Individual study: A recovery program for the natterjack toad (Bufo calamita) in Britain
Denton J.S., Hitchings S.P., Beebee T.J.C. & Gent A. (1997) A recovery program for the natterjack toad (Bufo calamita) in Britain. Conservation Biology, 11, 1329-1338
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Translocate natterjack toads
A replicated, before-and-after study in 1972–1995 at dune and heathland sites in England, UK (Denton et al. 1997) found that at least six translocations of natterjack toad Bufo calamita eggs resulted in expanding new populations and eight showed initial signs of success. Two of three dune sites had breeding within three years and the third (> 5 years old) established one of the largest populations. Five of 17 translocations on heathland were successful, with stable or increasing adult numbers and breeding for at least five years. Six less than three years old, all produced toadlets in their first year. Six failed (five pre-1980) with no successful metamorphosis. Ten successful translocations were to sites with new ponds, in heathland six were concrete and one butyl plastic lined. Nine were undertaken after 1991 and comprised translocations of eggs (two spawn strings, i.e. 5,000 eggs) each year for two years. Scrub clearance was undertaken at two dune and seven heath sites. One heath site had limestone added to acidic ponds. Low-density sheep or cattle grazing (<1 animal/3 ha) was established at one dune and two heath sites. Spawn strings were counted and toadlet production estimated.
A replicated, before-and-after study in 1972–1995 of 10 dune and heathland sites in England, UK (Denton et al. 1997) found that extensive vegetation clearance, along with other terrestrial and aquatic habitat management, increased or maintained natterjack toad Bufo calamita populations. Abundance and range increased at four of the 10 sites. Success at another four sites was not yet clear, although toads persisted. At two sites, where vegetation clearance was less complete, populations continued to decline. At six sites where scrub removal was needed but not possible, populations remained low or were maintained by artificial methods (e.g. common toad removal). Clearance of invasive scrub and woodland and rotovation to clear patches of ground was undertaken. Low-density sheep or cattle grazing (<1 animal/3 ha) was also established at some sites (all/part year) to control succession. New ponds were created at most sites. Small numbers of ponds were treated with limestone. Translocations were made to some restored habitats. Ponds were monitored by counting spawn strings and estimating toadlet production.
Create ponds for natterjack toads
A replicated before-and-after study in 1972–1995 at 26 dune, heathland and salt marsh sites in England, UK (Denton et al. 1997) found that pond creation, along with terrestrial habitat management and translocations, maintained or increased natterjack toad Bufo calamita populations at the majority of sites. At 46% of sites, new ponds were considered by the authors to have prevented extinction. At an additional 19% of sites, populations increased following pond creation. There was no effect of new ponds at 27% of sites. At all 26 sites, at least one and usually most new ponds were used by toads within 1–2 years of creation. Over 200 ponds were created by excavation over 25 years. Some were lined with concrete. Vegetation clearance was undertaken at 10 sites. Low-density sheep/cattle grazing was established at seven sites and a small number of acidic ponds were treated with limestone. Twenty translocations to restored habitat were also undertaken. Ponds were monitored by counting egg strings and estimating toadlet production.
Add lime to water bodies to reduce acidification
A before-and-after study in 1972–1995 of ponds at three heathland sites in England, UK (Denton et al 1997) found that adding limestone to ponds resulted in the establishment of a translocated population of natterjack toads Bufo calamita at one site, metamorphosis at a second, but no population increase at the third site. The translocated population was dependent on limed ponds at the one site. At the second site, metamorphosis occurred at several previously acidic ponds. However, at the third site, the population did not increase (see (2)). Three sites received minimal powdered limestone (to raise pH to 7) in early spring. At one site, silt (with accumulated sulphate) was removed during the summer (pH increase: 4.5 to 5.5). Pond creation, vegetation clearance and establishment of livestock grazing were also undertaken at some sites. Ponds were monitored by counting spawn strings and estimating toadlet production.