Large Vocal Repertoire Research Articles

Alarm Calls of the Australian Magpie (Gymnorhina tibicen): Predators Elicit Complex Vocal Responses and Mobbing Behaviour

Mobbing calls are produced by many avian species as part of a defence strategy against predators. However, as most studies have described small prey species, little is known of mobbing by species large enough to inflict harm on the predator when working cooperatively. We investigated the mobbing calls of the Australian magpie (Gymnorhina tibicen tibicen), a large, territorial songbird known to be exceptionally vigilant and to attack predators. We were particularly interested in this species because it has a very large vocal repertoire. Magpie groups (N=45) in semi-rural and rural locali- ties were presented with taxidermic specimens of three predators, two species of eagle and a monitor lizard, the latter known to be a risk to their eggs and nestlings. We identified five distinct types of alarm calls, one of which (a complex, tonal call of more than two syllables) was elicited almost exclusively by the eagles in environments where they are known to be a threat to magpies. This alarm call usually preceded intense swooping attacks of the eagle models and often contin- ued during the attacks. A harsh and noisy call of one syllable was the most frequently produced call and appeared to indicate level of arousal. The lizard did not elicit the multi-syllable call or any swooping attacks but it did elicit the harsh call. Some other call types showed less stimulus specificity although a two-syllable call was elicited more commonly by the eagles than lizard. Hence, this species has an acoustically complex, multi-syllable alarm call to signal the presence of an aerial predator in contexts of genuine threat, and this call is markedly different from the harsh single-syllable call, which indicates arousal level and is used most frequently when mobbing a monitor lizard.

Universal Features in the Singing of Birds Uncovered by Comparative Research

Aside from some exceptions, songbird species differ in the structure of their singing and usually also in the size and performance mode their song repertoires. In the past, most studies concentrated on the species specific differences of singing, and thereby contributed to a better understanding of their diversity. In our approach, however, we focussed on the opposite perspective; i.e. we investigated whether and how far songbirds share structural song properties. To have a solid data base we focussed on four species of thrushes which were famous for their large vocal repertoires. The two Asian bird species were Oriental Magpie Robins (Copsychus saularis) and Shama Thrushes (Copsychus malabaricus), the two European species the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (Luscinia luscinia). The latter were incorporated into a sample 40 other European songbird species (Table 1) serving as a framework for our comparative approach (Figure 2, 4). Besides well-known differences among species, our analyses of song material yielded some remarkably similar relationships between structural and functional song properties, which often were shared even by unrelated species. In particular measures of song durations were usually related to song application during vocal interaction. And, individual variation of song duration was mainly a result of differences in syllable repetition within trilled song sections. Although some of these findings were predicted already by former studies (see Todt, 2004), their essentials can be based now on profound data sets of detailed measurement.Keywords: European Thrushes, Asian Thrushes, Copsychus saularis, C. malabaricus, song structure, signal lengths.doi: 10.3126/on.v6i1.1648Our Nature (2008)6:1-14

Acoustic communication in the Lusitanian toadfish, Halobatrachus didactylus: evidence for an unusual large vocal repertoire

The Lusitanian toadfish Halobatrachus didactylus (Bloch & Schneider) (Batrachoididae) is a well-known sound producer that has an unusual large acoustic repertoire for fish. This repertoire consists so far of five distinct sound categories: boatwhistles, grunt trains, croaks, double croaks and a mixed grunt–croak call. Sixteen males that spontaneously occupied artificial concrete nests placed in the intertidal zone of the Tagus estuary (Portugal) were recorded over 8 days in June/July 2006. During the analysis of the recordings new sound emissions were found. Long grunt trains that sounded to the human ear like a running engine were heard. These sounds differ from the normal grunt trains by having a lower amplitude, a much longer duration (tens of seconds versus <1 second) and more grunts per call. Other new sound emissions (e.g. triple croaks) were also registered but were heard less frequently. The incidence of the various sound types is given.

Responses of Male Tropical Mockingbirds (Mimus Gilvus) to Variation in Within-Song and Between-Song Versatility

AbstractDespite their large vocal repertoires and otherwise highly versatile singing style, male mockingbirds (Mimus spp.) sometimes sing in a highly repetitive fashion. We conducted a playback experiment to determine the possible signal value of different syllable-presentation patterns during simulated male intrusions in the Tropical Mockingbird (Mimus gilvus), testing the hypothesis that more repetitive singing represents a stronger threat and generates a stronger aggressive response. Responses were measured in terms of approach and singing behavior and were analyzed using McGregor’s (1992) multivariate method. We also introduce the use of survival analysis for analyzing response variables for which subjects do not perform the behavior in question in at least one of the replicates (known as “right-censored variables” in the statistical literature). As predicted by theory, experimental subjects responded more aggressively to songs composed of a single note than to variable ones. However, versatility at the between-song level had an opposite effect: high song-switching rates generated stronger responses than low ones. Given the lack of a statistical interaction between within-song versatility and switching rate, we conclude that these two parameters may serve independent purposes and possibly transmit different information. We discuss the possibility that the signal value of variation in vocal versatility lies in the mediation of territorial conflicts, the attraction of female partners, the mediation of conflicts over access to reproductive females, or some combination of these functions.Respuestas de Machos de Mimus gilvus a Variación en Versatilidad Vocal Dentro- y Entre-cantos

RESPONSES OF MALE TROPICAL MOCKINGBIRDS (MIMUS GILVUS) TO VARIATION IN WITHIN-SONG AND BETWEEN-SONG VERSATILITY

Despite their large vocal repertoires and otherwise highly versatile singing style, male mockingbirds sometimes sing in a highly repetitive fashion. We conducted a playback experiment to determine the possible signal value of different syllable presentation patterns during simulated male intrusions in the Tropical Mockingbird (Mimus gilvus) testing the hypothesis that more repetitive singing represents a stronger threat and generates a stronger aggressive response. Responses were measured in terms of approach and singing behavior and were analyzed using McGregor's (1992) multivariate method. We also introduce the use of survival analysis for analyzing response variables for which subjects do not perform the behavior in question in at least one of the replicates (known as 'right-censored variables' in the statistical literature). As predicted by theory, experimental subjects responded more aggressively to songs composed of a single note than to variable ones. However, versatility at the between-song level had an opposite effect as high song switching rates generated stronger responses than low ones. Given the lack of a statistical interaction between within-song versatility and switching rate, we conclude that these two parameters may serve independent purposes and possibly transmit different information. We discuss the possibility that the signal value of variation in vocal versatility lies in the mediation of territorial conflicts, the attraction of female partners and/or the mediation of conflicts over access to reproductive females.

Babbling behavior in the sac-winged bat (Saccopteryx bilineata)

Infant babbling in humans and a few other primates plays an important role in allowing the young to practice the adult vocal repertoire during early behavioral development. Vocalizations uttered during babbling resemble, to some degree, the acoustic structure of adult vocalizations and are often produced in long bouts independent of any social context. Similar behavior, termed subsong or plastic song, is known from a variety of songbirds. Here, we show that pups of the sac-winged bat (Saccopteryx bilineata), a species with an unusually large vocal repertoire, produce renditions of all known adult vocalization types during bouts of vocalizations, which appear to be independent of a distinct social context. Babbling occurs in pups of both sexes, even though only adult males, not females, utter all different vocalization types produced in infancy. To our knowledge, this is the first evidence of babbling in a nonprimate mammal and suggests that infant babbling may be necessary for the ontogeny of complex vocal repertoires.

Acoustic features of song categories and their possible implications for communication in the common nightingale (Luscinia megarhynchos)

Summary In many passerine species, males sing more than one distinct song type. Commonly, songs are assigned to different song types or song categories based on phonological and syntactical dissimilarities. However, temporal aspects, such as song length and song rate, also need to be considered to understand the possible functions of different songs. Common nightingales (Luscinia megarhynchos) have large vocal repertoires of different song types but their songs additionally can be grouped into two distinct categories (particular groups of song types): whistle songs and nonwhistle songs. Whistle songs are hypothesised to be important to attract migrating females. We studied temporal properties of whistle songs and nonwhistle songs and examined the relationship between those song parameters and song output parameters, such as song rate and song length. To investigate how song parameters vary among males, we calculated the coefficients of variation for different song traits. We found that the variation in the proportion of whistle songs was significantly higher among males than variation in other song parameters. Furthermore, the proportion of whistle songs was negatively correlated with other song output patterns. These findings suggest that the production of whistle songs might be constrained and/or that whistle songs and their succeeding pauses may act as a functional unit in communication.

Repetition patterns within harp seal (<I>Pagophilus groenlandicus</I>) underwater calls

Rhythmically repeated calls used during vocal communication have important implications for the extent to which pinnipeds successfully transmit information over long distances and during times of high levels of background noise. Harp seals (Pagophilus groenlandicus ) have a large vocal repertoire and many of their underwater vocalizations consist of multiple elements. Between-call and within-call variability of element and interval durations for the thirteen multiple-element call types were very consistent. These elements are repeated regularly in predictable patterns. Three distinct patterns were identie ed with respect to the timing of call intervals: all intervals 1 s (long-long pattern) and intervals alternating between 1 s (shortlong pattern). Harp seal multiple-element calls are rhythmically repeated and elements of the calls occur at highly predictable intervals. Rhythmical repetition would likely enhance the probability of a call being detected and could serve to identify the species of the caller.

Is Quantity of Song Type Use in Adult Birds Related to Singing During Development?

Songbirds with large vocal repertoires often show individually distinct profiles in the quantity of using their different song types. Factors involved in determining how often a song type is used have been identified in the social domain, e.g. the singing routines of territorial neighbours. In this study, I investigated the role of song development in the formation of individual performance profiles. I examined whether and how the amount of motor practice during vocal ontogeny would account for profiles of song type use in the adult singing. The study was carried out on hand-reared nightingales (Luscinia megarhynchos) which are particularly appropriate subjects for this kind of approach. A clear positive relationship was discovered between the ontogenetic 'age' of imitations (i.e. time of emergence) and the performance rate of these song patterns. Also time of emergence played a role in whether song patterns were discarded from the adult repertoire. I assume that vocal practice plays a role in selectively consolidating song type memories, whose respective strengths then contribute to differential performance observed in the adult birds.

How songbirds deal with large amounts of serial information: retrieval rules suggest a hierarchical song memory

Many songbirds develop remarkably large vocal repertoires, and this has prompted questions about how birds are able to successfully learn and use the often enormous amounts of information encoded in their various signal patterns. We have studied these questions in nightingales (Luscinia megarhynchos), a species that performs more than 200 different types of songs (strophen), or more than 1000 phonetically different elements composing the songs. In particular, we investigated whether and how both song repertoires and song performance rules of nightingales were coded by auditory stimuli presented in serial learning experiments. Evaluation of singing episodes produced by our trained birds revealed that nightingales cope well with an exposure to even long strings of master song-types. They can readily acquire information encoded within and between the different master songs, and they memorize, for example, which master song-types they have experienced in the same learning context. Imitations of such song-types form distinct sequential associations that are termed “context groups”. Additionally, nightingales develop other song-type associations that are smaller in size and termed “package groups”. Package formation results from constraints of the acquisition mechanisms which obviously lead to a segmentation of auditorily perceived master song sequences. Further experimentation validated that the song memory of nightingales is organized in a hierarchical manner and holding information about “context groups” composed of packages, “package groups” composed of songs, and songs composed of song elements. The evidence suggests that implementation of such a hierarchical organization facilitates a quick retrieval of particular songs, and thereby provides an essential prerequisite for a functionally appropriate use of large vocal repertoire is in songbirds.

Vocal Repertoire of the Long-Tailed Manakin and Its Relation to Male-Male Cooperation

We examined the vocal repertoire of lek-mating Long-tailed Manakins (Chi- roxiphia linearis, Pipridae) in Monteverde, Costa Rica. Males in this genus are unusual in performing a cooperative courtship display, including duet songs and coordinated dual-male dance displays. Males give at least 13 distinct vocalizations, several of which occur in clear behavioral contexts. By observing the behavioral context and the sequence in which calls were given, we found that the most frequent calls occurred during three types of activity: song bouts, dance, and noncourtship interactions. The responses of males to playback of six vocalizations indicated that the calls function as much in mediating cooperative inter- actions as in expressing male-male agonism. The evolution of the large vocal repertoire in Long-tailed Manakins may be associated with their unique social system based on long- term, cooperative relationships among males.

Degenerate hearing and sound localization in naked mole rats (Heterocephalus glaber), with an overview of central auditory structures

Behavioral tests of absolute sensitivity and sound localization in African naked mole rats show that, despite their communal social structure and large vocal repertoire, their hearing has degenerated much like that of other subterranean species. First, their ability to detect sound is limited, with their maximum sensitivity being only 35 dB (occurring at 4 kHz). Second, their high-frequency hearing is severely limited, with their hearing range (at 60 dB sound pressure level [SPL]) extending from 65 Hz to only 12.8 kHz. Third, determination of the effect of duration on noise thresholds indicates that, compared with other animals, mole rats require a sound to be present for a much longer duration before reaching asymptotic threshold. Finally, they are unable consistently to localize sounds shorter than 400 ms and cannot accurately localize sounds of longer duration, raising the possibility that they are unable to use binaural locus cues. Thus, it seems that the essentially one-dimensional burrow system of a subterranean habitat produces severe changes in hearing comparable to the changes in vision that result from the absence of light. To explore the relation between vision and sound-localization acuity, retinal ganglion cell densities were determined. The results indicate that naked mole rats have a broad area of best (albeit poor) vision, with maximum acuity estimated at 44 cycles/degree. That mammals with wide fields of best vision have poorer sound-localization acuity than those with narrower fields is consistent with the thesis that a major function of sound localization is to direct the gaze to the source of a sound. However, the fact that subterranean mammals have little use for vision in a lightless environment suggests that they represent an extreme case in this relationship and may explain the fact that, unlike surface-dwelling mammals, they have virtually lost the ability to localize brief sounds. Finally, despite their very limited auditory abilities, the major brainstem auditory nuclei, although relatively small, appear to be present.

Vocalizations of the South African cliff swallowHirundo spilodera

The vocalizations of both adult and juvenile South African cliff swallows Hirundo spilodera are described. This swallow has a large vocal repertoire considering that it is a highly colonial species, and at least seven distinctive calls are recognized. In chicks there is a gradual change in the food soliciting call and it develops into the contact call. Contact calls of both chicks and adult birds were individually recognizable.

The agonistic vocalisations of Rattus villosissimus

All sounds produced by R. villosissimus during agonistic behaviour were recorded for spectrographic analysis. The social context of sound production was noted, along with any immediate overt changes in the behaviour of recipient rats. The effect of sounds on an opponent was also tested by playing prerecorded sounds to individual rats and observing their behaviour. R. villosissimus possess a large vocal repertoire. They produce five basic sounds in the audible range: squeal; squeak; tooth chattering; hissing; coughing. Squeals consist of a whole range of graded intermediates, allowing a great potential for communication. Most sounds appear to have little immediate overt effect on the behaviour of opponents. Suggestions are made as to their significance in communication.