Leiopelma hamiltoni 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Amphibia Anura Leiopelmatidae

Scientific Name: Leiopelma hamiltoni McCulloch, 1919
Common Name(s):
English Hamilton's Frog, Stephens Island Frog
Taxonomic Source(s): Frost, D.R. 2015. Amphibian Species of the World: an Online Reference. Version 6.0. New York, USA. Available at:
Taxonomic Notes: The Maud Island population was previously considered to belong to this species, but was described as a new species, Leiopelma pakeka, in 1998 (Bell et al. 1998). However, Holyoake et al. (2001) considered them to be evolutionarily significant units of the same species based on a study of partial 12 S ribosomal RNA and cytochrome b gene sequences, although no formal taxonomic change was made as a result of this study. There is ongoing discussion and research into this subject.

Assessment Information [top]

Red List Category & Criteria: Vulnerable D1+2 ver 3.1
Year Published: 2015
Date Assessed: 2015-07-21
Assessor(s): IUCN SSC Amphibian Specialist Group
Reviewer(s): Luedtke, J.
Contributor(s): Bell, B., Bell, E., Easton, L., Bishop, P., Clerke, P. & Wren, S.
Facilitator/Compiler(s): Wren, S.

Leiopelma hamiltoni has been assessed as Vulnerable because the number of mature individuals is estimated at less than 1,000 (VU D1), the area of occupancy (AOO) is smaller than 20 km² and it is found in just two threat-defined locations. While the population is very small and restricted, as a result of conservation efforts there is no evidence of ongoing declines or fluctuations in number of mature individuals, extent of occurrence (EOO), AOO, quality of habitat or number of locations or subpopulations, so there is no justification for a higher threat category under criterion B or C. However, there are several plausible threats that could rapidly drive this species to be Critically Endangered or Extinct. It therefore qualifies for the Vulnerable category under criterion D (VU D1+2).

Previously published Red List assessments:

Geographic Range [top]

Range Description:The only naturally occurring population of L. hamiltoni is confined to a single rock tumble (c. 600 m2) on Stephens Island - Takapourewa, Cook Strait, New Zealand. Translocation to an adjoining area on Stephens Island with man-made refugia was attempted in 1992 (Brown, 1994), but with limited success as many frogs homed back to the original site (Tocher and Brown 2004). A more successful translocation has been carried out to a site (c. 400 m2) on a nearby island, Nukuwaiata, in the Marlborough Sounds; frogs were moved to this site in both 2004 and 2006 and appear to be establishing well. Due to ongoing and potential threats, the species is thought to occur in two threat-defined locations - one on each island. It has maximum area of occupancy of 1 km2 and maximum extent of occurrence of 2 km2.
Countries occurrence:
New Zealand
Additional data:
Estimated area of occupancy (AOO) - km2:0-1Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:1-2
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):60
Upper elevation limit (metres):280
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The most recent estimate for the Stephens Island population indicates a population size of approximately 300 adults (Tocher et al. 2006). Since this estimate was made 71 individuals have been translocated to Nukuwaiata Island (split between two translocations in 2004 and 2006) with the aim of establishing a second sub-population. Juveniles and sub-adults have been detected in recent monitoring trips at the Nukuwaiata Island site (S. Wren, pers. comm. July 2015) which indicates that the translocated individuals are establishing at the new site and the population is increasing. While juveniles have been recorded during monitoring of the Stephens Island site, very few sub-adults and new adults seem to be recruited into the population (E. Bell pers. comm. July 2015) so further analysis is necessary to evaluate the population size and trend. As such the total population size is estimated to be 300-800 individuals.
Current Population Trend:Increasing
Additional data:
Number of mature individuals:300-800Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:

Leiopelma hamiltoni became restricted to a boulder bank near the summit of Stephens Island, an area which was once denuded of vegetation but is now covered with regenerated native forest thanks to conservation efforts. This species has been translocated to similar habitat, a boulder bank in native forest, on nearby Nukuwaiata Island.

The lifespan of these frogs is not well known, but individuals of the closely related L. pakeka have been recorded at over 40 years old. Its is thought that sexual maturity is reached at 4-5 years and that individuals may reproduce every other year, giving it a generation length of approximately 20 years.Very little else is known about the reproductive ecology of this nocturnal species, although it is known that small clusters (<15) of large unpigmented eggs are laid terrestrially in damp situations in sheltered areas on the ground or under rock plies. Eggs undergo direct development without a larval stage (Bell 1985).
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):20
Movement patterns:Not a Migrant

Use and Trade [top]

Use and Trade: There are no records of the species being utilized or traded.

Threats [top]

Major Threat(s):

The introduction of non-native mammalian species (e.g. Rattus rattusRattus exulans, and mustelid species) combined with deforestation was probably the major driver of the massive historical declines in both range and population size. It is also thought that predation by the native Tuatara (Sphenodon punctatus) may have had an impact on the small frog population at the Stephens Island site.

Today introduced mammalian predators remain a potential threat; non-native species are currently kept from the islands through strict quarantine procedures, but an invasion would be likely to have a massive impact on the remaining population. Future fire events are also a threat to L. hamiltoni because of the species’ very small distribution size and remote location. Chytridiomycosis is a potential future threat; this disease has been identified in New Zealand in the closely related L. archeyi, but to date this disease has not been recorded on either of the islands where L. hamiltoni occurs. The population remains small and is split between just 2 small sub-populations, so the species is also vulnerable to stochastic events (Bishop et al. 2013). 

Conservation Actions [top]

Conservation Actions: Conservation Actions In Place
Initial fencing of the frog site, to exclude livestock, followed by a forest regeneration programme, has effectively restored a young native forest canopy and undergrowth to the site on Stephens Island. A Tuatara-proof fence has also been constructed around the frog habitat to protect L. hamiltoni from possible predation.

A small intra-island translocation was carried out in 1992 to a site near the frog bank where habitat restoration had been carried out, and the Tuatara-proof fence was extended to protect the new site (Brown 1994). This was of limited success as some individuals re-homed back to the source site and only a small number seem to have remained at the translocation site (Tocher and Brown 2004). A more successful translocation was carried out in two stages to nearby Nukuwaiata Island in 2004 and 2006; a total of 71 individuals were moved and monitoring has recorded a good number of recaptures of translocated individuals, as well as offspring at the new site (S. Wren Pers. com. July 2015). Regular population monitoring is ongoing at both sites.

Strict quarantine protocols are in place for everyone visiting these islands, in order to stop colonization by mammalian predators or the introduction of disease. Both islands where L. hamiltoni is found are within protected areas; both Stephens Island and Nukuwaiata Island are within Nature Reserves. Through its Native Frog Recovery Group and 2013-2018 Native Frog Recovery Plan, the NZ Department of Conservation (DOC) administers conservation management of this species and permits appropriate species research; Stephens Island is managed jointly between DOC and local iwi Ngati Koata.

Conservation Needed
Maintaining existing biosecurity and hygiene protocols at island sites is essential for the continued survival of this species. Annual monitoring of both sub-populations should continue to ensure they remain healthy.

Additional translocations could be considered in the future to further spread the risk, although only after population modelling has been carried out to ensure that this will not have a detrimental impact on the small donor populations.

Lack of public awareness of cryptic native frogs does not aid conservation efforts; increased public awareness of this species would be of benefit.

Research Needed
There is still debate regarding the taxonomic status of this species with relation to L. pakeka – research is necessary to define whether these represent one or two species, as this has implications on conservation management.

Data, including life-history data necessary for developing population models and providing guidance for translocations, are lacking for this species, and research should continue to determine life-history parameters.

Citation: IUCN SSC Amphibian Specialist Group. 2015. Leiopelma hamiltoni. The IUCN Red List of Threatened Species 2015: e.T11451A66654406. . Downloaded on 23 September 2018.
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