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Trewby et al (2014) Impacts of removing badgers on localised counts of Hedgehogs

Title: Impacts of removing badgers on localised counts of Hedgehogs, PLOS One DOI: 10.1371/journal.pone.0095477, 2014

Authors: I.D. Trewby, R. Young, R.A. Macdonald, G.J. Wilson, J. Davison, N. Walker, A. Robertson, C.P. Doncaster & R.J. Delahay

Country: UK

Background to study

An experimental test using the Randomised Badger Culling Trial (RBCT) to investigate the effects of reducing badger abundance on populations of hedgehog.

Method

  • Longitudinal hedgehog surveys (4-6 years) were conducted within four of ten areas where RBCT was being implemented (Herefordshire, Wiltshire, Staffordshire/Derbyshire, Cotswolds).
  • Within each area, three matched trial areas (~100 km2) of similar badger density had been randomly assigned proactive badger culling, localized reactive culling following TB in cattle or experimental controls with no badger culling. Hedgehog surveys were carried out in the same areas to enable comparisons between areas where badger densities reduced and where they remained unchanged.
  • Hedgehog surveys consisted of spotlight surveying 12 fields (9 pasture and 3 amenity grassland) between 23.00 and 03.00 three times each year. Each hedgehog was given a temporary marking and the number of different hedgehogs recorded per area per year was used as a relative index of abundance.
  • The influence of treatment type (badgers culled vs. badgers not culled) and year of culling on the relative density of hedgehogs was assessed using regression analyses.

Key results

  • In amenity grassland, hedgehog density nearly doubled in badger culling areas compared with no culling areas with mean hedgehog density ranging from 0.2-1.0 and 0.9-2.4 hedgehog ha-1 where badgers were not culled and where they were culled, respectively.
  • Results suggest that lethal control of badger populations may result in changes to the structure of the wider predator community, including hedgehogs and whilst the increase in numbers may reflect a change in behaviour rather than density of hedgehogs, radio-tracking studies in one of the trial areas found that hedgehog ranging patterns did not alter in response to badger culling. Therefore, the increase in hedgehog numbers is likely to reflect a true increase in hedgehog density resulting from reduced predation and higher survival.
  • In pasture fields, only 12 individual hedgehogs were found in 22% of fields which prevented statistical analysis on the influence of badger culling on hedgehogs in this habitat type.

Key messages to landowners and managers derived from these results

  • Amenity grasslands have a high ecological value for hedgehogs and thus management of these areas for hedgehogs needs to be a priority.
  • Management of badger populations in the UK can have important ecological consequences on hedgehogs and other species which may result in changes at lower trophic levels and thus should be an important consideration when addressing future management of bovine TB in the UK.   

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