grass snake egg-laying sites

[Will Atkins]

Hi All

this question was prompted by a friend who sent me a photo of a 'natural' ie non-anthropogenic egg-laying site for grass snakes that was recently discovered in a local park - it was in the bowl of a tree, where the process of decomposition was presumably generating some warmth.

It prompted me to wonder what proportion of egg-laying sites for grass snakes (and other species, like Aesculapians) are anthropogenic and what are more 'natural' - in other words, how dependent are grass snakes on humans in this regard? In the UK we tend to find most sites in compost heaps etc, but of course this is because of observer bias - we see snakes near these structures and sure enough that's where we find clutches of eggs and hatchlings. A valuable conservation technique is to construct these heaps in areas with grass snakes present - or is it? is a lack of egg-laying sites really a limiting factor for grass snakes in an otherwise 'optimal' habitat? Of course, it will vary with location and human presence, but I would like to know in a 'typical' rural habitat whether grass snakes are really so dependent on artificial sites as is sometimes assumed...

So I wonder if anyone knows of research into this question? I guess you would have to track female grass snakes (maybe using radio telemetry) ahead of their oviposition to get an unbiased view of site selection for egg laying in a variety of habitats / locations / even in different countries?? Any information gratefully received, as ever

Cheers

Will

[Rémon ter Harmsel]

My guess would be that most of the breeding site in the northern parts of its range are man-made. Even more so, it might be possible that without them, the distribution range would be quite a bit smaller, according to http://www.researchgate.net/publication ... Antichrist

[Will Atkins]

thanks very much for the link - very interesting hypothesis, it certainly makes sense for grass snakes to use dung heaps etc back in prehistoric times, thereby becoming associated with human patterns of settlement. I would like to investigate the proportion of 'natural' vs 'manmade' egg laying sites in the present day using radiotracking - I was sent this paper:

Movements, Home Range Size and Habitat Use of Radio-Tracked Grass Snakes (Natrix natrix)
in Southern SwedenAuthor(s): Thomas MadsenSource: Copeia, Vol. 1984, No. 3 (Aug. 1, 1984), pp. 707-713

but the sample size was only four females and the 'choice' of egg laying sites was (apparently) limited in the study area to 2 manure heaps. It's also interesting to speculate about how new egg-laying sites are found - is it newly mature females, for instance? the fact that 'ideal' compost heaps can take several years to be used suggests high fidelity to traditional locations. Or maybe what looks ideal to a human is simply not providing the thermal / humidity conditions required by a gravid snake. So many questions, as ever in Zoology...

[Mario Schweiger]

it is no Natrix but Z. longissimus.

In Czech republic (Karlovy Vary) they built these heaps for egg laying, but also for hibernation (photo shot at the end of February).
When looking to the surroundings there, one wouldnt believe, that this is necessary.
But since, the population is increasing steady.

[Will Atkins]

thanks Mario - so was the population size really limited by egg laying sites? so hard / impossible to say, with all the other factors to consider...

[Liam Russell]

There's been a bit of research on natural vs anthropogenic egg-laying sites in Natrix natrix

This paper suggests that the utilisation of man made egg-laying sites has allowed grass snakes to expand their range further north than would be possible if they were restricted to natural sites:
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2010.01730.x/full

This paper compared natural vs man-made eggs sites and found considerably better success in man made features.
http://link.springer.com/article/10.1007/s10531-012-0308-0

(this second paper is in Mario's database http://vipersgarden.at/PDF_files/PDF-4692.pdf)

[Will Atkins]

thanks Liam, much appreciated, those will be my weekend reading!