RAUK - Archived Forum - Marsh verses Common the debate!

Do Marsh Frogs impact on Common Frogs?

Discuss....

Well you know my views Jon. Recently my fears were backed up when talking to a competent environment officer at a site I surveyed for reptiles in Kent.

He has known the site for over 20 years. Once 'common' frogs were indeed common at the site. Then marsh frogs began to colonise. Now there are no common frogs at all, replaced by abundant numbers of marsh frogs. He even personally witnessed a marsh frog predating an adult common frog. What more evidence do we really need to start regarding marsh frogs as a serious threat to our native herpetofauna?

It may be fact that practically everything eats common frogs.. but to be predated at every lifestage by a more adaptable species capable of using rivers systems for dispersal,that also competes for habitat and prey items, can only have one consequence in the long term for the common frog.. extinction

It hasnt happened in 100 years so when will this happen? the common frog was already on the verge of extinction before the rise of the garden pond - which is now reportly the stronghold for the species in many eastern and southern counties. Why hasnt the marsh frog wiped out the common frog in Europe? I know they have been living together quite happily while the UK Common frog populations havent -  

One incidence of a Marsh Frog eating an adult common frog means pretty much nothing really - apart from we already know that Marsh Frogs are capable of eating other frogs - We need to improve the chances for the Common frog - the biggest population in Essex is estimated at 600 frogs - not a very large population compared to other populations in the UK -

At a local nature reserve near my parents there use to be a breeding colony of frogs 10 years ago,  a large breeding colony of toads 30 to 35 years ago - the population has crashed - no toads breed at the site and frogs are only occassionally seen - though the biggest Essex crested newt population occurs in the last remaining ponds.

The flooded water meadow where the frogs breed has now become dry in the late spring - no frog tadpoles survive we have lost a natural frog breeding site - this winter the meadow is going to have scrapes put into it to provide shallow water bodies and we hope that the frogs will breed in a few years time - Habitat and land use change would be the prime force in reducing common frogs - I believe this is well documented - while currently there is no evidence that Marsh Frogs have impacted on common frogs in the same way

Are there any papers on this possible impact?

JC

The competent Environment Officer has he got regular counts of Frogs in his site? this would be interesting stuff to look at

In my experience very few surveys are undertaken of herpetofauna by wardens and other conservation staff - yet they try to make statements about reptiles and amphibians with out any data to back them up - there is a nature reserve in Essex which is a subject of a new book and it states that Adder thrive in the conditions provided by the 360 tracked digger which is brought in to remove the adders habitat - something called heathland restoration - whoops gone a bit off topic there....

Does your guy have the counts over 20 years?

JC

Clearly Marsh frogs have occupied empty niches where common frogs have declined from other factors - such as changes in land use over the last 50 years or so

It would be worth investigating the impact of marsh frogs on common toads as they occupy similar habitats - large water bodies which are often stocked with fish - places where frogs do not breed successfully - however common frogs breed successfully in garden ponds which mimic the natural water bodies which frogs would spawn in - which happen to have disappeared from the countryside -

The Marsh Frog is beyond wholesale control in Kent wouldnt you say? maybe we need to look at control in certain circumstances -

Maybe the Marsh Frog will become the naturalised frog species - a similar situation has occurred with the Brown Hare which pushed out the Mountain Hare but is now a key species in the UK's Biodiversity Action Plan - I am not suggesting for one minute that the Marsh Frog should be conserved in any way shape of form

The site you mentioned it would be good to see the changes in land management aswell as the increase in Marsh Frog numbers - and the decrease in Common Frog numbers - you may find that common frog numbers were already declining and that the Marsh Frogs filled the void - a more successful coloniser as you say - if the alien species is not the cause of the decline why are you worried about this species?

If we cannot show the mechanism how Marsh frogs compete with common frogs then people will not take the issue seriously - many people I talk to tend to think that there is no link between the two species - I know I know -

The chytridiomycosis angle is a very worrying prospect esepcially as Marsh Frogs are still be transported around the countryside and are being sold in pet shops!

JC

So we should be sampling marsh frog populations to monitor any for this disease - perhaps through student research work?

JC

How about  aproject looking at the possible impacts of marsh frogs on common frogs? - as the evidence is not as clear as some people seem to think it is - there are lots of factors that are also acting on common frogs - the major one being habitat loss and modification which reduces suitable habitats for common frogs while the more adaptable marsh frog can now infiltrate to colonise the last remaining stronghold for the common frog - the garden pond

though not many people are looking at the non garden populations of common frogs - mainly as they have declined to very low numbers or that people consider the 'common' frog to be numerous and are doing just fine - which we all know they are not.....faced with the added threat of marsh frogs, disease, genetic inbreeding etc not to mention cats, pheasants, and other predators we do need to look at habitat creation and enhancements to try and see if this would help

J 

the last remaining stronghold for the common frog - the garden pond

I know this - we have populations which number 600 - a small population compared to others in the country granted but there may be larger populations in Essex - we just dont know about them - talking about assumptions - the threat from Marsh Frogs towards common frogs is a BIG assumption based on anecdotal evidence from Kent -

The Upland populations would help determine the threats which face the frogs in the South and South East comparison studies would be helpful - saying that Marsh Frogs are spreading northwards - though not sure how they would fair in higher ground?

JC

I've been lucky enough to watch a local Marsh frog population over the last few years. The pond has a good common frog population too. Common and great crested newts are present.  Both species will predate each others young hoppers but mostly they leave each other alone. In the summer the commons disappear into the meadow and the greens stay by the water. The greens will take anything that comes their way, they wait and ambush. They are visual hunters and I would say that the main part of their diet is flying insects. As hoppers disapear mostly at night the majority of the population is safe.

Snake population is thriving by the way.

Two years ago there was a massive drop in population of commons. There was also a big fish kill and I have strong suspicions that all was not well with the environment. I saw only two tortoiseshells and no peacocks that year! Things recovered last year we shall see what this spring brings by the number of returning commons.

The greens are a very welcome neighbour and their population increase locally, is in my opinion helping the familly needs of the egrets and the now resident bittern.

Rom

Hi Rom

Very interesting to hear about your observations - where abouts are you? Have you seen the frogs being caught by the egrets?

Regards

JC

This is just the sort of observation I feel we need to hear about.

I'm in no way convinced that the marsh frog has a direct impact on common frogs and will own up to playing devils advecote on the suject to some extent. I have however had anecdotal comments from Kent that are enough for me to think we should at least monitor the situation if and when possible in just the way Rom has done.

Replacement of a species doesn't just occur because of direct conflicts.. it's just as likely that marsh frogs could replace a common frog population after a natural or environmentaly caused decline in the common frog population. The presense of marsh frogs being enough to prevent re-establishment of the original common frog population. Rom is in a position to observe if this can happen first hand or if the common frog population recovers, I hope it is possible to continue monitoring this interesting situation and let us know what happens.

The result will  probably as is often the case with wildlife depend on the actual given site, the interaction between species being of such a complex nature that generalisation is of little use. I would like to see just this sort of monitoring at a number of sites where both species occurs so that useful conclusions might be drawn.

Hi,

Im in Somerset and we have a good population in the Ham Wall RSPB reserve. (nr Glastonbury)

No I have not seen them being caught by egrets - I should be so lucky. But I seen evidence of herons getting them.

There are now newer and more effective chemicals out there being used by farmers. This when combined with runoff gets into our water ways. I would be interested in frog population variance in environments that are suddenly changed and the use of chemicals ceases. It could be why the domestic pond is successful.

In another forum debate was going on about spawning times. I saw no frogs last year until March, yet in 2003 before the kill the frogs were in amongst the ice and leaves in January. In massive numbers.

From what Ive seen its temperature that drives the greens to spawn. In a shallow pond that could be May or June before it gets into the steady 15teens. Dont assume that they only spawn once like our commons. If its cool or a late spawning the tadpoles with overwinter.

   Rom

Julia Wycherley would be very interested in hearing about the population - if you could get some sound recordings of  the mating calls then Julia can then work out which species are present.

In her British Wildlife Paper April 2003 - water frogs were located in peat workings at Shapwick Heath, Somerset levels is that near you?

Breeding activity in pool frogs commence as the ambient temperature reach about 16C while marsh/edible prefers higher temperatures - full activity with minimum temperature is 18C - Wycherley 2003 - Water Frogs in Britain British Wildlife - for info

Regards

JC

All,

just a thought. Epping Forest hasn't got a marsh frog population has it? But the frogs at two sites that I visit every spring has had their populations plummet. Of course, it could be kids with jam jars as the whole place is packed at weekends but could it be that over time, certain areas just evolve from one habitat into another habitat by pollution run off or natural change? The only noticeable difference that I've seen in terms of wild life is the ponds have acquired some foreign terrapin residents over the last few years. mind you, I do think that EF is not nearly the wild life haven that it once was.

R

Hi Rob, I've no doubt something is going on with common frogs and your suggestion is very plausible and certainly would explain declines at some sites I've observed over the last 20 years. Simply the habitat changed or the dynamics or the pond changed, for example GCN arrived.

I've never thought marsh frogs are the primary or only cause of common frog declines, my worry is that where both species already occur it is unlikely that common frogs will ever be able to re-establish if we work out what is happening to common frog populations. This isn't just at isolated sites, there now appears to be large areas of Kent where the 'commonly encountered frog' is actually the marsh frog.

Hi Rob

The green frogs in Epping Forest are either Pool or Edible frogs - it they are pure Edible then they will die out if they do not have the parent species to mate with - Pool or Marsh. I suspect that they are pool frogs - any sound recordings of their mating calls would help to determine this

If you are worried about the good old common frog perhaps looking at fish stocks would help explain declines - ponds which never have had fish in the past are usually stocked with fish either offically or unofficially I am sure that the fish would eat a hell of alot more tadpoles than the green frogs - of course once the common frogs have become locally extinct in a fish pond - marsh can easily survive with fish - thus fill a recently emptied niche - so we need to look at what niches common frogs require and provide more of these - bringing back water meadows on a large scale may help - reversing the decline in dew ponds etc etc

JC