Natterjacks in Cumbria

NATTERJACK TOADS

Cumbria has two of the largest colonies in England of the Natterjack Toad at Drigg and Sandscale Haws; indeed the twenty or so Cumbrian populations account for around 65% of the UK's population (upto 25% at Sandscale alone). This comical yellow-striped toad (males have a throat with a blue sheen, whereas females have a white throat speckled black) prefers the seasonal shallow pools characteristic of sand dunes that warm up quickly in the sun, but is also found at 150 metres above sea level in the seasonal pools of Subberthwaite Common in the south-west foothills of the Lake District. Here the local farmer was adamant that he heard them calling in spring but nobody would believe him - until the experts had a look and found evidence of all six amphibians at this site!

The pools liked by the Natterjack tend to be ones that dry out during the summer, hopefully after the toadlets have left. This, and the lack of vegetation in the pools, deters the Common Toad, the presence of whose tadpoles have been shown to depress the growth of Natterjack tadpoles when they occur together. Where large numbers of Common Toads occur, Natterjack success is therefore low. At Ainsdale, Southport, there has been much success from re-locating Common Toads away from Natterjack pools. Natterjacks themselves use a similar strategy and readily colonise new pools, getting in before Common Toads and Frogs find them. They also lay upto three times as many eggs per string as the Common Toad.

Breeding often fails if the spring weather is dry, but as they have the longest breeding season of any native amphibian they can sometimes recover if a heavy spell of rain happens late on. Fortunately they only need about one good year in five to avoid serious difficulties - at Sandscale a good year might comprise several hundred thousand toadlets born on the reserve, a bad year just a few thousand! Because of the late laying of spawn (typically early April in Cumbria), the natterjack tadpole develops faster than any other species of amphibian; from laying to metamorphosis may take only four weeks in hot weather. When the toadlets emerge they are less than a centimetre long, but already have the yellow stripe in place. The Natterjack is a heavily protected species and must not be disturbed.

A serious threat to the well-being of Natterjacks emerged in 2007 following the discovery of the chytrid virus in the county. This virus has devasted amphibian species in Australia and elsewhere; it affects the skin and effectively suffocates the species, as they breathe through the skin. Tests are being carried out to determine the extent of the virus, but worryingly some populations have been shown to have as many as 40% of their number infected.