It is people and their pets – not greys squirrels – that pose the greatest threat to Britain's indigenous red squirrel population.
That is the conclusion of a veterinary pathologist in Cornwall, who has spearheaded a project to investigate the devastating population decline in recent years.
Vic Simpson said: "This report is the most comprehensive investigation yet undertaken into the causes of mortality in red squirrels in the UK."
Mr Simpson, who has conducted the research in conjunction with four other scientists, has been a veterinary pathologist for more than 40 years, studying wildlife diseases both in the UK and in Africa. In 2001 he set up the Wildlife Veterinary Investigation Centre Chacewater, near Truro, in order to specialise in researching diseases of native wildlife.
Mr Simpson explained that while it is well-known red squirrels die from squirrel pox – a disease carried by grey squirrels – the greys themselves show no symptoms of pox. This led the team to look at other causes of premature deaths in the red squirrel population.
The author of numerous scientific papers, ranging from lead poisoning in swans to heartworm in foxes, Mr Simpson won the BBC Lifetime Achievement Award in 2001. He said that although the latest research was carried out on red squirrels found dead on the Isle of Wight, Scotland, Cumbria and Anglesey, the report had special relevance to Cornwall because Cornwall Red Squirrel Project wants to reintroduce the species on The Lizard and in West Penwith.
There are currently no red squirrels in the wild in Cornwall but there are captive populations at Trewithen at Probus and Paradise Park in Hayle. Red squirrels have also recently been released on Tresco under a separate project instigated by countryside writer and campaigner, Robin Page.
The new report, based on ten years of research, reveals that more 60% of red squirrel deaths were due, directly or indirectly, to human activities. Roads were the single most common cause, with attack by domestic cats and dogs second.
On the Isle of Wight cats were indirectly responsible for one in six red squirrel deaths, due to infection by toxoplasma parasite.
Mr Simpson said: "Cats carry the parasite in their intestines. Here it produces spore-like bodies called oocysts which are passed out in the cat's faeces. Squirrels then become infected by foraging in contaminated areas, such as gardens."
The toxoplasma parasite can also cause serious disease to other species, including humans.
Other human-related causes of death in red squirrels include rat traps, poisoning by bait put down for rats, and electrocution. The research has also thrown up previously unrecognised diseases in red squirrels, including four types of cancer.
CRSP project co-ordinator and trained ecologist, Natasha Collings, said: "This paper confirms how fragile our island and remnant populations of red squirrel in the UK are, and also underlines the importance of carefully designed and managed captive breeding populations. The study shows how certain populations suffer from particular health issues and so highlights how genetic diversity is important when pairing up squirrels for captive breeding with an eye to their future release. It is because these populations are so fragile that here in Cornwall we are hoping to provide red squirrels with a foothold in the South West once again."
In their conclusion, the authors of the report say: "The impact of human activities on the health and welfare of red squirrels merits more attention. There is also a need for continued disease surveillance. As this study has shown, red squirrels are affected by a wider range of diseases than previously described."