Understanding and managing the impact of predation on wild birds, some lessons from Essex

I have just spent a delightful weekend with the family  exploring the Stour Estuary.   It reminded me just how great Essex is for wildlife.  

And it's set to get even better.  

Last autumn (see here), I visited our Wallasea Island Wild Coast Project. This is an enormous (6.7 km²) coastal wetland being created in Essex (south of the Stour) by the RSPB and its partners Crossrail, Defra and the Environment Agency. It’s the largest coastal wetland re-creation project ever attempted in the UK.

David Wooton's aerial image of Wallasea showing the transfer of material from a barge to raise the level of the land before breaching the sea wall.

Although this wetland has ‘wild’ in its name and, when completed, will be an enormous area of wild-looking habitat, I was  struck by the site’s detailed and creative design. And, the thinking underlying this design included, amongst other things, consideration of how to minimise the impacts of predation on nesting birds. 

As always, our approach to the issue of predation is based on evidence.  Our 2007 review of the evidence of the impacts of predation on wild birds concluded that generalist ground predators, such as foxes, can sometimes reduce the population levels of their prey, and a more recent (soon to be published) review confirms these findings.  By contrast, the evidence that breeding songbird numbers are limited by predation is weak. Rather, there is compelling evidence – some of it experimental – that changes in farming practices have led to the declines of many farmland songbirds, and emerging evidence that numbers of some woodland songbirds have declined due to long-term changes in woodland structure.

So, at Wallasea, we have created lots of different types of islands for birds to nest on, which foxes in particular, will have difficulty reaching. These include designs aimed at providing suitable conditions for nesting redshank, ringed plovers, terns and hopefully eventually even spoonbills. So far, we have constructed an amazing 67 islands there. Creating this large number of islands will mean that, even if a fox or badger is able to swim across to some of them, there should still be plenty more ground predator-free islands for birds to successfully nest on. 

And, at Wallasea, we are also currently excavating a nearly 4km long, deep ditch, in which to install an anti-predator fence. The fence will be constructed so that it lies mainly in the water, with just its top protruding. Foxes and badgers will be unable to jump over this fence, because they are unable to jump from a ‘swimming position’. This design also means that the anti-predator fence will be invisible to people looking across the site, hence helping preserve the ‘wild’ character of the place.  This is clever stuff and the end result is a bit like a ha-ha! 

But, unfortunately, at many other nature reserves, we have far less ability to reduce levels of predation through site design.  Sadly RSPB nature reserves are becoming relatively isolated hot spots, in areas of poor habitat that supports relatively high densities of predators: the result is a little like having Fort Knox and leaving the door open!  

The long term vision has to be to restore our coasts and wetlands; reconnecting rivers with their flood plains, to enable wader populations to grow, and for their distribution to be restored to more natural densities.  But for now, we are far from that, and conserving the remaining populations is proving challenging.  

The RSPB seeks to manage its reserves through sound habitat management yet at some sites, we have had to take the decision to kill generalist predators, especially foxes, to increase the breeding success of some of our most threatened bird species. Often these birds just have nowhere else to nest nearby. And, even at Wallasea, we will probably still have to kill a small number of foxes in the future, to maintain the site’s ground-nesting bird populations. 

As I have written previously (see here and here), vertebrate control on RSPB reserves is only considered where the following four criteria are met: 

• That the seriousness of the problem has been established;
• That non-lethal measures have been assessed and found not to be practicable;
• That killing is an effective way of addressing the problem;
• That killing will not have an adverse impact on the conservation status of the target or other non-target species. 

Below, I summarise numbers of vertebrates killed on RSPB reserves by us and our contractors during 2013/14. I have not included vertebrate control commissioned by third parties as part of existing rights. 

As these tables show, there are four main situations where the above criteria are met. These are to: 

• Increase breeding productivity of ground-nesting birds (mainly waders), principally by controlling foxes;
• Protect nesting seabirds;
• Reduce numbers of deer where they are having a detrimental impact on the vegetation, especially by overgrazing the ground flora in woodlands and preventing tree regeneration.  Often deer management is undertaken to prevent damage or aid recovery of nationally important wildlife sites;
• Benefit water voles by killing non-native mink.

By sharing this information, I hope that you have a clearer understanding of our philosophy, policy and practice designed to create landscapes where wildlife (whether predator or prey) can thrive. 

*Feral means populations derived from captive animals