Answer: Sign stimulus
Explanation:
The sign stimulus also refers to releaser. It is the stimulus which elicit a response in an organism. For example, the red belly is the sign stimulus for the male sticklebacks to provoke the attack another male.
According to the given situation, the cheeping sound of the young chicks is an alert for the parents for danger or hunger so this elicit a protective response in parents and thus the cheeping sound of the young chicks is indicative of sign stimulus.
