These hook-beaked birds are known for skewering their insect and other small prey onto spikes such as thorns and barbed wire.
They may have developed the technique by accident, when prey they were wedging into forks of branches to manipulate, perhaps because they lack strong talons, became stuck on thorns.
By repeatedly using the same spikes, the birds ended up with caches of food. Nowadays, males use these food stores, along with display items such as rags, snail shells and the membrane-coated faecal sacs produced by nestlings, to attract females.
Males with bigger caches tend to breed with the earliest-arriving females, producing more fledglings. They may even win two mates. By caching, a bird can mark his territory, hoard supplies for leaner times and store toxic prey, such as lubber grasshoppers, until the chemicals they contain decompose.
The development of this technique may also have been an accident, with males first impaling the vivid insects to attract mates before later discovering that they became safe to eat.
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Main image: Red-backed shrike. © Prisma Bildagentur/UIG/Getty
