  In this paper we address the problem of inferring social structure and
dominance relationships in a group of rhesus macaques (a species of monkey)
using only position data captured using RFID tags. Automatic inference of the
social structure in an animal group enables a number of important capabilities,
including: 1) A verifiable measure of how the social structure is affected by
an intervention such as a change in the environment, or the introduction of
another animal, and 2) A potentially significant reduction in person hours
normally used for assessing these changes. Social structure in a group is an
important indicator of its members' relative level of access to resources and
has interesting implications for an individual's health and learning in groups.
There are two main quantitative criteria assessed in order to infer the social
structure; Time spent close to conspecifics, and displacements. An interaction
matrix is used to represent the total duration of events detected as grooming
behavior between any two monkeys. This forms an undirected tie-strength
(closeness of relationships) graph. A directed graph of hierarchy is
constructed by using the well cited assumption of a linear hierarchy for rhesus
macaques. Events that contribute to the adjacency matrix for this graph are
withdrawals or displacements where a lower ranked monkey moves away from a
higher ranked monkey. Displacements are one of the observable behaviors that
can act as a strong indication of tie-strength and dominance. To quantify the
directedness of interaction during these events we construct histograms of the
dot products of motion orientation and relative position. This gives us a
measure of how much time a monkey spends in moving towards or away from other
group members.

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