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.

The main objective of this study was to provide a description of the possible patterns of rat behaviour in the exploration box. Both age and sex of the animals were controlled. The measures taken assessed changes in the patterns of behavioural activity over time. Sex did not differentiate the rat's behaviour significantly. Two patterns of developmental changes were found. The results of cluster analysis with a sequential data sets lead to the conclusion that there are at least two levels of regulation of rat behaviour: activation and content organization. It was also shown that rat behaviour in the exploration box is not stereotyped but highly plastic. The results are discussed in terms of development, sex differences and individual differences.

Two experiments have been performed in young (7 days old),  middle-aged (28 days old) and old (49 days old) Drosophila melanogaster. In Experiment 1, the inhibitory conditioning of the Proboscis Extension Response (PER) to sucrose was displayed under three Inter-Trial-Interval (ITI) schedules: 1, 2 or 4 minutes. The results did not reveal any age-related impairment of short-term-memory. The PER suppression performance was higher in middle-aged and old flies than in young ones, whatever the ITI. In Experiment 2, the habituation of the PER to sucrose was induced to investigate the hypothesis of an age-related increase of the non associative processes involvement (sensory adaptation, motor fatigue) in the PER suppression. The results showed that  once such peripheral effects were removed, suppression performances no longer varied with age.