title: Calibrating animal-borne proximity loggers.
abstract: Growing interest in the structure and dynamics of animal social networks has stimulated efforts to develop automated tracking technologies that can reliably record encounters in free-ranging subjects. A particularly promising approach is the use of animal-attached 'proximity loggers', which collect data on the incidence, duration and proximity of spatial associations through inter-logger radio communication. While proximity logging is based on a straightforward physical principle - the attenuation of propagating radio waves with distance - calibrating systems for field deployment is challenging, since most study species roam across complex, heterogeneous environments.In this study, we calibrated a recently developed digital proximity-logging system ('Encounternet') for deployment on a wild population of New Caledonian crowsCorvus moneduloides. Our principal objective was to establish a quantitative model that enables robustpost hocestimation of logger-to-logger (and, hence, crow-to-crow) distances from logger-recorded signal-strength values. To achieve an accurate description of the radio communication between crow-borne loggers, we conducted a calibration exercise that combines theoretical analyses, field experiments, statistical modelling, behavioural observations, and computer simulations.We show that, using signal-strength information only, it is possible to assign crow encounters reliably to predefined distance classes, enabling powerful analyses of social dynamics. For example, raw data sets from field-deployed loggers can be filtered at the analysis stage to include predominantly encounters where crows would have come to within a few metres of each other, and could therefore have socially learned new behaviours through direct observation. One of the main challenges for improving data classification further is the fact that crows - like most other study species - associate across a wide variety of habitats and behavioural contexts, with different signal-attenuation properties.Our study demonstrates that well-calibrated proximity-logging systems can be used to chart social associations of free-ranging animals over a range of biologically meaningful distances. At the same time, however, it highlights that considerable efforts are required to conduct study-specific system calibrations that adequately account for the biological and technological complexities of field deployments. Although we report results from a particular case study, the basic rationale of our multi-step calibration exercise applies to many other tracking systems and study species.
authors.affiliation: Department of Zoology University of Oxford South Parks Road Oxford OX1 3PS UK; Present address: School of Biology Centre for Biological Diversity University of St Andrews Sir Harold Mitchell Building St Andrews KY16 9TH UK.
authors.forename: Christian
authors.initials: C
authors.lastname: Rutz
authors.affiliation: School of Biology Centre for Biological Diversity University of St Andrews Sir Harold Mitchell Building St Andrews KY16 9TH UK.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Morrissey
authors.affiliation: Department of Zoology University of Oxford South Parks Road Oxford OX1 3PS UK.
authors.forename: Zackory T
authors.initials: ZT
authors.lastname: Burns
authors.affiliation: Department of Electrical Engineering University of Washington Seattle WA 98195 USA.
authors.forename: John
authors.initials: J
authors.lastname: Burt
authors.affiliation: Department of Electrical Engineering University of Washington Seattle WA 98195 USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Otis
authors.affiliation: Department of Zoology University of Oxford South Parks Road Oxford OX1 3PS UK; Present address: School of Biology Centre for Biological Diversity University of St Andrews Sir Harold Mitchell Building St Andrews KY16 9TH UK.
authors.forename: James J H
authors.initials: JJ
authors.lastname: St Clair
authors.affiliation: Department of Physics and Centre for Networks and Collective Behaviour University of Bath Bath BA2 7AY UK.
authors.forename: Richard
authors.initials: R
authors.lastname: James
keywords: Corvus moneduloides; Encounternet; animal social network; biologging; business card tag; contact network; direct and indirect encounter mapping; reality mining; transceiver tag; wireless sensor network