Shrikes impale prey mainly to secure a dead animal so they can tear the carcass into smaller pieces at leisure, rather than to kill it. The source describes the grey shrike, or common butcher-bird, as generally killing by strangulation before fixing the prey on a thorn.[1]
Mr. Selby recorded a direct observation of this behaviour involving a hedge-sparrow. The shrike hovered over a hedge with the bird in its bill while choosing a suitable thorn. After the shrike was disturbed, the sparrow was found firmly secured to the twig by the tendons of its wing.[2]
In the same account, mice and other small quadrupeds are also described as being transfixed. The lesser shrike is said to hang up surplus insects to dry when it has killed more than it can immediately eat, leaving its hedge resembling a small butcher’s shop.[3][4]
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