Sandscale Haws Natterjack Toads
Sandscale Haws National Nature Reserve is home to one of the largest remaining Natterjack Toad populations in the UK. This unique amphibian is well known for the extraordinary chorus of the male toads during the breeding season when the loud rasping calls can be heard up to a mile away on a still night. Numbers of this species declined dramatically during the 20th Century and populations at many sites went extinct over this period. The declines were predominately attributed to habitat loss and today there is an estimated population of just 4000 adults in the country, making our colony of around 1000 adults hugely important in terms of the conservation of this species.
As Natterjacks are nocturnal and can range over large areas outside of the breeding season, the easiest way to monitor the population is to undertake an annual spawn count. The spawn is laid in long rows of black eggs and differs from Common Toad spawn in that it separates out in to a single row of eggs after a day or two. As each female generally will breed once per year and there is an approximate 1:1 ratio of males to females simply doubling the spawn count gives a reasonable estimate of the population level. This data can be used to monitor changes in the population level over time.
In recent years a lot of work has been undertaken looking at the genetics of the Natterjack Toad populations across the UK. This has shown that there are currently 13 native and 16 re-introduced populations but that the vast majority of Natterjacks survive in the native populations showing how important it is that no more populations become extinct. The Sandscale Haws population is linked to nearby populations along the coast at Askam and Dunnerholme but the other nearby population on North Walney National Nature Reserve, cut off by the Walney Channel, have been genetically isolated for a long period of time.
At Sandscale Haws there are over 40 pools, approximately half of which will be used by Natterjacks in a typical year. Most of these are seasonal in nature and the actual number of pools and the depth of the water across the site can vary dramatically from year to year. The breeding season typically starts in early to mid-April but will be delayed in a cold spring. In a wet year there can be over 20ha of water to survey and whilst this may seem daunting it is important that we have good population data for this species to ensure that our conservation work is being effective. Therefore, much of the Rangers time in April and May is spent surveying the pools, trying to find and record as many spawn strings as possible. As with most of our work volunteer help is essential and the task could simply not be accomplished without them.
Natterjack Toads have adapted to breed in temporary pools that typically dry out by mid-summer. This means that it is a race against time for the spawn to hatch and the tadpoles to develop and metamorphose before the pools dry up. A dry spring may mean that many of the toads choose not to breed and those that do may be unsuccessful. There is little value in comparing counts from year-to-year but comparing data over longer periods does reflect trends in population levels. The highest count recorded at Sandscale to date was 600 spawn strings in 1989 whereas the highest count from recent years was 527 in 2011 indicating that the population has been more or less stable over this period. By contrast the low count of 194 strings in 2009 reflected the exceptionally dry spring rather than any true decline in the population. The 2015 total was 468 spawn strings but toadlets only emerged from 5 out of 17 pools as many pools dried up during June.
Natterjack Toads enjoy a high level of protection in the UK and it is illegal to harm or disturb them at any time. To avoid accidental disturbance two of the best ways to see this species are to join an official guided walk or to visit the viewing pools near to the car park at Sandscale Haws. The best time to visit is usually from mid-April until mid-May from dusk onwards when most males will be at the breeding pools and the chorus can be heard across the site. Look out for the annual guided walks run by the Sandscale Haws Rangers.