We have chickens, and they do the same thing. They listen for cues from other species, and rightly so. We have an adopted (just showed up one day) guinea hen who has a jungle type squawk she makes whenever a predator, including a local sharp-shinned hawk is present. When she pipes up, everyone takes cover. Ironically, when she makes the noise, our barn cats look to start hunting/ crouching. They are fantastic predators.