Comparison of behavioural patterns is frequently used in order to evaluate phylogenetic relations

of species.  We suggest a method for evaluating the complexity of ethological patterns based on the notion of Kolmogorov complexity. This method furnishes ethologists a new tool for quantitative comparative analysis of sequential data, that is, ethological ‘‘texts” (Reznikova et al., 2012; Ryabko et al., 2013). Here we consider hunting behaviour in small mammals towards the cockroach Nauphoeta cinerea. Complete hunting patterns ending with the prey capture were compared in Rattus norvegicus (125 encounters), Apodemus agrarius (83), Lasiopodomys gregalis (23) and Sorex araneus (76).  Behavioral units (19 in total, common for all species), singled out from video records and denoted by letters, served as an alphabet. We reduced the obtained files to equal initial length, compressed them with the use of the compressor 7-zip and compared ratios of compression in stereotypes of different species. The application of the compressor revealed that the hunting stereotypes in rats were characterized by the greatest complexity by the Mann–Whitney–Wilcoxon test: 0,486 in comparison with 0,425 in striped field mice A. agrarius, 0,428 in  narrow-headed voles L. gregalis, and 0,436 in common shrew S. araneus. (p<0,01). Rats' hunting stereotypes also appeared to have greatest redundancy and to be less predictable. We revealed the negative correlation between the ratio of compression and the proportion of bites within hunting stereotypes (r= -0,818 n=20 p<0,01).  In sum, the most complex behavioural stereotype in the Norway rat differs essentially from other species, whereas two other rodents are similar with each other and with the specialized predator such as the common shrew.
The study has been supported by the Russian Scientific Fund (14-14-00603)