Institute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, United Kingdom
Quantifying the synchrony of behavior between animals is important in understanding group dynamics. Rook & Penning (Appl. Anim. Behav. Sci. 32:157-166, 1991) proposed an index of synchrony based on the well-known kappa coefficient of agreement. This is calculated as K = P(A)-P(E)/P(M)-P(E), where P(A) is the number of pairs of animals which are engaged in the same activity expressed as a proportion of the total possible number of pairs, P(E) is the expected proportion of pairs synchronized and P(M) is the maximum possible proportion that could be synchronized. The method not only quantifies the degree of synchrony but also provides a test of departure from chance synchrony.
The method has now been generalized , by appropriate definition of P(A), P(E) and P(M) from basic combinatorics, to allow the study not only of overall synchrony within a group of animals but also the synchrony of specific activities, the pattern of synchrony over time, the synchrony of particular sub-groups including pairs, the degree of synchrony of particular individuals and the degree to which activities occur at the same time within a group. These enhanced analyses should prove useful in elucidating some of the mechanisms underlying observed bahavior and may have important practical applications, for example in the identification of sub-clinical disease.
By combining these methods with more traditional tools, such as dominance hierarchies and analyses of the spatial arrangement of animals within groups, an enhanced understanding of social interactions between individuals should be possible.