The correct answer is option 3: Birds. The syrinx is the voice box in birds. This specialized vocal organ is located at the base of the trachea, where it bifurcates into the bronchi. Unlike the larynx in mammals, which is located in the throat, the syrinx in birds is located at the lower end of the trachea, near the junction of the bronchi. It is responsible for producing the sounds that birds use for communication, such as songs and calls. The syrinx in birds is unique in its structure and allows for the production of a wide range of sounds and complex vocalizations. It is not found in amphibians, reptiles, or mammals.