Wild pig culling can backfire on disease control if it increases movement and contacts

Intensive culling does not always reduce disease risk in the way managers expect. A new US study shows that trapping and toxic baiting can substantially increase wild pig movement and contacts between surviving animals, potentially facilitating pathogen spread. By contrast, short, intensive aerial culling caused comparatively little behavioural disturbance.

The study monitored 122 GPS-collared wild pigs in Texas and compared three removal methods: aerial operations, trapping and an experimental toxic bait. Researchers used a before–after, control-impact design to measure changes in movement and social contacts.

Trapping increased movement and contacts

The strongest behavioural effects followed trapping. During trapping, wild pigs increased the distance they travelled by 51.4%, compared with a 9.7% decrease among controls. After trapping, treated animals still moved 33.6% farther than before. Contacts also increased. During trapping, contact duration rose by 147.1% in treated pigs, while it fell by 58.2% in controls. The number of different pigs contacted also increased.

For infectious disease control, that matters: more movement can increase spatial spread, while more contacts can create additional opportunities for transmission.

Aerial culling disturbed behaviour less

Aerial operations produced a very different response. They lasted only three consecutive days and caused minimal changes in movement or social contact, apart from a reduction in movement speed relative to controls. The three methods also differed substantially in population reduction. In the study areas, trapping reduced wild pig density by 89.9%, aerial culling by 51.8%, and toxic baiting by 23.3%.

Direct relevance to African swine fever

The study is particularly relevant to African swine fever preparedness in countries such as the United States and Australia, where rapid elimination of an infected wild pig population could become necessary after an incursion. For ASF, however, one important trade-off remains: aerial culling may disturb surviving pigs less, but carcass recovery can be poorer than with trapping. Since infected carcasses are a major source of ASFV transmission, leaving carcasses in the environment could undermine control.

The authors therefore suggest that combined strategies may be more effective, for example, using aerial operations first to reduce population density rapidly, followed by ground-based methods to improve carcass recovery and eliminate remaining animals.

Culling intensity alone is not enough: the method used can reshape animal behaviour and therefore alter disease transmission risk. Wildlife disease control must account not only for how many animals are removed, but also for what the survivors do afterwards.