Which of the Following is a Sign Stimulus

Question

Which of the following is a sign stimulus?
A) a cuckoo chick evicting the original chicks in the nest
B) a mother rat picking up young rats and returning them to the nest
C) the open mouth of a peeping baby bird
D) an innate learning

Accepted Answer

The open mouth of a peeping baby bird acts as a sign stimulus to trigger a specific behavior from the parent, typically feeding. This is a direct, innate trigger for a specific response, fitting the definition of a sign stimulus.