Bat bridges and signs on nests: nature conservation’s epic fails – and how to avoid them

<span>The pipistrelle bat wasn’t fooled by a bridge pretending to be a tree.</span><span>Photograph: Hugo Willcox/Foto Natura/Mind</span>
The pipistrelle bat wasn’t fooled by a bridge pretending to be a tree.Photograph: Hugo Willcox/Foto Natura/Mind

It seemed like a good idea at the time: build metal bridges over busy roads and bats would confuse them with trees, it was argued. They would then try to soar over the pylons and, having been tricked into flying higher than normal, would avoid being struck by lorries and buses travelling on the road below. A widespread wildlife problem for the UK would be solved at a stroke.

It was a persuasive vision, and to realise it, a total of £2m was spent on building 15 bat bridges across Britain, from Cumbria to Cornwall. “However, there was one problem,” said Professor William Sutherland of the Conservation Science Group at Cambridge University. “The bridges didn’t work.”

Conservation researchers found that bats – from tiny pipistrelles to common noctules – were unimpressed by the metal gantries which they were supposed to confuse with trees. As a result, they continued to fly at low, unsafe heights over busy roads. “The trouble was the plan was based on faith and not on science,” added Sutherland.

It is an issue that is still too common in conservation today, he argues. Evidence is either gathered too rarely or used ineffectively, a process that is leading to faulty decision-making and wasted resources. His group has been set up to halt this trend and to ensure that scientific evidence is used properly before attempting to boost biodiversity or protect an endangered species. Good ideas must be backed by good evidence before being adopted widely, it is argued.

As an example of proper, evidence-based approaches to conservation, they point to the story of the large blue butterfly. Phengaris arion was virtually extinct in the UK by the end of the last century but was successfully reintroduced using painstaking care to assess the real causes of its decline.

The large blue relies on red ants to raise its young. Its larva is parasitic and feeds on red ant grubs. “The crucial discovery – made by the Oxford ecologist Jeremy Thomas – was that large blues only sought out one species of red ant, Myrmica sabuleti, and it was declining in numbers.

“However, by changing grazing practices on grasslands where M sabuleti lived, its fortunes and numbers were restored, and in turn so were those of the large blue. This was achieved by understanding the threat, testing solutions and then acting upon the results.”

Sutherland pointed to the strict rules that are used in gathering evidence before actions are taken in medicine, the aviation industry and building design. “In these fields, a strict set of procedures – at the beginning of an operation or at take-off – are followed before any action is taken. That is what we need to do in conservation before we launch a project or take action. We have to be sure our actions are effective.”

This last point was demonstrated by a Finnish study which looked at 10 of the most common actions that have been taken in recent years to protect European birds of prey such as the Montagu’s harrier and the white-tailed eagle. Six of those actions were found to be very effective. Two of them had no effect. And two of them were actually harmful, said Sutherland.

Relocating nests to fenced off areas proved to be very successful in protecting young raptors, for example. In contrast, marking nests to warn bird-spotters and others that they contained fledglings tuned out to be harmful because research showed these resulted in high losses of chicks from nests. “The fact that harm was done to raptors in the name of protecting them clearly illustrates the need to take action that is evidence-based and relies on strong background research.”

To provide such a service, the Cambridge team operates by gathering all relevant evidence about conservation projects from journals to create a database that contains more than 3,000 review articles. “If you want to know what to do about a conservation problem, you can then just look it up and get an answer.

“If you had done that for bats and road-crossings, for example, you would have found a number of much more promising solutions, including the construction of underpasses and culverts.”

It is crucial that conservation projects are seen to be effective, added Sutherland. “People support conservation in the same way that they give money to cancer research – in the latter case because they know cancer practice is good and getting better, but they still want scientists and doctors to find out more and to improve treatments.

“The same goes for conservation. They want things to get better. However, we have to make sure we have decision-making processes that get the best results we can in terms of boosting biodiversity. Some organisations, such as the Woodland Trust, do it well, but too often this is not being done properly by others.”

Future projects

Conservation scientists have identified a range of issues that will need careful evidence-based responses in coming years.

Earthworms play a key role in soil fertility and nutrient recycling. Studies suggest their numbers are now declining dramatically in the UK, and populations need to be restored.

• Numerous plans have been put forward to use oceans to absorb increased amounts of carbon dioxide, including plans to intensify algal growth by using fertilisers. But their global impacts must be properly assessed.

• Incidents of wildfires and biomass burning are expected to become more frequent as the world heats up. Dealing with the release of harmful aerosols will require careful planning.

•Turning to hydrogen as an alternative to burning fossil fuels will significantly help the fight against climate change. However, leakage from hydrogen-production plants could have damaging impacts.