TB: The science behind the decisions

More than three decades ago ecologists started monitoring badgers in an area of farm and parkland, near Stonehouse, Gloucestershire.

The vicinity was considered to be a ‘hotspot’ at a time when the incidence of bTB had been greatly reduced in the UK cattle population and prevalence in wildlife was reasonably unknown - but little did scientists know how important their work at Woodchester Park would become in later years, when the disease in both cattle and badgers exploded.

The tracking and testing of badgers has continued since the mid-1970s, making the park a completely unique scientific resource. The experts working there are regularly asked to provide Defra with information to aid bTB policy decisions.

Fera (the Food and Environment Research Agency, part of Defra) oversees Woodchester Park and the man running Fera’s wildlife and emerging diseases programme is Robbie McDonald.

Public perception

He is quick to point out he is not emotionally attached to the badgers he and his colleagues observe, saying the creators of Wind in the Willows and similar books and films ‘have a lot of answer for’ in terms of the general public’s perception of cuddly, friendly creatures.

“We have to take the emotion out of it,” he says. “Where are we now? What are the facts of the situation? What is the way forward?”

His answers to those questions are entirely based on the work done at Woodchester Park - and farmers keen to see a badger cull will be disappointed to learn Mr McDonald does not believe the science supports that route.

Researchers have access to 10sq.m, most of which is parkland owned by the National Trust and the rest neighbouring farmland. There are 24 established badger groups within that area and currently around 200 individuals.

Mr McDonald says this is reasonably high and numbers vary considerably year-on-year depending on the amount of food available. As a general rule only one female in the social group will breed every 12 months, although two may breed in a plentiful year and none when food is hard to come by.

Litters can be up to 10 cubs but usually only two or three survive infancy. Average life expectancy for those that do reach maturity is three to four years, although five to six years is ‘not exceptional’ and 10 years possible.

Because of the link between breeding and food availability there is no particular relationship between the number of badgers and sett size. Mr McDonald says they see peaks and troughs of numbers but not ‘never-ending growth’ of populations at Woodchester Park, as food does not increase. But, he argues, if there was a cull more females would breed more regularly, as there would be the same amount of feed for fewer animals.

Mr McDonald says social groups can vary from two to 22 animals, although six would be about the average, apart from in South West England where larger groups are more common.
Research at Woodchester Park has shown social groups to be fundamental to animal behaviour. A lot of badgers spend their entire life within the same group, meaning most of them will be related. When they do move they tend to go to another group, rather than establish a new sett, and so setts are often many years old. The main sett, the centre of a social group, can vary in size with smaller, outlying setts around it.

This means a group will not give up its home readily and is dedicated to defending the area. There are rigid boundaries around setts, which Mr McDonald says are sometimes clearly visible because badgers spend so much time ‘patrolling’ the perimeter.

Radio tracking

With the use of radio tracking equipment and special collars the researchers know individuals interact a lot within their own social group but rarely with other groups. Mr McDonald says badgers will know of other nearby groups but rarely venture over boundaries, unless they became aware of a change.

This is one of his biggest arguments against culling, as he says the disappearance/reduction of one group will cause badgers from another group to go and ‘investigate’ the vacated area, taking their diseases with them or picking up new infections in the process.

“Transmission of disease reduces where there’s a stable social system,” he says, explaining that disease peaks are usually seen the year after a period of upheaval and that it takes a long time to return to a stable situation again.

Therefore, the benefit of culling a population is outweighed by the detrimental affect on neighbouring populations. He says a huge number of badgers would have to be killed to make a difference and while it is cheap and easy to trap and exterminate animals in the early days of a cull it gets harder and more expensive as time goes on.

At Woodchester Park the level of TB has gone up and down over time, and this does not appear to be linked to the number of animals. This is because some infected badgers stop and start shedding the disease (the reason/timing of this is unclear) and there is, of course, some natural movement between social groups.

It is mostly males that decide to try and join a new social group, usually because a nearby sett has lost numbers (for example, if some have died from disease or road kill) or food is in short supply.

But Mr McDonald argues in usual circumstances, when culling has not taken place, transmission between cattle and badgers is more common than between different badger groups. Currently there are setts at Woodchester Park with infected animals while neighbouring setts are TB free.

Some individuals are more prone than others to range further and investigate new areas (such as farm buildings). Interestingly, more badgers caught in farm buildings have bTB than those caught nearer their sett - but researchers do not know if those badgers have picked up TB because they move around more or if they move around more because they have TB.

Good practice

“But it doesn’t really matter which one it is - don’t worry about that, just find a way to stop them getting in,” says Mr McDonald, arguing it is ‘good practice’ to keep all wildlife away from feed as much as possible for all types of bacteria, not just Mycobacterium bovis. When infected badgers excrete M.bovis in farm buildings it is unclear how long the bacteria can survive, although it is known to thrive in damp, wet, dark areas.

Mr McDonald says all wildlife is ‘opportunistic’ so while badgers enjoy wet pasture with lots of worms they will eat whatever is readily available, whether they stumble upon unsecured farm buildings, carrion, insects or nests of rabbits and bees; Mr McDonald will not comment on if they would take small lambs.
Badgers do seem to have a preference for maize, but he says he cannot recommend farmers stop growing it, as badgers will readily eat other cereal crops if they become available.

Woodchester Park

• The badger ecology project at Woodchester Park, Stonehouse, Gloucestershire, started in mid-1970s, making it the longest running badger research programme in the UK
• The area monitored in the project covers 1,000 hectares (2,471 acres), a large chunk of which is owned by the National Trust
• Work done at the park now comes under the Government’s Food and Environment Research Agency (Fera), which was previously the Central Science Laboratory (CSL), Fera advises the Government on many topics, including bTB
• Fera employs around 900 people, 25 of whom work at Woodchester Park as part of the wildlife and emerging diseases programme
• Bovine TB dominates the wildlife and emerging diseases programme, although issues such as rabies and sheep scab are also included
• Current work done with the badgers includes three main areas:
  1. The ecology study, which has been ongoing since the 1970s
  2. Vaccine work, including testing the safety of the injectable vaccine and training people to administer it; utilisation of an oral vaccine is also being considered
  3. Biosecurity research looking at affordable and effective ways to keep badgers out of farmyards

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