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Posted by: Hannah Maben - BSc (Hons) MIEEM on 17/03/2011

The weather is becoming milder and amphibians are stirring out of hibernation and there have already been several sightings in ponds.  This indicates the start of the great crested newt survey season (mid-March to mid-June)!  In preparation, Ecosulis has reflected back on our newt survey results from 79 ponds in 2010 and considers how the relatively new Habitat Suitability Index (HSI) is being used and what benefits it brings to the consideration of newts and works affecting newt habitat.

In 2010 Ecosulis undertook great crested newt surveys of a total of 92 water bodies throughout England.  There are lots of analysis opportunities with these results; however we have looked back at our great crested newt survey results from 2010 and consider if there is any correlation between the results of the Habitat Suitability Index (HSI) of a pond and presence of great crested newts and compare our findings with published papers and guidance. 

Following this review consideration is given in respect to the value of the HSI in support of planning and European Protected Species Licence (EPSL) applications in respect to development.

HSI Score / Presence of Great Crested Newts

In 2008, Natural England’s licensing team started requiring information on the HSI of water bodies supporting great crested newts.  The HSI for great crested newts was developed by Oldham et al. (2000) and is applied according to guidance set out by the National Amphibian and Reptile Recording Scheme (NARRS 2007). 

The HSI is a numerical index, for which scores between 0 and 1.0 indicate the suitability of the habitat.  The scoring system is shown in Table 1 below.  Oldham notes some correlation between the HSI score and the presence of great crested newts; however, some ponds with poor HSI scores have been found to support great crested newts and likewise ponds with an excellent HSI score often do not support great crested newts.  There is also a positive correlation between the HSI score and population size of a pond i.e. generally the higher the HSI score the greater the population size. The HSI is therefore a means of assessing the suitability of a water body to support great crested newt, but is not a substitute for presence/absence surveys

Assessment of Ecosulis 2010 Results

Ecosulis has reviewed their HSI assessment and great crest newt survey results from 2010 to see how these compare to those within the HSI guidance. 


The following table provides a summary of the HSI score and results of great crested newt presence / absence surveys of ponds surveyed by Ecosulis in 2010.

Table 1: Summary of HSI Score and Presence of Great Crested Newts for Ponds Surveyed in 2010


Suitability (based on HSI Score)

Number of ponds (out of 86* surveyed)

No of ponds supporting GCN (%)

Poor (>0.5)


0 (0)

Below average (0.5-0.59)


4 (40)

Average (0.6-0.69)


23 (72)

Good (0.7-0.79)


19 (68)

Excellent (>0.8)


1 (100)



*only 79 of the 93 ponds surveyed had HSI assessments completed in 2010

From the above table, it is apparent (even in the absence of detailed statistical analysis) that the HSI is an effective method for assessing the likelihood of a pond to support great crested newts.  Our survey results show that the higher the HSI score the more likely a pond is to support great crested newts; however, some ponds with below average suitability were recorded as supporting great crested newts and newts were absent from some ponds with good suitability.   Our results from 2010 therefore support the published papers and guidance that the HSI is not a substitute for presence/absence surveys, but can help to consider their likely presence.

People planning works to a pond or terrestrial habitats surrounding a pond (typically newts can use habitats up to 500m from a pond) should therefore undertake a full presence/absence survey between mid-March and mid-June in accordance with the Great Crested Newt Mitigation Guidelines (2001).

Population Size

Figure 1 shows the positive correlation between the peak count of great crested newts (highest number of great crested newts recorded during any one survey using one survey method) and the HSI score. 

Whilst not as pronounced as that within Oldham’s paper the results of Ecosulis’s surveys show a positive correlation with the peak number of great crested newts recorded generally being greater within ponds with a higher HSI score.  Again, there are exceptions to this, but the trend is clear.

Use of HSI in Respect to Planning Applications and EPSL Applications

Great crested newts and their habitats are protected by European and UK legislation and as such they are a material consideration in the planning process.

Depending on the development proposals, site location and current conditions an HSI assessment may be sufficient to assure the Local Planning Authorities (LPAs) that the presence of great crested newts is unlikely and as such further surveys are not required prior to planning being determined.  However, following two recent judicial reviews (Woolley 2009; and, Morge 2010), it is becoming increasingly common for LPAs to demand presence/absence surveys and, if present, population surveys, impact assessment and detailed mitigation proposals prior to determining planning applications. 

European Protected Species Licences (EPSL) in Respect to Development can only be issued if presence of a protected species is confirmed and impacts are likely.  An EPSL application requires full survey information including the HSI score and the results of great crested newt presence/absence and population surveys.  Such licences can only be obtained once full planning permission has been obtained and other “derogatory tests” under the EU Habitats Directive 1992 are met.

Acknowledgements - Thanks to Fen Braund and Mike Williams for helping me collate all the 2010 newt survey data!


Amphibian and Reptile Group (2010)ARG UK Advice Note 5: Great Crested Newt Habitat Suitability Index.  Amphibian and Reptile Group

Oldham et al. (2000) Evaluating the Suitability of Habitat for the Great Crested Newt (Triturus cristatus).  Herpetological Journal. Vol. 10 pp143-155

Categories: Ecological Consulting
Tags: Great Crested Newts | Habitat Suitability Index | Newt Surveys
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