Bureau Waardenburg
Varkensmarkt 9
4101 CK Culemborg
the Netherlands
T: +31 (0) 345 512710
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Kruipers in de polder
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Distributions of amphibians

We have investigated the distributions and habitat preferences of amphibians (and a fish species) in the South-Holland polder areas of Alblasserwaard and Vijfheerenlanden. The species studied include great crested newt (or northern crested newt), natterjack toad, moor frog and weatherfish. This study was carried out in close collaboration with Stichting Landschapbeheer Zuid-Holland (Foundation for the South-Holland Landscape). Based on the results a number of pilot projects were established that aimed to improve the area for these species. These pilot projects will be expanded in the future.

Great Crested Newt
In 2005, surveys were carried out for the great crested newt. The distribution of this species in the Vijfheerenlanden and Alblasserwaard was found to be strongly linked to the presence of dykes. This species was restricted by the lack of suitable waters for breeding. In particular, the construction of waters that are not colonised by fish were identified as a priority for this species.

Natterjack Toad
Surveys for natterjack toads were carried out in 2004 and 2005. These were undertaken during evenings with good conditions for calling toads. The locations of calling toads were later visited in order to establish the ecological characteristics of these sites and to determine the optimum habitat for the natterjack toad in the Vijfheerenlanden and Alblasserwaard. Suggestions as to improvements in the habitat for this species were then made.  In addition to the data from surveys, the distribution of calling toads was determined from observations from nature- and birdwatchers. The analysis revealed a correlation with soil type. On the basis of older data the distribution had not changed. The results revealed the importance of habitat management of the ditches for this species.

Moor Frog
Surveys for moor frogs were conducted in 2004 and 2005. In 2004, the survey focused on calling individuals, and in 2005 the aim was to identify areas where frogs were found along roads. The surveys aimed at establishing the distribution of the moor frog in the area and identifying the factors determining this distribution. In addition to survey data observations were collected from nature- and birdwatchers. The results revealed that moor frogs were present throughout the entire area, although the highest concentrations were within the reserve areas. There was also evidence to suggest that, in line with the decline in numbers, moor frogs are retreating into these areas. This is probably a result of agricultural intensification and changes in land management. the moor frog showed preference for both agricultural and peatland areas, probably relating to the ease of digging. Recovery measures should focus on the management of ditch margins, less intense land use and the flooding of meadows.

In 2005, weatherfish were surveyed across the whole of South-Holland. As well as trapping, which took place in a total of 15 polders, observations were collected by third parties. The results revealed that weatherfish were fairly widespread but occurred in low densities within Vijfheerenlanden and Alblasserwaard. Various sources indicate that the species has declined in recent years and in many places has disappeared.  The intensive management of ditches is likely to have played some role in its decline. Measures aimed at management of the entire habitat rather than individual ditches are likely to be of most benefit.

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