Natterjack Toad

Its hind legs are relatively short compared with those of a common toad or a frog, so it is not built for the long springing jumps other anurans use. Instead it moves in fast, mouse-like scurries across open ground, which works well on the flat, sparsely vegetated sand and short turf where it lives — habitats where there is little cover to leap between anyway and speed over open distance matters more. This distinctive gait is why it is often called the "running toad." Combined with the yellow stripe down its back, the run is one of the quickest ways to tell a natterjack from a common toad in the field.

For its size, extraordinarily. A 7-centimetre toad produces a rasping, pulsing call that a person can hear from one to two kilometres away across open country on a calm night, and it is generally regarded as the loudest call of any European amphibian. The male inflates a single large vocal sac under the chin that acts as a resonator, and dozens or hundreds of males calling together from a breeding pool create a continuous churring roar. The volume matters because natterjacks breed in scattered, short-lived pools, and females need to be able to locate a chorus from a long way off.

It is a deliberate trade-off. Shallow, temporary, sun-warmed pools have two big advantages — they are too ephemeral to support fish and many aquatic invertebrate predators, so natterjack eggs and tadpoles face far less predation than they would in a permanent pond, and the warm water speeds tadpole development. Natterjack tadpoles can complete metamorphosis in as little as three to six weeks, among the fastest of any European amphibian, which is an adaptation to this race against evaporation. The risk is obvious — if a pool dries before the tadpoles transform, the entire batch dies — so natterjacks spawn several times through the spring and summer to spread the bet.

It is at the northwestern edge of its European range in Britain and was always somewhat localised, but it declined severely through the 20th century, disappearing from about three-quarters of its former sites. The main causes were loss and "improvement" of open sandy habitat — coastal dune systems stabilising and scrubbing over as grazing stopped, heathland being lost to agriculture, forestry, and development, and the drainage or acidification of its shallow breeding pools. It is now a protected species confined to around 60 sites, mostly dune coasts and a few inland heaths, and is the subject of active conservation — creating and clearing breeding scrapes, grazing to keep habitat open, and reintroductions to former sites.