International Journal of Comparative Psychology

Changes in the structure of the peep vocalization of female domestic chicks reared in pairs from day three post-hatching were investigated. Recording began on day five with each chick being recorded in isolation twice weekly over a ten week period post-hatching. Spectrographic analysis shows that the peep call develops an increasingly complex structure from the second week post-hatching with additional components introduced as the chicks age. Nine acoustic parameters (duration, maximum frequency, minimum frequency, difference between maximum and minimum frequency, peak frequency, peak frequency range, peak amplitude, energy and average power) of four different peep calls were analysed. Significant differences were found between the four types of peep call on seven of the nine acoustic parameters. Discriminant analysis showed that the different types of peep call could be accurately determined on the basis of these results. Correlations of the call parameters showed that the calls displayed lower levels of stability as call structure became more complex. Chicks also displayed high inter-individual variation and relatively low intra-individual variation over call parameters. Results are discussed in relation to hen-chick, chick-chick communication as the broody period declines.