Abstract:

Vertical temperature and wind gradients exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modeling of 15- and 30-Hz sound propagation in measured atmospheric conditions predicts that infrasonic African elephant calls can have ranges exceeding 10 km and will be highly directional in the presence of wind shear. The calling area is maximized under temperature inversions with low wind speeds. The calling area can expand and contract by an order of magnitude in 24 h. Topography, regional weather patterns, seasons, and climate variation modify this cycle. Similar influences affect the somewhat higher frequency calls of lions and may be a selective pressure toward their crepuscular and nocturnal calling behavior. Coyotes and wolves, which also live in areas with strong and prevalent nocturnal temperature inversions, show similar calling patterns, maximizing their chances of being heard over the longest possible distances. The pronounced dawn and evening vocalization peaks in other animals including birds, frogs, and insects may reflect the same influences, in combination with other factors which selectively limit high-frequency sound propagation. Atmospheric conditions therefore need to be taken into account in many studies of animal behavior. [Work supported by NSF Grant Nos. ATM92-07924 and ATM-9529315. Thanks to Peter Marler for useful comments.]