Killdeer — Broken-Wing Display

The killdeer (*Charadrius vociferus*) performs a "broken-wing display" (also called injury feigning or distraction display) when a terrestrial predator approaches its ground nest. The bird moves away from the nest while simulating an injured, highly catchable bird — drooped wings, fanned depressed tail, conspicuous orange rump, alarm calls — luring the predator away, then suddenly "recovering" once the nest is safe.

What the Signal Is

The display sequence:

1. The bird first runs silently from the nest to draw predator attention away from eggs/chicks
2. Turns its tail toward the predator, displaying the threatening orange rump
3. Crouches, droops wings, and lowers tail — simulating a grounded, injured bird
4. Escalates with increasing intensity: wings held higher, tail more fanned and depressed
5. May escalate to alarm calls and other disturbances to reinforce the impression of vulnerability
6. Once the predator has followed far enough from the nest, "recovers" and flies off

The intensity of the display scales with reproductive investment: minimal during egg-laying (bird simply walks away from nest), peaks after chicks hatch (when young are mobile but still vulnerable), then decreases as chicks become more independent.

The Ungulate Display

A second, distinct signal: when large ungulates (grazing animals) approach the nest, the killdeer raises its wings, exposes its rump, lowers its head, and charges at the animal. This is not deception — it is a direct threat display designed to deflect a non-predator that might accidentally crush the nest. The display has been documented to sometimes be fatal to the displaying bird, making it a genuine costly signal.

Honest or Deceptive

Deceptive. The broken-wing display presents false information — that the bird is injured and catchable — to redirect predator attention. This is classic Peckhamian mimicry (aggressive deception for protection), exploiting the predator's evolved search image for vulnerable prey. The receiver's response (pursuing an apparently easy target) is the behavior the sender is exploiting.

The display is receiver-targeted: killdeer use the broken-wing display against predators and the charge display against non-predators (ungulates). This context-appropriate switching implies some discrimination of threat type.

Acquired or Innate

Innate. The display appears across populations without evidence of social learning. It is a fixed action pattern triggered by proximity of a predator to the nest during the breeding season, modulated by reproductive stage.

Intensity Calibration

One of the most revealing features: the intensity of predator responses changes systematically through the breeding cycle. During egg-laying, the most common response to predators is simply to leave the nest quietly. As incubation progresses, intensity increases, peaking after hatching. After the chicks become more independent, response intensity decreases again.

This calibration reflects the changing cost-benefit ratio: a bird's egg is less valuable than a chick close to fledging, so the parent invests proportionally more in defense as reproductive investment accumulates.

Open Questions

• Does the killdeer "know" the nest is safe when it ceases the display, or does it use a distance rule?
• The orange rump flash at the start of the display may function as an additional signal to the predator, not just a byproduct of posture — this hasn't been fully separated out
• Whether the broken-wing display is more effective against naive predators (who haven't been deceived before) vs. experienced ones is not well-studied