Common features and individual differences in nurse grunting of domestic pigs (Sus scrofa): A multi-parametric analysis

The nursing vocalisation of domestic pigs was investigated with respect to common features and individual differences. The sow's repeated grunting dur ing nursing can be regarded as a contact call and a signal of the mother to start and synchronise the suckling behaviour of the piglets. Analyses in t he time domain revealed the gross structure of the call, whereas in the fre quency domain the fine structure of single grunts was investigated. Three p arameter groups with parameter vectors extracted from single grunts centred around the maximum of the grunting rate were used for classification of fr equency patterns. The parameter vectors were compared by a discriminant fun ction analysis. The main results are: (1) a strong correlation in the time course of the nurse grunting between the sows; (2) an individual frequency pattern of the single grunts as demonstrated by the discriminant analysis w ith erroneous discriminations of less than 1.6% if an optimum set of featur es of the amplitude spectrum was included. Thus, it can be concluded that a common structure of the time course of the nurse grunting is the typical i nter-individual characteristic of the vocalisation. Individual differences between sows occurred in the absolute grunting rate, however. Major individ ual differences were found in the frequency pattern of the single grunts an d were expressed over the whale frequency range of a grunt. Hence, based on the parameter groups 'whole amplitude spectrum' and 'cepstrum', individual sows could well be distinguished whereas this was not the case using only single features of the amplitude spectra. Taken together, the results show that there is a species-typical pattern in the nurse grunt ing that could be recognised by all piglets, and an indivi dual label that could be used to discriminate the own mother from other nur sing sows.