Consider the difference between two alarm calls: “Hey!” and “Duck!” The first could cause the receiver to just look around, and maybe move into danger rather than out of it. The second carries information, not just alarm. For many years, researchers considered all animal alarm calls devoid of any meaning, like a human’s inarticulate shout. But careful observation in the field brought new information. Animals do not always respond the same way to dangers. Even the lowly barnyard bantam possesses a small vocabulary of danger signals. In response to the mere sight of a predator invading the yard, a bantam emits a high-pitched Kuk Kuk Kuk. On the other hand, if she spies a hawk circling overhead, she’ll shriek a single long call.
To call a behavior deliberate communication, however, scientists look for some indication that the sender intends to communicate, and they look for a response from the receiver. Bantams satisfy both criteria in their alarm calls.
Red Junglefowl male and female
1881, Hume and Marshall, Game Birds of India, Burmah and Ceylon
From Wikipedia
First, bantams call about predators much less often if no other bantams are around. Called the audience effect, this appears to indicate an awareness of whether or not the call will do any good. If it were merely an emotional alarm, the chickens should squawk under all circumstances, just as a human might scream at a scary sight, whether or not anyone else can hear. Second, the bantams’ two calls trigger two clearly different responses. A bantam who hears the ground-predator cluck cranes her neck, scans the ground and runs to the middle of the yard, where she could see, for example, a weasel creeping from under the henhouse. A bantam who hears the flying-predator scream, however, looks upward and runs for cover. Fortunately for researchers, bantam hens and roosters see and believe in television. A video of a raccoon or a red-tailed hawk elicits the appropriate call, and the call elicits the appropriate response.
Both bantams and the Burmese Red Junglefowl, the wild ancestor of domestic chickens, also call to announce food. The call, a low series of single-note clucks called tidbitting, conveys more than satisfaction at finding food. Cocks rarely send their food call except when in the presence of food and within sight of a hen. And hens rarely cluck about food unless they have chicks. Junglefowl tune the food call to suit the food. For an excellent food source—say a juicy grub—they cluck more often and more rapidly. And hens respond less readily to an indifferent food call. Although newly hatched chicks do respond to high-quality and low-quality food calls differently, they also learn to discriminate better as they gain experience.
Domestic cocks sometimes food-call when no food is present, or advertise high-quality food when the food they have is actually of low quality. Some researchers call this behavior deception, but as the food call functions both as a call to food and a call to mate, the cock may not be guilty of false advertising after all.