Understanding and managing the impact of predation on wild birds
Some lessons from Essex.
Written by: Martin Harper
Published: 15th May 2015
Topic: The impact of predation on wild birds.
The Wallasea Island Wild Coast Project is an enormous (6.7 km2) coastal wetland being created south of the Stour in Essex 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.
Although this wetland project has ‘wild’ in its name and, when completed, will be an enormous area of wild-looking habitat, it has a detailed and creative design. The thinking underlying the design included, amongst other things, consideration of how to minimise the impacts of predation on nesting birds.
The RSPB's approach to the issue of predation is based on evidence. A 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. A more recent 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. There is also emerging evidence that numbers of some woodland songbirds have declined due to long-term changes in woodland structure.
At Wallasea, lots of different types of islands have been creared for birds to nest on, which foxes in particular, will have difficulty reaching. Some of the islands have been designed to provide suitable conditions for nesting Redshanks, Ringed Plovers, terns and hopefully eventually even Spoonbills. At the time of writing 67 islands have been constructed. Creating this large a number of islands means that, even if a Red 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.
At Wallasea, a nearly 4km long, deep ditch has also been excavated for the installation of an anti-predator fence. The fence will lie mainly in the water, with just the top protruding. This will exclude foxes and Badgers as they're unable to jump when swimming. 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.
Unfortunately at many other RSPB nature reserves it's not possible to reduce levels of predation through site design. RSPB nature reserves are becoming relatively isolated hot spots where large numbers of prey species attract large numbers of predators.
The long term vision has to be to restore 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 - to increase the breeding success of some of the most threatened bird species - generalist predators are killed, especially foxes. Often the birds have no alternative nesting sites nearby. And, even at Wallasea in future a small number of foxes may need to be killed to maintain the site’s ground-nesting bird populations.
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.
The table below summarises the number of vertebrates killed on RSPB nature reserves by the RSPB and its contractors during 2013–14. This does not include 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;
- Benefit Water Voles by killing non-native Mink.
By sharing this information, it is hoped that you have a clearer understanding of the RSPB's philosophy, policy and practice designed to manage landscapes where wildlife (whether predator or prey) can thrive.
*Feral means populations derived from captive animals.