In species using a hider strategy where the young remain hidden in the undergrowth after birth (see Langbein & Putman, 1992), there is a selection pressure for young to be silent CH5424802 nmr to avoid detection by predators. Because the offspring are mobile and may change hiding places, acoustic recognition of the dam is essential to maintain maternal care in these species (Fisher, Blomberg & Owens, 2002). Fallow deer fawns thus only leave their hiding place in response to the recognition of the distinctive fundamental frequency

of their dam’s call, while the dam does not recognize the call of the fawn (Vannoni et al., 2005; Torriani et al., 2006). On the other hand, in species using a follower strategy and in species where offspring are mixed with other same-aged offspring, mutual recognition between mother and young is vital for the survival find more of offspring (banded mongoose: Muller & Manser, 2008; northern fur seals: Insley, 2001; sheep: Searby & Jouventin, 2003). Recognition is likely to have evolved via different selection pressures on mother

and young: for young animals, non-recognition of their mother may lead to death, whereas for the mother, non-recognition of their young may lead to the loss of one breeding season (Trivers, 1971). These differential pressures mean that acoustic recognition between mother and offspring may be asymmetrical (Insley, 2001). Thus in fur seals, pups attend to the harmonic structure and tempo of female calls to identify their mother (Charrier et al., 2003b), while mothers appear to attend to the properties of the energy spectrum (frequency modulation and amplitude contour) to identify their pup (Charrier, Mathevon & Jouventin, 2002). Playback experiments in which the harmonic structure of maternal calls has been modified have unambiguously shown that this manipulation irrevocably impairs recognition in fur seal pups (Charrier et al., 2003b). For some mammals and specifically for several primate species including humans, filter components

play a substantial role in the acoustic distinctiveness of individuals (baboons: Owren et al., 1997; red deer: Reby et al., 1998; rhesus monkeys: Rendall et al., 1998; also click here see Fischer et al., 2001). This appears to be primarily an acoustic consequence of morphological individuality. For example, Rendall (2003a,b) used statistical algorithms to show that baboon grunts were individually distinct across several acoustic parameters (notably tempo, F0 and formant structure), but that formants provided the highest degree of differentiation between individuals due to the less reliable, dynamic nature of tempo and F0. While most studies have focused on individual differences occurring within the same call types, there is some evidence that in some non-human mammals, individuals have idiosyncratic voices, like human speakers.