Frog and toad populations on the increase in the Netherlands

In the past few years frogs and toads have been on the increase in Netherlands as calculations conducted in the period 1997- 2004 indicate. The recent increase follows a period of decline which started in the 1950s. The increase in frog and toad numbers is at variance with a global downward trend.

Frogs and toads, 1997-2004

Protective measures, water quality improvement and digging of breeding pools pay off and soon have a positive effect on the size of the population, because frogs and toads breed rapidly.

Frogs

The European tree frog population has the fastest growth rate. This species, mainly found in the regions of Twente, the Achterhoek and Zeeuws-Vlaanderen has grown by an annual 20 percent and the total European tree frog population in the Netherlands has multiplied by four since 1997. Due to protective measures, the European tree frog population improved considerably in the Twente and Achterhoek regions. The increase in common and green frogs since 1997 is less considerable: the annual increase was 6 and 4 percent respectively. Pool and moor frog populations, species chiefly found on sandy soils, have remained stable throughout.

European tree frog

Toads

The frequently found common toad population has increased by 3.5 percent annually since 1997. The yellow-bellied toad population also increased. This species is under serious threat internationally and is exclusively found in five quarries in the province of Limburg. The largest part of the yellow-bellied toad population is found in a quarry near a small village named 't Rooth. Due to protective measures, the population recovered in 2000 and 2001. This species remains particularly vulnerable, because the population is small and confined to only a few locations. Other indigenous toad species, such as the midwife toad, also found in Limburg, the common spadefoot toad and the natterjack have as yet not been mapped so accurately that statements can be made about recent population developments.

Tom van der Meij (CBS) and Gerard Smit (RAVON Werkgroep Monitoring)