Meeting Abstract
Echolocation has evolved in bats, cave dwelling birds, some shrew, and Odontocetes (toothed whales, dolphins, and porpoises). The production of echolocation signals is linked to respiratory cycles in both bats and birds, usually at a high energetic cost. Unlike their terrestrial counterparts, the conservation of oxygen is paramount for Odontocetes that echolocate while holding their breath underwater. To determine whether echolocation under water is also associated with a large energetic cost in delphinids, we used flow-through respirometry to measure the metabolic cost of click production at depth in trained male bottlenose dolphins (n=2). As expected, metabolic rates (MR) decreased upon submergence during control (silent) and click production trials, concomitant with reduced respiration rate and metabolic adjustments associated with the dive response. The reduction in MR during submergence was less when dolphins produced clicks, compared to when they were silent. On average, MR during submerged clicking was 1.1 X MR during submerged silence. MR increased linearly with increasing cumulative energy flux density (cEFD) of all clicks produced during bouts; however, most MRs measured during click production were within the range measured for silent dolphins. Thus, the energetic cost of click production in submerged bottlenose dolphins is negligible. Unlike bats, dolphins produce echolocation signals independent of respiratory cycles via a complex nasal structure that recirculates air while breath-hold diving. This minimizes oxygen consumption while clicking, and consequently, dolphins echolocate at a low energetic cost.
