At a least tern nesting site in Mission Bay, about two dozen volunteers worked to pull out invasive weeds and help clean up the site for the upcoming nesting season. As one worker approached a small cluster of primrose, a killdeer dashed out and began making a trilling sound. It watched everyone around him, intently and, then, went back to the cluster and acted like he was sitting on a nest. When another person approached, the bird immediately acted like it was hurt and ran away, flopping around. He thoroughly convinced the person that he was hurt until she saw that he was OK a minute later. For at least an hour, he guarded that spot, acting like he was sitting on a nest. Then, he flew off. There was no nest or eggs anywhere around.
Killdeer are known for their “broken wing act”. When a predator approaches, they flop around and act like they’re hurt or have a broken wing, luring the predator away from the well hidden nest on the ground. They aren’t the only bird that does a distraction display. Many birds do similar things to protect their nest. Most ground-nesting birds do some sort of display to lure predators away and as well as a few tree and cliff-nesting species.
Though the broken wing act is the most well known, killdeer also have other ways to “trick” presumed predators. When screaming and doing a broken wing act doesn’t work, they will fly around a predator in circles making it look like there are many killdeer around. They also will run around and act like they’re sitting on a nest or brooding a chick only to get up when the predator goes to look. They even seem to notice when you can’t see them and will change their positions so that they’re more visible and get you to notice.
Most of these tricks, combined with camouflage, seem to be successful most of the time. However, once in a while a parent killdeer will lose its life while performing. Or, the predator is so dead set on finding the chick that they pay no attention to distractions. But, the acts do seem to work enough to ensure that the species survives. Why was the killdeer at the least tern site doing this act without anything to protect? No one knows for sure. But this behavior is most likely driven by their hormones and it is the beginning of nesting season.