Feeding kinematics of Kogia and Tursiops (Odontoceti: Cetacea): characterization of suction and ram feeding.

The feeding kinematics of dwarf and pygmy sperm whales (Kogia sima and K. breviceps) and bottlenose dolphins Tursiops truncatus were characterized and compared incorporating the Ram-Suction Index (RSI). Mean RSI data support a suction feeding strategy for Kogia (-0.67+/-0.29; mean +/- s.d.) and a ram feeding strategy for Tursiops (0.94+/-0.11; mean +/- s.d.). Tursiops displayed two ram-based feeding behaviours: open gape approach, where gape was at least 50% of maximum in the first video field, and closed gape approach, where gape increased near food items. Four feeding phases were identified in both odontocetes: preparatory, jaw opening, gular depression and jaw closing. The mean Kogia feeding cycle duration (470+/-139 ms) was significantly shorter (P<0.003) than all Tursiops groups (pooled: 863+/-337 ms; open gape approach: 1211+/-207 ms; closed gape approach: 662+/-207 ms). Kogia mean maximum gape angle (39.8+/-18.9 degrees), mean maximum opening and closing gape angle velocities (293+/-261 deg. s(-1) and 223+/-121 deg. s(-1), respectively) were significantly greater (P<0.005) than pooled Tursiops mean maximum gape angle (24.8+/-6.6 degrees), mean maximum opening and closing gape angle velocities (84+/-56 deg. s(-1) and 120+/-54 deg. s(-1), respectively). Negative Kogia RSI values were correlated with increasing maximum gular depression and retraction, wide gape angle, and rapid opening gape angle velocity. Kinematic data support functional hypotheses that odontocetes generate suction by rapid depression of the hyoid and tongue.