METEOROLOGY AND ELEPHANT INFRASOUND AT ETOSHA NATIONAL-PARK, NAMIBIA

Measured vertical profiles of temperature and wind an used to model in frasound propagation over a representative high savanna habitat typica lly occupied by the African elephant, Loxodonta africana, to predict c alling distance and area as a function of the meteorological variables , The profiles were measured up to 300 m above the surface by tethered balloon-borne instruments in Etosha National Park, Namibia, during th e late dry season. Continuous local surface layer measurements of wind and temperature at 5 and 10 m provide the context for interpreting th e boundary layer profiles. The fast field program (FFP) was used to pr edict the directionally dependent attenuation of a 15-Hz signal under these measured atmospheric conditions, The attenuation curves are used to estimate elephant infrasonic calling range and calling area, Direc tionality and calling range are shown to be controlled by the diurnal cycle in wind (shear) and temperature. Low-level nocturnal radiative t emperature inversions and low surface wind speeds make the early eveni ng the optimum time for the transmission of low-frequency sound at Eto sha, with range at a maximum and directionality at a minimum, As the n ight progresses, a nocturnal low-level wind maximum (jet) forms, reduc ing upwind range and calling area, The estimated calling area drops ra pidly after sunrise with the destruction of the inversion, Daytime cal ling areas are usually less than 50 km(2), while early evening calling areas frequently exceed 200 km(2) and are much less directional, This marked diurnal cycle will be present in any dry savanna climate, with variations due to local topography and climate, Calling range and low -frequency sound propagation cannot be effectively understood without knowledge of meteorological controls. (C) 1997 Acoustical Society of A merica.