Reaction to conspecific degraded song by the wren Troglodytes troglodytes: Territorial response and choice of song post

We investigated the response of the wren Troglodytes troglodytes to playback of a territorial song degraded by long-range propagation. It appears that the wren is sensitive to this degradation since the territorial reaction is less intense with the degraded song than with the undegraded one. However, the degraded song is still considered by the receiver as a specific territorial aggressive signal. This differential response suggests that the male wren can use the degradation characteristics of the signal to adapt its territorial reaction. Indeed, in response to this stimulus, the receiver wren chooses a higher song post. By so doing, the bird improves both the propagation distance of the emitted song and the receiver's ability to hear the opponent's song. This behavioural change may correspond to a communication strategy, counteracting the environmental constraints on sound propagation. Therefore, in response to sound degradation during long-range propagation, birds may have developed behavioural adaptations complementary to the various adaptations concerning song structure and coding-decoding processes.     

Steroid accumulation in song nuclei of a sexually dimorphic duetting bird,the rufous and white wren

This study tested the hypothesis that the relative proportion of neurons that are hormone sensitive in avian song control nuclei is related to the basic motor ability to sing, whereas the absolute number of such neurons is related to the complexity of song behavior. Either [³H]testosterone (T) or estradiol (E₂) was injected into male and female rufous and white wrens (Thryothorus rufalbus), a tropical species in which females sing duets with males but have smaller song repertoires than males. Autoradiographic analysis indicated that there were no sex differences in the proportions of T or E₂ target cells in two song nuclei: the high vocal center (HVC) and the lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN). The density of labeled cells per unit volume of tissue did not differ between the sexes in either song nucleus. Males have larger song nuclei, however, which is consistent with their more complex song behavior, and therefore have a greater total number of hormone-sensitive neurons in these regions than do females. Comparison of these results with measures of hormone accumulation in zebra finches, canaries, and bay wrens supports the hypothesis presented. © 1996 John Wiley & Sons, Inc.     

A compact statistical model of the song syntax in Bengalese finch

Songs of many songbird species consist of variable sequences of a finite number of syllables. A common approach for characterizing the syntax of these complex syllable sequences is to use transition probabilities between the syllables. This is equivalent to the Markov model, in which each syllable is associated with one state, and the transition probabilities between the states do not depend on the state transition history. Here we analyze the song syntax in Bengalese finch. We show that the Markov model fails to capture the statistical properties of the syllable sequences. Instead, a state transition model that accurately describes the statistics of the syllable sequences includes adaptation of the self-transition probabilities when states are revisited consecutively, and allows associations of more than one state to a given syllable. Such a model does not increase the model complexity significantly. Mathematically, the model is a partially observable Markov model with adaptation (POMMA). The success of the POMMA supports the branching chain network model of how syntax is controlled within the premotor song nucleus HVC, but also suggests that adaptation and many-to-one mapping from the syllable-encoding chain networks in HVC to syllables should be included in the network model.     

Song matching in a long-lived,sedentary bird with a low song rate: The importance of song type,song duration and intrusion

Territorial songbirds often match the song features or singing patterns of rivals, commonly as an aggressive signal. Most studies of song matching have been on Northern Hemisphere species with short lifespans and high song rates, but vocal matching is predicted to be affected both by longevity and territorial stability. We studied song matching in males of the white-browed scrubwren, Sericornis frontalis, a long-lived, sedentary, territorial Australian songbird. We quantified natural song rate and diversity, and then conducted three playback experiments to test: (a) whether males match by song type; (b) how they respond physically and vocally to territorial intrusion; and (c) whether they match by song length, and use it as an agonistic signal. Males naturally had very low song rates, singing on average less than three times per hour, and moderate repertoires, with an estimated mean of 17.5 song types for individual males. Males did not engage in extended counter-singing bouts. The first experiment showed that males matched the song type of immediate neighbours almost 90% of the time, if that type was in their repertoire. The remaining experiments revealed that song-type matching was an aggressive signal; males responded more aggressively to, and were more likely to match, playback simulating a neighbour's territorial intrusion than song from their shared boundary. Males did not match songs by length, but they produced longer songs after simulated intrusion. Males also responded more aggressively to playback of longer songs that simulated intrusion, but less aggressively to longer songs from the territory boundary. Overall, we show that sedentary, long-lived songbirds with low song rates, can use song-type matching as an aggressive signal to communicate with neighbours and intruders. Song length had a different role in communication, possibly related to individual quality or territory ownership.     

A reafferent and feed-forward model of song syntax generation in the Bengalese finch

Adult Bengalese finches generate a variable song that obeys a distinct and individual syntax. The syntax is gradually lost over a period of days after deafening and is recovered when hearing is restored. We present a spiking neuronal network model of the song syntax generation and its loss, based on the assumption that the syntax is stored in reafferent connections from the auditory to the motor control area. Propagating synfire activity in the HVC codes for individual syllables of the song and priming signals from the auditory network reduce the competition between syllables to allow only those transitions that are permitted by the syntax. Both imprinting of song syntax within HVC and the interaction of the reafferent signal with an efference copy of the motor command are sufficient to explain the gradual loss of syntax in the absence of auditory feedback. The model also reproduces for the first time experimental findings on the influence of altered auditory feedback on the song syntax generation, and predicts song- and species-specific low frequency components in the LFP. This study illustrates how sequential compositionality following a defined syntax can be realized in networks of spiking neurons.     

Neighbour recognition by resident males in the banded wren, Thryothorus pleurostictus, a tropical songbird with high song type sharing

Several studies and reviews have suggested that the ability to discriminate between neighbours and strangers decreases as neighbour song repertoire size and song type sharing increase. We tested the recognition capabilities of territorial male banded wrens by comparing the aggressive approach responses of focal birds to three playback treatments: shared song types sung by an adjacent neighbour (neighbour song), shared song types sung by unfamiliar birds (mimic song), and unshared song types sung by unfamiliar birds (unfamiliar song). All three treatments for each male were broadcast from the same location on the territorial boundary shared with the appropriate neighbour. As expected, focal males responded nonaggressively to the neighbour treatment and aggressively to the unfamiliar song treatment. The approach response to the mimic treatment was statistically indistinguishable from the unfamiliar treatment and significantly higher than the neighbour treatment, suggesting that most males were able to recognize unfamiliar singers even when the song types played were very similar to those of their neighbours. The relative strength of responses to the mimic varied: some males treated the mimic song with low aggression levels typical of responses to neighbour song. Repertoire sizes of focal and neighbour birds, the fraction of song types shared among neighbouring males, and the similarity of neighbour and mimic song types did not explain this variation. Therefore, within the short 3-min period of our playback experiments, some birds may have used repertoire composition as a recognition cue and confused the mimic with the neighbour. Copyright 2001 The Association for the Study of Animal Behaviour.     

A simple explanation for the evolution of complex song syntax in Bengalese finches

The songs of Bengalese finches (Lonchura striata var. domestica) have complex syntax and provide an opportunity to investigate how complex sequential behaviour emerges via the evolutionary process. In this study, we suggest that a simple mechanism, i.e. many-to-one mapping from internal states onto syllables, may underlie the emergence of apparent complex syllable sequences that have higher order history dependencies. We analysed the songs of Bengalese finches and of their wild ancestor, the white-rumped munia (L. striata), whose songs are more stereotypical and simpler compared with those of Bengalese finches. The many-to-one mapping mechanism sufficiently accounted for the differences in the complexity of song syllable sequences of these two strains.     

The importance of calling song and courtship song in female mate choice in the variable field cricket

Male field crickets produce calling songs, courtship songs, tactile signals and chemical signals. Although calling songs are known to play an important role in female mate choice, the importance of the other signals in mate choice is poorly understood. In the variable field cricket, Gryllus lineaticeps, females select mates, in part, based on variation in male calling song. Females prefer higher chirp rates, a trait which is partially dependent on male nutrient intake, and females prefer longer chirp durations, a trait which appears to be independent of male nutrient intake. We tested whether females also have preferences based on variation in male courtship song, and whether the structure of male courtship song varies with nutrient intake. First, we reexamined female preference for calling song chirp rate. Then, we examined: (1) female preference based on courtship song chirp rate; (2) the relative importance of calling song and courtship song chirp rate; (3) the nutrition dependence of courtship song chirp rate; and (4) the correlation between calling song and courtship song chirp rate. As reported previously, females preferred higher calling song chirp rates, and in addition, preferred higher courtship song chirp rates. Females were more likely to switch from a speaker broadcasting more attractive calling song to a speaker broadcasting less attractive calling song when the attractive calling song was associated with an unattractive courtship song than when it was associated with an attractive courtship song. Preferences based on courtship song may thus cause females to alter the choices that they made based on calling song. Males that received greater nutrients did not produce higher courtship song chirp rates. There was no correlation between calling song and courtship song chirp rate. As a result, the two traits may provide information to females about different aspects of male quality. Copyright 2000 The Association for the Study of Animal Behaviour.     

Song matching, overlapping, and switching in the banded wren: the sender's perspective

Interpreting receiver responses to on-territory playback ofaggressive signals is problematic. One solution is to combinesuch receiver-perspective experiments with a sender-perspectiveexperiment that allows subjects to demonstrate how their choiceof singing strategies is associated with their approach behavior.Here we report the results of a sender-perspective study onthe banded wren (Thryothorus pleurostictus) and combine informationon context and results of previous receiver-perspective experimentsto clarify function. Territorial males were presented with a5-min playback consisting of song types present in their repertoire.We assessed the degree to which the subjects' song-matchingrate, overlapping rate, and song-type versatility were correlatedwith their approach latency, closeness of approach, latencyto first retreat, and time spent close to the speaker. Maleage, breeding stage, and features of the playback stimuli werealso considered. Song matching was associated with rapid andclose approach, consistent with the receiver-perspective interpretationof type matching as a conventional signal of aggressive motivation.Overlapping was associated with earlier retreat and togetherwith the aversive receiver response to our previous overlappingplayback experiment suggests that overlapping is a defensivewithdrawal signal. High versatility was associated with slowerfirst retreat from the speaker and high levels of reciprocalmatching between subject and playback. Males with fledglingssang with particularly low versatility and approached the speakeraggressively, whereas males with nestlings overlapped more andretreated quickly. Finally, older males matched more but overlappedless.     

The evolutionary importance of behavioural development: the ontogeny and phylogeny of bird song

It has been proposed that ontogeny may be an important constraint on the evolution of morphological traits. In this paper, ontogeny is discussed as a possible constraint on behavioural evolution. A literature review of the development of song in oscine birds (Passeriformes; Passeres) shows that song development follows von Baer's law; that is, that development proceeds from early, generally distributed stages to later, specialized stages. Song ontogeny is found to parallel phylogeny in a lineage of sparrows (Emberizidae; Emberizinae). Possible cases of paedomorphosis (slowing down or truncation of development) in bird song are discussed, specifically in the family Mimidae and in the reed warbler, Acrocephalus palustris (Muscicapidae; Sylviinae). Finally, the implications of developmental constraints for the study of the adaptive significance of behaviour are discussed.     

Principles of structure building in music,language and animal song

Human language, music and a variety of animal vocalizations constitute ways of sonic communication that exhibit remarkable structural complexity. While the complexities of language and possible parallels in animal communication have been discussed intensively, reflections on the complexity of music and animal song, and their comparisons, are underrepresented. In some ways, music and animal songs are more comparable to each other than to language as propositional semantics cannot be used as indicator of communicative success or wellformedness, and notions of grammaticality are less easily defined. This review brings together accounts of the principles of structure building in music and animal song. It relates them to corresponding models in formal language theory, the extended Chomsky hierarchy (CH), and their probabilistic counterparts. We further discuss common misunderstandings and shortcomings concerning the CH and suggest ways to move beyond. We discuss language, music and animal song in the context of their function and motivation and further integrate problems and issues that are less commonly addressed in the context of language, including continuous event spaces, features of sound and timbre, representation of temporality and interactions of multiple parallel feature streams. We discuss these aspects in the light of recent theoretical, cognitive, neuroscientific and modelling research in the domains of music, language and animal song.     

The importance of neural aromatization in the acquisition,recall, and integration of song and spatial memories in passerines

This article is part of a Special Issue “Estradiol and cognition”.In addition to their well-studied and crucial effects on brain development and aging, an increasing number of investigations across vertebrate species indicate that estrogens like 17β-estradiol (E₂) have pronounced and rapid effects on cognitive function. The incidence and regulation of the E₂-synthesizing enzyme aromatase at the synapse in regions of the brain responsible for learning, memory, social communication and other complex cognitive processes suggest that local E₂ production and action affect the acute and chronic activity of individual neurons and circuits. Songbirds in particular are excellent models for the study of this “synaptocrine” hormone provision given that aromatase is abundantly expressed in neuronal soma, dendrites, and at the synapse across many brain regions in both sexes. Additionally, songbirds readily acquire and recall memories in laboratory settings, and their stereotyped behaviors may be manipulated and measured with relative ease. This leads to a rather unparalleled advantage in the use of these animals in studies of the role of neural aromatization in cognition. In this review we describe the results of a number of experiments in songbird species with a focus on the influence of synaptic E₂ provision on two cognitive processes: auditory discrimination reliant on the caudomedial nidopallium (NCM), a telencephalic region likely homologous to the auditory cortex in mammals, and spatial memory dependent on the hippocampus. Data from these studies are providing evidence that the local and acute provision of E₂ modulates the hormonal, electrical, and cognitive outputs of the vertebrate brain and aids in memory acquisition, retention, and perhaps the confluence of memory systems.     

Habitat density, song structure and dialects in the Madagascar paradise flycatcher Terpsiphone mutata

Bird song is an important signal for long-distance intraspecific communication. Thus, song characteristics are expected to have undergone adaptive modification to maximise propagation through the environment. Acoustic properties of song should be correlated with the habitat in which they are broadcast, and neighbouring individuals should sing similar songs because they share the same local acoustic environment. We tested these predictions by investigating associations between habitat characteristics and song attributes in the Madagascar paradise flycatcher Terpsiphone mutata . We also examined whether song dialects were distributed non-randomly through the study site and which features of habitat density best explained these associations. We found that individuals on territories in denser habitat sang longer songs at lower frequencies. Features of song structure were related to both understorey and canopy cover density. The distribution of dialects within the study site was also strongly associated with variation in understorey cover. These findings suggest that habitat variation contributes to maintaining microgeographic variation in song structure in this species.     

Geographical variation in calling song of the field cricket Teleogryllus oceanicus: the importance of spatial scale

We compared calling songs of the field cricket Teleogryllus oceanicus from 15 sites within six regions of two continental areas, Oceania and Australia. The cricket was introduced to Hawaii, where it is subject to an acoustically orienting parasitoid fly not found elsewhere in its range. In a principal components analysis (PCA) of song from all populations combined, the first five components had eigenvalues greater than one, and collectively accounted for over 80% of the total variation. Means for all song components varied significantly among sites, and different components varied at the three levels of analysis (continent, region and site). The principal way in which sites differed was along a gradient in increasing song length, pulse duration and intervals between song elements. Crickets from Oceania had a significantly greater variance in their song than Australian crickets, driven largely by the high variance in Hawaii. Geography explained a substantial amount of variation in song, despite the likelihood of serial bottlenecks having occurred as the species moved from island to island. Because female crickets appear not to focus on the short chirp as a component of mate choice, a lack of selection may allow this song component to vary more widely.     

Independent evolution of song structure and note structure in American wood warblers

This study addresses the issue of how evolutionary convergence within shared environments shapes some features of bird song while leaving others unaffected, using as an example the songs of 51 North American wood warblers (Parulinae). I combined published information on breeding habitats and evolutionary relationships to show that the structure of warbler songs is correlated with habitat, whereas the structure of the notes that comprise the songs is relatively unaffected by habitat and more closely related to phylogenetic history. The results confirm known relationships between bird song and habitat, including correlations between song frequency and the type and density of canopy foliage, and between the number and arrangement of notes in the song and foliage density and moisture. More importantly, the results suggest that individual notes and whole songs are to some extent functionally independent, because the configuration of notes shows more evidence of evolutionary constraint than does the way notes are assembled into songs.