The conservationist's dilemma - 4

Written by: Martin Harper
Published: 4 Sep 2017
Topic: Science, policy and practice of the impact of predators on wild birds

Using 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 policy that is agreed by the RSPB Council.

The RSPB first seeks evidence of the problem, checks whether there is a non-lethal solution, and if so, implements that. In many cases this does the job needed.

At the RSPB’s Otmoor nature reserve in Oxfordshire the team of staff and volunteers has created a wonderful wetland habitat for waders such as Lapwings, Redshanks and Snipe. The management of the site has also aided the return of Bitterns, Marsh Harriers and Cranes. Otmoor is providing the missing link to the wetlands in the Fens in the east and those in the Somerset Levels to the west.

There is an electric fence around the field called ‘Big Otmoor’ (shown below), which is designed to exclude mammals and has been instrumental in driving up the breeding success of Lapwings.

It may seem incongruous to see a big fence in the middle of a nature reserve, but this level of management is the RSPB's response to the fragmented nature of the countryside and its motivation to re-engineer wildlife back into the landscape. The fence was installed in 2010 and, as can be seen from the graph below, it has protected the wading birds and there have been more chicks for visitors to see and to join the thriving population.

Anti-predator fences are performing well across the RSPB's reserve network. At the time of writing, there were fences at 28 reserves protecting breeding waders over 874 hectares. At sites with anti-predator fences, Lapwing productivity is 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 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 methods of predator control are always preferred, they 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.

Only when we have satisfied ourselves of all these things will we make a decision.

* Using results of previously published studies, the RSPB completed a review of the impact of predation on birds. Its results are consistent with those of its 2007 review: despite high and increasing densities of predators, there was little support that predation limits populations of pigeons, woodpeckers and songbirds, whereas evidence suggests that ground-nesting seabirds, waders and gamebirds can be limited by predation.

The two tables below show the lethal vertebrate control undertaken (for both conservation and other reasons) on RSPB reserves between 2015-16. Some of the numbers are lower than in the previous year as 2014–15 was a 17-month period due to the change in reporting date.