Dept. of Environmental Sci., Univ. of Virginia, Charlottesville, VA 22903
Univ. of Mississippi, University, MS 38677
Etosha Ecological Institute, Namibia, Africa
Atmospheric conditions conducive to long-range transmission of low-frequency sound as used by elephants are found to exist in the Etosha National Park in Namibia during the late dry season. Meteorological measurements show that strong temperature inversions form at the surface before sunset and decay with sunrise, often accompanied by calm wind conditions during the early evening. These observations are used in an acoustic model to determine the sensitivity of infrasound to the effects of (a) the strength, thickness, and elevation of temperature inversions, and (b) the growth and decay of an inversion typical of dry, elevated African savannas. The results suggest that elephant communication range more than doubles at night. Optimum conditions occur 1--2 h after sunset on clear, relatively cold, calm nights. At these times ranges of over 10 km are likely, with greatest amplification occurring at the lowest frequency tested. This strong diurnal cycle in communication range may be reflected in longer period changes in weather and may exert a significant influence on elephant behavior on time scales from days to many years.