The latest issue of British Birds magazine includes a detailed article on red-backed shrikes in Britain and Dartmoor in particular. “Return of the butcher bird? Prospects for recolonisation of the Red-backed Shrike in the UK and priorities for conservation” by Mary Davies and Leigh Lock, British Birds 109 (2016) pp 8-20.
The red-backed shrike is a small predatory bird and a migrant, it is also known as the butcher bird because of its habitat of impaling captured prey on a thorn until it is ready to eat it. The species used to be widespread in Britain but started to decline in the mid 19th century. This decline accelerated after 1945 and by 1989 it was extinct. I saw the last pair of breeding red-backed shrikes in Thetford Forest back in 1988.
Between 1990 and 2010 there were only sporadic breeding records in Britain.
By hedera.baltica from Wrocław, Poland (http://creativecommons.org/licenses/by-sa/2.0)%5D, via Wikimedia Commons
Red-backed shrikes bred on Dartmoor from 2010 to 2013 but non breeding individuals were present between 2007 and 2014. In total it is thought that 15 young were raised.
Red-backed shrikes need extensively managed farmland with patches of scrub. They feed on large insects and favour beetles. In colder weather when such prey is hard to find they will catch lizards, small mammals and birds.
The reasons for the decline in the species are not fully understood but clearly relate to changes in habitats and the availability of their favoured prey. The use of pesticides in agriculture today has massively reduced the availability of insects and the intensification of agriculture has reduced considerably the diversity of species-rich habitats.
The recolonisation of Dartmoor by the shrikes was unexpected and their demise is not fully understood but it is thought that habitat quality and food availability (in good summer weather) was adequate to sustain a breeding population. It would seem that cold wet weather in the summer may have put adverse pressure on the species which affected breeding success. In 2012 during a prolonged period of wet weather supplementary feeding of the birds with meal worms was tried but unfortunately both nests still failed.
Time will tell as to whether red-backed shrikes return to Britain and indeed Dartmoor. Climate change has made the prospect of this more likely. The conservation bodies, particularly the RSPB, The Dartmoor National Park Authority and Devon Birds seem to have now developed a plan which will hopefully lead to a more enduring successful outcome next time.