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The Boto, Inia geofrennsis, is found in the Amazon and Orinoco basins. Its echolocation shows a predominance of spectral peaks around 100 kHz:
These values come from a selection of clicks made on the basis of their intensity, not their direction of origin relative to the axis of the beam. Many clicks collected in this way are bimodal and the lower mode shows a different distribution of peak frequencies:
One interesting feature of data collected in this way is that it represents the clicks received by a static hydrophone. To better represent the input to the T-POD analogue processor, these spectra were collected via a T-POD hydrophone, which is an undamped (mechanically) cylindrical piezo-ceramic. An analysis of these data suggests that the C-POD will be able to distinguish encounters with these species. Mixed groups would be difficult, but would be rarely seen. The Boto is readily monitored using the T-POD but the range of spectral peaks from Botos overlaps that from the sympatric Tucuxi, making it very difficult to distinguish the two species in T-POD data. Botos commonly show fast modulation of click rates, as shown below.
This is raw data, not filtered by the software. The white marks are clicks that the software excludes as not being part of the train. The Pulse Repetition Frequency (click rate) is shown on the Y axis, but is calculated simply from the interval between successive clicks, irrespective of how they are classified by the software. So this is very clean data with low levels of extraneous noise. This is typical of data collected in the Amazon when it is not raining! The Boto has a long beak, prominent melon and small dorsal ridge (scarred in the animal pictured below) instead of a fin.
For more information on this species, please visit the Convention of Migratory Species web site.
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