Giraffe Helmholtz resonance

Many animal species, including elephants and okapi, use sounds above and below the range of human hearing to communicate. A longitudinal study presented here suggests giraffe produce infrasonic vocalizations using Helmholtz resonance. Recordings were made of giraffe (Giraffe camelopardalis) in controlled indoor conditions and naturalistic outdoor conditions. The portable recording and analysis system consisted of a trigger oscilloscope; DAT recorders; Nagra IV-SJ and computers. Each signal was low-pass/high-pass filtered and FFT and STFT were performed using PolynesiaTM real-time scrolling analysis. In controlled recordings and in naturalistic situations two types of signals were identified: audible bursts [(11Hz (75dB+/-3) to 10,500Hz (80dB +/- 3)] dominant frequencies between 150-200Hz and covert vocalizations [(14 Hz (60dB +/-3) to 250-275 Hz (30dB +/-3)] dominant frequencies between 20-40 Hz. Both audible and covert signals coincided with neck throw or head toss behaviors. The shape of the giraffe's respiratory apparatus during this behavior and the frequencies produced implicate Helmholtz resonance as a production mechanism. In naturalistic recordings, two of the five infrasonic vocalizations identified were produced during close range social interactions, suggesting that giraffe use these vocalizations to communicate with con-specifics. The social functions, air and seismic transmission mechanisms of these vocalizations should be further assessed.