I would like to draw your attention to the following recent publications which should be of interest to anyone working on the impact of anthropogenic noise on the behaviour of marine mammals (abstract below).
Götz, T & Janik, V.M. (2011): Repeated elicitation of the acoustic startle reflex leads to sensitisation in subsequent avoidance behaviour and induces fear conditioning. BioMedCentral Neuroscience 12:30. doi:10.1186/1471-2202-12-30 The article and all supporting video material can be accessed through: http://www.biomedcentral.com/1471-2202/12/30 The paper also refers to an earlier publication that used a similar methodology. Please email: [email protected]<mailto:[email protected]> for a pdf (see abstract below). Götz, T & Janik, V.M. (2010): Aversiveness of sounds in phocid seals: psycho-physiological factors, learning processes and motivation. Journal of Experimental Biology 213, 1536-1548. Best, Thomas Dr Thomas Goetz Research Fellow Sea Mammal Research Unit University of St Andrews KY16 8LB, St Andrews Scotland/UK Götz, T & Janik, V.M. (2011): Repeated elicitation of the acoustic startle reflex leads to sensitisation in subsequent avoidance behaviour and induces fear conditioning. BioMedCentral Neuroscience 12:30. doi:10.1186/1471-2202-12-30 Abstract Background: Autonomous reflexes enable animals to respond quickly to potential threats, prevent injury and mediate fight or flight responses. Intense acoustic stimuli with sudden onsets elicit a startle reflex while stimuli of similar intensity but with longer rise times only cause a cardiac defence response. In laboratory settings, habituation appears to affect all of these reflexes so that the response amplitude generally decreases with repeated exposure to the stimulus. The startle reflex has become a model system for the study of the neural basis of simple learning processes and emotional processing and is often used as a diagnostic tool in medical applications. However, previous studies did not allow animals to avoid the stimulus and the evolutionary function and long-term behavioural consequences of repeated startling remain speculative. In this study we investigate the follow-up behaviour associated with the startle reflex in wild-captured animals using an experimental setup that allows individuals to exhibit avoidance behaviour. Results: We present evidence that repeated elicitation of the acoustic startle reflex leads to rapid and pronounced sensitisation of sustained spatial avoidance behaviour in grey seals (Halichoerus grypus). Animals developed rapid flight responses, left the exposure pool and showed clear signs of fear conditioning. Once sensitised, seals even avoided a known food source that was close to the sound source. In contrast, animals exposed to non-startling (long rise time) stimuli of the same maximum sound pressure habituated and flight responses waned or were absent from the beginning. The startle threshold of grey seals expressed in units of sensation levels was comparable to thresholds reported for other mammals (93 dB). Conclusions: Our results demonstrate that the acoustic startle reflex plays a crucial role in mediating flight responses and strongly influences the motivational state of an animal beyond a short-term muscular response by mediating long-term avoidance. The reflex is therefore not only a measure of emotional state but also influences emotional processing. The biological function of the startle reflex is most likely associated with mediating rapid flight responses. The data indicate that repeated startling by anthropogenic noise sources might have severe effects on long-term behaviour. Future, studies are needed to investigate whether such effects can be associated with reduced individual fitness or even longevity of individuals. Götz, T & Janik, V.M. (2010): Aversiveness of sounds in phocid seals: psycho-physiological factors, learning processes and motivation. Journal of Experimental Biology 213, 1536-1548. Abstract Aversiveness of sounds and its underlying physiological mechanisms in mammals are poorly understood. In this study we tested the influence of psychophysical parameters, motivation and learning processes on the aversiveness of anthropogenic underwater noise in phocid seals (Halichoerus grypus and Phoca vitulina). We compared behavioural responses of seals to playbacks of sounds based on a model of sensory unpleasantness for humans, sounds from acoustic deterrent devices and sounds with assumed neutral properties in different contexts of food motivation. In a captive experiment with food presentation, seals habituated quickly to all sound types presented at normalised received levels of 146 dB re. 1 mPa (r.m.s., root mean square). However, the fast habituation of avoidance behaviour was also accompanied by a weak sensitisation process affecting dive times and place preference in the pool. Experiments in the wild testing animals without food presentation revealed differential responses of seals to different sound types. We observed avoidance behaviour at received levels of 135-144 dB re. 1 mPa (sensation levels of 59-79 dB). In this experiment, sounds maximised for 'roughness' perceived as unpleasant by humans also caused the strongest avoidance responses in seals, suggesting that sensory pleasantness may be the result of auditory processing that is not restricted to humans. Our results highlight the importance of considering the effects of acoustic parameters other than the received level as well as animal motivation and previous experience when assessing the impacts of anthropogenic noise on animals.
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