Of the six species of amphibians and six reptiles indigenous to Britain, one of each, the natterjack toad and the sand lizard, have major strongholds in coastal dune systems. Both these species are now local in occurrence and declining, and are protected under the Wild Creatures and Wild Plants Act 1975. They should not be removed or even handled by anyone without a licence to do so from the Nature Conservancy Council.
The natterjack toad
The natterjack (Bufo calamita) is a small, relatively agile toad which runs rather than hops on its stumpy legs. Although found in a variety of habitats in Western Europe generally, in Britain it is limited to sandy soils where it can burrow easily. Although it was known until recently at a number of inland sites, notably the heaths of the Weald and East Anglia, it appears to be extinct or virtually so at all these places and is confined now to a few coastal areas. The most important of these are in Merseyside between Southport and Altcar and on the north side of the Solway, with smaller colonies around the Cumbria coast. A small colony survives on the Cheshire coast while in the East the natterjack persists at Saltfleetby, Lincolnshire, and at Holkham and Winterton Dunes, Norfolk (Prestt, Cooke and Corbett, 1974, p233).
Like all amphibians, the natterjack depends on suitable freshwater habitats in which to breed and to pass the early stages of its life history. The major cause of its decline is loss of breeding habitat and, to a lesser extent, an increase in man-made barriers to migration and dispersal.
This century, over 80% of natterjack breeding sites in Britain have been lost. The toads are relatively defenceless against predators, especially in the breeding period, so that small colonies may be wiped out by birds, voles and snakes.
The main way to improve conditions for the natterjack besides protecting its remaining sites, is to create or maintain suitable breeding pools, ponds or ditches. Its natural spawning places are shallow pools. It is thought that adults can survive up to fifteen years of drought. But climatic changes and the lowering of water tables due to increased demands of agriculture and housing may have disastrous consequences on breeding success, since the tadpoles are killed if their ponds dry out before metamorphosis is complete.
At Ainsdale Sand Dunes in Merseyside, Saltfleetby in Lincolnshire and Winterton Dunes and Holkham in Norfolk, the Nature Conservancy Council have dug a number of natterjack breeding pools and shallow scrapes. Small pools can be dug by hand, but it is usually cheaper to get an adequately big and deep pool dug by machine. Experience at Ainsdale indicates that the best equipment is a low-ground-pressure bulldozer, which can make smooth scrapes and grade the spoil into the surrounding landscape. The depth required depends on local conditions but it is important to have at least parts of some pools hold water through mid-summer. On the other hand, pools should not be dug too deep or they will not favour natterjack development and may even be infiltrated by salt water which underlies the fresh water table of sand dunes near the sea. At Ainsdale, the serapes are designed to dry out in August or September during average summers, since the tadpoles have metamorphosed by this time. Where a mechanical excavator is used, pools should be designed and located to minimise movement of equipment over the fragile surfaces of slacks. Further points include:
- Natterjack pools or scrapes should be kidney shaped, where possible, with the convex side facing south and the ‘peninsular’ side to the north.
- Shallow margins are essential, since natterjacks drown easily and may not even attempt to breed in steep-sided ditches. The sides should be as smooth as possible, otherwise tadpoles may gather in small depressions and be left high and dry as the water level drops. Spoil from the excavation can be placed along one or more sides to provide a burrowing and hibernating place for adults and young toads.
- Tadpoles need warm water to develop – generally above 20 degrees C (68 degrees F) and optimally above 25 degrees C (73 degrees F). Deep water and shade from trees may keep the water too cool. Also in deep, shaded pools natterjack spawn and tadpoles tend to be at a competitive disadvantage with frogs and common toads (Bufo bufo) and are more likely to fall prey to newts, carnivorous insects and other predators which thrive in these conditions. There is also some evidence that common toads and frogs exert an inhibitory influence on natterjacks, causing the tadpoles to develop more slowly than normal.
- Aquatic vegetation, or at least a few sods or one or more tree trunks on the bottom of the pool, helps the survival of tadpoles, especially for protection from ducks, waders and other birds. Natterjacks must have bare sand areas around the pool in which to burrow.
- Management work should be carried out from late August to mid October to reduce the chance of destroying tadpoles or hibernating adults. Although their life history varies from site to site, natterjacks generally hibernate from late October to March or April. Their short, powerful limbs are adapted for burrowing into sandy soil, in which they can go as deep as 3m (10′). The mating and spawning period is mid-April to the end of June and tadpoles leave the water between early June and mid-August (Smith, 1951). The natterjack develops through all the stages from spawn to young toad in four to eight weeks, compared with ten to twelve weeks for the common toad and frog. In some years, the tadpoles may emerge in two broods, due to a cool spell of weather occurring mid-season between early and late warm weather.
- At Formby, Merseyside, new pools are dug to about 1m (3′) depth in October, and fenced immediately after (see below). It is difficult to get the pool to just the right depth, so that it is shallow enough to warm up, but deep enough that it does not dry out in July. ‘Emergency’ digging, when the tadpoles are hatched, is not very successful. Apart from the disturbance caused, the tadpoles are reluctant to move into the newly dug and cooler areas. In the first year after digging, pools are usually satisfactory in terms of water level, but have few toads using them. The second year is normally the best, with a good hatching of tadpoles and toadlets. In the third year, vegetation starts to come in, shading the water and keeping it cooler, and so less suitable for metamorphosis.
- The toadlets metamorphose in the water, and can find the walk up the dry sand difficult. They tend to stay in the water until it rains, when they can more easily get a footing. The toadlets crawl into cracks in the sand, and can easily be squashed by people walking around the edge of the pond. At Ainsdale NNR, pine brashings are put down in a 2m (6′) strip around the pond. These provide protection for the toadlets. The brashings are put down in July, as if done any earlier there is more time for children to disturb them.
- An alternative method in areas of public access is to fence around each pool. At Formby, 1.1m (321′) chestnut paling is used, encircling the pond about 2m (6′) from its edges. Explanatory notices discourage people from climbing in. These notices and other publicity have increased public awareness to such an extent that complaints are made if the pools are allowed to fill in, even though this may be part of the natural cycle.
The sand lizard
The sand lizard (Lacerta ogilis) is confined in Britain to mature lowland dry heaths and sand dunes in the southern half of the country. These habitats provide the subsoil warmth necessary for the hatching of eggs and they are only slowly overgrown by vegetation. The sand lizard was once present over a scattering of sites but is now confined to four general areas: the Merseyside coastal dunes; the heaths of Surrey, northeast Hampshire, southeast Berkshire and northwest Sussex; the southwest Hampshire heaths; and the heaths and coastal dunes of southeast Dorset. All four areas have experienced severe declines in this century, and on its coastal sites the Merseyside population is down to perhaps individuals although the Dorset population is considerably larger. The Merseyside lizards are probably a distinct race which have been isolated from those of other sites for at least 2,000 years (Prestt, Cooke and Corbett, 1974). Merseyside is the northern edge of their range.
Because sand lizards are highly colonial and stray only a short distance from their basking and nesting sites, local road or housing developments can destroy entire colonies. Collecting (mainly by children) is still a problem and may finish off remaining individuals, especially the males which are a vivid bright green (in Lancashire, yellow-green) in the breeding season. Fires are also a major threat, while magpies and stoats take their toll.
In general, protection and creation of habitat is difficult, as sand lizards, like natterjack toads, are adapted to an unstable habitat. In the case of the natterjack, it is the interface of sand and water which is crucial, whereas the sand lizard needs the changing conditions where bare sand is slowly colonised by vegetation. A suitable site may only remain so for a few years, so the job of managing a threatened population is a constant one.
The British Herpetological Society and the Nature Conservancy Council have constructed vivaria in parts of the country where sand lizards occur, to breed them for release into suitable habitats. This is a specialised operation and no one should attempt it without advice from the BHS and a permit from the NCC to keep lizards.
In areas of heathland, such as in Dorset, habitat can be improved by clearing sandy patches on gently south facing slopes, for basking and egg-laying. Clearance is done by simply pulling or digging out the heather to leave a bare sandy patch about 2 x 3m. In one such project, about 14 patches were cleared in an area of about 60 x 40m. This can be done virtually any time of year on ground where no sand lizards yet occur. A mechanical rotovator has also been used to keep the patches clear of vegetation in subsequent years. This must be done in May or June, after the adults emerge, but before the eggs are laid. For the same reason, May and June is also the time chosen for ploughing the firebreaks to keep them clear of vegetation. This is done every other year. The Merseyside population of sand lizards is distributed amongst about 20 breeding sites, some of which are completely isolated by urban development, golf courses and so on, and thus it is difficult for the lizards to spread. Normally, lizards will move only about 100m from their nesting and basking sites, although exceptionally they may move up to a maximum of about 700m. Great effort is put into protecting the remaining population and sites, including the release of individuals bred in vivaria. These are released on sites where numbers are low, on those where sand lizards were known to exist in the past, and onto new sites which have suitable vegetation and aspect. The natural development from marram grass to a suitable mix of vegetation can take 15 to 20 years, so short cuts have to be taken to create new habitats. The technique being tried is to transplant turfs of ‘fixed dune’ vegetation, from an area where marram is dying off and is being replaced by sand sedge. The transplanting is done in April. Individual plants of marram are also dug or pulled in the normal way, as these are too deep rooted to be transplanted successfully as turfs. The turfs are laid on the chosen new site, cleared bare of any existing unsuitable vegetation such as shrubs or non-native species, to leave about 10% bare sand. The clumps of marram are planted amongst them. On steep banks, simple steps or paths are helpful so that the progress of the new colony can be checked.
Another technique used is to cut turfs as shown, to create small bare patches for basking and egg-laying. This was done about every 15-20 metres along a suitable south facing bank.
