Action: Translocate toads
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- Two of four studies (including two replicated studies) in Denmark, Germany, the UK and USA found that translocating eggs and/or adults established common toad breeding populations. One found populations of garlic toads established at two of four sites. One found that breeding populations of boreal toads were not established.
- One before-and-after study in Denmark found that translocating green toad eggs to existing populations, along with aquatic and terrestrial habitat management, increased population numbers.
- Three studies (including one before-and-after study) in Germany, Italy and the USA found that 33–100% of translocated adult toads reproduced, 19% survived up to six years or some metamorphs survived over winter. One replicated study in South Africa found that translocated Cape platanna metamorphs survived up to 23 years at one of four sites.
As there is a larger literature for natterjack toads Bufo calamita than other species, evidence is considered in a separate section.
Supporting evidence from individual studies
A before and after study in 1986–1992 of a created pond in wet pasture near Ahlerstedt, Germany (Schlupp et al. 1989, Schlupp & Podloucky 1994) found that translocated common toads Bufo bufo bred in the new pond every year. Population size did not differ significantly before and after resettlement (522 vs 590). In 1987, 29% of migrating toads chose the created pond rather than their original pond (across a road). By 1988 the proportion was 75% and by 1992 it was 99%. Marked individuals indicated that 83% of the population used the new pond (91% of males; 67% of females). An amphibian fence with pitfall traps was installed along 400 m of road. Toads captured were placed in the created pond (53 x 20 m). A temporary mesh fence around the pond allowed toads to reach but not leave the pond in spring 1986–1990. All animals were tagged.
A study in 1991–1992 in Wyoming, USA (Johnson 1994) found that a translocated pair of Wyoming toads Bufo baxteri bred in the first year. In 1992, tadpoles were produced from eggs laid within the breeding enclosure in the release pond. Toads did not breed in the original pond, the only remaining wild population. Female and juvenile toads were captured from the wild and overwintered in captivity for four months. One of the females and a wild-captured male were released into a breeding enclosure within the release pond.
A replicated study in 1986–1993 of 13 created ponds in a reserve in England, UK (Cooke & Oldham 1995) found that translocated eggs and adult common toads Bufo bufo established breeding populations. The first naturally laid eggs were recorded in the second year. In 1988, 64% of male and 89% of female toads captured were already marked, suggesting that most adults were introduced rather than natural colonizers. The proportion marked dropped to 15% in 1990 suggesting a 64% loss of male toads in the first year, reducing to 39% in the second and 42% in the third year. The toad population was estimated at 200–300 adults in 1993. Up to 12–13% of eggs were lost to collection and 16–39% to desiccation each year. In 1985, 13 ponds were excavated. Half a million toad eggs were introduced in 1986 and 5,911 marked adults in 1987. Adults and eggs were monitored 1–3 times/week in spring 1986–1993.
A before-and-after study in 1986–1994 of a created pond in Gifhorn, Germany (Baumann 1997) found that translocated common spadefoot toads Pelobates fuscus bred in the new pond. Mortality rate of translocated toads was high, with only 19% of toads recaptured in 1993–1994. Monitoring indicated that 33% of translocated toads reproduced in the created pond. A total of 152 juveniles were recorded in the pond in 1990. From 1989, toads were captured using drift-fencing with pitfall traps along the side of the road. Toads were marked and translocated across the road to the pond (700 m²) created for amphibians within forest in 1988. Monitoring was undertaken using drift-fencing with pitfall traps either side of the road and around the pond.
A replicated, before-and-after study in 1994–1997 in Jutland, Denmark (Jensen 1997) found that translocated adult and head-started tadpole garlic toads Pelobates fuscus established breeding populations in two restored, but not two created ponds. The authors considered failure might have been due to predation because of the lack of vegetation and introduction of sticklebacks Pungitius pungitius. Forty-three toads were captured from a pond being eliminated by development. They were translocated to a restored pond. Four egg strings were laid in captivity and produced over 2,000 tadpoles. They were released at different stages before metamorphosis into the same restored and one created pond (n = 1,000). Two ponds had been restored and two created in 1994–1995. Toads were monitored by tadpole and call surveys.
A replicated, before-and-after study in 1995–1999 at two sites within a National Park in Colorado, USA (Muths, Johnson & Corn 2001) found that a breeding population of boreal toads Bufo boreas was not established from translocated eggs. At one site, only 12 tadpoles were recorded during the first week after release. Following that only two toads were recorded in 1997. At the other site 333 metamorphs were captured and marked in the first two weeks, but none were recorded in 1997–1999. Hatching success did not differ significantly between the original and release sites (69 vs 38–72%). Seventeen eggs masses were collected in July 1995 and June 1996. Half of nine, and six complete egg masses were translocated to two sites, where toads had been absent for five and eight years. A small number of eggs were placed in predator-proof boxes to compare hatching success between original and release sites. Following translocation of eggs, a 0.01–0.09 km2 area was searched 1–3 days/week in April–September 1995–1999. Metamorphs were toe-clipped.
A study in 1998–2000 in the Lombardy District, Italy (Gentilli et al. 2002) found that translocated head-started common spadefoot toad Pelobates fuscus insubricus tadpoles metamorphosed successfully and survived over winter. Metamorphosis occurred in both years and some juveniles were found in spring 2001. Eggs were collected from sites close to the release sites. Eggs were hatched in semi-natural conditions in captivity. In 2000, two thousand tadpoles were raised in captivity. In 2000, tadpoles with developing hind limbs were released to six new and restored ponds and habitat in five natural parks.
A before-and-after study in 1986–1997 of five ponds on coastal meadows on Avernako island, Denmark (Briggs 2003, Briggs 2004) found that there was a significant increase in green toad Bufo viridis population following translocation of eggs, along with pond creation and restoration and reintroduction of grazing. The population increased from 20 in 1988–1990 to 920 in 1995–1997. Pond occupancy increased from one to seven and the number of ponds with breeding success increased from zero to five. In 1989–1997, one pond was created and four restored by removing plants and dredging. Cattle grazing was reintroduced to 25 ha of coastal meadows and abandoned fields. In 1994–1995, a total of 14,500 eggs were translocated to four of the ponds. Populations were monitored annually in 1990–1997 during two or three call and visual surveys and dip-net surveys.
A replicated study in 1988–2011 at four water bodies in the Western Cape, South Africa (Measey & de Villiers 2011) found that some translocated Cape platanna Xenopus gilli metamorphs survived for over 23 years. A year after release, seven frogs were recorded at one of the four release sites (the site that had received the most metamorphs). Nine years later in 1998, six females were captured, three of which were marked. In 2008 and 2011, frogs were recorded at the same site. Two of the frogs in 2008 and one in 2011 had been marked in 1998. In 1988, 154 metamorphs were translocated 25 km to four water bodies (one received 69) where the species was historically present. Monitoring was conducted in 1989–1990, with additional visits in 1998, 2008 and 2011. In 2008 and 2011, baited funnel traps were placed at each release point.
- Schlupp M., Kietz R., Podloucky R. & Stolz F.M. (1989) Pilot project Bracken: preliminary results from the resettlement of adult toads to a substitute breeding site. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 127-135.
- Johnson R.R. (1994) Model programs for reproduction and management: ex situ and in situ conservation of toads of the family Bufonidae. Pages 243-254 in: J.T. Collins, K. Adler & J.B. Murphy (eds.) Captive Management and Conservation of Amphibians and Reptiles, Contributions to Herpetology Vol. 11, Society for the Study of Amphibians and Reptiles. Ithaca, New York.
- Cooke A.S. & Oldham R.S. (1995) Establishment of populations of the common frog Rana temporaria and common toad Bufo bufo in a newly created reserve following translocation. Herpetological Journal, 5, 173-180
- Baumann K. (1997) The population ecology of the common spadefoot toad (Pelobates fuscus) near Leiferde (district Gifhorn, Germany) with special regard to the effect of its artificial relocation into a new breeding-pond. Braunschweiger Naturkundliche Schriften, 5, 249-267
- Jensen B.H. (1997) Relocation of a garlic toad (Pelobates fuscus) population. Memoranda Societatis pro Fauna et Flora Fennica, 73, 111-113
- Muths E., Johnson T.L. & Corn P.S. (2001) Experimental repatriation of boreal toad (Bufo boreas) eggs, metamorphs, and adults in Rocky Mountain National Park. Southwestern Naturalist, 46, 106-113
- Gentilli A., Scali S., Barbieri F. & Bernini F. (2002) A three-year project for the management and the conservation of amphibians in Northern Italy. Biota, 3, 27-33
- Briggs L. (2003) Recovery of the green toad Bufo viridis Laurenti, 1768 on coastal meadows and small islands in Funen County, Denmark. Deutsche Gesellschaft für Herpetologie und Terrarienkunde, 14, 274-282
- Measey G.J. & deVilliers A.L. (2011) Conservation introduction of the Cape platanna within the Western Cape, South Africa. Pages 91-93 in: Global Re-introduction Perspectives: 2011. More case studies from around the globe. IUCN/SSC Re-introduction Specialist Group & Abu Dhabi Environment Agency, Gland, Switzerland.