“…For example, song type length reflects competitive ability of males Hoopoe (Upupa epops) (Vivaldi et al, 2004). Females of several species have also been found to prefer some special song types (Vallet and Kreutzer, 1995;Foerster, 2002); these may be ones that are difficult to produce so that only males of high quality can master them (Slater, 2003). Studies also suggest that the receivers that focus solely on physical song characteristics of a male may gain information about the male's willingness to escalate a fight (Dabelsteen and Pedersen, 1992); its previous experience or age (Lambrechts and Dhondt, 1986;Welling et al, 1995); current body condition (Godfrey and Bryant, 2000) and social rank in a network of territorial individuals (Otter et al, 1997).…”