By Will Watson
(This article is a modified version of that published in Great Crested News October 2001 Issue 2 which is funded by English Nature, Froglife and the Herpetological Conservation Trust. It is also a development on information given by Will Watson in Worcestershire Record No 9 pages 28-29).
Like most counties only casual records of great crested newts existed in Worcestershire before 1986. However, these showed the species to be widespread throughout the county. In 1986 the National Amphibian Survey, organised by Rob Oldham and Mary Swan from Leicester Polytechnic, was launched with funding from the Nature Conservancy Council. In 1987, Phil Williams and myself conducted a blanket amphibian survey of the Warndon Parish in Worcester City; 410ha of biodiverse rural landscape scheduled for development.
Forty-five ponds were present and great crested newts were found in twelve of them in the first year. The ponds were studied over the 10-year period of the development, recording great crested newts from 25 of the Warndon ponds. Lyppard Grange, with 187 individual adult crested newts recorded in one evening, is still the best-recorded site in Worcestershire.
Mainly from the mid 1990s onwards attention was focused on other parts of the county to find out if this high rate of occurrence was part of a pattern experienced elsewhere. Over a 14-year period (between 1987 and 2000 inclusive) I surveyed 387 ponds at least once for amphibians. A total of 335 of those ponds contained one or more species of amphibians, representing 86% of the total. An impressive 190 of those ponds surveyed contained great crested newts. This is a 49% occurrence rate for this species. About 90% of the surveys carried out were targeted at all five common species and involved a minimum of ten minute sampling, either netting or torching. Only 10% of survey work carried out involved just egg searching and so was biased towards smooth and great crested newts.
Using this knowledge, last year I concentrated amphibian surveying, within areas where there are high rates of great crested newt occurrence. Typically these areas contain clusters of ponds. At Hanbury Hall, a National Trust Estate, 26 ponds were sampled within just 1.5kmē. Great crested newts were found in 21 of these ponds. This does appear to be quite an exceptional area for crested newts (pers. com Jim Foster). Surveys of smaller ponds clusters within Worcestershire have revealed a similar rate of occupancy.
It is possible to compare the Worcestershire results with a similar survey conducted in Cheshire by the Pond Life Project during 1995 and 1996 (see table). A similar number of ponds were surveyed in Cheshire and found to support 31% occupancy by great crested newts. It should be noted that this work was carried out between May and July - not an ideal time for recording adult newts. Recent detailed surveys in Cheshire are now indicating that great crested newt occurrence is well in excess of 50% (pers. com Julian Whitehurst).
These landscapes contain what is known as 'core pondscapes' with pond densities of between 5 to 10 ponds or more per square kilometre. Pondscapes can also be defined as continuous habitats - where there is a constant movement of species (not just newts) between still water-bodies. Great crested newt meta-populations exist where there are two or more ponds within a 300 metres radius where there is regular movement of animals between ponds. The early indications suggest that at Hanbury Park these populations are linked. It could be, in such situations, that meta-populations are spread over 10s if not 100s of square kilometres. Pondscapes, which support large numbers of newts, are the most important great crested newt habitats not only nationally but also internationally. Recognition of the value and important of such habitats has been slow. Ironically counties supporting fewer ponds or lower pond densities have been able to concentrate more effort on comprehensive site evaluations, which have then enabled site designations and management objectives to be fulfilled. In the counties in west midlands where there is high pond density and crested newt occurrence it has been a struggle to fulfil many of the biodiversity objectives.
Some geographic areas support large populations of great crested newts and others do not. The factors, which influence their distribution, have intrigued for some considerable time. We have known for a long while that there is strong correlation between pond density and great crested newt occurrence, but there is more to it than that? Worcestershire covers an area of 1,735kmē with approximately 5,000 ponds, each covering less than 2ha in area (derived by looking at recent Ordnance Survey maps). The average pond density in Worcestershire is 2.9 per 1km square. Both Cheshire and Suffolk have far more ponds, but Suffolk does not have anything like the same rate of occupancy by crested newts - so why the differences?
Geology clearly has an important influence on great crested newt distribution. A common feature of all three counties is that clayland landscapes dominate. The Cheshire plain contains both glacial boulder clays and Mercia Mudstone. In Worcestershire Mercia Mudstone occupies about 40% of the county and Lower Lias clays about 20% with the greatest density of ponds being on the Mercia Mudstone. This substrate contains bands of Tea-green Marl; water within such pond s usually has a pH towards the basic side of neutral. Other studies have shown that great crested newts are best suited to ponds that are slightly alkaline. If most of Suffolk ponds on boulder clay are neutral or mildly acidic this may, at least in part, explain why there are less great crested newts in that county.
Biodiversity objectives clearly guide us towards trying to identify every single great crested newt pond on a county basis to fulfil our targets. In areas of high pond density, such as Cheshire and Worcestershire, this is unrealistic given the 10 year timescale. Individual evaluation of ponds based upon the size of a population is crucial in furthering our understanding on the species - but it must not be the sole facet for site designation. Designations should also reflect the importance of pondscapes. This would parallel work carried out by the Pond Life Project, the Pond Conservation Trust, and others, where they are attempting to identify the intrinsic and generic biological value of pondscapes. Recognition of pondscapes also directs the emphasis on ponds not as individual sites but as continuous habitats where there is a constant movement of species (not just newts) between still water-bodies. The risk is that if we fail to identify the core pondscapes (which are arguably significant habitats on a global scale) counties such as Cheshire, Staffordshire, Shropshire and Worcestershire will be disadvantaged - there are just too many sites to survey and evaluate and not enough additional resources fulfil biodiversity targets. A better way might be to identify particular landscapes which best meet the requirements of great crested newts. We do not need to find every last great crested newt pond to make these conclusions. In order to achieve these aims we would have to define our parameters in terms of the percentage of ponds that we need to look at to based our conclusions. We would also need to carry out further research into factors such as geology allied with great crested newt distribution data and pond density. Once we have a comprehensive distribution map, the next and probably most exciting phase of work would be focusing on the evaluation of pond clusters. This work would involve the recording of adult newts during the breeding period using the most appropriate method according to the conditions. Sites thoroughly surveyed on such a basis should then be worthy of consideration for Special Wildlife Site, SSSI or SAC designation.
One of the consequences of the national SAP (Species Action Plan) so far is that two counties with the lowest occurrence of great crested newt in Great Britain, Devon and Cambridgeshire, have the three of the best crested newt sites in Britain. There is a strong argument for resources to be targeted strategically according to pond density and known great crested newt distribution rather than the current ad hoc county basis. I am certain that until more resources are made available to protect our pondscapes, these sites will remain vulnerable to all the inherent risks that threaten ponds.
|No. Ponds (approx)||5,000||16,000|
|Pond density per 1kmē||2.9||6.9|
|No of ponds surveyed for amphibians||387||380|
|No. Ponds containing GCN||190||119|
|GCN occurrence rate||49||31|
|Estimated county total of GCN ponds||2,500||4,960|
|County average occurrence per 1kmē||1.44||2.13|
|Pond loss in the last 100 years.||30%||61%|
Table above shows Great crested newt occurrence in Worcestershire and Cheshire
Tailpiece: Great-crested newt tadpole
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