They also, however, do another trick with much larger creatures. From Cornell's bird guide:
The broken-wing act used to lead predators from the nest would not keep a cow or horse from stepping on the eggs. To guard against large hoofed animals, the Killdeer uses a quite different display, fluffing itself up, displaying its tail over its head, and running at the beast to attempt to make it change its path.When you picture this, remember the size of the creature-- smaller than a pigeon-- running in full force at full-size horse, to try to change its course. That's what I call chutzpah.