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Alarm calls form an important element in wild creatures' defences, and it is fascinating to find how often one species warns another of danger. A woodpigeon, for instance, can perfectly well leave a tree silently, but when it departs with a loud clap of its wings, fellow-pigeons, rooks, crows, pheasants and others get immediate notice that something unpleasant is in the offing.

Blackbirds mob owls with high, hysterical twittering, but switch to a low "tuk, tuk" whenever they see a ground predator such as a fox, cat or stoat. Wrens tick like alarm clocks if they detect that kind of prowler, and a cock pheasant which persists in giving off single calls has almost certainly spotted a fox. Jays, on the other hand, screech indiscriminately at all enemies, whether grounded or airborne.

Male deer generally remain silent, except during the annual rut; but females give hoarse barks when they see or scent danger, and the alarm call of a fallow doe, for example, will communicate itself to a roe or a muntjac. Humans, in other words, can glean much information about events in the countryside purely by listening.