The male red-breasted robin is highly territorial and will attack rival males that encroach in his territory.

The male red-breasted robin is highly territorial and will attack rival males that encroach in his territory. Experiments show that the mere presence of a pile of red feathers will induce territorial behavior in the male robin. This is an example of which of the following behaviors?

 A. classical conditioning

 B. imprinting

 C. operant conditioning

 D. sign stimulus