The giraffe, a savanna ungulate, possessing limited auditory vocalizations, was found to produce infrasound. Recordings were made of 11 Giraffe (Giraffe camelonardalis reticulata), at the North Carolina Zoological Park in Asheboro, North Carolina and the Riverbanks Zoo and Botanical Garden in Columbia, South Carolina. A portable system (7Hz - 22 kHz) was used to record the vocalizations. Analysis was conducted in real-time in the field using a portable trigger oscilloscope and National Instruments Polynesia. Real-time analysis consisted of Hamming FFT's and time domain displays. The signals were also analyzed in the lab using Polynesia and Momentum Data System's DSP Works. Each signal was low-pass/high pass filtered, and FFT's and spectrographs were performed. Audible signals contained frequencies from 11 Hz (75dB+/-3) to 10,500 Hz (80dB +/- 3) with dominant frequencies between 150-200 Hz. Inaudible vocalizations detectable by real-time analysis and trigger scope, measured from 14 Hz (60 dB +/-3) to 250-275 Hz (30dB +/-3) with dominant frequencies between 20-40 Hz. A behaviour known as a neck throw appeared to be correlated with the signals, leading the researchers to theorize that Helmholtz resonance, (V=c2S/( 4π2Lf2) was responsible for the production of the vocalizations. Additionally, the decibel levels of the inaudible signals decreased rapidly over 40 Hz, which suggests that the vocalization may be designed to be a covert form of communication. The hypothesis that giraffe, like okapi, elephant, whale, and rhinoceros produce infrasound, was supported.
