Data from: Calibrating animal-borne proximity loggers

1. 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. 2. In this study, we calibrated a
recently developed digital proximity-logging system (‘Encounternet’) for
deployment on a wild population of New Caledonian crows Corvus
moneduloides. Our principal objective was to establish a quantitative
model that enables robust post hoc estimation 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. 3. 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. 4. 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.