The Effect of Hemosporidian Infections on White-Crowned Sparrow Singing Behavior

Bird song and territorial defensive behavior have intraand inter-sexually selected functions (Andersson 1994; Catchpole & Slater 1995). For a sexually selected signal to be an honest indicator of quality, it may be costly (Zahavi 1975; Searcy & Yasukawa 1996; but see Vehrencamp 2000). Song bouts may take time away from foraging (Searcy & Yasukawa 1996), and may also increase predation risk (Gil & Gar 2002). Singing may also have some intrinsic energetic cost because it is an aerobic activity and requires potentially exhausting use of the ventilatory muscles of the body wall (Oberweger & Goller 2001), although recent studies suggest this cost is minimal (Ward et al. 2003). Males which are in some way energetically compromised may be less able to engage in singing for territorial defense and mate attraction (Ward et al. 2003). Thus, song could be a reliable indicator of male quality. The Hamilton–Zuk hypothesis states that because male secondary sex characters require extra resources to produce and maintain, they might be differentially affected by pathogens (Hamilton & Zuk 1982). Sexually selected behaviors, like song, may be more strongly affected by parasites than morphological traits because they are relatively plastic and thus take less time to express the consequences of parasitic infection than morphological traits (Møller et al. 2000). Song traits that are sexually selected could thus serve as reliable indicators of a male’s infection status to competing males as well as to prospective mates. A number of studies have linked repertoire size, song rate and length of song bouts with male health (Møller 1991a; Buchanan et al. 1999). Females tend to prefer exaggerated song traits that can be negatively influenced by pathogens (Radesater et al. 1987; Alatalo et al. 1990). However, females probably use multiple cues to select a mate (e.g. Buchanan & Correspondence Daniel T. Blumstein, Department of Ecology and Evolutionary Biology, University of California, 621 Young Drive South, Los Angeles, CA 90095–1606, USA. E-mail: [email protected]