A comparison of breeding bird populations inside and outside of European Badger Meles meles control areas

Abstract

Capsule: Analyses of survey data reveal no clear effects of the removal of European Badger Meles meles, a top predator in Great Britain, on bird populations. Aims:To investigate the effects of licensed Badger culling on bird populations in southwest England using ongoing monitoring data.Methods: Breeding Bird Survey data, were used to compare population growth rates inside and outside Badger cull areas in southwest England over a five-year cull period (2013)(2014)(2015)(2016)(2017), following a five-year baseline period (2008)(2009)(2010)(2011)(2012). Comparative analyses of population growth rates of ground-nesters and of other species tested for potential influences of badger predation. We also compared species richness and diversity before and during culling in treatment and control areas.Results: Most results were non-significant (46 of 58 species) but, where population growth rates were significantly different, they were higher for five species, and lower for seven, in cull areas. Ignoring significance, 33 population trends were more positive and 25 more negative within Badger cull areas.However, ground-nesting species more likely to be sensitive to Badger predation, as a group, were not more responsive. Species richness declined significantly between pre-culling and culling periods in all areas, but diversity was unaffected and these metrics showed no spatial effects of culling. Conclusion:There was no evidence for broad or consistent effects that support the existence of causal effects of Badger removal. Results for Skylark and Lapwing suggested positive and negative culling effects, respectively, for these potentially sensitive species. Management and subtle habitat composition differences between study areas, and small sample sizes, may have limited power, but there was no evidence that this affected inference. Monitoring and evaluation must continue as culling continues and is expanded, potentially increasing study power. Future research could also evaluate the potential ecological and demographic mechanisms behind Badger removal effects on birds. AHVLA (AnimalHealth and Veterinary Laboratories Agency) 2014. The efficacy of badger population reduction by controlled shooting and cage trapping, and the change in badger activity following culling from 27/08/2013 to 28/11/2013. Report to Defra.

Breeding bird population trends during 2013–2019 inside and outside of European badger control areas in England

“…Accounting for the false discovery rate across all tests, there was just one positive and six negative associations in the Badger Presence Analysis, and no positive and one negative association in the Badger Removal Analysis. These findings contrast with Kettel et al., (2021), equivalent to the Badger Presence Analysis, which indicated a negative effect of treatment in only 25 of 58 species examined. However, the present study updates Kettel et al.…”

“…By defining the status of each BBS square on a per-year basis as inside or outside a treatment area (as in Kettel et al, 2021; Badger Presence Analysis), we were able to include squares where treatment began in different years (2013)(2014)(2015)(2016)(2017)(2018)(2019) in single models (Freeman & Newson, 2008). Similarly, true culling intensity data (Badger Removal Analysis), 0 represented no culling having taken place, and x > 0 represented a normalized number of badgers removed from that 1-km square.…”

“…The modelling approach is an extension of Freeman and Newson (2008) and has been used with BBS data in Baker et al (2012) and Kettel et al (2021). A log-linear approach was used to estimate the effect of badger control on individual species' population growth rates, and spatio-temporal covariates were incorporated into models.…”

“…Here, we present the results of a new study extending the work of Kettel et al. (2021), using data from two additional culling years, further regions under culling treatment and a measure of local cull intensity, all of which should provide an increase in study power over that available in Kettel et al. (2021), such as by allowing a minimum sample size that is double that used previously.…”

“…These scheme data, in conjunction with information on culling presence and intensity, have the potential to reveal whether badger removals are affecting breeding bird populations. Here, we present the results of a new study extending the work of Kettel et al (2021), using data from two additional culling years, further regions under culling treatment and a measure of local cull intensity, all of which should provide an increase in study power over that available in Kettel et al (2021), such as by allowing a minimum sample size that is double that used previously. This study, therefore, provides an important further assessment of a high-profile policy initiative, using the best data that are available.…”