29 January 2026

 

Background

This note summarises ARC’s views on “Investigating the Status of Britain’s Lost Frogs: Prospects for Rewilding” (Tweats, 2026), hereafter referred to as the “Lost Frogs report”. ARC was pleased to be consulted by Celtic Rewilding on a draft of the report in late 2025.

The report is framed as a review on the status of three amphibian species not currently recognised as ordinarily resident in Great Britain. Our interpretation of the report is that there is a clear ambition to work towards the introduction or reintroduction of these three species, subject to a feasibility study. ARC has considerable experience with these species, largely via work on the continent.

 

Norfolk Pond Habitat /Tony Gent

General comments

ARC welcomes explorations of topics that could advance the conservation of amphibians and reptiles, even when they appear to challenge conventions or long-held views. The Lost Frogs report touches on issues that are at times contrary to accepted positions, and we think it is useful to bring such issues into the open for discussion, and where necessary debate. Long-held views can sometimes be challenged and lose validity if new evidence or new standards are accepted. From this perspective, we note that the Lost Frogs report has generated a substantial amount of interest, debate and concern in the core amphibian conservation community.

 

Comments on species status

Note that for the purposes of this comment, we use Natural England’s definition of native status (Pouget and Sabel, 2025). Essentially, this is that the species has some documented presence in the Holocene without having been introduced by humans.

Moor frog Rana arvalis: We agree with the Lost Frog report’s main conclusion that this species was likely present as a native species earlier in history, during the early-late Saxon period (c400-1,100 AD), based on subfossil evidence (Gleed-Owen 2000). This presence in southern England appears consistent with our understanding of its European range (Gleed-Owen, 2000; Roček & Šandera 2008). We note that the Lost Frogs report suggests an eighteenth-century literature source potentially refers to this species because of its “livid” or blue-grey colour, but we suspect that this description could equally apply to common frogs R. temporaria.

Agile frog Rana dalmatina: We agree with the Lost Frog report’s main conclusion that this species was likely present as a native species earlier in history. It has been recorded from early-middle Saxon (c600-1,100 AD) subfossils (Gleed-Owen 2000).

Common or European tree frog Hyla arborea: We disagree with the Lost Frog report’s conclusion that the available evidence points to this species having been present as a native species. Whilst there are reports in the literature that could conceivably attest to the species being present in the last 500 years, we do not find this compelling evidence for native status. The references are often rather vague in terms of identifying features that would be diagnostic of this species, or ambiguous about whether the account refers specifically to presence in Britain. We would expect that there would be more unambiguous evidence of the species presence were it actually to have occurred here. We do accept that there is inherent ambiguity in older literature, which complicates a status assessment, and that the species is less likely to appear in the archaeological record than some other amphibians (though we think the Lost Frogs report somewhat exaggerates this point, since for example there are finds of H. arborea in Britain during the Pleistocene [Böhme 2010]). The Lost Frogs report notes that the species could have been present as a native species before being extirpated by the mid 18^th century by a combination of land use change, loss of the beaver, and human exploitation. This is an interesting theory, but we suggest that it requires further exploration to check its robustness. Overall, we do not feel the evidence here provides sufficient strong case for concluding that the species was native during the Holocene. We welcome further investigations into the possible native status of this species, and remain open to reviewing our conclusions should more compelling evidence be provided.

 

Comments on (re)introduction potential

In the case of R. arvalis and R. dalmatina, we think there is a valid case for assessing whether reintroduction is desirable. We take issue with the term “feasibility” since this implies an assessment of whether it would be possible – in practical terms, setting aside the regulatory issues for now - to release the species and for it to form a viable population; we suspect that the answer would be yes. In our view, however, the first question is whether it would be desirable to reintroduce the species, regardless of whether and how it might be achieved. Former presence as a native species is one important criterion for a reintroduction, but it is not the only one. Generally speaking, the further back in time the species was present as a native, the less compelling the case for reintroduction, not least as conditions will likely have changed substantially. We suggest that for a reintroduction proposal for R. arvalis and R. dalmatina, there should first be a case made to outline why the species should be re-established. Subsequent to that, the standard steps in assessing the feasibility of a conservation translocation should be followed, using domestic and international guidance. Particular attention should be paid to examining how these species might have formed part of wetland ecosystems before extinction, the potential causes of extinction, and how those might be remedied.

In the case of H. arborea, given that we believe the evidence for native status is weak, we do not concur with a translocation on the grounds of re-establishing an extinct species. However, we note that the Lost Frogs report (Table 5, p.125) suggests other potential reasons for introducing the species, that do not rely on an assumption of native status. We also note the comments in the Foreword suggesting that this species should be introduced to improve its prospects in the face of the adverse impacts of climate change. We believe these potential justifications for translocation are insufficiently expanded in the Lost Frogs report. Whilst we do not discount that they may have merit, they would involve a substantial shift in convention: introducing a species widely recognised as non-native, and thereafter (presumably) actively conserving it. Whether that is for reasons of public engagement, as the Lost Frogs report suggests, or other purposes, it would require a significant change in how non-native species are regarded by society in general, by the nature conservation sector, and importantly in a regulatory sense. Introducing non-native species also carries well-documented risks. We think that such a profound change needs broad, cross-taxonomic and ideally international agreement on objectives and standards. ARC has generated discussions on this topic in relation to amphibians and reptiles in Great Britain (e.g. Foster, 2022) and we note that there are increasing calls to explore whether potentially irreversible threats like disease and climate change should prompt a re-think of conservation conventions, especially on trans-boundary assisted colonisation (e.g. Lundgren et al, 2026). We look forward to engaging further with that discussion, but for now we do not think H. arborea meets emerging criteria (e.g. D’Andrea et al, 2025) for an assisted colonisation to Britain.

 

Important context: the risks of premature translocations

Translocations are recognised as an important tool in recovering nature, and ARC has used the method to generate positive outcomes for Britain’s threatened reptiles and amphibians (see ARC website article here, for example). Translocations also carry risks and involve substantial costs to undertake to good practice, and so the pros and cons need careful weighing (see ARC website article here).

As well as ecological and socio-economic risks, translocations can divert attention from addressing key actions to conserve existing species. In particular, introducing a “new” species would bring an expectation of resources to support its active recovery, and there would be costs to a range of stakeholders from doing so. Hence, we believe that introducing species should only be done where there has been a careful consideration of the benefits to restoring the species as part of a wider approach to nature conservation, and weighing the potential risks. The reintroduction may well have negative impacts on efforts to conserve other species. We do not think that this situation automatically discounts a reintroduction R. arvalis or R. dalmatina, it simply means the case needs to be compelling. As the Lost Frogs report is framed as a status report rather than a reintroduction proposal, we would anticipate further work to explore these issues in depth, before a decision on whether or not to reintroduce is made.

 

Suggestions for further investigation

We note that the Lost Frogs report has generated renewed interest in the possibility of restoring lost species of amphibians, or potentially enhancing our fauna with non-native amphibians. We note with interest the comment released by Celtic Rewilding shortly after the publication of the Lost Frogs report (Celtic Rewilding, 2026), in which it outlines a decision to focus on feasibility studies for R. arvalis and R. dalmatina, with less priority on H. arborea. The statement also emphasises that the project is focusing on research and assessment, and is not yet seeking to initiate a translocation. We broadly welcome that statement.

 

ARC’s suggestions for further investigation are:

• To focus initially on the rationale for a potential reintroduction of R. arvalis and/or R. dalmatina, rather than practicality of a translocation.
• To ensure that key conclusions, especially those that appear to challenge existing understanding, should ideally be published in a peer-reviewed journal, in order to allow scientific scrutiny.
• Reports and, most importantly, peer-reviewed papers should ideally be based on evidence from completed investigations, rather than initial exploratory work such as the climate modelling presented in the Lost Frogs report; whilst we think this sort of modelling could be valuable, reporting on work that is only partially complete and insufficiently explained risks undermining confidence in conclusions.
• Media reporting of further investigations should be handled in way that minimises the chance of adverse misreporting. We note that Celtic Rewilding has expressed regret about some misleading media reporting on their work. ARC has received numerous queries about the resulting media coverage. We have concerns that some landowners might even commit offences by releasing animals without the necessary permission, after picking up misleading messages. We are also concerned that the public may be misled into accepting questionable narratives about species status and reintroduction plans.

 

Concluding remarks

We thank Celtic Rewilding for engaging with ARC over the Lost Frogs report, and we look forward to further discussions. We hope that the above comments will help others understand ARC’s views on the report’s conclusions, and where we suggest further work could be best directed. With a topic that has potential to challenge long-held views, we think that open discussion is best, and we encourage others to engage with Celtic Rewilding (as per the 22 January 2026 statement). In that regard, we also welcome the chance for the UK amphibian conservation community to discuss the Lost Frogs report at the upcoming Herpetofauna Workers Meeting in Glasgow, 31 January-1 February 2026.

 

References

Böhme, M. (2010). Ectothermic vertebrates, climate and environment of the West Runton freshwater bed (early Middle Pleistocene, Cromerian). Quaternary International, 228(1-2), 63-71.

Celtic Rewilding (2026). Celtic Rewilding Statement on the Britain’s Lost Frogs Project (22 January 2026). URL: https://celtic-rewilding.co.uk/wp-content/uploads/2026/01/Lost-Frogs-Project-Statement-1.pdf

D'Andrea, R., Barabás, G., Dalrymple, S. E., Foden, W., Genovesi, P., Krishnadas, M., Leibold, M.A., McPeek, M.A., Moehrenschlager, A., Rodriguez, J.P. & Akçakaya, H.R. (2025). Ecological Risk–Benefit Analysis for Assisted Colonization. Global Change Biology, 31(11), e70613.

Foster, J. (2022). Does climate change herald a new herpetofauna for the UK? Views held by attendees at a conservation conference in 2021. Unpublished report. Amphibian and Reptile Conservation Trust, Bournemouth. URL: https://www.arc-trust.org/Handlers/Download.ashx?IDMF=93ef597a-206c-40d5-ab9f-1c45383b8342

Lundgren E, Svenning J-C, Schlaepfer MA, et al. Many pasts, many futures: Navigating the complexities of species reshuffling to help prevent extinctions. Cambridge Prisms: Extinction. 2026;4:e2. doi:10.1017/ext.2025.10010.

Pouget, D. and Sabel, J. (2025). Using species conservation translocations as a tool for nature recovery. Natural England blog. URL: https://naturalengland.blog.gov.uk/2025/03/26/using-species-conservation-translocations-as-a-tool-for-nature-recovery/

Roček, Z. & Šandera, M. (2008). Distribution of Rana arvalis in Europe: a historical perspective.In: Glandt, D. & Jehle, R. (eds) Der Moorfrosch/The Moor Frog. Zeitschrift für Feldherpetologie, Supplement 13, 135-150.

Tweats, H.-J. 2026. Investigating the Status of Britain’s Lost Frogs: Prospects for Rewilding. Churchill Fellowship report, London. URL: https://www.churchillfellowship.org/ideas-experts/ideas-library/investigating-the-status-of-britains-lost-frogs/