Pier Francesco Ferrari; (inset, left) Elizabetta Palagi

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Birds raise false alarm to scare off predators

Birds are shameless eavesdroppers, listening and reacting to the calls of other species. If one bird spots danger and raises an alarm, other species will flee, too. Now, new research indicates that some birds exploit this tendency in order to protect their nests from would-be pillagers. Pied currawongs (Strepera graculina)—a species of large black bird found in Australia—regularly feast on nestlings of the brown thornbill (Acanthiza pusilla, pictured). At a fraction the size of a currawong, the diminutive songbird can't rely on its might to spook the nest-raiding bandits. But if they can make the currawongs think a fearsome hawk is swooping in, that's another story. Rather than impersonating the predator itself, the thornbill imitates a chorus of other bird species sending up an alarm that warns of an aerial predator, according to a new study published today in the Proceedings of the Royal Society B. The researchers studied brown thornbills near Canberra, testing their reaction to a dummy currawong near their nest, coupled with recorded sounds of nestlings in distress. In response, the thornbill parents imitated alarm calls from between one and four different species, some of which can be heard in this video. Next, the researchers played recordings of the thornbills' alarm call imitations to currawongs. Those that heard the alarms were likely to scan the sky for predators or fly away, which would give threatened nestlings a chance to escape.