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RAUK - Archived Forum - feeding habits question

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feeding habits question:

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will
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Posted: 24 Sep 2008

I have a question about grass snake feeding habits; we know that some grassies (individuals and populations) avidly take common toads whilst others don't seem to.  Is there any evidence that this difference has any genetic basis or is it simply that a hatchling faced with nothing but toadlets will become habituated to the presumably more challenging / distasteful meal of a toad and graduate to bigger toads if in a frog-free zone ?  If the latter, can a frog-eating grassy adapt to a change in circumstances and start eating toads if frogs become less plentiful ?

Cheers, Will

 


armata
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Posted: 24 Sep 2008
Mm, interesting. I think that it is just a matter of what is most abundant. e.g. If a grass snake is on heathland then toads will be predominant.
'I get my kicks on Route 62'
Mark_b
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Posted: 27 Sep 2008

There isn't really any research on why some grassies exhibit this behaviour, it just seems that some of them have a preference for e.g. toads, which could just be due to toads being the most nourishing compared to energy expenditure, or it could well be habituation.

 

I wouldnĘt class a toad as a challenging / distasteful meal to a grass snake anyway, the toads secretions donĘt affect them apparently and all that inflating they do to make them selves look big ąą pah, grassies just laugh ą as they slowly consume them ą. pushing the air out like a whoopee cushion .. mmm

 

These animals could well be feeding on other creatures as well, unless we watch the animals 24/7 and more importantly all year round, we canĘt be sure. But I think grass snakes are adaptable enough to change diet if circumstances change.

 


armata
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Posted: 28 Sep 2008
Years ago witnessed a grass snake raiding a blackbirds nest, i.e. nestlings. So yes, they adapt.
'I get my kicks on Route 62'
will
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Posted: 29 Sep 2008
Thanks Tony and Mark; I guess if anyone has had captive grassies and been unable to find frogs for them it would be interesting to know if the snakes readily adapted to toads (and vice-versa)
GemmaJF
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Posted: 30 Sep 2008

Will native Natrix in captivity will take live fish, newts, frogs or toads without hesitation regardless of the animals apparent previous preferences, the important issue seems to be the movement not the specific prey item.

Most will instantly adapt to eating goldfish in captivity. From my very early observations of a 'toad' eating population, i.e. one where the norm was for toads to be regurgitated on capture, specimens from the population would avidly feed on palmate newts, frogs or any small fish if they were offered in captivity. Palmate newts were readily available to this population but I only once saw an adult from this population actively hunting for palmate newts in the wild, though I observed sub-adults taking them regularly.

I think it is entirely down to what is available and what would constitute a satisfying meal. I'm deeply distrustful of studies which show a particular item in the diet as a 'specialism' as it may simply be seasonal abundance or site specific and I believe Natrix to be a generalist.

In my view it could not be proven that there was some form of preference within a population unless it could also be established that the alternative prey item occurred in the same abundance and offered the same nutrition/effort of capture ratio at the site. I simply don't think this is the case with frogs and toads. I tend to think that one tends to find large numbers of common frogs in different habitats to where one finds large numbers of common toads and grass snakes are likely to be found preying on them when either situation occurs and are mobile enough to prey on different amphibian populations as the fancy takes them. So a result of 'toad' eating population becomes very suspect in my opinion, as it most likely reflects 'toads abundant' - hence why the grass snake population is detected.

One strange thing though, I've never heard of a population in the UK that generally regurgitate fish when captive Natrix will happily take them, so perhaps there is generally a bias towards amphibians in wild UK Natrix populations.

Of course the captive situation doesn't really prove anything either, a predator placed in a small space with a possible prey item is very likely to eat it! This might be quite different to the situation when they are actively hunting for prey in the wild.

I ought to point out that my days of throwing palmate newts to grass snakes ended many years ago when doing such things didn't seem quite so un PC  Though I always figured that they would have been eating something if they were in the wild so it didn't matter in the greater scheme of things.

The last captive I had proved to me something I had often wondered about though, many say that native Natrix will convert to dead mice, I have never ever actually observed this, I've seen them sniff at dead mice but never seen the feeding response triggered in a Natrix of native origin by a dead mouse. Some European specimens yes, but never ever one from the UK.

On occasion I have been asked by people who had sick or injured grass snakes in their care what they should do as the animal would not feed on dead food. In nearly every case the answer was to offer live prey which instantly would trigger a feeding response, fish being the most easily obtainable. Hours of wiggling bits of dead trout in front of my last captive proved to me that movement was a key trigger and oddly, that being dead was a very good reason for the grass snake to drop the item instantly after striking at it.

GemmaJF39721.7981828704
Gemma Fairchild, Independent Ecological Consultant
will
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Posted: 01 Oct 2008
Thanks Gemma - I guess that's a pretty definitive answer !
Robert V
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Posted: 03 Oct 2008

 

Gemma,

about the fish thing. I know and have photographs of many incidents in EF where Natrix take fish in large numbers from small ponds.

Cheers

Rob


RobV
Suzi
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Posted: 03 Oct 2008
We have had pix on here of a grass snake taking ornamental fish. Nice pix of them swallowing the fish. Not nice for the fish or their owner I guess!
Suz
GemmaJF
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Posted: 04 Oct 2008
I knew they took fish in the wild (god only knows how many emails I get that state that a grass snake ate ALL the fish in a garden pond  and I know if the fish are small they really will take five or so in one sitting), I was thinking more along the lines of a whole population that generally takes fish instead of amphibians. I'm mainly interested as it is fairly well known that a diet of only live fish in captives is eventually detrimental to their health, so perhaps this is why we don't see exlusive fish feeding in the wild??? Just pondering
Gemma Fairchild, Independent Ecological Consultant
Vicar
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Posted: 04 Oct 2008
My preferred diet is steak & chips...but if I'm hungry I'll consider a burger. If I'm really hungry I might even consider fresh vegetables :P

I suspect that the diet of British snakes encompasses a wide range of prey, almost anything living, of appropriate size, that they can fit down their throat.

Their chosen habitat will naturally provide more opportunity for some prey species than others. Clearly the snake's evolution will also make it more successful against some prey species than others - hence apparent specialisation when assessed statistically.

"There are three kinds of lies:
  • lies,
  • damned lies,
  • and statistics."



Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
Alan Hyde
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Posted: 04 Oct 2008
[QUOTE=GemmaJF]

The last captive I had proved to meįsomething I had often wondered about though, many say that native Natrix will convert to dead mice, I have never ever actually observed this, I've seen them sniff at dead mice but never seen theįfeeding response triggered in a Natrix of native origin by a dead mouse. Some European specimens yes, but never ever one from the UK.


[/QUOTE]

Gemma, I had one UK captive Graff snake that would take voles.



O-> O+>
AGILIS
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Posted: 04 Oct 2008
hi all & Al thats because their Britishkeith
   LOCAL ICYNICAL CELTIC ECO WARRIOR AND FAILED DRUID
GemmaJF
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Posted: 04 Oct 2008

Al were they live or dead voles?


Gemma Fairchild, Independent Ecological Consultant
Stanislaw
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Posted: 04 Oct 2008
Sorry I didn't understand all your posts, you are writting that grass snakes can eat other animals than amphibians?

I have read in many publications that grass snake is monophagic species (eats almost only amphibians), so I thought that maybe there is corelation between number of amphibians and number of grass snakes. For exaple when number of amphibians is falling then number of natrix natrix is falling to. Are there any informations, research about that correlation?

And what about juveniles grass snakes? What do they eat? Invertebrates or maybe juveniles amphibinas?
I apologize for my english :-)
Mark_b
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Posted: 04 Oct 2008

I believe the point of the thread was about certain populations of grass snake that only appear to eat a particular species of amphibian most of the time, whether this is actually the case and why is not known!

From my literature research I found examples of grassies feeding on .... fish, small mammals, nestling birds, invertebrates (earthworms, bees, slugs and juveniles snapping at & consuming robber flies) and reptiles (common lizards and slowworms)

 "On the Greek archipelago of the Cyclades the grass snake predominantly feeds on geckos, lacertid lizards and small mammals"

Very clever buggers!


Stanislaw
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Posted: 05 Oct 2008
interesting, in one polish book author says that in all 100 stomaches in dead grass snakes he found amphibians. Has anyone observed grass snake hunting on fish in river? I've seen natrix hunting on fish only in lakes.
I apologize for my english :-)
Alan Hyde
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Posted: 05 Oct 2008
[QUOTE=GemmaJF]

Al were they live or dead voles?

[/QUOTE]

Hi Gemma,
The voles were live.
I was a young teenager and I remember this well as, i standing there with my brother worrying like mad incase the vole bit the snake inside on the way down.
It took the vole back end first .

Alan Hyde39726.1880208333
O-> O+>
David Bird
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Posted: 05 Oct 2008
What do Grass Snakes feed on when they are living on heathland where Toads and Palmate and Smooth newts are in very short supply as are small mammals ? I know that the size of Grass Snakes I see in numbers are a lot smaller than in lowland river valleys or ponds where amphibians and fish are plentiful. It is a pity that the PhD that had been suggested looking at the DNA of prey species from the faeces never went ahead. I know several people said that we know what they feed on already, which I thought was very short sighted and not exactly true.
I have mentioned this in another thread but there is a record of Natrix regurgitating and adult female Sand Lizard in Dorset. Stanley,J. 1993 B.H.S.Bull.42 p.29.
British Herpetological Society Librarian and member of B.H.S Conservation Committee. Self employed Herpetological Consultant and Field Worker.
Suzi
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Posted: 05 Oct 2008
Many year ago my brother caught a grass snake in Lake Windermere in the shallows (3-4ft water). I can only think it was after minnows as they were common in the vicinity. The perch and trout would have been in deeper water. Unless it was just having a swim.
Suz

- feeding habits question

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