Air Date: Week of February 12, 1999
Both a songbird and predator, the Northern Shrike (as in "strike") is not the most welcome visitor in New Hampshire in the winter. It has the most unfortunate habit of impaling its prey.
KNOY: It's perhaps appropriate that Valentine's Day falls in the cold, dreary month of February. It reminds us to look for love at unexpected times and in unexpected places. As Living on Earth commentator Sy Montgomery warns us, you never know where a Valentine might show up, or just what form it might take.
MONTGOMERY: It's worse than finding a dead rat in the basement. It's worse than discovering a smooshed squirrel on the driveway. You know it's a really bad day when you find a finch skewered on the hawthorne tree and a mouse impaled on the barbed wire fence. It looks like the handiwork of some demented youth. But no, it's stranger still. This is the work of a song bird.
This avian version of Vlad the Impaler looks much like a mockingbird but has a distinctive black stripe through the eye and a curved beak. It's the infamous butcher bird of the north, a.k.a. the northern shrike. Perched high in a tree, sitting up right like a hawk, the northern shrike considers most little birds and mammals fair game. Chickadees, finches, sparrows, voles, mice. It will even kill prey larger than itself, including big bluejays, starlings, and rats.
A predatory song bird is a concept disturbing enough. But what the shrike does after the kill is even more unsettling. It will fly to a perch beside a thorn or along some barbed wire, and then carefully skewer the victim there, leaving it impaled like some furred or feathered cocktail frank.
To a biologist, the shrike's unique enthusiasm for impaling other creatures is as intriguing as it is gruesome. The behavior almost certainly first evolved to help these little birds eat. Butcher birds lack the tearing talons of hawks, owls, and eagles, so they use those skewers as utensils to help them eat their meat, the way we use knife and fork.
But that's not the whole story. Males impale more prey than do females, and they do so especially during the breeding season. At that time, the birds may skewer not only their usual victims but also pieces of cloth and eggshells. Why? To find out, Israeli researcher Ruben Yosef conducted an experiment. Like a crazed Robin Hood, the researcher robbed impaled prey from rich male shrikes, and then skewered the stolen items on thorns in the territories of shrikes less fortunate. The result: the ladies took notice, and went for those males who, thanks to the researcher, had the best collection of corpses.
The sometimes gruesome larder is a courting male shrike's equivalent of flowers and candy. A song bird's Valentine.
(Music up and under: "My Funny Valentine.")
KNOY: Commentator Sy Montgomery is author of Nature's Everyday Mysteries. She comes to us from New Hampshire Public Radio.
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