RAUK - Archived Forum - Marsh frog - impacting upon common frog??

Purely anecdotal, but I've received a number of reports from the public in Kent claiming that the arrival of marsh frogs has led to the decline of common frogs and native newts. One lady has even reported a crash in the grass snake population at a pond now dominated by marsh frogs but previously used by smooth newts and common frogs. I feel it is an area that needs to be looked into. (Why they may have caused the local grass snake population to crash I have no idea at all, you would have thought the local grass snakes would have welcomed their arrival).

If anyone wants to take a closer look at these populations I do have contact details. To be honest it is something I've found difficult to advise about and worrying at the same time. In particular, there is a consistency in the reports that they often state that it only takes a few years after the marsh frogs arrive, for native species to appear to become totally extinct.

Thanks Gemma

I'm pretty sure that marsh frog is one of the main reasons we have a strong grass snake population, so I too am puzzled by your contacts report of their decline.

Its interesting that you mention newts as well.  These seem to do fine in all marsh frog populated ponds that I know of...

Right

I would say that it not just marsh frogs that impact on common frogs - take  for instance the humble smooth newt or even the great crested newt - both of these species seem to impact greatly on common frog tadpoles -

I have had two successful spawnings over 2004 and 2005 I had a good hatch of tadpoles but all were gone within a few weeks as the smooth newts move into my small garden pond.

We have a thriving marsh frog population in Essex - Hadleigh Castle Country Park - They are really occupying an empty niche - yet we also have a very low Common frog population - which may always have been low - yet a few hundred yards up the hill in back gardens we have a thriving common frog population!

I have seen massive declines of Common frogs over the Essex countryside without the presence of Marsh Frogs - in fact many countryside ponds are not actively managed - there are fewer water meadows providing the temporary ponds/waterbodies which Common Frogs need to breed - rather than blame the marsh frog maybe we need to look at the changes in habitats - which seem to benefit Marsh Frogs and not our native common frog. If we can balance the needs of both As you say they coexist in Europe -

In gardens of course there tends to be an increase in Common frog populations - I have noticed that my pond was colonised by common frogs two years after it was built - in 2004 - 

I can also report that grass snakes in Hadleigh are doing rather well feeding on the Marsh Frogs, while the herons, little egrets are also feeding on them - not to mention the amount of food available to aquatic inverts - feeding on the tadpoles (MF) water beetles and their larva plus many other species possibly feed on marsh frog tadpoles -

I am getting fed up with these 'scapegoats' which we find to cover our misuse of our natural resources etc etc. I do find the issue interesting and I enjoy monitoring the occurence of marsh frogs in Essex - they are still spreading - with the help of humans - we have removed a small population from Davy Down Country Park while they have also manged to get into Rainham Marshes - The RSPB are worried about the effects on crested newts - yet they do not seem to have any effect on crested newts - apart from provide yet another food source (possibly)

The rangers at Hadleigh were concerned that the marsh frogs were eating all the aquatic inverts in their pond dipping ditch/platform - they must have eaten them all - when you look at other factors - introduction of fish (sticklebacks) the 20 times a year pond dipping sessions you can see other factors that have caused a decline.

The Marsh Frog has been reported as benefiting several species - grass snake, medicinal leech, grey heron, little egret and of course the Bittern.

It would be good to look at predator prey relationships within our studies - I fail to see why grass snakes would decline due to marsh frogs - perhaps they were cane toads?

It is often the case that grass snakes eat all the fish in a garden pond - yet it was most likely to be the neighbours cat or the Grey Heron -

The paper on canterbury grass snakes suggests that the artificially high numbers of snakes - by feeding on marsh frogs may also harm our native amphibians????? errrr

Regards

Jon

Thanks for this input Jon

I appreciate that there are many factors that influence common frog populations, I was just highlighting numerous reports and observations that common frog seems to have declined in areas where marsh frog has become more abundant.  Perhaps I didn't make the two arguments entirely clear - I certainly donÆt regard Marsh frogs as  completely unwelcome visitors as I'm sure (at least at Heathrow) there is in fact a net gain in terms of supporting grass snakes, aquatic inverts and birds.  Other amphibians also seem to do well.  The study I mentioned predicted no significant impact of marsh frog upon aquatic invert populations due to the wide variety of prey taken and the fact that despite the frogs aquatic nature the items were primarily terrestrial.  The tadpoles no doubt help the Dytiscus, dragonfly and other predatory taxa.  I saw a heron attempting to swallow a fully grown marsh frog which it struggled with for some time, eventually getting it down.  No bittern, as yet though!

To conclude - I was simply interested if anyone else has observed marsh frog and common frogs coexisting or situations where one has (apparently) resulted in the absence of the other.  It seems that they should coexist and that predation is probably not an issue but it is hard to ignore the decline or absence of common frog in my area - despite the presence of good habitat.  Like I said this could be due to other factors that are also affecting UK populations as a whole.

Regards

Jon, I agree with you sentiments and also agree we shouldnÆt blame the marsh frog without solid evidence - many other factors could be to blame for crashes in common frog populations. I do feel though we should look to see if there is an impact on common frogs due to marsh frog competion in a scientific rather than anecdotal sense before it is 'too late'.

We had colonisation by Rt in the first season in our Essex garden pond, no breeding this year but the population increases daily with more little heads visible all the time, very encouraging, but as you know Essex is very underrated for herps, we find them practically everywhere we look!

At the other end of the spectrum consider the number of sickly looking or colour mutated common frogs one comes across these days. Though it seems more occur in suburban areas, they are found increasingly in the wider countryside, if indeed you can find any common frogs at all in the wider countryside.

My concern is that if we are loosing common frogs to disease, lack of genetic variability and habitat loss, will the marsh frogs ability to take up alternative niches and also potentially out-compete Rt in classically good habitat, lead to the demise of Rt as the UK's 'common' frog, replaced by a European invader.. think grey squirrel.

Rana temporaria to me has colonised the many urban and suburban ponds while the marsh frog in my experience lives in completely different habitats - well they can survive in habitat which the common frog cannot for instance fishing ponds.......ah theres another factor the stocking of fish into ponds.......does wonders in turfing out frogs

I would say that the interaction of the marsh frog and the common toad would be interesting - dont both have tadpoles that are distasteful to fish and other predators that chew they prey.

I feel we need to carry out a study of these animals - the feeding study at the Barns Wetland Centre forced the contents of the frogs stomach by using saline water or distilled - you can obtain a DEFRA license to enable release back into the site which the animal came from - or you could try and kill them but I am sure we would have plenty of discussion of how best to dispatch a marsh frog - I am sure we want to avoid this considering the furore from other sections of society -

I am leading a survey of the marsh frogs at Hadleigh Castle Country Park this coming saturday 21st May - we are meeting at Benfleet station at 9am - could you make that Gemma?

Regards

JC

Oh I forgot I was thinking Brown Hare rather than grey squirrel - well the Brown Hare is the grey squirrel of the lagomorphs

Yet it is a Biodiversity Action Plan Species?

JC

Jon, you state that 'to you' marsh frogs colonise totally different habitat to common frogs, the subject of this thread is the decline of common frogs at a site where they were known in good numbers before the arrival of marsh frogs.

It is not a case that they live in a seperate niche and are therefore not a threat, the truth is they can colonise BOTH habitats suited to Rt and those that are not. Therefore we will see a steady increase in the spread of marsh frogs and one suspects the decline of the common frog.

When I stated think grey squirrel, I was suggesting one looks to the mechanism of the decline of the native red squirrel, not the same story at all as the brown hare.

Isn't the argument of whether or not Marsh frogs are causing a recordable decline irrelevant to the fact that they are 'aliens' and by definition will have unpredictable consequences on local ecosystems, whether we can currently detect them or not? 

This thread reports on 'benefits' to grey heron and grass snake populations by provision of alternative food sources, but surely this can lead to increasing predator numbers, which will have impacts down chain on prey species other than the Marsh frog. I believe that we should be looking to control these invasive species before they cause any irreversible damage to UK ecology, even if there is a risk that we put in effort remove a species that may not have an impact had we left it alone.

Like Gemma said, if Marsh frogs are allowed to spread until they replace natives as the 'common' frog at will be too late to do anything about it.

P.S. if you intend to study gut contents of an alien frog you would either require a DEFRA license to allow re-introduction, or a Home Office license to 'dispose' of the frogs (I believe 'pithing' is the accepted method ).  Unless you decide to look after the fellas in captivity that is.

errr I dont see the logic - surely if the marsh frog is the preferred prey of a a particular predator possibly due to the higher numbers of this animal in the wider countryside rather than in garden ponds where the common frog has its stronghold -

We need to look at the habitat requirements of Common frog - I feel that temporary pools are favoured - their tadpoles can survive lower oxygen levels unlike the Common toad which breeds in deeper ponds or lakes - It may be similar for the green frogs - which do better in brackish, deeper waterbodies, ditches, rivers all habitats where common frogs do not survive well- You can link the decline of the common frog to the steady rise in the numbers of newts

How would we start recording data on this issue? I thought that maybe I could record the occurence of common frogs after the removal of Marsh Frogs at Davy Down - though this was a recent introduction - so they wouldnt have had any effect on the Common frogs - mainly because there no or very few Common frogs.

I am going to create some new waterbodies at Hadleigh Castle Country Park as compensation for the effects of a Shrill Carder Bee project where scrub is going to be removed for grassland creation - I plan to create small pools on the marsh - hopefully common frogs may breed for the first time in years - I also plan to look at the numbers of frogs in local gardens which are located close to the established population of marsh frogs in the Benfleet downs.

I am leading a survey on the 21st May this saturday 9am benfleet station car park.

JC

Other factors that should be considered when seeing common frog declines in gardens - Red leg disease, pesticides, permanence of ponds, fish, herons, grass snakes etc - it is possible that the marsh frogs do not have any impact on our native frogs rather they are increasing while the native frogs are declining due to other factors

JC

Well I know of one site where pool frogs are living side by side with Common Frogs in a garden in Basildon. The many frog populations in Essex are within urban areas - while the species has declined in the wider countryside - no marsh frog interaction there - but we have expanding marsh frog populations which are in areas where the common frog is already in decline - or at very low numbers due to lack of suitable breeding habitats - I suspect that the frog needs small water bodies which allow faster growth rates for the tadpoles.

I have found common frog tadpoles recently within tractor rutts which are very large - too large to be eaten by the small newt species thus allowing more froglets to emerge.

while many garden ponds have large newt or fish populations which I would imagine take many of the tadpoles and reduces recruitment.

I feel we need to look at the habitats very closely to see what can be done to help the common frog.

I was wondering if anyone would like to help with a one to two day survey in Essex. We have a new population of Marsh frogs to monitor in the Mardyke River - I am planning to go out and survey this river system on the 22nd and 23rd June

Regards

Jon

The loss of countryside ponds - temporary pools especially - may have reduced the numbers of Temporary Frogs (the translation of its latin name Rana temporaria) - they need warm shallow pools to ensure that tadpoles develop quickly

I have suspected that the ponds left in the countryside are deeper and have many predators - garden ponds also sometimes have low recruitment - plus the effects of pesticides, slug pellets and other chemicals may also have a role along with genetics which would reduce frog populations.

Marsh Frogs tend to live in habitats which the 'temporary' frogs do not normally live within - for example rivers, fishing lakes etc - with the onset of 'red leg' disease and mass mortality (causes often unknown) it is hard to link temporary frog declines with the spread of Marsh Frogs - as both live side by side on the mainland in Europe

Marsh Frogs would eat young grass snakes - but this would be a rare event in their diet - which mostly consist of aphids (LWC study K Merry, 2004) or Water Hog Lice (LWC study K Merry, 2004)

Young grass snakes would also be predated on by crows, starlings, and other predators - but studies have shown that the yellow markings in the collar on young snakes protect it from bird attacks - as they may associate this with distasteful insect colours there is a paper on this......

Jon

Jon, it would be worth looking into woodland ponds regarding common frogs and creating suitable habitats. The largest breeding aggregations I've recorded are at well lit woodland ponds. Here you can count common frogs in hundreds not tens such as is the case with most garden ponds. They don't seem to have a problem surviving alongside small newt species at such ponds either, possibly due to sheer weight of numbers.

It really saddens me that our most familiar amphibian is in serious difficulties and most seem to think that garden ponds will save the species. The small garden populations will never replace the sight of many hundreds of healthy common frogs skipping across the surface of a pond on a sunny spring morning.

I would also repeat that I have had numerous first hand reports from pond owners in Kent that state the arrival of marsh frogs caused a crash in common frogs numbers and other native species. I would be surpised Jon if aphids form much of an adult marsh frogs diet, though they do eat common frogs I am reliably told....

What seem to be being missed here is that though marsh frogs will use niche habitats not usually inhabitated by common frogs which has greatly aided there spread across Kent (along with human introductions), once they are in an area they will invade the habitats that common frogs are traditionally known to use, and that includes garden ponds..

I don't think comparing what lives side by side in mainland Europe has much merit either, it is clear that our natives are significantly different in many respects to their European cousins. UK common frogs evolved without competition from a more aggressive and adaptable species.. did someone mention grey squirrels??