Underground and Underestimated: The Trouble with Counting Badgers

As DEFRA have begun their latest national badger population count, Badger Trust digs into why keeping track of these elusive creatures proves to be so difficult.

Why do we need to count wildlife?

Keeping track of populations is really important when managing wildlife. If we don’t know the size of populations, we can’t see how they change in response to different factors or human interventions. 

Ideally, wildlife populations should be counted regularly, allowing us to spot any changes early, and intervene if we see anything concerning. For badgers, there have been national badger surveys in England and Wales on three occasions – the first in the 1980s (Cresswell et al., 1989), then 1990s (Wilson et al., 1997), and most recently between 2011-2013 (Judge et al., 2014; 2017).

This means that it’s been over 12 years since the last surveys finished, and so we are well overdue for an updated count. This count is even more crucial, as culling in England over the last decade has removed over half (51.1%) of that last estimated population (58.5% of the estimate for England). This new estimate will therefore tell us just how much of an impact the cull has had on the overall population. 

But of course, counting wildlife that is notoriously shy, elusive and nocturnal is not without challenges. Frustratingly for surveyors, badgers simply refuse to come out of their setts and stay still while they are counted, so researchers have had to come up with ways that get an idea of population sizes without having to count every single badger. 

How do we count badgers? 

Badgers are, by nature, very secretive and nocturnal animals. As endearing and special as this makes them, it also makes them very difficult to count. 

We can, however, very clearly see the signs they leave behind in the world, whether it’s paths, latrines, paw prints or setts. Using these signs, along with knowledge of badger ecology, scientists can make estimates indirectly. For example, studies have estimated populations based on counting setts or field signs (Tuyttens et al. 2001; Sadlier et al. 2004), counting culled badgers in closed areas (Sleeman et al. 2009), or genetic studies (Scheppers et al. 2007; Jacquier et al. 2021). 

“To count the number of badgers in a given area, we need two pieces of information: the number of badger clans, and how many badgers live in those clans.”

DEFRA’s survey methods use two pieces of information to directly count the number of badgers in a given area: the number of badger clans, and how many badgers live in those clans. Theoretically, if we know this information, we can estimate the overall number of badgers living in an area. 

Estimating the number of badger clans is quite simple – each clan holds a territory, within which there will usually only be one main sett, which will be the main hub of activity for the clan. Experienced surveyors can identify these main setts, and we can fairly confidently say that the number of main setts is equal to the number of badger clans in an area. 

Estimating the number of badgers in a clan is where it gets trickier. There are currently no sure-fire ways to determine how many badgers live in a main sett. Some main setts with three entrances may be home to 14 badgers, whereas huge setts with 100 entrances may only house two or three badgers. 

Previous studies, including the DEFRA surveys, have estimated the number of badgers in a sett using genetics (Judge et al., 2017), but this method is time-consuming and expensive. As a result, very few setts can be surveyed to provide an average estimate, and this causes a lot of uncertainty in the final numbers, which we will discuss more below. 

How can we scale this up nationally?

So using the above methods, we can be confident we can get an idea of the number of badger clans in an area, and potentially the size of those clans, to give us an overall count, or ‘abundance’. However, we can’t realistically survey every single inch of the country to get a national population count. So, we take a smaller survey area and extrapolate this information across the rest of the country.

For example, if this is our study area, it is likely that the total number of setts found on the northern half of our woodland below would equal the number on the southern half. So we could just survey the northern half and then double our findings to get an overall estimate. 

In practice, scientists will also consider any factors that might skew the population to one particular place, such as habitats, regions or terrain. This is why we need to survey as many varied places as possible to make sure that our results are as accurate as they can be when the estimates are scaled up to larger areas. 

So how accurate are the DEFRA survey results? 

DEFRA’s new population survey began this year, following the methods outlined above. While no method is perfect, this approach is one of the most established and comparable to the previous estimates, despite being considerably uncertain. 

We often talk about uncertainty in population estimates, but where does that uncertainty come from? It comes from the sampling methods applied - as we discussed earlier, we are basing our estimate on part of the whole study area, so there is inevitably some uncertainty, which is where the 95% confidence interval comes in.

The last estimate was 485,000 badgers in England and Wales – scientists are 95% confident that the true number of badgers is somewhere between 391,000 - 581,000 badgers. 

The last estimate was 485,000 badgers in England and Wales, with a 95% confidence interval of 391,000–581,000. That means, based on the data collected, the scientists are 95% confident that the true number of badgers is somewhere between 391,000 - 581,000 badgers. It’s a scientific way of saying, ‘We can’t know exactly, but this is a reliable estimate with a margin of uncertainty’. 

This 95% confidence interval is relatively wide (190,000 badgers), suggesting that there is quite a lot of uncertainty. While this is still useful to understand overall population size, it also shows that precise badger population estimates should always be interpreted carefully. 

In the last survey, a major source of uncertainty was the clan size estimates.

The map below shows the estimated average clan sizes in each of the Land Classification Groups (regional habitat divisions that DEFRA use in their surveys). We have also indicated the number of social groups that were surveyed to get that average estimate - in some areas as few as 3 groups! 

Unfortunately, these estimates from 2011-2013 surveys are likely no longer valid in many parts of England, as culling is likely to have reduced average group sizes, and we know that culling impacts social group dynamics (Woodroffe et al., 2006; Carter et al., 2007). 

In order to get the most accurate estimate for the total badger population and reduce that uncertainty, DEFRA needs to ensure that they calculate their average clan sizes across as many badger clans as possible. 

Another major limitation of DEFRA’s previous surveys is that they did not include urban habitats, where badgers are increasingly found. 

What are the implications of poor population monitoring? 

We have looked at why counting badgers is so hard, and why the estimates we get are so uncertain. DEFRA have said they have monitored badger populations when deciding on minimum and maximum cull figures but are unable to tell us population estimates for each area. How then, could badger populations possibly have been monitored effectively over the last decade of culling?  

DEFRA told us that they monitor badger populations when deciding on minimum and maximum cull figures, but are unable to tell us population estimates. 

Furthermore, Natural England often cites ‘healthy badger populations’, without the evidence to back it up. In reality, no one knows how many badgers there are in England and Wales, and even when DEFRAs study is published (likely 2027-2028), the results need to be interpreted carefully, given the uncertainty that comes with these methods. 

Additionally, the proposed changes to the Protection of Badgers Act within the Planning and Infrastructure bill further highlight the need for more robust population monitoring, as Natural England will need to determine the risk of a development on the badgers, in line with Schedule 6:  

P&IB Schedule 6. Part 2. (7)(b): “Natural England or the Secretary of State must not grant a licence under this section in relation to an area in England unless satisfied that the grant of the licence is not detrimental to the survival of any population of badgers”

Ultimately, if we want to make responsible decisions about how we manage and protect badgers, we need to start with good data. That means counting them properly, across all types of habitats, using methods that reflect the true complexity of badger ecology. Without this, talk of “healthy populations” or “evidence-based” policy is unfounded. As DEFRA’s latest survey continues, it’s vital that the results are interpreted with care, transparency, and context. Badgers may be underground and elusive, but that doesn’t mean they should be overlooked. If we want to ensure they have a future on our landscape, we need to make sure they’re not lost in the margins of poor monitoring and uncertain estimates.