Dispersal patterns in a medium‐density Irish badger population: Implications for understanding the dynamics of tuberculosis transmission

Abstract

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 7 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 traveled 308 km and passed through 22 different territories during dispersal. Knowledge of badgers' ranging behavior during dispersal is crucial to understanding the dynamics of TB transmission, and for designing appropriate interventions, such as vaccination.

Extra Territorial Excursions by European badgers are not limited by age, sex or season

“…Although our dataset excluded those badgers which were in the process of dispersing successfully (see Methods), long ETEs may have been produced by unsuccessful dispersal attempts. This idea is supported by the finding that most dispersing females begin their dispersal in January or February 6 . While relatively few females made ETEs in January (Fig.…”

“…5), we believe these long ETEs were made by non-breeding females making unsuccessful dispersal attempts, as breeding females are aggressive towards non-breeding females during pregnancy and while suckling cubs 8,30 . This idea is supported by the finding that most dispersing females begin their dispersal in January or February 6 . While relatively few females made ETEs in January (Fig.…”

“…Within November, it was the older females which invested most heavily in ETEs ( Figure S8). Since male badgers tend to disperse over shorter distances 6 , older females were likely to be related to many of the neighbouring males. To avoid inbreeding, the older females would, therefore, have needed to undertake longer ETEs to find less closely-related males.…”

“…Several territorial mammals exhibit pre-dispersal prospecting 20,21,26,52,54,55 . While we excluded badgers, which were later found to be in the process of dispersing, from this analysis (see Methods), we did see evidence of pre-dispersal prospecting by badgers in our study area 6 . Since successful dispersers were excluded from our analyses, any pre-dispersal prospecting which was captured in this study must have been made by badgers which were unsuccessful in their dispersal attempts.…”

Badger territoriality maintained despite disturbance of major road construction

“…Badgers were categorised into one of three ranging status categories - traditional rangers, dispersers or super-rangers - on the basis of their behaviour at the time that the GPS location was recorded. Dispersers (confirmed retrospectively) were badgers in the process of moving permanently from one social group to another social group (Gaughran et al . 2019).…”