Shrikes are nondescript and ubiquitous birds that have made a name for themselves as the leatherfaces of the animal kingdom. They don't just eat their prey, they impale it on spikes and display is as part of their courtship ritual. That's nasty enough, but they have one other trick up their sleeves.
A shrike doesn't look scary, but its larder would probably make your run back to civilisation if you encountered it during a hike. These birds eat bees and wasps, lizards and mice, and other birds -- but not right away. Instead they find a spiky branch or a high thorny cactus and impale their prey on its spikes. Once they have an impressive cabinet of horrors, filled with dead or dying impaled animals, they will invite a potential mate by to display their prowess. Then, presumably, they have dirty bird sex right in front of the bodies of their victims.
A shrike isn't a danger to any human, but it's the terror of small animals the world over. So why would a number of song birds fly directly toward shrike calls? It seems odd, but they do. One study showed that, given a tape player playing a blank tape, a player playing five minutes of of American Robin song, and a player playing five minutes of Northern shrike song, the shrike song attracted the most small songbirds.
The study wasn't done on a whim. It was meant to provide some formal confirmation of what bird-watchers have been saying for some time -- shrikes will mimic the calls of songbirds in order to lure the birds over to them. Shrikes do have calls meant to communicate with their own species. Young shrikes will make "begging calls" to get their parents to feed them. Older shrikes have warning calls. But a good deal of shrike "song" is actually meant to imitate their food, so their food will come up close, only to be attacked, murdered, and impaled.