TOOLS OF THE (INFRASONIC) TRADE
Autonomous Recording Units (ARUs), developed by the Bioacoustics Research Program at Cornell University, are used to continuously record elephant vocalizations in forested areas. (click on 'Acoustic arrays' in the panel at right to learn more about how arrays work). These units have performed extremely well in the very difficult climate of Africa's tropical rainforests. Our biggest 'problem' has actually been damage to the power cables caused by inquisitive chimpanzees!
Units are hoisted into trees, to protect them from elephant damage, and left to collect long recordings of elephant vocalizations as well as gunshots and the sounds of numerous other vocal species.
© Ruth Starkey
© Nicolas Bout
In spite of the effort needed to carry equipment and power supply tens of kilometers through the forest, the hard part really comes after the forest sounds have been recorded. Acoustic files are 'real time', so the challenge is to locate sounds of interest within the matrix of 'background' sounds. Developing automated detectors that can recognize and mark the sounds of interest is a major focus of the programming group of the Bioacoustics Research Program. Elephant calls provide a particular challenge because of their very low frequencies.
One of the rewards of analyzing sound recordings from our study sites is stumbling across an interesting looking spectrogram, taking a listen, and realizing that we have the territorial chest-beating of a lowland gorilla silverback, or the morning wake up advertisement of a great touraco! Click the buttons below the following spectrograms to hear these fascinating sounds.