Summertime and the living is easy in our garden, except if you happen to feed on earthworms. Then the withered lawn and parched earth of August drive a number of our neighbours to take special measures. The most conspicuous indicator of summer drought is a bit of avian behaviour that’s more often heard than seen.
It results in a small hollow hammering noise of shell on stone and, aside from the wider hush enveloping our flowerbeds, you could easily overlook its quiet rhythmic tap. Yet a song thrush at its anvil is as redolent of Claxton at this particular moment in summer as the bell-like notes of full-blown song on late July evenings.
I’m guessing it is largely a hedge-bottom business, because the snails themselves also collect in those shaded, damper conditions beneath the brambles. But I also wonder whether there is another factor at play.
When he was a postdoctoral student at Oxford and before Zootime (1957) went on air or The Naked Ape (1967) was written, the immensely versatile Desmond Morris published a paper on snail-eating thrushes. It was a very thorough piece of work – after 61 years it is still cited as a key document on the subject.
Morris showed that the “anvil” was not a stone selected by tradition or habit, but for its geographical proximity to where the snails were first caught. He also showed that the hammering action involved the thrush holding its prey by the shell lip or the flesh, and that successful breakage was followed by a bill-wiping phase to clean away the slime and shell fragments.
Morris’s other revelation, which contradicted earlier ornithologists including the great Victorian authority William Yarrell, was that blackbirds lacked the necessary coordination and “nervous equipment” to master this snail-breaking technique. But they have found a way to enjoy the savour of freshly cracked mollusc. They sit, wait and watch, then steal them off their smarter but smaller song thrush relatives.
I surmise that this piracy, which is known technically as kleptoparasitism, explains why our song thrushes are as keen on the shaded seclusion of the hedge bottom as they are on snail flesh itself.
