So what’s the evidence for that?

Why does SNH erect an electric fence around the Forvie tern colony? Why do RSPB use ponies to graze at Loch of Strathbeg? What about placement of bat boxes, or methods used to control invasive species?

All these actions require resources and we all want to make the best use of what is available to us. In an ideal world, conservationists will know what has worked before and, crucially, what has not worked, so that the same mistakes are not repeated. In reality, results from conservation interventions may be difficult to access. They might be hidden deep in scientific papers, or in unpublished reports. To compound the problem, “publication bias” means that successful projects are far more likely to be publicised than are those that did not work out as planned.

Fortunately, tools are increasingly being made available to help conservation professionals and members of the public alike to use evidence when managing species, habitats and local spaces. Everything from erecting bird nest boxes to selection of protected areas on a global scale can be underpinned by evidence. Initiatives such as Conservation Evidence distil and summarise evidence on the effectiveness of conservation actions, and these outputs are feely available to all. Not every conservation action has been studied in detail and substantial evidence gaps exist. But where evidence is available, not taking account of it could be wasteful. Worse still, it might even harm the focal species or habitat.

If you want to make a difference, why not add to the evidence base yourself? There are many opportunities locally to do so. For example, there is little evidence that Swift nesting boxes benefit local populations. Monitoring box visitations across the breeding season could indicate how successful boxes are at producing fledged young.

A topical local example of where evidence can enhance conservation outcomes is in providing crossing structures during road building schemes. Eighty wildlife-adapted culverts, two “green bridges” and a squirrel rope-bridge were constructed along the recently opened Aberdeen Western Peripheral Road (AWPR). But do such structures work?

Green bridge

A “green bridge” over AWPR (Photo: Ian Francis)

Fortunately, there is a growing volume of literature on use of crossings by wildlife. For example, some studies show that toads favour underpasses that are at least 75 cm diameter, with soil bases and without water flowing through. Green bridges can reduce vehicle-animal collisions, especially wide bridges associated with barrier fencing. There are evidence gaps too, of course, and the effectiveness of rope-bridges at reducing squirrel mortality appears not to have been researched. Some studies, particularly from Australia, do show that tree-dwelling mammals will use-rope crossings when these link canopy to canopy. However, the potential for the AWPR squirrel rope-bridge, on which each end reaches down to a treeless ground level, to reduce squirrel mortality somewhat stretches credulity.

Red Squirrel rope-bridge over a road connecting to AWPR, near Dyce. (Photo: Ewen Cameron)

A Red Squirrel rope-bridge over a road connecting to AWPR, near Dyce. (Photo: Ewen Cameron)

If you want to make a difference, why not add to the evidence base yourself? There are many opportunities locally to do so. For example, there is only limited evidence about how useful Swift nesting boxes are. We do know a bit about optimising the insides of the box for encouraging Swifts to use them, but less about whether or not the boxes benefit local populations overall. Monitoring box visitations across the breeding season (to determine duration of occupancy) could indicate how successful boxes are at producing fledged young. This could be compared with outcomes at nests in more traditional situations or used to show which designs work best (e.g. swift-brick or retrofitted box) or which placement is most successful. And evidence impact is maximised when it is made available to others. Conservation Evidence journal provides a way of mobilising quantitative assessments of the outcomes of conservation interventions to international audiences. Carefully structured monitoring in your local town really could influence conservation actions across Europe and beyond.

Evidence is powerful. Use it. And add to it.

Top right image shows a tunnel in Kent that has achieved some success in linking habitats used by newts (Photo: Silviu Petrovan)

Newt tunnel

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Nick Littlewood

Conservation Evidence at University of Cambridge