Frogs and toads throughout Western Europe are breathing a sigh of relief and looking forward to a carefree summer. For the most grueling experience on the amphibian calendar - migration - is all but over.
Migration is a hazardous business. The trek from winter habitats to breeding sites in lakes and ponds can mean a 11/4-mile journey, often across busy roads. And until recently as many as 50 percent of grass frogs and 80 percent of common toads (or Bufo Bufom, to give them their proper title) used to fall victim to passing vehicles.
Over the past decade, however, a growing army of volunteers, backed by local and even national governments in Western Europe, have marched to the rescue. Enormous amounts of time, effort, money, and ingenuity have been invested in what has become an annual spring rite to preserve the wandering amphibians. The casualty rate has been dramatically reduced.
To the uninitiated, the interest generated by these little creatures is, to say the least, bewildering. As a British nature lover points out, frogs and toads have long suffered from ''a bad public image.'' But that is changing and changing fast.
So these days, when the word goes out across Europe that frogs and toads are on the march, volunteers from Scandinavia to the Netherlands and Switzerland to West Germany reach for their gum boots and prepare to mount ''toad patrols'' along known migration routes.
The local press and radio muster extra recruits. In parts of Holland, activists even resort to telephone campaigns, and a Dutch national ''toad-saving day of action'' was organized last year.
The volunteers settle down at the roadside with thermos flasks for a two- to three-week vigil during which they will spend five or six hours each evening trapping thousands of the migrants in plastic buckets sunk into the ground. Then they ferry them to safety across the road.
Plastic buckets are all very well (a conservation group near Zurich saved some 8,000 frogs by this method last year), but gradually, more sophisticated techniques are being introduced. West Germany currently leads the way in toad safety, with Holland and Switzerland close behind.
Delegates from these countries attend international ''toad-crossing'' symposia each year to help them keep abreast of the latest developments. In many rural areas of West Germany the federal government has installed official traffic signs - a green triangle with a frog in the middle - which warns motorists: ''Beware toads crossing.''
Conservation groups in Holland and Switzerland have painted and set up their own warning signs, to the dismay of officialdom. But Swiss and Dutch police are proving very amenable. They help carry toad-laden buckets - and even close roads on heavy migration routes between dusk and dawn, bringing traffic to a grinding halt.
But the most technologically advanced projects, already introduced in Switzerland and West Germany, involve building ''toad tunnels'' under roads and highways. Both the Swiss and West German authorities now budget for these when drawing up plans for the construction of new autobahns. In Switzerland, ecologists advise the federal and cantonal governments on the best spots for ''toad tunnels'' before road construction begins.
The most complex of these systems is at Cossonay in Switzerland, where two parallel tunnels 12 meters long have been built side by side. Why two? To provide for two-way traffic, of course: one for outward, the other for inward migration. But, as Kurt Grossenbacher of Bern's natural history museum explains:
''Tunnels are not proving very popular with toads; they like to see the horizon when migrating and have trouble adapting to new situations. We find that many of them tend to turn back.''
So, if the toads won't go to the ponds, the ponds must come to the toads - and it's already happening. Fine mesh fences are strung out along the roadside to deter toads and frogs from trying to return to the pond they have in mind, while conservationists create an identical, artificial pond on the side the creatures are coming from. Experts say it is too soon to tell how many will fall for it. But in Switzerland, according to the locals, plenty of them already have. There are currently six toad- and frog-filled artificial ponds near Bern alone.
There is a serious aspect to all this. Industry, urbanization, drainage projects, intensive farming, and new roads have done a lot of damage to European wildlife since World War II. The natural habitats of many frogs and toads have been polluted or destroyed and, says Keith Corbett of the British Herpetological Society, their numbers have declined considerably. By cutting road casualties, conservationists have helped halt the decline - and helped focus attention on other amphibian species, such as the great crested newt, which are in serious danger of becoming extinct.