Alternative spawning grounds in the forest to stabilize the local amphibian population

Problem:

The resident populations of the common toad (Bufo bufo) and the common frog ( Rana temporaria ) appear to have declined sharply in recent years. One possible cause is the heavily trafficked Limmattal road. The migration route is secured with a mobile fence in the spring and monitored by volunteers. However, the return migration, as well as the migration of juvenile animals to their terrestrial habitat (forest), remains unprotected. The return migration is further hampered by a footbridge, up to two meters high, that runs alongside the road. Although it has been equipped with exit aids, it still presents a significant obstacle.

Measure :

A new pond was created in a heavily waterlogged area of the forest. Because the soil there is very loamy and there is constant groundwater pressure, no pond liner or other sealing was necessary to create a permanently water-filled pond. To facilitate spawning for common toads, larger branches were anchored at various heights in the bank.

Method:

The pond was dug out by hand with shovels.

Result:

As early as spring 2025, the pond was used as a spawning ground by some common frogs ( Rana temporaria ). However, no spawn strings of the common toad ( Bufo bufo ) have been observed so far.

Ecological added value:

The animals that find the newly created forest pond and use it as a spawning ground no longer need to cross the Limmattalstrasse. After metamorphosis, the juveniles are already in their terrestrial habitat. This eliminates the high mortality rate associated with crossing the road. In the long term, this can contribute to stabilizing the local populations.

What's next:

The pond will be monitored for the next two years. If it becomes apparent that an increasing number of individuals are using the pond as a breeding ground, additional ponds will be created at other suitable locations in this area.