by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog (Osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. Territorial behaviour Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders (Plethodon cinereus) has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred