Change in great crested newt Habitat Suitability Index between 1996 and 2007 assessed using lowland Countryside Survey data 2012

Abstract

This study investigated whether lowland pond habitats improved for the great crested newt (Triturus cristatus) over the period 1996 to 2007, using data collected for the Countryside Survey. It did not involve records of Great Crested Newts in the analysis, but focused on habitat suitability for the species.

Based on a dataset of 77 ponds sampled for the Countryside Survey in both years, there was a small (2.6%) non-significant increase in great crested newt Habitat Suitability Index (HSI) values between 1996 and 2007. A second analysis comparing data from a larger number of ponds (from 116 1 km squares in 1996 and 172 1 km squares in 2007) showed a similar (non-significant) increase in HSI over the 11 year period. However, these data were less robust as a measure of change than the re-sampled ponds largely because of differences in the methods used in the 1996 and 2007 surveys.

The most recent Countryside Survey data (2007) suggest that c. 25% of lowland ponds are currently in ‘Good’ or ‘Excellent’ condition for great crested newts. This compares with 22% in 1996. Over this time there was a suggestion that the ponds least suitable for great crested newts improved slightly, with ponds in the ‘Poor’ category moving to ‘Below Average’. Analysis of the individual Suitability Index variables which are combined to calculate HSI scores showed that two indices changed significantly between 1996 and 2007 and were mainly responsible for the increase in calculated HSI. These were (i) the net number of ponds per 1km square (P<0.05) and (ii) the quality of surrounding land use for amphibians (P<0.01). The increase in pond density is in agreement with the national trends observed in Countryside Survey between 1998 and 2007.

Overall the findings suggest that there may have been a small increase in the suitability of ponds for great crested newts in the lowland countryside between 1996 and 2007 as a result of pond creation and possibly land-use change. The observed increase in pond numbers in Great Britain between 1998 and 2007 suggests that this trend is likely to be real. However, a larger sample of ponds would be needed to prove that the HSI trends observed are statistically significant.