31st May 2012
Two leading scientists have spelt out likely consequences of uncertainties in accounting for the proportion of badger populations culled. A letter by Prof. Christl A. Donnelly of Imperial College, London and Prof. Rosie Woodroffe of the Institute of Zoology, London appears in the current issue of the international science journal Nature.[1].
David Williams, Chairman of the Badger Trust, said: “We welcome this work which further undermines the Coalition Government’s statement that the cull would be science led. It also serves to endorse our view that the results of free shooting cannot be accurately estimated [2]. The letter also underlines the crucial points that killing too few would risk making matters worse while the alternative of killing too many risks wiping out the entire local population.
The extra cost to the agricultural industry of sufficiently detailed badger population surveys has not been allowed for, further undermining any estimated benefits to farmers”.
Under the heading “Reduce uncertainty in UK badger culling” the letter notes that the Coalition Government’s plans to license badger culling for the control of tuberculosis (TB) in cattle were controversial whereas, by contrast, the Welsh Government decided to vaccinate badgers rather than kill them.
The letter continues: “Extensive badger culls may reduce cattle TB (C. A. Donnelly et al. Nature 439, 843–846; 2006), but complex disease dynamics mean that killing too few animals can actually increase it (C. A. Donnelly et al. Nature 426, 834–837; 2003). However, culling too many badgers risks local extinction, contravening the Bern Convention on the Conservation of European Wildlife and Natural Habitats. Natural England, the agency monitoring the cull, will therefore be required to set minimum and maximum cull numbers for each licence. But the effects are difficult to predict.“Targets for licences will draw on regional estimates of badger abundance, but badger densities are uncertain, owing to their secretive behaviour. Surveys of TB-affected areas in Gloucestershire, where one of two pilot culls is planned, indicate a mean density of 3.3 badgers per square kilometre, with a 95% confidence interval of 2.4–4.6 and substantial local variation (D. Parrott et al. Eur. J. Wildl. Res. 58, 23–33; 2012).
“As well as measurement uncertainty, there will be random (Poisson) variation about mean densities, and binomial variation around mean capture probabilities. These three sources of uncertainty together mean that licensed culling of 344 badgers — intended to represent 70% of badgers within a 150-km2 area — could eradicate anywhere between 51% of the resident badger population (risking an increase in cattle TB) and 100% (risking a breach of the Bern Convention).
“This uncertainty cannot be eliminated, but could be reduced by detailed badger surveys before and after each cull. This would increase culling costs, which are already projected to exceed the financial benefits for farmers”.
[Signed] Christl A. Donnelly MRC Centre for Outbreak Analysis and Modelling, Imperial College London,
London, UK. c.donnelly@imperial.ac.uk Rosie Woodroffe Institute of Zoology, Regent’s Park, London,
UK. Competing financial interests declared; see
http://www.nature.com/nature/journal/v485/n7400/full/485582a.html (author information).
NOTES
[1] http://www.nature.com/nature/journal/v485/n7400/full/485582a.html