Why Do Toads Migrate in Spring? Toad Crossings Explained

Why toads return to the same pond

The common toad spends most of its life on land, in woods, hedgerows, meadows and gardens. It needs water only to breed, and it is unusually loyal to particular ponds. Studies of marked toads have found that most adults return to the pond where they hatched, and in one study more than 80% of males marked as juveniles came back to their home pond. Many ignore other ponds that look just as suitable, even ones closer to their summer homes.

This behavior, called breeding site fidelity, makes sense for the toad. A pond that produced a toad is a pond that has already proved it can raise tadpoles: it holds water through spring and summer, has the right plants, and its tadpoles survive. Common toads prefer fairly large, deep, permanent ponds and lakes, and such waters are scarce in many landscapes. Going back to a known pond is safer than gambling on an untested one.

There is a social advantage too. If every toad heads to the same few ponds, males and females are sure to find each other. On a good night, hundreds or even thousands of toads may arrive at one breeding site.

When do toads migrate?

The timing depends on the weather. In much of western and central Europe the main migration happens between late February and April, earlier in the mild south and west and later in the north and in the mountains.

Toads usually move after dusk, and they need the right conditions:

• Mild temperatures: they rarely travel far when the air is below about 5 °C (41 °F).
• Damp weather: light rain or wet ground keeps their skin moist and lets them move without drying out.
• Darkness: moving at night reduces the risk from predators and the sun.

On a warm, wet night toads may keep walking until morning, but if the temperature drops they stop and hide. The whole migration at one site can last a few weeks, with peaks on the best nights. Some toads begin the journey in autumn and spend the winter close to the pond, ready for a quick start in spring.

How do toads find their way?

How a slow-moving toad finds a pond it may not have seen for a year is still being studied, but research points to several cues working together:

• Smell: toads appear to recognize the scent of their home pond and its surroundings.
• The Earth’s magnetic field: experiments suggest toads can use magnetic cues to orient.
• Landmarks and sight: familiar shapes of the landscape and the outline of hedges or trees.
• Sounds: the calls of other toads at the pond may help over the last stretch.

Toads that scientists moved more than 3 km (2 mi) away have still found their way back to their chosen pond. Many migration routes follow streams, ditches and hedgerows, which is why toad crossings are often found where a road crosses a watercourse.

What happens at the pond

Males usually arrive first and wait in the shallows, while females come later. Many males do not wait at all: they meet a female on the way and climb onto her back, gripping her under the arms in a hold called amplexus. The larger female then carries the smaller male the rest of the way. Pairs like this are a common sight on roads during the migration.

At the pond, males often outnumber females several times over, and rivals try to push each other off. Once she is ready, the female lays two long strings of eggs that the pair wind around water plants. Females leave soon after spawning, while males may stay for weeks hoping for another mate. After breeding, the adults return to land and disperse to their summer feeding areas. For more on the life of these toads, see the common toad profile.

Toads and roads

The common toad’s loyalty to old routes has a serious downside in the modern world. When a road is built across a migration path, toads keep using the same route. They move slowly and often stop or sit on the road surface, so traffic can kill large numbers in a single night.

In Europe the common toad has one of the highest roadkill rates of any amphibian. In a study in the Netherlands, roughly 30% of migrating females were killed on a quiet country road carrying only about ten vehicles per hour. Losses like this, year after year, can wipe out local populations.

Road deaths are one reason for long-term declines. A 2016 analysis of counts made by British toad patrols estimated that common toads in the UK had declined by about 68% over 30 years. Habitat loss, the disappearance of ponds and changing weather have also played a part.

Toad patrols, tunnels and crossings

Across Europe, people have found ways to help toads cross safely:

• Toad patrols: volunteers walk known crossings on migration nights, pick up toads and carry them across the road in buckets. In Britain the charity Froglife coordinates a national network of registered toad crossings.
• Warning signs: “toads crossing” signs ask drivers to slow down at busy sites.
• Road closures: some minor roads are closed at night during the peak of the migration.
• Tunnels and fences: low fences guide toads to tunnels running under the road. Such toad tunnels have been built in Germany, the Netherlands, Belgium, Britain, Italy, Poland and other countries.

Toad patrols do double duty. Every toad they carry is counted, and these records, kept over decades, have become one of the best sources of information on how amphibian numbers are changing.

Do other toads migrate?

Many toads and frogs make breeding migrations, but few are as dramatic as those of the common toad. In North America, the American toad moves to ponds, flooded fields and shallow wetlands on warm, rainy spring nights, and males announce the breeding site with a long, musical trill. Its migrations are usually more spread out, partly because it breeds in a wider range of shallow waters.

In the northeastern United States, the first warm, rainy spring nights, often called “Big Night,” bring mass crossings of salamanders, wood frogs and other amphibians, and local groups organize road patrols much like those in Europe.

Toads that survive the journey can return for many breeding seasons, since common toads may live for a decade or more in the wild. Learn more in How long do toads live?