Abstract:
Many animals (including humans) change the loudness of their vocal signals according to distance from a receiver and background noise. The mechanisms underlying this change remain poorly understood. The song of the male zebra finch has many parallels to human speech and provides a good model to understand mechanisms involved in changing vocal signal loudness. Previous studies have shown that zebra finches increase song amplitude when distance from a female increases. However, these were recorded with a microphone fixed above the cage without controlling for changes in amplitude with changes in position of the bird relative to the microphone. More recent studies from our lab measured song amplitude with a microphone implanted on the head of the male zebra finch. The head implanted microphone showed no consistent trend in song amplitude with increasing distance from the female, but signals also showed considerable day-to-day variation suggesting a malfunction of the microphone. To eliminate the possibility of microphone malfunction and to record amplitude more accurately, I implanted birds with 2 microphones on their heads. Using this setup, I first showed that signals were correlated across the two microphones for the most part. However, there was some amount of uncorrelated noise in both microphones and I characterized some sources of this noise. Second, I did not find any significant change in song amplitude with changes in distance and/or background noise. Overall, these results demonstrate the potential of using a two-microphone system to further characterize vocal amplitude.
