The conservationist's dilemma: an update on the science, policy and practice of the impact of predators on wild birds (5)

Recently, I had the pleasure of paying my first visit to our Loch of Strathbeg reserve in Aberdeenshire. The office window has one of the best views in the whole of the RSPB as it looks directly onto a tern island which, thanks to the installation of a predator fence, creates a cacophony.

Loch of Stratbeg (Andy Hay, rspb-images.com)

Built over the winter of 2013-14 to exclude otters which were feasting on eggs, the fence has helped the reserve go from 10 pairs of common terns and 30 pairs of black headed gulls raising no chicks at all in 2012 or 2013 to 178 pairs of terns and 36 black headed gulls in 2017 raising almost 300 chicks. This year looks to be equally successful.

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

As I have written in previous years (for example see here), deciding to introduce any form of predator control (lethal or non-lethal) is something we never take lightly. It’s always based on evidence* and guided by our Council-agreed policy.

The RSPB’s approach to any type of predator control means that we first seek evidence of a problem, check whether there is a non-lethal solution and if so implement that. In many cases (as for the terns at Loch of Strathbeg) this does the job needed.

We now have fences at 28 reserves protecting breeding waders over 874 ha. At sites with anti-predator fences, lapwing productivity has been consistently above that necessary for population maintenance (0.6 chicks fledged per pair), even though at most sites only a proportion of the suitable habitat is protected by the fence.  The graph below shows mean Lapwing productivity at RSPB reserves with anti-predator fencing, at which 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.

But non-lethal methods, whilst always our preferred way of doing things, are 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.

Vertebrates controlled on RSPB reserves in 2016/17

Below are tables summarising the vertebrate control undertaken by RSPB and our 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 here.

a)      For conservation reasons