The conservationist's dilemma - 5

Written by: Martin Harper
Published: 28 Jun 2018
Topic: Science, policy and practice of the impact of predators on wild birds

The office window at the RSPB's Loch of Strathbeg reserve has one of the best views in the whole of the RSPB. It overlooks tern island which, thanks to the installation of a predator fence, creates a cacophony.

The fence was built over the winter of 2013–14 to exclude Otters, which were feasting on the eggs. It helped the reserve go from having no Common Tern or Black-headed Gull chicks in 2012 or 2013 to almost 300 chicks!

This is a reminder of the postive impact that fences erected to exclude predators can have on breeding productivity of ground nesting birds.

Introducing any form of predator control (lethal or non-lethal) is something the RSPB never takes lightly. It’s always based on evidence* and guided by the RSPB Council-agreed policy.

Introducing any form of predator control (lethal or non-lethal) is something the RSPB never takes lightly. It’s always based on evidence* and guided by the RSPB Council-agreed policy.

At the time of writing there are fences at 28 reserves, protecting breeding waders over 874 hectares. At sites with anti-predator fences, Lapwing productivity has been consistently above that necessary to maintain population levels (0.6 chicks fledged per pair), even though at most sites only a proportion of the suitable habitat is protected by fencing. The graph below shows the mean average Lapwing productivity at RSPB reserves with anti-predator fencing where productivity has been regularly monitored. Bars show + one standard error. The figures above the bars show the number of reserves with anti-predator fencing, at which productivity was monitored.

While non-lethal predator management is always preferred, it is not always practical. Lethal 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.

If we can satisfy ourselves of all these things, then we can be sure to make the right decision.

Below are tables summarising the vertebrate control undertaken by the RSPB and its contractors on reserves during the period 1 September 2016 to 31 August 2017, and during the period 1 September 2015 to 31 August 2016 for comparison. Only reserves where control was undertaken during the year have been included. Vertebrate control commissioned by third parties as part of existing rights is not included.

* Plus 133 killed (by shooting and Larsen trap) through the Curlew Trial Management Project, although this includes individuals killed in the wider area, not just on the reserve itself

** Plus 20 killed (by shooting) through the Curlew Trial Management Project, although this includes individuals killed in the wider area, not just on the reserve itself

*A review of the impact of predation on wild birds based on 81 relevant scientific papers and reports covering 908 cases where the effect of a predator on changes in the numbers of a prey species had been measured. The headlines from the review are that…

…Predator numbers have increased in the UK over the last decades.

…The UK has very high densities of Red foxes and crows compared to other European countries.

…Seabirds, waders and gamebirds are limited by predation whereas pigeons, birds of prey, owls, woodpeckers and songbirds are not. A few exceptions to these general statements exist.

…There is a real need for research to understand how landscape-scale management could be used to provide longer-term sustainable solutions to reduce the numbers of generalist predators and their impacts on species of conservation concern.