The Influence of Surface Atmospheric Conditions on the Range and Area Reached by Animal Vocalizations

Abstract

Low-level vertical changes in temperature and wind exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modelling of low-frequency sound propagation in measured atmospheric conditions predicts that the calls of the savanna elephant at these frequencies can have ranges exceeding 10 km and that the calls will be highly directional in the presence of wind shear. Calling area is maximized under temperature inversions with low wind speeds. Calling area changes substantially over 24 h periods; on any given day, the calling area undergoes an expansion and contraction which may be as large as one order of magnitude. This cycle is modulated by topography, regional weather patterns, seasonality and possibly by climate variation. Similar influences affect the somewhat higher-frequency calls of lions and may be a selective pressure towards their crepuscular and nocturnal calling behaviour. 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 field studies of animal behaviour. A simplified method for estimating sound propagation during field studies is presented.

Auditory communication, meteorology and the Umwelt.

“…These con- Staaden and Romer's (1997) excellent study strongly suggesting that male bladder grasshoppers exploit meteorological conditions to maximize the range of their mating calls. This study shows that meteorological conditions can have powerful effects over ranges as little as 150 m. Three previous articles (Garstang, Larom, Raspet, & Lindeque, 1995;Larom, Garstang, Payne, Raspet, & Lindeque, 1997) and my dissertation (Larom, 1996) used the Fast Field Program (FFP), a computer model developed at the National Center for Physical Acoustics in Oxford, Massachusetts, to predict propagation of very-low-frequency elephant calls. The simplest possible call models were used; 15-and 30-Hz sine waves in a parametric study under idealized atmospheric conditions, and a 15-Hz signal for a more focused range analysis, predicting propagation based on actual atmospheric conditions measured at Etosha National Park during SAFARI.…”

“…Three previous articles (Garstang, Larom, Raspet, & Lindeque, 1995; Larom & Garstang, 1997; Larom, Garstang, Payne, Raspet, & Lindeque, 1997) and my dissertation (Larom, 1996) used the Fast Field Program (FFP), a computer model developed at the National Center for Physical Acoustics in Oxford, Massachusetts, to predict propagation of very-low-frequency elephant calls. The simplest possible call models were used; 15-and 30-Hz sine waves in a parametric study under idealized atmospheric conditions, and a 15-Hz signal for a more focused range analysis, predicting propagation based on actual atmospheric conditions measured at Etosha National Park during SAFARI.…”

Does Social Complexity Drive Vocal Complexity? Insights from the Two African Elephant Species

“…Savanna elephants appear to be able to recognize each other from the harmonic structure of some rumbles up to a distance of 2.5 km, enabling them to coordinate interactions over long distances and to form extensive vocal recognition networks [ 24 , 84 ]. Simulation models suggest that when conditions are optimal, savanna elephants may be able to detect rumbles over distances of up to 10 km [ 100 ]. Models of the attenuation of forest elephant rumbles based on amplitude measurements of rumbles recorded in a Central African rainforest suggest that forest elephant rumbles attenuate faster than savanna elephant rumbles [ 98 ].…”

Overview: Animal acoustic communication and the role of the physical environment.

“…Furthermore, geological and topographical characteristics of these substrates have varying effects on the attenuation and degradation of these seismic signals, and evidence suggests that elephants may select certain substrates as staging points for communicating seismically to increase the distances over which their signals propagate (Arnason, Hart, & O'Connell-Rodwell, 2002). Similarly, animals may be selective in maximizing their ability to detect communicative signals, for example, by listening early or late in the day when thermal inversions increase the distance that airborne signals propagate (Larom & Garstang, 1997; Larom, Garstang, Payne, Raspet, & Lindeque, 1997).…”