Bite a mouse in the back of the neck and don’t let go. Now shake your head at a frenzied 11 turns per second, as if saying “No, no, no, no, no!”
You have just imitated a hunting loggerhead shrike (Lanius ludovicianus), already considered one of North America’s more ghoulish songbirds for the way it impales its prey carcasses on thorns and barbed wire.
Once the shrike hoists its prey onto some prong, the bird will tug it downward “so it’s on there to stay,” says vertebrate biologist Diego Sustaita. He has witnessed a shrike, about the size of a mockingbird, steadying a skewered frog like a kabob for the grill. A bird might dig in right away, keep the meal for later or just let it sit around and demonstrate sex appeal (SN Online: 12/13/13).
Shrikes eat a lot of hefty insects, mixing in rodents, lizards, snakes and even small birds. The limit may be close to the shrike’s own weight. A 1987 paper reported on a shrike killing a cardinal not quite two grams lighter than its own weight and then struggling to lift off with its prize. Recently, Sustaita got a rare chance to study how the loggerheads kill their prey to begin with.
Conservation managers breed one loggerhead subspecies on San Clemente Island. That’s about 120 kilometers west of where Sustaita works at California State University San Marcos. Sustaita set up cameras around a caged feeding arena and filmed shrikes, beak open, lunging to catch dinner. “They’re aiming for the prey’s neck,” he says.
BIRD SHAKES In a caged feeding station for conservation breeding, a loggerhead shrike demonstrates its pounce, bite and shake approach to hunting a mouse.
That’s a very shrikey thing. Falcons and hawks attack with their talons, but shrikes evolved on the songbird branch of the bird tree — without such powerful grips. Instead, shrikes land on their feet and attack with their hooked bills. “The bite happens at the same time the feet hit the ground,” Sustaita says. If the mouse somehow dodges, the shrike pounces again, “feet first, mouth agape.”
Reading several decades of gruesome shrike papers, Sustaita first believed the real killing power came from the bird’s bill, with bumps on the side, wedging itself between neck vertebrae and biting into the spine. Shrikes definitely bite, but based on videos, he now proposes that shaking may help immobilize, or even kill, prey.
Sustaita and colleagues discovered that the San Clemente shrikes fling their mouse prey with a ferocity that reached six times the acceleration due to Earth’s gravity, or about what a person’s head would feel in a car crash at 2 to 10 miles per hour, the researchers report September 5 in Biology Letters. “Not superfast,” he acknowledges, but enough to give a person whiplash.
In a small mouse, such shaking looks more damaging. Video analysis showed that the mouse’s body and head were twisting at different speeds. “Buckling,” Sustaita calls it. Just how much damage twisting does versus the neck bite remains unclear. But there’s a whole other question: How does a shrike manage not to shake its own brain to mush?