I read Biological Sciences at The Queen’s College, Oxford (1999 – 2002) and graduated with a First Class degree. My assessed review paper was on bat sonar and moth defences ‘Specialisations for microchiropteran echolocation and moth defence co-evolution‘ and for my independent research project I analysed acoustic recordings using an artificial neural network to investigate ‘Is Humpback Whale Song a Language?‘
The humpback whale, Megaptera novaeangliae, produces the most complex vocalisations of all 77 cetacean species, which have been dubbed by Payne and MacVay (1971) as “songs”. These songs are hierarchical in nature, with rules seemingly governing their organisation and evolution over breeding seasons. No one hypothesis of the song’s function adequately explains its complexity and structure, except perhaps for the theory that it constitutes the first non-human language yet discovered. Buck and Suzuki (1999) have applied Information theory to analyse a sample of humpback song converted into a stream of symbols using a self-organising neural network (SONN). This theory can be used to determine the maximum amount of information contained within a coded sequence by the unpredictability of the next symbol. Different assumptions can be made about the nature of the sequence; the next symbol is randomly determined (thus no hierarchical structure is possible within the sequence), or the probability of the next symbol is dependent on the previous one, or two symbols (0th, 1st and 2nd Order Markov models respectively). It was found that a first-order assumption could not reasonably model humpback song, meaning that humpback song possesses a hierarchical structure suggestive of language. The low rate of information transmission, about 0.1 – 0.6 bits per second, may ensure reliable communication over long distances in noisy, unpredictable acoustic conditions.
The suborder Microchiroptera contains approximately 800 species of bats with a sophisticated biosonar system used to actively interrogate the local environment and analyse the retuned echoes to extract information on obstacles and potential prey in the flight path. Most are insectivorous and hunt with aerial-hawking or gleaning tactics, although some, such as Noctilio leporinus, predate on fish and use echolocation to detect localised surface ripples. Much research has been conducted into the neurophysiology of echolocation with its superb acoustic discrimination capabilities, including very fine temporal and frequency resolution. This review covers firstly bat call design and hunting behaviour, and the neural basis of their capabilities. The second half deals with the question of a bat-moth co-evolutionary arms race.