The Hammer and the Snail

The song thrush is a frequent visitor to our gardens, probing around on the ground in search for anything that it can find, e.g. snails, worms, insects, berries. During the summer the song thrush exhibits a bizarre behaviour, performed by few other bird species: extracting snails from shells using a tool.

When worms, the most favoured food source, are in low supply, particularly in droughts, conspicuous banded snails become the preferred prey. Away from predators and prying eyes the thrush takes the snail to a flat, hard object called an anvil. Examples of anvils include rocks, the top of a wall, paving slabs. Here the clever individual grabs the lip of the snail shell and repeatedly bashes it against the anvil, breaking the shell and revealing the juicy nutritious snails.

Shells

Over time a pile of shells will build up as the thrush repeatedly returns to its specially selected anvil. Studies have shown these anvils are a local hotspot of bird diversity in a number of ways. Firstly, the sound of breaking shells may attract sparrowhawks and other birds of prey, as cracking shells indicates an occupied bird which is an easy target. The large number of shell fragments draws in a large crowd, as small birds collect and eat small pieces of shell which contain high amounts of calcium, useful for producing eggs and for maintaining health.

In the thrush’s eyes, our gardens may be seen as the perfect location to have an anvil; secluded and protected from predators both on the ground and from the sky and a great place to find snails.