What impact do badgers have on other wildlife?
The badger population in England and Wales has increased in recent decades (Judge et al. 2014, Judge et al. 2017), although in cull areas in England there are likely to be declines. Badgers are our ‘largest predators’ and although their diet is mainly invertebrates (worms, snails etc) and plant matter, badgers will eat other mammals, amphibians and birds. Changes in badger numbers therefore have the potential to impact other species and this is an issue which receives a lot of attention in the ongoing debate around badgers and bovine TB. Much of the discussion is focused on hedgehogs and ground nesting birds, partly because while badger number have increased in recent decades, these species have undergone significant declines, and many people suggest these changes are connected.
So are badgers to blame for falling hedgehogs and ground nesting birds? And will culling badgers lead to changes in other species?
To address these questions I have produced a two-page fact sheet which can now be found on the factsheets page of this website, the TBhub and can also be downloaded by clicking the image below. This factsheet summarises the published literature on relationships between badgers with hedgehogs, ground nesting birds and also foxes.
Summarising these topics into two pages is always a challenge and it is not possibly to include every study or elaborate on every point. In addition to the contents of the fact sheet, below is some more details on hedgehogs and ground nesting birds.
Additional points on the effect of badger culling on hedgehogs.
Several studies have shown a negative association between badgers and hedgehog numbers (ie hedgehog numbers are lower in areas with higher badger activity/density), but the best evidence for the effects of badger culling on hedgehogs comes from this paper which I co-authored from Trewby et al. (2014)
Trewby, I.D., Young, R., McDonald, R.A., Wilson, G.J., Davison, J., Walker, N., Robertson, A., Doncaster, C.P. & Delahay, R.J. (2014) Impacts of Removing Badgers on Localised Counts of Hedgehogs. PLoS ONE, 9.
This paper involved conducting nocturnal spotlight surveys for hedgehog in RBCT cull areas. Hedgehog numbers were counted in pasture fields and amenity grassland (playing fields, village greens, parks etc), which is a key habitat for hedgehogs. Analysis of the data found that in cull areas there was a significant increase in hedgehog numbers in amenity grassland (hedgehog numbers roughly doubled), while in cull areas there was no such increase. This paper demonstrates that badger culling is likely to benefit hedgehog numbers. However, there are a couple of important points to consider:
- This increase was in amenity grassland only (essentially non-farmland). In pasture fields there were too few sightings of hedgehogs to conduct meaningful analyses, even after culling.
- The effect was significant (hedgehogs did increase), but the effect was quite variable (look at the figure).
So while culling does seem to benefit hedgehogs, it does not guarantee a doubling of hedgehog numbers across the whole cull area. Instead there is evidence for a variable increase in a specific habitat types.
Additional points on the causes of hedgehog declines
A recent study was published in nature scientific reports partly addresses this question.
Williams, B.M., Baker, P.J., Thomas, E., Wilson, G., Judge, J. & Yarnell, R.W. (2018) Reduced occupancy of hedgehogs (Erinaceus europaeus) in rural England and Wales: The influence of habitat and an asymmetric intra-guild predator. Scientific Reports, 8.
The study involved using tracking tunnels to survey for hedgehogs in areas where badger activity was also quantified in the recent national survey (Judge et al. 2014). The results found that hedgehog activity declined with increasing badger activity, consistent with badgers have a negative impact on hedgehogs. But this is not the whole story…
This study only found hedgehog activity in 22% of areas surveyed, suggesting hedgehogs were absent from a large part of the English countryside. The analyses also found that even in areas with no badgers present, hedgehogs were only present in 31% of areas surveyed, meaning around 70% of areas had no hedgehogs (even if there were no badgers recorded). This suggests that is a combination of factors affecting hedgehogs (ie badgers are important, but they are not the only factor) and the authors suggest that wider habitat changes are responsible. To quote the authors…..
“In summary, much of the blame for the perceived hedgehog decline in the UK has focussed upon the impacts of badgers as both a competitor but especially as a predator (e.g.34). Although our findings support the negative relationship between the two species, this relationship is likely to be complex, involving elements of predation, competition and avoidance; in the context of the latter, areas associated with human habitation appear to mitigate against some of the negative effects of badgers. At the same time, however, rates of hedgehog occupancy were low even in the absence of badgers, and badger setts were not recorded in 47.9% of sites surveyed. Collectively, this suggests that intensive management of rural areas is negatively impacting both these generalist terrestrial insectivores”
To further quote the authors….” the combined effects of increasing badger abundance and intensive agriculture may have provided a perfect storm for hedgehogs in rural Britain, leading to worryingly low levels of occupancy over large spatial scales.”
Additional points on badgers and ground nesting birds
The decline of farmland birds in the UK and the rest of Europe has been extensively studied for decades and there are a number of great reviews of the subject (see Donald, Green & Heath 2001; Newton 2004). Predation can be a factor for some species, but changes in the wider countryside are widely believed to be the primary factors driving declines in birds, as well as wildflowers, insects and other animals. For a summary of the factors affecting farmland birds see this page from the RSPB. For a summary of the factors driving changes in UK wildlife see the State of nature report, compiled by a large number of conservation and research organisations.
The British Trust for Ornithology (BTO) also has records of population trends, along with summaries of likely causes of population changes on the website ‘bird trends’, for example see this page on skylarks.
I stress that by mentioning the above I do not aim to ‘blame farmers’ for these changes, as changes in farming practices and the wider countryside are driven by many economic, social and political factors. There are also many good examples (contained in the report above) of how certain farming practices can have huge benefits for wildlife.
The above reports, papers and sources relate to large landscape changes in bird populations. As stated in the summary sheet there will be examples of localised areas (such as nature reserves or breeding colonies) where badgers, foxes and other predators can have impacts on breeding birds such as terns. This in part is because many bird species (particularly ground nesting species) are confined to small protected areas or fragments of suitable habitat, making them vulnerable to predators.