Filtering tiny zooplankton from the sea, baleen whales have three options for getting a good mouthful of water. They can slurp it up, swim continually with their mouths open or lung forward intermittently. Jeremy Goldbogen from The University of British Columbia explains that humpback whales and other rorqual species have adopted the lunging approach to feeding. However, their foraging dives are much shorter than the foraging dives of whales that continually filter the sea, which suggests that the energetic cost of lunging is significantly greater than the cost of constant filtering. Curious to know whether lunge-feeding whales breathed harder as a result of their exertions, Goldbogen and colleagues successfully tagged two humpback whales off the California coast to record their foraging lunges and the number breaths they took after returning to the surface (p. 3712).
Analysing the results, the team found that the animals take longer dives when they lunge more. The animals also take more breaths when they return to the surface after a long dive than they do when they surface after shorter dives.
So surfacing humpback whales breath more heavily after a series of lunges, but this doesn't necessarily mean that lunge diving is more energetically costly than simply sitting beneath the surface and not exercising, such as when singing.
Comparing dive lengths between lunging and singing whales, Goldbogen found that the singing whales could remain submerged for twice as long, and that lunging whales breathed three times harder when they returned to the surface. So lunge feeding is certainly an energetically costly alternative to other more sedate feeding styles.
- © The Company of Biologists Limited 2008