New study implicates raptors in Welsh black grouse mortality

The results and recommendations of a four-year study published in the latest edition of the science journal Wildlife Biology raises concerns about the impact that predators such as foxes and raptors are having on one of our most threatened birds, the rare black grouse.

The study was carried out by independent researchers Gordon and Christine Bowker and assisted by scientists from The Game Conservancy Trust on the Lake Vyrnwy nature reserve in North Wales, owned by Severn Trent Water and managed by the Forestry Commission and RSPB Cymru.

During the study, scientists investigated rates of survival and reproductive success in black grouse and discovered that of the 39 full-grown black grouse that were radio-tagged as part of the research, only one was alive at the end. Mostly the birds had been killed by predators. It is considered that 64% of the black grouse were killed by raptors, probably either goshawk or peregrine and 36% by red foxes.

Commissioned by Severn Trent Water the research raises important questions about the future conservation of this important red-listed species of high conservation concern. During the last century the black grouse (Tetrao tetrix) have declined in number and range in most parts of Western and Central Europe, and in some places, the species has become extinct.

Major factors responsible for black grouse decline include habitat loss, changes in land use or changes in forest management. This new study, however, highlights predation as another important factor that is linked to the bird's continuing decline.

Dr David Baines, The Game Conservancy Trust's director of uplands research said, "We are particularly concerned about the Welsh black grouse population, which may once again be declining following a brief period of recovery. We predict that fewer than 200 males now remain. Severn Trent Water has invested heavily in black grouse recovery and so they initiated this important research to identify the reasons for these declines before it is too late."

Low survival of juvenile and adult birds, largely due to predation by raptors combined with poor reproduction appears to have caused the observed decrease in black grouse at Vyrnwy. Since their full legal protection in the UK, goshawks and peregrines, the principal raptor predators of black grouse in this study, have significantly increased in abundance. Since its introduction in the early 1960s goshawks have increased by 16% per annum. The peregrine population has also thrived and it is now 145% of its pre-1940 level following recovery from the effects of organo-chloride insecticides in the 1950s. Dr Baines comments, "Increases of this magnitude, together with over-grazing by sheep reducing heather habitat quality and afforestation, have probably resulted in increased raptor predation on grouse."

However, in northern England the future of the black grouse population is much more encouraging. Recent spring counts of the rare black grouse in northern England reveal that the population in 2007 has increased to an estimated 1,200 males, a 55% increase since 1998 when the population was just 773 males.

Dave Baines explains, "Black grouse use a mixture of habitats from woodland and scrub, heath and rough grass to blanket bog, and do best where there is a mosaic of habitats. In northern England the population is responding extremely well where habitat improvements in combination with predator control are being undertaken by moorland gamekeepers."

The conclusion of the research clearly identifies the impact that predation by raptors is having on black grouse at Vyrnwy. Dr Baines concludes, "This is very compelling evidence about the cause of black grouse declines and is consistent with an equally dramatic decrease in red grouse in the same study area. If we are to conserve this iconic species in Wales and increase its numbers, then clearly further research needs to be carried out on the control of foxes as well as reducing the impact from protected raptors."