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Providing evidence to improve practice

Action: Translocate frogs Amphibian Conservation

Key messages

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  • Eight of ten studies (including five replicated studies) in New Zealand, Spain, Sweden, the UK and USA found that translocating frog eggs, juveniles or adults established breeding populations at 100% or 79% of sites. Two found that breeding populations of two species were initially established but went extinct within five years or did not establish.
  • Five studies (including one replicated study) in Italy, New Zealand and the USA found that translocated juveniles or adults survived the winter, had high survival, survived up to two years, or up to eight years with predator exclusion. One study in the USA found that survival was lower for Oregon spotted frogs translocated as adults compared to eggs and lower than that of resident frogs. Five studies (including three replicated studies) in Canada, New Zealand and the USA found that translocations of eggs, juveniles or adults resulted in little or no breeding at one or three of four sites.
  • Two studies (including one before-and-after study) in the USA found that 60–100% of translocated frogs left the release site and 35–73% returned to their original pond within 1–32 days. Two before-and-after studies New Zealand and the USA found that frogs lost weight during the 30 days after translocation or became heavier than animals at the donor site.

 

Supporting evidence from individual studies

1 

A study in 1990–2000 on Stephens Island, New Zealand (Brown 1994, Tocher & Brown 2004) found that three of 12 translocated Hamilton's frog Leiopelma hamiltoni survived within the new habitat for at least eight years. Evidence of breeding had not been recorded by 1992. Only one juvenile was ever recorded, in 1996. Eight frogs survived the first year and were recaptured 61 times by 2000. Three were not recorded at the release site after 1994, but two were found back at their original habitat (76–89 m). After eight years, 42% of translocated frogs had been recaptured compared to 47% marked at the original site. Recaptured frogs showed variable weight changes between translocation and 1992 (+23%, −12 to +55%). In May 1992, frogs were translocated 40 m to a new rock-filled pit (72 m2) in a forest remnant. A predator-proof fence was built around the new habitat to exclude tuatara Sphenodon punctatus and the area was ‘seeded’ with invertebrate prey. Frogs were surveyed regularly from November 1990 to May 1992 (90 visits), intermittently in 1992–1996 and at least four times annually (over six days) in 1997–2000.

 

2 

A replicated study in 1986–1993 of 13 created ponds in a reserve in England, UK (Cooke & Oldham 1995) found that translocating common frog Rana temporaria eggs established breeding populations. The first naturally laid eggs were recorded in 1988 (92 clumps). The peak count was in 1989 with 162 egg clumps. Numbers of emerged froglets were high in the first year, but low in the second. Up to 12–13% of eggs were lost to collection and 16–39% to desiccation each year. In 1985, 13 ponds were excavated. Local frog spawn was introduced to the ponds in spring 1986 (200 clumps), 1987 (150), 1990 (8), 1991 (4) and 1993 (14). Monitoring was 1–3 times/week in spring 1986–1993.

 

3 

A replicated, before-and-after study in 1987–1997 in Jersey, UK (Gibson & Freeman 1997) found that agile frog Rana dalmatina breeding populations were established from translocated eggs. Translocated eggs hatched and were successfully reared at all three sites. Populations started breeding within two to three years of release and then bred most years. In 1987, six egg masses were removed from a polluted pond and translocated to a garden pond (1 m2). In 1993, two enclosures in a second pond were stocked with translocated eggs. Surviving frogs were translocated to a third pond in 1994.

 

4 

A study in 2000 at Guadalupe Dunes, California, USA (Rathbun & Schneider 2001) found that eight of 11 translocated California red-legged frogs Rana aurora daytonii returned to the original pond within a few days. All seven adults left the release ponds between 24–48 hours after release. Six returned to the original pond in 1–9 days; one was found dead there. The five surviving were translocated again and four remained at the release pond for at least 10–17 days. The fifth adult was found back at the original pond within 32 days having travelled 3 km. Two juvenile frogs also returned to the original pond a number of times; the other two were not recaptured. In February 2000, seven adult and four juvenile frogs were marked and translocated 2 km, from a polluted pond to three natural ponds. The original pond was pumped dry at the end of February. Frogs were monitored by radio-tracking for a month.

 

5 

A replicated study in 1998–2000 in the Lombardy District, Italy (Gentilli et al. 2002) found that translocated head-started Italian agile frog Rana latastei tadpoles metamorphosed successfully and survived over winter. Metamorphosis occurred in both years. Eggs were collected from sites close to the release sites. Eggs were hatched in semi-natural conditions in captivity. In 2000, a total of 12,000 tadpoles were raised in captivity. Tadpoles with developing hind limbs were released to new and restored ponds and habitat in five natural parks. Tadpoles were released at two sites in 2000 and seven sites in 2001.

 

6 

A replicated, before-and-after study in 1995–2000 of two created ponds in Ohio, USA (Weyrauch & Amon 2002) found that translocated gray tree frogs Hyla versicolor did not reproduced in created ponds. Evidence of reproduction was not recorded, although frogs were heard calling at one pond in 2000. Ponds were created in 1995–1997 and were 2–4 m deep. Vegetation, plankton and organic matter (from local wetlands) were added. Gray tree frog larvae (0–35) and metamorphs (0–4) were translocated to the pond in spring 1996–1998 and 2000. Monitoring was undertaken using drift-fencing and pitfall traps surrounding ponds, dip-netting and egg counts.

 

7 

A replicated study in 1999–2002 in Alberta, Canada (Kendell 2003) found limited evidence of breeding by translocated head-started northern leopard frog Rana pipiens. Seven released frogs were recaptured, another three were heard calling and one egg mass was observed at the site surveyed. Three to six egg masses were collected from the wild each year and reared to metamorphs in two man-made outdoor ponds. Predators were excluded or removed where possible. Between 1999 and 2002, a total of 6,500 captive-reared frogs were tagged and released at three new sites. Surveys were undertaken at one release site in May–July 2002.

 

8 

A before-and-after study in 1999 on an alpine fell in Kings Canyon National Park, California, USA (Matthews 2003) found that translocated mountain yellow-legged frogs Rana muscosa lost weight during the 30 days after translocation. Translocated frogs lost an average 1.2 g in body mass, whereas resident frogs gained 2.5 g over the same period. Seven of the translocated frogs returned to their original capture site, five moved the 206–485 m in 11–30 days. Four frogs moved in the direction of their capture site and nine remained at the translocation site. Twenty frogs with transmitters fitted were translocated 144–630 m to other ponds and lakes that were not typically used. Frogs were monitored intensively for 30 days in August and then surveyed using passive integrated transponder (PIT) tags. Translocated and 18 randomly selected resident frogs were weighed at the start and end of the study.

 

9 

A replicated, before-and-after study in 1998–2003 of 14 ponds in Gipuzkoa province, Spain (Rubio & Etxezarreta 2003) found that translocated adults, along with head-started and captive-bred juvenile stripeless tree frogs Hyla meridionalis established breeding populations in 11 ponds. Translocated adults survived in good numbers and returned to 12 of 14 ponds. Mating, eggs and well-developed larvae were observed in 11 of the ponds; froglets were also recorded in some ponds. Introduced predators, dense vegetation, eutrophication and drying resulted in reduced survival and reproduction in some ponds. A small number of additional ponds were colonized by the species. Thirteen ponds were created and one restored, with vegetation planted in 1999–2000. In 1998–2003, a total of 1,405 adults were translocated to the ponds. Eggs were also collected, reared in captivity (in outdoor ponds) and released as 871 metamorphs and 19,478 tadpoles into eight of the ponds. An additional 5,767 captive-bred tadpoles were released.

 

10 

A before-and-after study in 1984–2003 on Maud Island, New Zealand (Bell, Pledger & Dewhurst 2004) found that translocated Maud Island frogs Leiopelma pakeka established a population that remained relatively stable. Losses of translocated frogs were offset by local recruitment. Numbers declined initially (survival: 64%), but annual survival rate was then high (97%). Seventy per cent of translocated frogs and 35 young recruits were (re)captured over the 20-years of monitoring. Survival of local recruits was 80%. Most frogs settled within the release site, but a few dispersed up to 26 m. Translocated frogs became significantly heavier (per unit length) than those in the source population; average range size did not differ (12 m2). Frogs were marked and translocated from one forest remnant to one 0.5 km away that had no Maud Island frogs. Forty-three frogs were moved in May 1984 and 57 in May 1985. Monitoring was carried out during 4–5 successive nights over 600 m2 at least twice annually until 1994 and then annually until March 2003.

 

11 

A before-and-after study in 1997–2002 of the translocation of 300 Hamilton's frog Leiopelma hamiltoni from Maud Island to Motuara Island, New Zealand (Tocher & Pledger 2005) found that the population established and stabilized. Losses of translocated frogs were offset by new recruits. High mortality and/or dispersal occurred during the first two months, followed by a constant high survival rate (71–100%). New juveniles were found every breeding season from 1998, just 10 months after the translocation. By August 2002, 155 of the translocated frogs and 42 recruits had been (re)captured. New recruits had survival rates of 29–88%. Frogs were toe-clipped and translocated 25 km to the predator free island in May 1997. Frogs were released into a 10 x 10 m grid with initial densities of 3/m2. Frogs were monitored by recapturing within the grid during two sessions of 5–10 nights in 1997 and four sessions in 1998. The grid and a 100 m2 surrounding grid were searched in August 1999–2002.

 

12 

A replicated, before-and-after study in 2003–2008 of 18 ponds within agricultural landscapes in western Scania, southern Sweden (Loman & Lardner 2006) found that although translocation of moor frog Rana arvalis and common frog Rana temporaria eggs initially resulted in breeding populations, they were extinct within five years. Common frog calling males were found at two ponds, eggs in eight and metamorphs in 12 release ponds. Moor frog calling males were found at one pond, eggs at five and metamorphs at nine ponds. Numbers of egg clumps peaked after two years. However, four years after the translocation, breeding was recorded in only two ponds and one year later those populations were extinct. Eggs were collected from south Scania and introduced into eight ponds in 2003 and 10 ponds in 2004 in six areas. Each pond received 20 egg clumps from each species. Ponds were monitored for metamorphs in June–July. Release ponds and other ponds within 750 m were monitored annually.

 

13 

A replicated, before-and-after study in 1994–1998 at four sites in meadow in Sequoia National Park, California, USA (Fellers et al. 2007) found that following translocation of mountain yellow-legged frogs Rana muscosa there was no evidence of reproduction at three sites and insufficient reproduction to maintain a population at the fourth. Survival of all life history stages was high in the first week and metamorphs and adults were present at end of the first summer. However, nearly all life history stages disappeared within 12 months of translocation. At one site there was recruitment of 28 adults from tadpoles. However, in 1997 all frogs at that site were sick or dead, thought due to chytridiomycosis and/or pesticides. A total of 22 of 135 frogs were found in nearby ponds. In 1994 and 1995, egg masses (2/site), tadpoles (0–108), sub-adults (0–25) and adults (0–31) were released at four previously occupied sites, 30 km from the original population. Release sites were monitored every 1–3 days in summer in 1994–1995, monthly in 1996–1997 and once in 1998. Visual surveys and adult captures were undertaken.

 

14 

A before-and-after study in 2004 of a pond in parkland in Lancashire, UK (Neave & Moffat 2007) found that translocated common frogs Rana temporaria established a breeding population. Frogs were translocated to the pond from a nearby building site in 2002 and monitored in spring 2004.

 

15 

A study in 2001–2004 of created ponds within a wetland in Oregon, USA (Chelgren et al. 2008) found that survival was lower for Oregon spotted frogs Rana pretiosa translocated as adults compared to those translocated as eggs. Frogs had a significantly lower survival rate during the first year after translocation, compared to the following three years (e.g. large frogs: 28–44% vs 48–74%) and non-relocated frogs. Annual survival rate was significantly higher for large frogs (>53 mm; 48–74%) compared to small frogs (40–53 mm; 5–39%). Survival increased with increasing pond age. Nine ponds were created in 2001–2004 using explosives (0.01–0.07 ha; 2 m deep). In spring 2001, nine spotted frog egg masses and in June–September 2001, 41 marked frogs were translocated to the four largest ponds, from a site 2.5 km away.

 

16 

A replicated study in 2005–2008 in a restored forested wetland in Lake County, Illinois, USA (Sacerdote 2009) found that translocated spring peeper Pseudacris crucifer tadpoles survived to metamorpohosis in enclosures in restored ponds. All tadpoles survived through metamorphosis. In 2008, 12 tadpoles were placed in two mesh enclosures (56 x 36 x 36 cm) in two restored ponds. Tadpoles were monitored 2–3 times/week until metamorphosis. Tadpoles were moved if ponds dried.

 

17 

A study in 2006–2009 in Zealandia, Wellington, New Zealand (Bell, Bishop & Germano 2010) found that survival of Maud Island frogs Leiopelma pakeka released in a predator-proof enclosure was high (93%), but in the wild was low. Numbers observed in the wild declined significantly, where house mice Mus musculus and little spotted kiwis Apteryx owenii were known predators. In the enclosure, two males were recorded breeding in February 2008 and 10 nearly metamorphosed young frogs resulted. Sixty frogs from Maud Island were placed in a 2 x 4 m predator-proof mesh enclosure in 2006. In April 2007, 29 were retained in the enclosure and 28 were released into the adjacent forest. Larvae found were moved to incubators to complete metamorphosis and then released into nursery pens.

 

18 

A before-and-after study in 2004–2011 of 71 Hamilton's frogs Leiopelma hamiltoni translocated from Stephens Island to Nukuwaiata Island, New Zealand (Tocher 2011) found that a breeding population was established. Production of juveniles, establishment of the new population and recovery of the donor population was slower than expected. However, by August 2011, repeated breeding had occurred and new recruits were almost at breeding age. There was no evidence of a decline within the donor population. Frogs were translocated between May 2004 and July 2006. Both the translocated frogs and donor population were monitored until 2011.

 

19 

A study in 2010–2012 in southwest Georgia, USA (Hill 2012) found that a number of translocated head-started gopher frogs Lithobates capito survived. Some froglets released in 2012 were observed later in the year and a large adult female released in 2010 was captured. Portions of egg masses were collected from one of the remaining breeding sites and transferred to partner institutions for rearing to metamorphosis. Tadpoles were reared outdoors in large tanks with plant matter from the egg collection site. Over 4,300 froglets were marked and released onto restored Nature Conservancy land, which lacked a natural population. In 2012, froglets were released directly into burrows as protection from drought. Monitoring began in summer 2012.

 

20 

A before-and-after study in the UK (Wilkinson & Buckley 2012) found that a small population of pool frogs Pelophylax lessonae was established from translocations. The frogs were healthy and had good survival rates, but the population did not grow as anticipated. Not all of the ponds were used by the frogs. In 2005, adults, juveniles and tadpoles were collected from Sweden and released at a recently restored site. Releases were repeated three times. Individual frogs were monitored.

 

Referenced papers

Please cite as:

Smith, R.K., Meredith, H. & Sutherland, W.J. (2019) Amphibian Conservation. Pages 9-65 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.