RAUK - Archived Forum - Posts by chas:

Not quite sure what is meant by your "sample images". Are they on the site? I would like to see them. I am, at present, doing some research on brown frog morphology which includes a discussion of colour and variety of marking  -- so I might find them useful. I am very interested, at present, on gaining information on the provenance of the common frog depicted on the RAUK site's "Species Identification" page.

Can you or the membership help on this?

Regarding earlier comments made on these pages:

a)      Re. GemmaÆs posting (14 Feb. 2003). The similarity between the E. Anglian pool frogs and those of Norway and Sweden was not just superficial and more than one pool frog ilium bone was found. The closeness of external appearance (compared to the European mainland) and voice (see Wycherley et al. under Inga Zeisset's post given earlier) was remarkable.

b)      Regarding John Burton's posting it would be best to read:

Tegelstr÷m, H. & Sj÷gren-Gulve, P. (2004). Genetic differentiation

among northern European pool frog (Rana lessonae) populations.

Herpetological Journal 4: 187-193.

 The authors conclude that the diversity found in Sweden's pool frog populations indicate that they are a relict population rather than being descendants of an introduction, and that the Swedish, Norwegian and British frogs are part of a northern clade.

Re. John Burtons last posting:

The part of Denmark nearest to Sweden (Sjealland) holds triploid, self-fertile populations of the edible frog R. esculenta and Bornholm holds an edible frog û marsh frog complex.  The edible frogs in SW Sweden are, like the Danish population, self-fertile hybrids and do not require the presence of  the pool frog (R. lessonae) or marsh frog (R. ridibunda) to perpetuate themselves.

If Sweden was colonised naturally, the view that Denmark should also hold pool frog populations, is to assume that post-glacial colonisation was a simple matter of south to north migration and also to assume that the pool frog is a generalist (and not a specialist or relict species, as is the case with northern clade pool frogs) as far as habitat is concerned.

We (Snell, C., Tetteh, J., Evans I. H. (in press)) have proposed that, based on the genetic evidence, on reaching the Baltic there was an east to west migration route to Britain with East Anglia as the first area colonised (bear in mind that the S. North Sea was dry land at that point and there were thousands of glacially created ponds ideal for amphibia; the Norfolk pingos being a relict landscape from that time).

Answer (to some extent, hopefully) to GemmaÆs last posting:

The pool frog is far from being a generalist in its habitat preference; in my view also, the pool frog is, among the green frogs, to some extent a pioneer species.  That is to say, it is more cold tolerant and moves more quickly to colonise new ground after the retreat of ice.

Pool frogs, are a relict species in Britain and to remain successful over time, need a large metapopulation structure with many suitable, fairly sunny ponds as they originally had at the Norfolk site which was rich in permafrost-created, pingo pools.  Heavy shading around their breeding ponds is something they cannot tolerate on their range edge as they need high pond temperatures. Research in Sweden has demonstrated the metapopulation dynamics underpinning the turnover in sub-populations in this sort of landscape, and helps to explain why they have a restricted range. The increasing coverage of wild woods, which occurred about 9000 years ago, would probably have affected range penetration across Britain because of higher shading levels. This, and the later declines in average spring and summer temperatures which exacerbated breeding pond temperature problems, would likely have caused a great range reduction. Moreover, the many actions of man had a major impact - including agriculture and the great fen drainages which, starting in the
1600s, still continue today (in which I include modern day borehole water extraction). In fact an early pool frog report (Fowlmere Fen, Cambs in the mid 1800s) was sadly about extinction through fenland drainage. For these reasons it is impossible, at this point, to know with confidence the full extent of their post glacial range in Britain.
However, it should be noted that Chris Gleed-Owen's subfossil finds did include bones from Lincolnshire and Cambridgeshire and the population genetically tested was the Norfolk population which died out in the late 1990s.

The processes leading to the highly fragmented natures of relict populations are well documented. Current distributions are influenced by past colonisation routes; the habitat around them may have changed considerably (naturally or through human action); they manage to persist in few isolated locations with suitable habitat and climatic conditions.
In the case of the last East Anglian population of pool frogs, they were found in the ancient Norfolk pingos and Norfolk has Britain's sunniest and arguably most continental climate. Isolated native populations, particularly near range edges, are not unusual - the sand lizard and natterjack are good examples here in the UK (see also Jan Pr÷jts's post).

 Re. John Burton's February 14^th post.

This post contains serious errors which need to be clarified to avoid any further confusion.

Re. "English (pool) frogs are almost certainly contaminated with introduced (edible frog) genes"

Pool frogs cannot be produced by matings between edible frogs û they can only be produced by pool frogs to pool frog matings. Diploid edible frog to edible frog matings, at most, can only producd female marsh frogs with no or limited viability, as far as a producing a non- hybrid species is concerned.

As the pool frog chromosomes are eliminated in diploid edible frogs before the production of eggs or sperm, edible frog to pool frog matings only produce more edible frogs (i.e. what amounts virtually to  F1s, anything to comparable to F2 generations are not produced), ôcontaminatedö pool frogs are not produced. Incidentally, the known introductions by Berney amounted to about 1500 individual frogs and not "thousands".

Re.  "As Boulenger believed, the specimens collected by Thurnall et al were all descended from known introductions"

This is a mistaken interpretation of Boulenger. To quote from Boulenger; "it is clear to me, therefore, that all the specimens (of lessonae) the capture of which has hitherto been recorded, whether from Cambridgeshire or Norfolk, are not the descendants of those introduced by Mr Berney, but are of Italian origin.  By whom and when they were introduced in this country I cannot venture to suggest."  (The Zoologist, 1884).

It is clear from this that he did not think they were from a ôknown introductionö. He assigned an Italian origin on the basis that, other than those he'd seen in Britain, they were otherwise only known from Italy and he assumed introduction in line with WooleyÆs suggestions that they may have been introduced by Italian monks. The basis of this assumption was eliminated when they were later found to naturally inhabit a large part of north Western Europe including, as it turned out, the specimens he was then examining in Britain.  The northern clade animals are too genetically dissimilar from those of Italy, Paris, etc.  to represent an introduction from those countries in historic times.

Re. John Burton's February 23^rd posting.

John indicates that he believes that my comments on BoulengerÆs view on the origin of the pool frogs in Britain are not really relevant and BoulengerÆs later work, The Tailless Batrachians of Europe, gives his views more clearly. The inference here being that these views backup the position, that Britain's pool frogs are from known introductions, stated in his post (John Burton,14 February, this forum) and refute the view that the pool frogs of Norfolk and Cambridge were not from a known introduction (Charles Snell, nineteenth of February, this forum). Perhaps to quote from Boulenger's later work will give clarity to this.

On pages 271-272 he states that Rana lessonae ôis perhaps introduced from Italy" and that "now however, that the habitat of the var. lessonae is known not to be confined to Italy, the origin of these colonies (in Britain) is more obscure than ever."

From my post (nineteenth of February, last two paragraphs) it is clear that Boulenger's later views even more closely support the views stated there and I fail to see why Boulenger's later work was quoted as evidence to the contrary. Once again I can only repeat that the view (14th of February, this site) that Boulenger considered that the Cambridge and Norfolk pool frogs were from ôa known introductionö is incorrect.

Re. John Burton's February 14^th  & 23^rd postings.

I entirely agree with John's figures for BerneyÆs edible frog introductions near Norwich, Norfolk. However, I was not contesting that spawn was included.  Like John I can only find certain evidence that Berney introduced ôtwo hundred frogs and a great quantity of spawn" in 1837 followed by "another lot" in 1841.  In reading Berney's letter quoted in The Zoologist, 1859 (p. 6539) it is unclear as to whether "another lot" after mentioning ôspawnö referred to just spawn or included frogs.  His later introduction in 1842 included 1300 frogs.  This still only leaves evidence for about 1500 frogs for certain released by Berney, and certainly, Newton's description of upwards of 1500 would perhaps have been more accurate if the 1841 introduction included some frogs as well as spawn.  However, I still cannot find evidence for John's description of ôseveral thousand frogs and spawnö released close to the Rana lessonae sites at the time of the Thurnall et al. finds and would welcome any reference to clarify this . However, it must be said that as Boulenger stated that frogs from the older sites in Cambridgeshire and Norfolk ôdiffer widelyö from the edible frogs at the introduction sites and were all pool frogs, it could be seen that continuing discussion of edible frogs on these pages may be misplaced.

Does anyone out there have any info. on the earliest dates of calling or spawning in the marsh frog -- even approx. (it's to assist some research)?

Many Thanks!

Lee, the calls are distinct - I expect Chris M. would have given a correct ID. There may be no connection then between the 2 populations.

A marsh frog call can be heard at  http://waterfrogs.csit.fsu.edu/PBhtmls/ridibunda.html#voice

This site has the other water frog calls for comparison

Pool Frog (Rana lessonae Camerano) in Europe: Evidence for Native Status

in Great Britain and for an Unusual Postglacial Colonisation Route.

Biological Journal of the Linnean Society. 85: pp 41-51

Hi John,
the earliest spawning in my outdoor vivaria is similar to the  one given on your posting.  On Birdbrook Nature Reserve it used to be approximately the last week in May, in fact, approximately synchronous with the pool frog colony north of Uppsala in middle Sweden.

The dates for pool frog spawn seem weeks later than the earliest spawning for marsh frogs - I'm still waiting to some records to be entered on another page on this site regarding marsh frog spawning dates!

David Bird's post about keeping the Norfolk specimens (Emys orbicularis) separate is an important issue.

Remains of the European pond tortoise have been found in East Anglia (and I believe particularly in Norfolk) dating back to as late as ca. 5000 years ago. Some authors, e.g. Marr, J. E., Shipley, A.E. (1904) describe the species as being once common in the fens. There is, therefore, no doubt that it is a native species, the question being, are the specimens presently being found the result of an introduction or the remains of a relict population which is, with climatic warming, possibly now able to breed with greater frequency? (In Poland they do not successfully breed most years but still maintain viable populations aided by their longevity). They presumably persisted for sometime after the date of the fossil finds; even as late as the time of the Roman invasion Britain still had a milder climate than at present.

There is also no doubt that introductions to East Anglia have occurred; for example some were released in Blaxhall and Little Glemham in Suffolk between 1894 - 95.

There have been sporadic sightings in Norfolk for some time.  Earlier on this site, I mentioned the finding of a large female in north Norfolk (Mike Linley- Anglia TV scientific contributor) and other posts do seem to be suggesting that these finds are not uncommon.  The earliest reference I can find is one accidentally excavated alive in fen peat at Ludham, Norfolk in 1904 where it had apparently dug itself in for hibernation.  During the milder climates experienced 5000 years ago, populations also existed in countries bordering the Baltic Sea, such as Denmark and Sweden.  The Danish and Swedish populations have also gone extinct in the interim whereas other populations around the Baltic still persist in north eastern Germany, Poland, Latvia and Lithuania. If the European pond tortoise story mirrors that of the pool frog Rana lessonae in Norfolk, post-glacial colonisation by Emys could have occurred in a west to east direction from the Baltic area. (See the Snell, Tetteh and Evans paper mentioned on the pool frog reintroduction pages on this website û I could email a copy if contacted by ôpmö button (private mail)).  The pool frog story was also complicated by introductions of the species or related species.  There is no doubt that some or all of the recent pond tortoise finds could be as result of introduction and genetic testing would be interesting to come to some kind of conclusion.  It would be my guess that if any of the Norfolk Emys have a chance of being native they ought to be more closely related to those in north-eastern Germany and Poland than to those in France or more southern European countries, as was the case with the pool frog.  (As late as about 9000 years ago there was a land bridge across the North Sea between Scandinavia, the Low Countries and East Anglia).

It has always been assumed in Denmark that the pond tortoise died out between the iron and Bronze ages, but as David Bird points out in his last post, some were found in the 1990s of unknown origin.  I have found two Danish web sites on Emys (in Danish) both seem to suggest that there are still some Emys in central Jutland.  One of the sites also indicated that there are a few on the island of Bornholm and that those on Jutland had been genetically tested (8 were caught and seven were tested) the results showing that the animals were not of the type found further south in Europe.  This, of course, increases the likelihood (but not proving the case) of there being being a relict population.

Re. query (Peter Sutton).

Whilst researching the pool frog, in case any were still left somewhere in the wild, I was sent a reference to "edible frogs" in or near the levels in Somerset dating back to the early 1900s (about 1925 as I vaguely recall).  I also seem to recall it was from a publication on wildlife local to the area.  I have unsuccessfully tried to search for his reference but will come back as soon as I have anything more concrete.  The author did leave the sense that the frogs had been there some while.  Whether they could possibly be the originators of the current population is an interesting speculation.

The issues surrounding the new Forest and South Essex colonies seem to require some urgent clarification.

I knew of one in Hyla arborea colony in a garden in Basildon.  I knew the owner (now deceased) and their origin was certainly not Turkey.  Perhaps we are talking about another colony that I haven't yet been informed of?  Having known the owner well, he at no point mentioned to me that any of these were taken to the New Forest. 

The New Forest colony near Beaulieu, described earlier by David Bird, has a history that goes back at least to 1910 and finally dwindling to extinction by 1987.

There were unconvincing rumours that the introduction of this older colony was via Mr Turner Turner who, it was rumored, brought them back from his travels in South Africa or from Monte Carlo on the Mediterranean.  As the new Forest colony were definitely Hyla arborea and that this species does not exist in either Africa all the Mediterranean region around Monte Carlo (where Hyla meridionalis exists) this story can be dismissed -- to my mind -- as one of the many myths that grow up around colonies of animals that seem to be out of place and need explanation. 

I wrote at some length, with illustrations, on the tree frog in Britain for British Wildlife magazine which goes deeper into the history ('Status of the Common Tree Frog in Britain', British Wildlife, Feb 2006, 153-160) if any mom wants to take the subject further.

Finally, the earliest records of the species in Britain start with Sir Thomas Browne in 1646 who wrote of them (when discussing frogs in Britain) being ôa little frog of an excellent Parrat green, that usually sits on Trees and Bushesö and later in that same century Dr Christopher Merrett (1667) lists them as part of British fauna. It is not inconceivable, therefore, that this hardy species was once part of our fauna.

Hyla arborea is a very hardy amphibian and can survive being frozen solid.  This ability allows it to live as far north as southern Sweden in Europe and east to the former East-Bloc states which get far colder than Britain.  It should be no surprise then, that this species (unlike the more southerly species such as the stripeless tree frog), can survive in Britain.

Thanks for that, Jon.

We do seem to be talking about the same colony of tree frogs in Essex.  The owner of a garden colony visited me in the late 70s and I gave him 10 to 15 common tree frog metamorphs (of completely uncertain origin) which started his colony.    When I last visited him before his death and praised his success in maintaining the tree frogs for so long, he never mentioned any others coming from Turkey. I also knew that he gave some to Martin Noble. What I was trying to separate more clearly in the minds of readers is that any of the New Forest wild living tree frogs had a known origin, either from Turkey or Essex.  Those which were turning up away from the original Hilltop pond did so before the Essex owner had given any to Martin.

Re. the Kidbrooke wall lizard colony.  At one point the numbers on this site exceeded (to my estimation) well over a thousand in all age classes.

The sites on which they were most numerous (the remains of demolished MoD buildings bordering the old A2, Rochester Way, SE3) became redeveloped.  The firm of consultants were employed to remove the lizards, and they did not disclose where they were moved to.  Although, bearing in mind it is illegal to re-release these animals into the wild, the options were probably very limited.  At the time of the siteÆs demolition some hatchlings were still emerging from an exposed sand layer underneath concrete capping.  Some still exists on a few surrounding sites and surrounding private gardens.  Many of the larger remaining sites, for example the Maritime Museum's Reserve Collection buildings (where they had never been as numerous as on the original MoD site), are also earmarked for future development.  The appearance of the lizards was very similar to the photographs on these pages.

This marsh frog issue is a very interesting one.  While IÆve perhaps wished in the past that they werenÆt around, they do seem to have made the marshes in Kent a livelier place.

While I was involved in waterfrog research about 10 years ago, I met a Mr Castle who was a major land owner on the Isle of Grain, Kent. He reported that neither he nor his father had recorded common frogs on their part the Isle of Grain and that the first frogs that they ever saw, locally, happened after the marsh frogs arrived.

Comparative studies on the habitats of the pool, edible and marsh frogs show that marsh frogs prefer larger bodies of water (Lakes, estuarine marshes etc.) as opposed to the pool frogÆs preference for smaller, shallower ponds and, unlike the pool frog, is able to more successfully share the water with fish. The hybrid edible frog has preferences approximately midway between these extremes for the parental species.

The marsh frogÆs optimal habitat is, therefore, not a resource ever exploited successfully by the common frog (this would explain the absence of common frogs on the Isle of Grain). I have found marsh frogs in pools on Grain which were extremely saline (the pools were occasionally fed by high tides and then evaporated in the sun which concentrated the salt levels), pools far too saline for common frogs. In view of the above, it could be seen that, a modern observer of wildlife on the North Kent Marshes may erroneously assume the lack of common frogs is something to do with the large number of Marsh frogs.

It is the experience of myself and others that the increased presence of the marsh frog has increased the numbers of grass snakes, and other predators which feed on the frogs or their larvae (egrets, herons, kingfishers, etc).  IÆve also seen a large eel take a half-grown marsh frog from the shallows of a marsh fleet near Allhallows, North Kent.  In fact, I have noticed other eels patrolling the shallows near marsh frog basking areas in daytime. I never noticed this diurnal patrolling behaviour in eels in the sixties (before the arrival of marsh frogs) when I regularly went eel fishing there! It would be interesting to know what effect the presence of the marsh frog has had on local biodiversity or biomass of certain predator species (including the aquatic predators such as eels û which no doubt exploit larvae and frogs as a new food source).

To continue the mammal analogy û think rabbit.  This introduced species (rabbit) must have been responsible for an increase in the numbers of buzzards, stoats, foxes, polecats, etc.

The effects on dragonflies and damselflies could be ambivalent.  Certainly the adult frogs eat adult damsel and dragonflies but likewise, larval dragon and damselflies are very partial to tadpoles.

I have no data on the effects marsh frogs in garden ponds and in view of the comments reported to Gemma is clearly an important issue. It would be useful to know how these marsh frogs are colonising small garden ponds, as these, in theory at least, are not the habitat of first choice.  Are they being brought in as tadpoles?

Marsh frogs are much more frost-tender than common or pool frogs, and unlike these two foregoing species û which hibernate on land (most female common frogs and all pool frogs) or in relatively shallow water (male common frogs) û marsh frogs hibernate in deep water to escape temperature extremes. Most garden ponds donÆt offer sufficient depth and a good frost lasting a few nights giving a good depth of ice should bump marsh frog off.

The following is another case where limited or short term observation can lead to the wrong conclusions.

Some weekends I am a volunteer warden on a small nature reserve where I have observed waterfrog numbers for 21 years. Six years after the arrival of the first water frogs on the site the common frog numbers collapsed to close to zero and by the end of the following year had reached zero and stayed at that level for seven years. It was suggested the water frogs could have had a possible influence on this.  However, common frog numbers had also collapsed over a lot of the areas of southeast London surrounding the site, in areas miles from any water frogs.  The cause was later attributed to virulent bacterial and fungal pathogens.

Marsh frogs should not be able to affect the breeding of the common frog as the timing of their mating behaviour and spawning is well separated as was reported earlier on these pages. The common frogs spawn û dependent on the yearÆs varying ambient temperatures û any time between late February in the end of March.  After this frenzy of activity the adults move away from water, often at considerable distances, for the rest of most of the year; the males returning to hibernate in the water. The marsh frog on the other hand has not left hibernation by the time the common frogs have spawned and dispersed û which leaves little time for them to interact.

I would imagine that the marsh frog may have effect on smaller British newts, should they (against habitat preferences!) live in the same water body and this may need more investigation. Against this, as somebody said earlier, newts themselves can have a very negative effect on anuran numbers by eating their larvae û especially the more palatable common frog larvae!

Clearly the marsh frog case is not straight forward and the trick is going to be deciding whether the pluses outweigh the minuses. Certainly, the biodiversity gains need consideration and I for one and not unhappy with the increased richness of wildlife on the marshes.  However, should this frog naturally (i.e. without human assistance) invade atypical habitats and be shown conclusively to have detrimental effects, then the case becomes more worrying. If the marsh frog manages to get to areas where the pool frog has been reintroduced, then the consequences could be more disastrous as the two species hybridise.  At present there are no obvious links of suitable habitat to create corridors to get the marsh frog and the pool frog populations to meet, however.

Regarding the different breeding times of these two frog species, I would be EXTREMELY grateful, for research purposes, for any marsh or edible frog records for the earliest time, in any year, that anyone has noticed a) calling, or, b) spawning (or just the finding of eggs).  Please state locality.