Music and Birdsong

The mid-twentieth century songs of popular singer Luiz Gonzaga include lyrics about northeastern Brazil’s traditional ecological knowledge. For individuals who predict rain and drought based on natural patterns in the region’s semi-arid backlands, Gonzaga’s music continues to lend credibility, clarity, and local significance to the practice known as rain prophecy. Through cultural history, lyrical and musical analysis, and ethnography, this article examines the process through which Gonzaga’s voice became a vehicle for the transmission of knowledge about the weather, suggesting that music produced through a profit-driven industry has played a role in the maintenance of local ecological knowledge.

The human capacity for speech and vocal music depends on vocal imitation. Songbirds, in contrast to non-human primates, share this vocal production learning with humans. The process through which birds and humans learn many of their vocalizations as well as the underlying neural system exhibit a number of striking parallels and have been widely researched. In contrast, rhythm, a key feature of language, and music, has received surprisingly little attention in songbirds. Investigating temporal periodicity in bird song has the potential to inform the relationship between neural mechanisms and behavioral output and can also provide insight into the biology and evolution of musicality. Here we present a method to analyze birdsong for an underlying rhythmic regularity. Using the intervals from one note onset to the next as input, we found for each bird an isochronous sequence of time stamps, a " signal-derived pulse, " or pulse S , of which a subset aligned with all note onsets of the bird's song. Fourier analysis corroborated these results. To determine whether this finding was just a byproduct of the duration of notes and intervals typical for zebra finches but not dependent on the individual duration of elements and the sequence in which they are sung, we compared natural songs to models of artificial songs. Note onsets of natural song deviated from the pulse S significantly less than those of artificial songs with randomized note and gap durations. Thus, male zebra finch song has the regularity required for a listener to extract a perceived pulse (pulse P), as yet untested. Strikingly, in our study, pulses S that best fit note onsets often also coincided with the transitions between sub-note elements within complex notes, corresponding to neuromuscular gestures. Gesture durations often equaled one or more pulse S periods. This suggests that gesture duration constitutes the basic element of the temporal hierarchy of zebra finch song rhythm, an interesting parallel to the hierarchically structured components of regular rhythms in human music.

Our research proposes the hypothesis that heterospecific territorial songbirds,living in the same community,coordinate their songs to manifest a cooperative behaviour.

By analysing the pattern of songs of a bird community inhabiting an environment at low fragmentation level (i.e. with a low internal turnover of species and individuals), we observed that heterospecific territorial songbirds tend to sing at the same time without masking reciprocal signals (i.e. without overlapping frequencies), even if using the same frequency range, at least during part of the day.

We recorded the acoustic emissions of the bird community at dusk in three different days. From each recording, we sampled the eight consecutive minutes richest in songs. Time and frequency coordinates were extracted for 1084 songs, emitted by 13 species. For each sample, temporal overlap among songs was verified at a short temporal scale (3 secs) with an overlap niche analysis (Pianka index). Songs overlapping both temporally and by frequency were compared with songs overlapping only in time, using ANOVA statistical method. Collected data were tested against randomly computed association data using Monte-Carlo methods (30.000 and 5.000 simulations respectively). We found both temporal niche overlap, and a significant tendency to avoid spectral overlap when vocalizations are temporally overlapping.

Temporal overlap is considered an aggressive signal if it determines spectral overlap as well, and thus signal masking. To angle both for temporal overlap and for avoiding signal interference seems to have not competitive functions, and it requires a complex short-time timing behaviour. Being apparently not functional, it requires an explanation in evolutionary terms.

We interpret the pattern of coordination among songs in this community as an expedient through which heterospecific cooperation is manifested. To sustain our hypothesis, we need to call on several mechanisms, as acoustic manifestations of birds are part of a complex net of intra and heterospecific communication:
- Heterospecific cooperation: different species aggregating in cooperative groups often need similar resources and thus act for a common purpose, with a lower rate of intra-group competition than for monospecific groups (Terborgh 1990, Goodale et al 2010);
- Communication networks and social information: from eavesdropping on interactions, an individual can draw inferences on reciprocal relations among individuals (McGregor e Dabelsteen 1996), or the presence of a suitable habitat (Danchin et al 2004);
- Dear Enemies effect (Fischer 1954): territorial species inhabiting the same environment for a sufficient period of time,often organize in neighbourhoods, whose components show no reciprocal aggressive behaviour and defend reciprocal territories;
- Functions of duets between conspecifics birds: the more a duet is coordinated, the higher is the emerging fitness and mates cohesion, and the more threatening the duet functions against intruders (Thorpe 1967, Seibt e Wickler 1977,Wickler 1980, Smith 1994). Coordinated duets require a long period of practice, which is costly in energetic terms.

On these basis, we sustain that coordinated songs among heterospecifics territorial neighbours could gain the same functions as duets between conspecifics (joint resource defence, signalling fitness, maintaining group cohesion).By attracting and/or repelling eavesdropping individuals, in the form of public information (Valone 1989), coordinated songs can influence the community structure. Indeed, composition of communities is driven more by cooperative than competitive interactions among species (Stensland et al 2003).

The same analysis performed on recordings of a community inhabiting an environment at a high fragmentation level (i.e. with a high internal turnover of species and individuals), showed a random or segregated pattern for the distribution of songs in time, confirming that coordinated chorusesareachieved only in stable neighbourhoods. Cooperative Dear Enemies relationships and coordinated chorusescan indeed be achieved only after a long period of negotiation and practice, respectively.
More experiments are needed to verify the proposed hypothesis, but it appearsas a plausible explanation of the pattern observed, with strong theoretical basis. This study is the first exploring the acoustic structure of a bird community in a temperate region, and one of the few exploring it in the world.

The solid but discrete relationship between Mathematics and Music is at least as old as Pythagoras. Mathematics relates with Music at the moment of tuning an instrument, since consonant notes are produced by sounds whose frequencies have interesting mathematical relationships. The problem of tuning a musical instrument began as a problem of proportions, when the instrument was the vibrating string, but became even more interesting when the piano was created, requiring a tempered tuning discovered only after the intervention of mathematicians. However, without any knowledge of arithmetic, birds from all over the world accurately reproduce the several intervals of the diatonic scale and sing melodies in different musical scales created by man throughout the ages, from the Greek modes to the diatonic scales of our days.

THRUSH begins with my reinterpretation of the same audio that Messiaen used for his transcriptions of the North American Songbirds, blackbird and wood thrush. These audio samples were digitized and analysed using PRAAT and C-Speech, from which I made new transcriptions that were more accurate representations of the physical acoustical signal. Of course, a temporal framework had to be established for these transcriptions, for which I decided to treat in a non-metrical fashion, since birds presumably do not think in terms of man-made meters and units. Then paired with the acoustical signal, I did research on the physical mechanism by which the birds produced sounds. These involved analyses of airflow, source, resonance and articulation for both blackbird and wood thrush. It was found that some bird species produce multiphonic & biphonic signals using paired bronchi, while others used a single bronchus. When using paired bronchi to produce two independent frequency contours, the dynamical interpretation would result in two simultaneous limit cycles; meanwhile, two independent frequency contours produced by a single bronchus would result in the occurrence of nonlinear phenomena, here interpreted as a torus. Such information may not be so important when writing for piano, but can have enormous implications when writing for wind, brass, string and voice.

Then secondly, these interpretations were paired with a binary code which resembles chance, but whose underlying principles were quite simple. This code was developed by a D. G. Champernowne, published in the Journal of the London Mathematical Society 8 (1933): 254-60. This code was used to generate time, pitch, scales, register, density and so forth. 

Third, the painting “Yellow Dots” by Sara Assari is interpreted on page 9. Thank you Sara!!!