Town birds such as starlings and sparrows may be in decline because they are simply too scared to breed. New research shows that Britain now has so many cats - more than nine million - that birds' fear of them may be having as great an impact on their decline as the numbers killed.
While most research into the decline has focused on the numbers of birds killed by cats, the new study suggests that so-called sub-lethal effects, or fear, may be reducing bird numbers by affecting eating patterns and fertility.
Songbirds are especially vulnerable because they are heavily outnumbered by cats: "We show that these sub-lethal/fear effects may be substantial for urban songbirds. When cat densities are as high as have been recorded in the UK, and even when predation mortality is low, a small reduction in fecundity due to sub-lethal effects can result in marked decreases in bird abundances,'' say the researchers from Sheffield University.
The report, which looks at whether domestic cats have any effect on bird reproduction, appears in Animal Conservation this week. It says there are an estimated 9.2 million cats in the UK.
"Predators influence prey populations not only by eating individuals, but also by altering behaviour, including foraging patterns and use of different habitats," the study continues. "It is emerging that the consequences of these effects may be larger than those of predation mortality.''
The widespread decline of rural and urban bird populations has been accelerating for some time. Species such as the starling and house sparrow have declined by up to 60 per cent in urban areas of the UK over the past 30 years. Current theories include a reduction in insect food and loss of nesting sites, as well as predation by domestic cats.