We compared the mobbing response to model snakes of two groups of captive-born common marmosets (Callithrix jacchus) differing in genetic relatedness, age and past experience. Mobbing vocalisations (tsik calls), other mobbing behaviour and attention to the stimulus were recorded for 2 min. intervals pre-exposure, during exposure to various stimuli and post-exposure. Marmosets in one group were vocally reactive to all stimuli, although more so to one particular stimulus resembling rearing snakes and modified images of it, whereas the marmosets in a younger and genetically unrelated group attended to the stimuli but made very few mobbing calls. The parent stock of the first group had suffered stress in early life and had developed a phobic response to a specific stimulus, which they had transmitted to their offspring. A third group, matching the older group in age range but genetically unrelated, was also found to be unresponsive to the stimulus that elicited the strongest response in the first group. Cortisol levels in samples of hair were assayed and a significant negative correlation was found between the number of tsik calls made during presentation of the stimuli and the cortisol level, showing that mobbing behaviour/behavioural reactivity is associated with low levels of physiological stress.

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Spontaneous pecking preferences toward symmetric or asymmetric stimuli were tested in newborn chicks (Gallus gallus). A preference for asymmetric patterns was found in naïve chicks (either 24 or 48 hours old), although a preference for symmetry appeared at retest after chicks had experienced standard rearing conditions (Experiments 1 and 2). Only food-experienced chicks preferred symmetric patterns; food-deprived and hand-fed chicks did not show any preference (Experiment 3). A key factor that allowed for the emergence of a preference for symmetry may relate to the improving of pecking sensorimotor skills occurring during active food manipulation. Possible explanations are discussed for the late emergence of the preference for symmetry and for the preference for asymmetry found in naïve chicks.

Spontaneous preferences towards possible prey have been little investigated using targets in motion. Preferences of domestic chicks (Gallus gallus) to peck at video-images of stimuli representing live insects moving along their longer body axis (i.e. "forwards") or along the shorter body axis (i.e. "sideways") were investigated. Chicks presented with both types of stimulus displayed a significant preference for pecking at stimuli moving sideways. This preference was already present on day 1 post-hatching, and it strengthened on day 6 for those chicks that had experienced pecking at live insects. Head angles used to fixate the stimuli prior to pecking were also analysed and were consistent (i.e. 30 degrees -35 degrees and 60 degrees -65 degrees ) with those reported for fixation of non-edible targets (larger stimuli at a distance). In a first control experiment the same video-presented stimuli were used but the insect's legs were removed to reduce flickering. In a second control experiment, paper-printed images of the whole insect were used. In both cases, the sideways direction of movement was clearly preferred. Overall, our data show that chicks have a spontaneous preference to peck at video-images resembling live insects moving along their shorter body axis. Sideways movement may constitute a crucial signal attracting chicks' attention and enhancing predatory responses possibly because of stronger stimulation of motion detectors.