Effect of culling on individual badger Meles meles behaviour: potential implications for bovine tuberculosis transmission.
Culling wildlife as a form of disease management can have unexpected and sometimes counterproductive outcomes. In the UK, badgers Meles meles are culled in efforts to reduce badger-to-cattle transmission of Mycobacterium bovis, the causative agent of bovine tuberculosis (TB). However, culling has previously been associated with both increased and decreased incidence of M. bovis infection in cattle. The adverse effects of culling have been linked to cull-induced changes in badger ranging, but such changes are not well-documented at the individual level. Using GPS-collars, we characterized individual badger behaviour within an area subjected to widespread industry-led culling, comparing it with the same area before culling and with three unculled areas. Culling was associated with a 61% increase (95% CI 27%-103%) in monthly home range size, a 39% increase (95% CI 28%-51%) in nightly maximum distance from the sett, and a 17% increase (95% CI 11%-24%) in displacement between successive GPS-collar locations recorded at 20-min intervals. Despite travelling further, we found a 91.2 min (95% CI 67.1-115.3 min) reduction in the nightly activity time of individual badgers associated with culling. These changes became apparent while culls were ongoing and persisted after culling ended. Expanded ranging in culled areas was associated with individual badgers visiting 45% (95% CI 15%-80%) more fields each month, suggesting that surviving individuals had the opportunity to contact more cattle. Moreover, surviving badgers showed a 19.9-fold increase (95% CI 10.8-36.4-fold increase) in the odds of trespassing into neighbouring group territories, increasing opportunities for intergroup contact. Synthesis and applications: Badger culling was associated with behavioural changes among surviving badgers which potentially increased opportunities for both badger-to-badger and badger-to-cattle transmission of Mycobacterium bovis. Furthermore, by reducing the time badgers spent active, culling may have reduced badgers' accessibility to shooters, potentially undermining subsequent population control efforts. Our results specifically illustrate the challenges posed by badger behaviour to cull-based TB control strategies and furthermore, they highlight the negative impacts culling can have on integrated disease control strategies.