Tigers have many vocalizations including chuffling, growling, prusten, gurgling, grunting, and roaring. It has been well documented that the tiger’s high-amplitude, low-frequency roars, which are thought to be territorial in nature [C. Packer and A. E. Pusey, Sci. Am. 276, 52–59 (1997)] transmit for miles. It has been suggested that because some tigers inhabit dense jungles with limited visiblity, the capacity to hear low frequency may be beneficial for sensing and locating prey [G. T. Huang, J. J. Rosowski, and W. T. Peake, J. Comp. Physiol. A (2000)]. In an effort to understand more about these low-frequency vocalizations and to provide data to other researchers testing hearing in anesthetized felids, 22 tigers, both Siberian and Bengal, are being recorded. A portable system can record from 3 Hz to 22 kHz. On-site real-time analysis of vocalizations is performed using a portable computer. Real-time and edited playback of sonic and infrasonic tiger vocalizations is facilitated by car audio speakers capable of producing frequencies from 10 Hz–22 kHz. Initial findings have documented fundamental frequencies of some roars at 17.50 Hz. Other vocalizations, including chuffling, have fundamental frequencies of 35 Hz ±5. Playback of both real-time and edited vocalizations appear to illicit behavioral responses, such as roaring, from male tigers.
A current hypothesis suggests the purr indicates contentment, however, cats purr when they are severely injured or frightened. Forty-four felids were recorded including cheetahs, ocelots, pumas, domestic cats, and servals. A Sony TCD-D8 Digital Audio Recorder (DAT) and Statham Radio microphones recorded the purrs. FFTs and spectrographs were performed using National Instrument’s Polynesia. An accelerometer was also used to measure domestic cat purrs. Every felid in the study generated strong frequencies between 25 and 150 Hz. Purr frequencies correspond to vibrational/electrical frequencies used in treatment for bone growth/fractures, pain, edema, muscle growth/strain, joint flexibility, dyspnea, and wounds. Domestic cats, servals, ocelots, and pumas produce fundamental, dominant, or strong frequencies at exactly 25 Hz and 50 Hz, the two low frequencies that best promote bone growth/fracture healing [Chen et al., Zhong. Wai Ke Za Zhi. 32, 217–219 (1994)]. These four species have a strong harmonic exactly at, or within 2 Hz of 100 Hz, a frequency used therapeutically for pain, edema, wounds, and dyspnea. An internal healing mechanism would be advantageous, increasing recovery time and keeping muscles and bone strong when sedentary. [Published with permission from the New Zealand Veterinary Journal; work supported by Endevco.]
Within the last ten years the Sumatran rhino population has dropped 50%, and only 200–300 individuals exist, with five in captivity. Their native habitat is dense tropical forest and they are solitary, therefore much of their behavior remains unknown. Sumatrans are the smallest living rhino, standing 0.9–1.5 m tall, and are covered in coarse, reddish-brown hair. The first Sumatran rhinoceros born in captivity in 112 years, and the first calf ever recorded, is 17 months old and weighs 448 kg. At the Cincinnati Zoo this male calf was recorded from 1–3 m, using two Statham radio microphones, and one TCD-D8 Sony DAT recorder (9 Hz–22 kHz). Analysis, including power spectrums, spectrographic functions, and cross correlations were performed using National Instrument’s Polynesia. Preliminary analysis indicates that the calf’s vocalizations are similar in structure to adult Sumatran vocalizations, although there are some distinctions. ‘‘Eeps’’ and ‘‘whales’’ that are found in adult repertoires are produced by the calf. However, signals from the calf are higher in frequency, and the calf does not vocalize as consistently as the adults. The calf has yet to produce a ‘‘whistle blow,’’ which is an adult vocalization that has a strong infrasonic component.
Several bioacoustic experiments required an affordable system capable of field recording, real-time analysis, signal editing, and real-time playback of infrasonic animal vocalizations. The synthesis of several types of recording devices and signal processing software has resulted in the capacity to record infrasound and perform analysis even during rain, heat, and high humidity. Small portable microphones and recorders can record in the field from 3 Hz to 22 kHz. On-site analysis including real-time FFT, color spectrographic function, filtering, cross-correlation, and other functions can be facilitated with the use of any portable computer with 92 Mbytes RAM. Signal editing, including frequency, amplitude, and cut/paste can be accomplished with readily available music signal processing software. Real-time field playback from 10 Hz to 45 kHz can be acheived by using portable car audio speakers. This system was used for the real-time analysis of elephant vocalizations, which were edited and played back immediately during recording sessions. It has also been used in field research involving tiger, binturong, rhinoceros, and giraffe. Tigers and elephants appear to respond behaviorally to real-time playback of original and edited vocalizations. [Work supported by National Instruments, Momentum Data Systems, and Sonic Foundry.]
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