Carnage on the carriageway: Millions of birds and animals die each year on Britain's roads. Can the death toll be reduced? Malcolm Smith on the wildlife holocaust

THE SURREY countryside between Chiddingfold and Chessington is rich in wildlife. Driving this 30-mile stretch every weekday, Colonel James Baker - a member of the Surrey Wildlife Trust - has seen an awful lot of it. Since 1987, he has counted several hundred rabbits, 51 badgers, more than 300 foxes, 27 roe-deer, well over 100 woodpigeons, and a host of other birds from tawny owl to song-thrush, jay to collared- dove. But his is an animal count with a difference. All of them were dead: 2,000 carcasses in seven years, each the victim of collision with a vehicle.

Yet this grisly total represents a fraction of the real kill. Many injured animals crawl away into the verges to suffer a slow, painful death. Birds struck by fast-moving vehicles catapult off the road, and large numbers of small birds, voles, mice and shrews, killed in the evening or at night, are removed by an array of nocturnal and dawn scavengers.

Birds have had the dubious distinction of a survey conducted especially for them. Bird corpses were counted - and, where possible, identified - at 166 locations throughout Britain during the summer of 1985. The survey covered all roads except motorways. It is the most recent such study, and the most comprehensive.

The results were depressing. A minimum of 30 million birds are killed on Britain's roads every year. Depending on the assumptions made in the statistical analysis, the death rate could be even higher: 70 million a year is not impossible.

Flattened wildlife is a familiar sight on roads worldwide - there is even a guide entitled The Flattened Faunae of the USA. Dr Fred Slater of the University of Cardiff has made a study of this gruesome topic. 'To the naturalist-traveller,' he says, 'corp- ses on the highway can provide clues to one's location. In Britain, squashed polecats tell you that you are in Wales or on the border with England. Squashed possums could almost replace the kiwi as New Zealand's national emblem.'

More roads, and many more vehicles using them year upon year, mean that the problem is getting worse. In 1960, Britain had 9.4 million registered vehicles and 313,000km of usable road. Today there are more than three times as many vehicles and 350,000km of road. That's why Colonel Baker, on his daily journey through Surrey, has recorded a steady increase in kills. In 1987 he counted 174 corpses: last year there were 359.

Not all roads are equally lethal. The type of road isn't as important as the habitat bordering it. Roads with hedges, trees and gardens at the side are the most dangerous, simply because they encourage birds to feed and often to breed cheek-by-jowl with cars. Sharp bends, especially if they are tree or hedge-lined, are particular bird black spots. Fewer animal accidents are recorded on motorways, which, with their wide verges without trees or hedges, harbour few birds, with the notable exception of mice-hunting kestrels.

Different species of birds, too, appear to vary in their susceptibility to traffic accidents. House sparrows top the league table (see box) with at least 9 million killed each year. Avid grain feeders, many are killed where arable fields border roads and around farm buildings.

Britain has between 2.6 and 4.6 million breeding pairs of house sparrows, one of our best-known birds which has, ironically, adapted itself to live in closer human contact than almost any other. By the end of each breeding season, Britain's sparrow population - if each pair, on average, raises eight young - can swell to 46 million. Between a fifth and a half end their days on Tarmac.

But bird species don't simply fall victim to road traffic in proportion to their abundance. Much must depend on their habitat preferences, their breeding and feeding preferences, their habits - whether they rarely move out of cover, for instance - and perhaps on how agile they are in flight. Chaffinches - birds of hedgerow, garden and field - are killed in relatively small numbers (0.8 million) compared with blackbirds, yet are more abundant.

Even more inexplicable is the small number of accidents involving pied wagtails. These attractive little long-tailed, black-and-white birds seem to spend an inordinate proportion of their lives flitting around on roads, picking up insects. Perhaps they have learnt a degree of traffic dodging that other birds haven't.

No animal has come to symbolise wildlife deaths on roads more than the hedgehog. Throughout the summer months it is difficult, on almost any road journey, not to see its squashed, bloody remains. Estimates of the number killed vary enormously: from 100,000 to 1.3 million a year. At worst, that could mean as many as four killed each year for every kilometre of road. Badgers are also frequent casualties. A survey in southern England in 1984 recorded just under 1,000 killed, mostly in spring at mating time, and late summer when young brocks disperse.

Ironically, some animals killed on roads are exploiting the food source created when insects collide with a vehicle. For hedgehogs, frogs and small birds, roads can be a dangerous fast-food joint as they scavenge the pickings. They in turn provide an easy food supply for cats, foxes, badgers, stoats, crows and magpies.

The rate at which many of these scavengers can remove whole corpses of small species is astonishing. Dr Slater quotes such an example from mid-Wales. After a March night when toads had been crossing a road to get to their breeding lake, he counted 179 corpses at dawn. By 8.30am, all of them had been removed by crows and magpies.

So how worried are conservationists by this carnage? 'For some species, such as otters,' says Jill Barton of the Wildlife Trust, 'road deaths are slowing their recovery and spread.' For other species, such as hedgehogs, accidents may be contributing to general decline. This doesn't necessarily mean that they are affecting total populations. The majority of young birds reared each year don't survive through to the next breeding season anyway. Most succumb to starvation, predators and winter weather.

Many conservationists are perhaps more concerned about the way roads break up animals' territories and habitats. 'This sort of fragmentation can lead to long-term stress on a population,' Ms Barton says.

Many toads die crossing roads that isolate their breeding marshes or ponds from the remainder of their habitat. According to Fred Slater, their mating behaviour makes them doubly vulnerable. 'Males sit upright on the road surface so that they can pick a female to piggy-back with to the water,' he says.

So what, if anything, can be done to reduce this tragedy? The Government's Highways Agency produces guidelines which include the design of tunnels to enable badgers, toads and frogs to cross the road. On new roads, the cost is met by the Department of Transport or local authority; on existing roads, by whoever wants the facility installed. A toad tunnel in West Sussex recently cost almost pounds 14,000.

For birds and flying insects it is much more difficult, if not impossible, to design road-safety measures. On new roads it might pay to keep tree and shrub planting well back from the edge to discourage birds from breeding. Planting high hedges or rows of trees on banks above a new road could help to funnel birds and butterflies across roads above the traffic rather than into it.

But on the majority of our existing roads, the carnage will probably rise as vehicle numbers and average speeds increase. Britain's roads have the poorest record in Europe for pedestrian accidents. There may be little hope for wildlife.-

Britain's most common road bird casulaties (in millions per year).

House Sparrow*9.3 - 20.4

Blackbird*8.4 - 17.7

Wood Pigeon*3.3 -4.6

Starling3.8

Song Thrush3.2

Magpie2.5

Pheasant1.2

Blue Tit1.1

Yellowhammer0.9

Robin0.8

Chaffinch0.8

Rook0.5

Skylark0.3

Pied Wagtail0.3

* A range is given for these species because more data is available.

Blind as a bird?

BIRDS are renowned for their good eyesight. Birds of prey such as kestrels and owls have eyesight that is at least three times better than ours for seeing detail.

Small birds have fast reactions and agile flight. Woodland species, like blackbirds and tits, flying at around 20 mph, manage to dodge trees, thickets of scrub and tangled branches. And they can do it in dim light. You don't find dead birds on woodland paths.

Why, then, on roads do birds collide with what must appear to them enormous objects, brightly coloured, often moving in a straight line and, sometimes, not travelling very much faster than the birds can fly? The problem is all to do with the way birds see the world around them.

Birds have their eyes positioned at the sides of their heads, looking outwards. They have excellent all-round vision. They can even move their eyes independently of each other, essential for spotting predators. The disadvantage is that, because the field of view of each of their eyes hardly overlaps, their binocular vision is poor. In pigeons, for instance, the overlap is only 20 degrees. We have excellent binocular vision with a 140 degree overlap and we see things stereoscopically - in 3D. To mimic a bird's monocular vision, cover one eye and walk around: it's harder to judge distances; the 3D vision has gone.

How do birds know if an object is too close for comfort? They may use parallax. This is what we experience when, as we walk forward, distant objects at our side appear to 'move' behind us much more slowly than objects very close to our side. If a bird is flying fast, parallax will give it a better overall impression of distance than 3D vision. But not for objects in front. One theory is that a bird's reliance on parallax frequently puts it on a collision course with cars.

For a bird to distinguish a moving vehicle when flying, the vehicle's image on the bird's retina must be moving relative to the other images it sees. All images are moving, though, because the bird is moving. If the vehicle doesn't appear to move more than other objects in its view, the bird will perceive it as part of the distant landscape, rather like clouds or mountains. It won't register as a threat. To compound the problem, we also know that birds' brains can only cope with a limited amount of information at once.

All is well, provided the flight path of the bird and the path of the vehicle don't cross. The bird will only realise that the vehicle is a threat when it gets so close that its image becomes larger by the second. Birds have evolved the best possible eyesight for spotting natural predators, but the slow process of evolution hasn't equipped them to cope with the biggest man-made one - the motor car.

(Photograph omitted)