ASR is an online resource that provides access to thousands of hours of recordings from across the Sound Archive. Three wildlife content packages are currently available through this resource – British Wildlife Recordings, Natural Soundscapes and Amphibians.
The Eurasian Bittern (Botaurus stellaris) is a characteristic bird of extended reed beds. Most easily the presence of bittern can be detected by their characteristic booming vocalizations. A booming sequence consists of a series of tonal calls with a fundamental frequency of approximately 150 Hz. The calls could be heard over distances of more than 1 km, but despite of their low frequency the exact position of the caller could be hardly estimated by an observer. In addition in areas with high population density it makes difficulties to discriminate individual birds by the acoustic characteristics of their calls. We assessed the number of booming bitterns in a large wetland area in the Northeastern part of Germany. A set of four-channel-recorders was used to record the vocalizations of the birds. The synchronization of the recording units was realized by recording a radio signal at each recorder at the beginning of the recording session. The position of callers was estimated by the directional information of each four-channel-recorder and the differences in the time of arrival of the acoustic signal at the different recording devices. Time differences were calculated using cross correlation techniques. The method allowed to distinguish between at least 14 booming bitterns in a reed bed area of only two square kilometres. The main advantages of the acoustic triangulation are that the method could be applied to large areas and the data acquisition could be realized by a single observer. The study was supported by the Deutsche Bundesstiftung Umwelt.
It is known that the song repertoire and versatility of the male Pied Flycatcher (Ficedula hypoleuca) correlate significantly with the amount of previous experience (older males have larger repertoire size), with the brightness of colour (differences between brown and black males), body mass and physical condition and the spring arrival order. Thus the species is an interesting test case for song complexity measures. Espmark and Lampe (Bioacoustics, 1993, Vol. 5, pp. 33 – 65) analysed the song complexity of male Pied Flycatcher with several different measures including number of elements and number of element types in the phrase and repertoire size. The song element is defined as the smallest (visually) separable entity in the spectrogram. Elements in turn are building blocks of syllables. A string of syllables that occur together in a particular pattern is called a phrase. In our study only phrase level complexity is considered. Da Silva and Vielliard (Advances in Bioacoustics 2, pp. 185-204) claim that repertoire size is inadequate for measuring the degree of monotonity or diversity of the song and propose the use of entropy or self-information as a complexity measure. We apply both of these approaches in this paper and compare how well the measures predict the age and physical condition of the singing male. The test data consists of male Pied Flycatcher songs recorded in Ruissalo Island, Turku, Finland, by Päivi Sirkiä with her students in 2006 – 2008.
Marine fishes where males defend nests and provide parental care often migrate from deeper to littoral waters to breed. In this study we describe seasonal patterns of shelter occupation in estuarine shallow waters and assess social aggregation in the Lusitanian toadfish (Halobatrachus didactylus, Batrachoididae), a vocal species with male parental care. Occupation of intertidal shelters was restricted to the breeding season but adult fish remained in the subtidal during the non-reproductive season, since they produced sounds throughout the year. Intertidal shelters were aggregated with up to five shelters found per 2 m segment of an 80 m transect. This aggregation probably resulted from social attraction since many segments were found unoccupied. Moreover, shelters contained on average two fish (maximum of nine). Based on size, shelters with multiple fish seemed to contain females, or possibly sneakers, but also more than one type I male, showing high social tolerance for conspecifics.
The Hazel Grouse (Bonasa bonasia), a sedentary bird species belonging to the grouse family, breeds across northern Eurasia, central and eastern Europe in dense, mixed coniferous woodland. While the territorial call is a good indicator of the grouse's presence, the role of acoustic cues is not clear. This study aimed to assess acoustic characteristic of the Hazel Grouse call and differences between sexes. Recording and playback experiments were performed in Alpes-de-Haute-Provence (France). The territorial calls of males (n=8) and females (n=5) were recorded in the field. Analyses of signals show that the male has a high-pitched ti-ti-ti-ti-ti call, and the female a liquid tettettettettet call. The frequency of the peak of maximum amplitude of calls was very high for such a large bird: 6841Hz ±786 for the male and 6034Hz ±476 for the female. After careful analyses, it turns out that the whole spectrum of the call was within the audible domain. Moreover, within-individual variability, that allows encoding of the individual identity, is higher in males (Cvb/Cvi=2.28) than in females (Cvb/Cvi<0.01). The particularity of producing such high frequency calls may reflect the necessity to improve localization efficiency in dense woodland, as high frequencies are associated to a better directionality. Moreover our results suggest that acoustic characteristics of male calls have sufficient inter-individual variability to allow the coding of individual identity.
