Observation and analysis of sonar signal generation in the bottlenose dolphin (Tursiops truncatus): Evidence for two sonar sources

Indirect evidence for multiple sonar signal generators in odontocetes exists within the published literature. To explore the long-standing controversy over the site of sonar signal generation, direct evidence was collected from three trained bottlenose dolphins (Tursiops truncatus) by simultaneously observing nasal tissue motion, internal nasal cavity pressure, and external acoustic pressure. High-speed video endoscopy revealed tissue motion within both sets of phonic lips, while two hydrophones measured acoustic pressure during biosonar target recognition. Small catheters measured air-pressure changes at various locations within the nasal passages and in the basicranial spaces. Video and acoustic records demonstrate that acoustic pulses can be generated along the phonic fissure by vibrating the phonic labia within each set of phonic lips. The left and right phonic lips are capable of operating independently or simultaneously. Air pressure in both bony nasal passages rose and fell synchronously, even if the activity patterns of the two phonic lips were different. Whistle production and increasing sound pressure levels are generally accompanied by increasing intranarial air pressure. One acoustic “click” occurred coincident with one oscillatory cycle of the phonic labia. Changes in the click repetition rate and cycles of the phonic labia were simultaneous, indicating that these events are coupled. Structural similarity in the nasal apparatus across the Odontoceti suggests that all extant toothed whales generate sonar signals using the phonic lips and similar biomechanical processes.     

ORPHAN-INDUCED LACTATION IN TURSIOPS AND ANALYSIS OF COLLECTED MILK

Two non-lactating, non-gravid female bottlenose dolphins, Tursiops truncatus , (SLA, age 32 yr and TOD, age 34 yr) began lactating within one week after being housed with a 6.5- and 6.75-month-old orphaned calf, respectively. Cooperative swimming and nursing behaviors were quickly evident in both cow/ calf pairs. During the first 2.5 mo a milk substitute, eventually in combination with some whole fish, was used to supplement nursing in both calves. After this initial period, supplemental feeding was discontinued. SLA then became her adopted calf s sole source of nutrition for the next 5 mo, followed by another 6 mo during which the calf shifted to a predominantly fish diet with occasional nursing. TOD's orphan also continued to nurse beyond the 2.5-mo supplementation period and began voluntarily accepting small quantities of fish, suckling continued over the next year while fish consumption increased. Using a modified human breast pump, trainers collected milk at intervals from the adult dolphins throughout the lactation period. The first milk collected from TOD (day 8 after housing with calf) and SLA (day 12 with her calf) contained 6.0% and 10.3% fat, respectively. On day 68 TOD's milk fat had increased to 23.5%, and on day 37 that of SLA measured 22.5%. These later values are similar to those reported for normally lactating bottlenose dolphins.