Two months ago, the government-advice body Natural England approved further licensed badger culls in parts of the United Kingdom in 2015. The aim is to reduce local badger densities by at least 70% to prevent the spread of tuberculosis (TB) to cattle (see go.nature.com/iiutvj). On the basis of the government's badger-population estimates, we calculate that these culls are unlikely to achieve the necessary reduction.
The latest minimum cull numbers derive from the lower 95% confidence bounds on population size estimates. For example, licensees in Dorset are required to kill at least 615 badgers in a population estimated at 879–1,547 animals (95% confidence interval). Killing this number would give an estimated population reduction of between 39.8% and 70% (95% confidence interval).
Equivalent confidence intervals for the 2015 (third annual) Somerset and Gloucestershire culls are, respectively, 50.8–70% and 54–70% relative to the baseline population estimates. It is therefore unlikely that a 70% or greater reduction can be attained by these minimum cull numbers, assuming that the population estimates are accurate.
Evidence from a randomized controlled trial shows that better prospects for the control of cattle TB are offered by badger populations that are either reduced by more than 70% or left undisturbed — and potentially vaccinated (C. A. Donnelly et al. Nature 439, 843–846; 2006). The choice depends on a range of epidemiological, economic, social and ecological factors.