Vocalisation in chicks (Gallus gallus dom.) during stepwise social isolation

Despite attempts to relate vocalisation of animals to their welfare status, very little is known in farm animals and in precocious birds. We analysed vocal expressions of 50 chicks during step by step social isolation. 91.20% of the recorded vocalisations (n = 21583 calls) consisted of four main call types: distress calls (43.72%) were characterised by declining frequency with high energy; short peeps (22.04%) by declining frequency, low energy and short duration; warblers (19.36%) by repetitive bow-type elements with low energy; pleasure notes (6.08%) by increasing frequency and low energy. 8.80% of calls were of other undefined nature. In all tests single isolated animals showed highest total vocalisation. When two different hatches were compared, total vocalisation differed significantly (P < 0.001, F-test). Changes of vocalisation during stepwise reduction of group size (beginning with four or more chicks) resulted in significant differences (P < 0.01, F-test) between steps. Low energy vocalisation (short peeps, warblers and pleasure notes) dominated in group sizes of three and more chicks. As group size decreased, the number of distress calls increased. Warblers and pleasure notes were absent when animals were isolated in the final step of the social isolation test indicating that a social target needs to be present for such call types to occur. It is concluded that vocalisation is strongly dependent on social contacts in the chick and that different degrees of social deficits find their expression in discrete changes in the pattern and elements of vocalisation. (C) 2001 Elsevier Science B.V. All rights reserved.