Environmental Influences on the Structure of Primate Vocalizations

Abstract

Under natural conditions vocal signals are embedded in background noises, and are degraded by the action of diffraction, reflection, frequency-dependent absorption, and refraction. A fuller appreciation of the evolution of communication systems may be achieved by developing an understanding of the impediments to communication which occur in the natural environment, and investigating possible adaptations in the structure of either productive and receptive systems which may act to counter these impediments. The idea that characteristics of vocal signals have evolved a form acting to counter ecological impediments to communication has received increasing attention over the past 2 decades. Although most investigators have addressed questions pertinent to the structure of bird song (Morton 1970(Morton , 1975Chappuis 1971;Jilka and Leisler 1974;Nottebohm 1975;Bowman 1979;Hunter and Krebs 1979;Wasserman 1979; Gish and Morton 1981;Brenowitz 1982;Heuwinkel 1982;Wiley and Richards 1982;Shy 1983; Co sen and Falls 1984;McGregor and Falls 1984;McGregor and Krebs 1984;Ryan and Brenowitz 1985) Selection may shape not only signal form (where more reliable or longer-distance transmission of information is advantageous), but also perceptual capabilities (where more complete or accurate reception of information is beneficial). In addition, selection may shape other aspects of communicative behavior, such as the timing of vocalizations or the choice of broadcast sites. In this chapter we briefly review some examples of possible environmental effects on perceptual capabilities and calling behavior; we then summarize the results of our studies on the acoustic ecology of equatorial African primate habitats, and fmally describe in more detail our ongoing work focused on how habitat acoustics influence the fidelity of calls broadcast in natural environments.1 Habitat Effects on Perceptual Abilities and Calling Behavior Brown and P.M. Waser (1984) found that arboreal, forest-living blue monkeys are up to 20 dB more sensitive to low-frequency sounds (signals 500 Hz and lower) than are semiterrestrial, more open-country rhesus monkeys. This difference in sensitivity paral-

THE ROLE OF ENVIRONMENTAL SELECTION IN INTRASPECIFIC DIVERGENCE OF MATE RECOGNITION SIGNALS IN THE CRICKET FROG, ACRIS CREPITANS

“…We used a cross correlation analysis to quantify degradation as a function of distance, similar to the method used by Brown and Waser (1988) to quantify primate call degradation. The higher the cross correlation coefficient, the more similar are two calls, and thus the less degradation.…”

Spectral characteristics of intense mew calls in cat species of the genus Felis (Mammalia: Carnivora: Felidae)

“…Morton 1975;Waser and Waser 1977;Wallschläger 1981Wallschläger , 1985Brown and Waser 1988;Wiley 1991;Brown and Gomez 1992;Brown et al 1995;Daniel and Blumstein 1998;Slabbekoorn and Smith 2002;Ryan and Kime 2003;Saunders and Slotow 2004;Blumstein and Turner 2005;Boncoraglio and Saino 2007). Data on diverse vertebrate taxa support this hypothesis (Morton 1975;Gish and Morton 1981;Wallschläger 1980Wallschläger , 1982Wallschläger , 1985Wallschläger and Nikolskij 1985;Masters 1991;Saunders and Slotow 2004;Slabbekoorn 2004;Seddon 2005;Nicholls and Goldizen 2006;Tubaro and Lijtmaer 2006), while in other taxa it is only supported weakly (Blumstein and Turner 2005;Boncoraglio and Saino 2007) or is not supported (Daniel and Blumstein 1998;Kime et al 2000;Saunders and Slotow 2004).…”

On the Occurrence of Nocturnal and Diurnal Loud Calls, Differing in Structure and Duration, in Red Howlers (Alouatta seniculus) of French Guyana

“…First, in in tensity, acoustic structure, and time of emis sion long calls conform best to the criteria for sounds designed to carry over long distances [39,40], In addition, by being emitted from the sleeping sites at the top of the emergent trees, they might be less attenuated or subject to reverberation than if given through the dense foliage by monkeys travelling during the day [36].…”