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IBAC 2015 - bioacoustics research

The International Bioacoustics Congress 2015 was a fantastic conference. Lots of fascinating research, in a great place (Murnau, Bavaria, Germany), and very well organised. Here I'm making some notes on the interesting research topics I encountered. I can't list everything because almost everyone at the conference was doing something fascinating! What a niche this is ;)

This was my first IBAC. I'd say the majority of people were animal communication or animal behaviour researchers, plus ecologists, sound archivists, a composer or two, a couple of industry people and a couple of computer scientists. (I didn't spot any acousticians/physicists, I was wondering if I would.) Lots of great people talking about animal sounds.

My own presentations went down well, I'm pleased to say. I had a talk about our Warblr bird sound recogniser (here's the journal paper, Stowell and Plumbley (2014)), and a poster about inferring the communication network underlying the timing of animal calls. (From the latter, lots of good conversation about whether cross-correlation was a good tool for the job. My answer is that it's perfectly fine for pairs. For larger groups it's tolerable if you have enough data, but I have a better way... need to write it up.)

My colleague Rob Lachlan presented his really neat work on vocal learning in chaffinches. Apparently chaffinch syllable transmission is one of the most precise cultural transmission processes that's yet been quantified. I'd imagine he could tell you more about how that might relate to questions of the birds' innate biases etc.

Now here are some good things that were new to me. (Note that I'm quite a bit biased towards birds rather than the other taxa.) I'll save all the zebra finch items until the end since they're interrelated and something I'm currently thinking about. First, miscellaneous highlights:

  • Stefan Schoeneich described tracing the exact set of neurons responsible for call detection in a cricket species. This was fascinating - it's only a handful of neurons, so how to the crickets do it? Stefan described how post-inhibitory rebound is a crucial piece of the puzzle since it's a very simple neural phenomenon that provides a "delay line" that the cricket uses to detect repetition. The important thing is that this delay line is the same mechanism in the caller and the listener. This enables co-adaptation: evolution can change the repeat rate without breaking the communication channel. (Rohini Balakrishnan told me afterwards that this is not a new idea, though it's novel to me - Stefan's contribution is to demonstrate the exact network that uses this mechanism.)

  • Diego Llusia presented a playback experiment to modify the timing of dawn choruses. Interesting to see this: playbacks often involve a single species, but this investigated the timing of a whole assemblage of chorusing bird species. The study raised lots of good questions - it'd be good to see more development of this line of inquiry.

  • There was a good session on female vocalisations (led by Michelle Hall). From a European-biased perspective we often think of birdsong as being largely a male preserve. Karen Odom talked about the patterns of usage in one species (troupials). The main thing I note is actually her finding published last year (Odom et al 2014, Nature Communications) that female song is highly likely to be ancestral in songbirds, i.e. the reason it's seen less often in the northern hemisphere is that it was dropped (multiple separate times) by evolution, as songbirds radiated north. Lauryn Benedict then discussed why this might be. Maybe we can find correlates in life history - i.e. maybe the songbirds that dropped female song concomitantly developed some other communication or behavioural pattern, and this might help us understand what happened? Lauryn's study found no correlation either with migration or dichromatism. She noted that studying this is tricky because although lots of songbirds are described as having no female song, in many cases this might be due to our own biases and failure to spot it (especially in non-dimorphic species). Lauryn showed that her lack of correlation was robust to this issue.

  • Coen Elemans showed his work on physical modelling of the songbird syrinx. He found that the "myoelastic aerodynamic" model (developed in the context of the human larynx) works well for the syrinx. This was a surprise to me, since many songbirds have two oscillators in the syrinx rather than one, and I would have suspected the model might noticeably fail to account for interactions between them. It seems his model is tested for bird species with relatively independent sets of vocal folds, so maybe this suspicion is yet to be fully tested.

  • Lots of interesting discussion around acoustic diversity indices during the ecoacoustics session (led by Jerome Sueur). I remain to be convinced that we have robust useful "acoustic index" measurements directly from the audio signal without heavy user configuration. In that context it was interesting to hear from the experience of others. For example Nadia Pieretti found the ACI useful and robust for her shallow marine soundscapes, while Gianni Pavan working with forest soundscapes found it too strongly affected by weather sound (wind, rain).

  • Karla Rivera-Caceres showed that when plain wrens develop a duet code - meaning a specific choice of syllables to combine into their duet - it's due to learned association between the syllables, and not a private code designated by individual ID.

  • Karen Rowe talked about automatic detection in practice - really interesting from my point of view, to see how people fare when they use automatic detectors for their immediate practical work. She had deployed Songmeters in the Grampians, using an occupancy framework, which means that they only need to know presence/absence not the whole set of calls - a single positive detection is all that's needed. They tested a two-pass approach with an initial detection pass, then a second pass using some of the already-detected syllables as templates. They found that the manual work involved (in checking false positives, tweaking the classifier etc) meant that the automation was not in fact more efficient! In their case it was approximately as efficient to do fully manual annotation.

  • Peter Slater gave an evocative talk on their study of many wren species. He noted various things about duetting, and male and female song, finding that these traits correlate with phylogeny. It seems wrens have, multiple times, developed introductory phrases to lead in to duets - that's an interesting fact, food for thought.

  • Andrea Thibault showed us the behaviour of foraging seabirds, and the calls they make just before diving - apparently to warn others of the impending dive.

  • Lisa Gill showed a poster on jackdaw "addressing" call. We (with Rob too) had a good chat about how to computationally analyse corvid "caw"-like sounds - still very tricky and non-obvious. Lisa also told me about her paper just accepted for eLife about zebra finch social networks and call patterns - very pertinent to me! Look forward to reading it.

  • A nice session on comparative work with music, speech and language (led by Carel ten Cate). Marisa Hoeschele described that songbirds are - in general - sensitive to absolute pitch not relative pitch. They're much easier to train to discriminate absolute pitch variation rather than relative. (This is notably unlike humans!) She then showed her experimental evidence that black-capped chickadees can do relative pitch discrimination, but they're much better at it when the stimuli are made of chickadee syllables rather than pure sinewaves. Particularly interesting since the chickadee syllables are fairly pure-tone, not harmonic stacks, so the difference might not be the presence of harmonics. It also shows that a simple pitch-following model is not sufficient to explain their good performance, there must be some other attribute that makes things accessible to them.

  • Vera Klimsova gave us all a lesson in how to listen like an impala, to alarm calls from other species (including other species that don't live near impalas). She also gave us all a lesson in how to do a talk when you're the last speaker of a 5-day conference - an entertaining and memorable talk!

Now the zebra-finch-based research:

  • Solveig Mouterde described her work on how zebra finch calls degrade as they propagate through the environment, and how that affects individual recognition, both for zebra finch listeners and for machines. I'd like to see more of this kind of work because I think there are still many issues that are not completely addressed by some of the older bioacoustic concepts. For example Solveig referred to "active space" - a useful concept, but one that needs to incorporate the complexities of perceptual and acoustic variation before it really gets to the issue of how far an animal can be heard. Solveig's work goes towards addressing that.

  • Pietro d'Amelio talked about duetting in zebra finch mate pairs, showing very consistent antiphonal calling patterns, some symmetrical, some asymmetrical.

  • Had a good chat with Manfred Gahr and Albertine Leitao about how to measure tutored vocal learning in zebra finches. I have an idea that it could be done usefully with feature learning, which would be good to study some time.

  • Nicole Geberzahn studied how individuality emerges in zf song, through an experiment with many tutors who were themselves all taught from the same song. She found that new phrases emerged by mechanisms such as repeating whole phrases or adding call-like syllables onto the end. In a recognition test, zf listeners heard individual identity to be encoded in syllable details, not in phrase structure.

  • Andries ter Maat presented the work of his student Hanneke Poot, finding that pupil syllables are often not shared with any of the tutors, and complete copies of tutor songs are very rare. (Unlike Nicole's test mentioned above, in this case the tutors were quite varied.) Also that zfs don't particularly choose their genetic or social father to learn from. He also noted that Tchernikovsky's sound similarity measures (as calculated by Sound Analysis Pro, that is) can depend strongly on the syllable type, so you need to apply some kind of standardisation procedure if you want to make global similarity comparisons.

  • Marie S A Fernandez looked at the calling patterns of zf pairs when they are together, separated, and then reunited. She found that the cross-correlation or Markov analysis found strong back-and-forth structure only while the birds were separated. (I wonder: if we could include all visual and other cues, would there in fact be a detectable structure in all cases? It would be a different structure with/without visual contact, presumably. Very hard to annotate all possible multimodal cues though.) Perez et al (2015)

  • Clementine Vignal studied zf negotiation over parental care, finding that the length of some zf conversations could predict the subsequent balance of parental care. (This correlation was over and above the obvious factors such as how much nest-time each parent had recently spent.)

  • Buddhamas Pralle Kriengwatana presented an experiment in which zebra finches were trained to discriminate very short audio clips of human "i"/"e" vowels. She showed that once trained, the zfs can generalise to clips from another language (with slightly different formant positions), which demonstrates a generalisation ability that is not just about formant frequencies, possibly some relative rather than absolute distinction. For me there's a niggling question: formants are not the only way that vowels differ - there's also aspiration etc - so I'd be interested to know how such confounds were avoided when using real speech recordings. Pralle's suggestion seems plausible, though, that the ability could be explained by a perceptual mechanism based on using the sound to infer some physical trait such as the volume of the mouth cavity.

To all at IBAC: my apologies if I misrepresent you here, missed you out, or misspelt your name! In particular I didn't manage to see much of the second poster session since I was myself presenting a poster.

At the end of the conference there was an organised visit to MPIO Seewiesen, where a lot of good bird studies are happening. I was most struck by the magnificent ravens, living in outdoor aviaries and showing off their awesome vocal skills.

What else? Well, lots more. A great hike organised in the wetlands around Murnau (Murnauer Moos). Bavarian beer and food. The mountains as a backdrop...

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