DOI: 10.5061/dryad.jwstqjq4k
title: Data from: Dispersal patterns in a medium-density Irish badger population: implications for understanding the dynamics of tuberculosis transmission.

description: European badgers (Meles meles) are group-living mustelids implicated in
 the spread of bovine tuberculosis (TB) to cattle and act as a wildlife
 reservoir for the disease. In badgers, only a minority of individuals
 disperse from their natal social group. However, dispersal may be
 extremely important for the spread of TB, as dispersers could act as hubs
 for disease transmission. We monitored a population of 139 wild badgers
 over seven years in a medium-density population (1.8 individuals/ km2).
 GPS-tracking collars were applied to 80 different individuals. Of these,
 we identified 25 dispersers, 14 of which were wearing collars as they
 dispersed. This allowed us to record the process of dispersal in much
 greater detail than ever before. We show that dispersal is an extremely
 complex process, and measurements of straight-line distance between old
 and new social groups can severely underestimate how far dispersers
 travel. Assumptions of straight-line travel can also underestimate direct
 and indirect interactions and the potential for disease transmission. For
 example, one female disperser which eventually settled 1.5 km from her
 natal territory travelled 308 km and passed through 22 different
 territories during dispersal. Knowledge of badgers’ranging behaviour
 during dispersal is crucial to understanding the dynamics of TB
 transmission, and for designing appropriate interventions, such as
 vaccination.
description: Badgers
 were tracked using Tellus Light GPS collars that weighed 240 g (Followit
 Wildlife, Lindsberg, Sweden). Data collection began in April 2010 and
 continued until October 2016, when all collars were removed. We aimed to
 capture as many badgers as possible within each social group. Collars were
 programmed to record four GPS locations a night, at 21:00, 23:00, 01:00
 and 02:00, for each collared badger (following MacWhite <i>et
 al.</i> 2013; Gaughran <i>et al.</i> 2018). Data were
 visualised in ArcMap (ArcGIS version 10.4.1). Badgers were
 sexed at each trapping event. Age was determined by dentition (Hancox
 1988; da Silva and Macdonald 1989) and general appearance. Age cohorts
 were defined as follows: cub (a badger in its first year); yearling (a
 badger in its second year), young adult (a 2- or a 3-year old), older
 adult (a 4- or a 5-year old) and aged adult (badger &gt;5 years old).
 A social group was defined as the group of badgers which were regularly
 trapped at the same main sett and whose home ranges overlapped during the
 time period in question (following (Macdonald <i>et al.</i>
 2008; Woodroffe <i>et al.</i> 2016). Thus, badgers were
 assigned to a social group based on their most frequent trapping location
 and, if collared, their GPS tracking data. Dispersers
 were defined, and confirmed retrospectively, as those badgers that were in
 the process of moving permanently from one social group to another social
 group. The majority of dispersers were identified using GPS (SI Fig. 1)
 and/or trapping records. Four dispersers were identified using genetic
 data (SI Text 1). Where we had GPS records for dispersal events,
 trajectory maps, which show the sequence of GPS locations, were made using
 the Point to Line tool in ArcMap (SI Figs. 2.1-2.13). When a badger was
 not wearing a collar during the dispersal event itself, maps were made for
 pre- and post-dispersal periods, or of exploratory forays (SI Figs.
 2.14-2.16). Social group territory boundaries were mapped in ArcMap
 (Gaughran 2018) and the centroids were used to estimate the straight-line
 distance moved by dispersers. We estimated the number of social groups
 between the new and old territories by counting how many social groups
 were intersected by the straight line. If a badger moved to an adjacent
 social group, this parameter was recorded as zero. Some collared badgers
 dispersed outside the study area, so the total number of social groups
 crossed was unknown. Accordingly, the straight-line distance between the
 centroid of their original territory and the centroid of the polygon
 encompassing their GPS locations in their new location was calculated. We
 divided the straight-line distance by 1313 m as this was<i>
 </i>the mean distance between main setts in the study area (SD ± 455
 m), to estimate the number of social groups crossed by the
 badger. A second
 analysis was also conducted to describe the trajectory each badger took
 during dispersal, considering each day’s travel rather than just the start
 and end points of the dispersal event. The creation of trajectories using
 the GPS locations of badgers allowed us to estimate much more accurately
 the distances travelled during the process of dispersal. Although these
 distances are underestimates, as they are derived from the straight-line
 distances between only four GPS locations a night, they are less
 negatively biased than straight-line distances between social groups. We
 counted the number of territories crossed by these trajectories. Where
 trajectories fell outside the known study area, we applied a 1.3
 km<sup>2</sup> grid (based on the mean distance between main
 setts) to the map and used the grid squares crossed by trajectories as a
 proxy for estimating the number of territories crossed by the dispersing
 badgers.