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What are animal social networks, and how are proximity logging radio tags used to study them?

All societies (human and animal) can be viewed as networks of interconnected individuals, linked by social, spatial, temporal, and other relationships. By studying network structure (the links between individuals) we can derive unique insights into the workings of the society, and better understand the behavioral strategies that individuals use to enhance their success. Social network analysis has been extensively developed and used for studying human societies and human behavior. Animals are also social, and researchers have applied social network analysis to animal societies and behaviors as well. To date, surprisingly complex social networks have been described in a wide range of species and taxa, including primates, cetaceans, ungulates, rodents, birds, fish, and insects.

Although there are unique insights to be gained by studying animal social networks, there are also unique problems. In particular, unlike humans, animals will not tell us where they have been and who they associate with, information that is key to studying a social network. Direct observation methods are usually used study animal social associations and movement patterns. However, in many cases observation is not possible, especially when animals must be continuously monitored for long periods of time, when animals behave cryptically (as they often do), or when animals are out of sight of observers (as with nocturnal, arboreal, or fossorial species).

For these reasons, new tools have been developed to allow researchers to monitor social associations on a continuous basis no matter where the animal subjects are. These wireless devices, variously called encounter or proximity logging tags, are worn by all study subjects and can detect and log the presence of other individuals wearing similar tags. When two such tags come to within a preset range, they exchange their unique ID codes and store the event as an “encounter” in a log file stored in memory. Later, the encounter logs are retrieved and analyzed to determine the association network structure. A successful deployment of proximity logging tags can generate hundreds of thousands of logs that provide a complete record of all interactions among tagged individuals over the lifespan of the tags.

encounter log to network graph

Hypothetical encounter logs of associations between 8 tagged subjects, and the resulting network graph. In the graph, ties (red lines) indicate detected encounters, tie thickness denotes encounter duration (longer encounters suggest stronger social bonds). In network analysis parlance, animals 1 and 4 have more links and therefore have greater centrality than the others in this group. These individuals may have greater social influence and serve as information hubs. Not shown in this figure, but potentially important, are the timing of encounters, encounter location, how close individuals were to each other, and behaviors that occurred during encounters. All of these additional social parameters will be collected Encounternet.