In praise of head extensions; or how the cormorant got its neck

A long neck has obvious pros and cons but in the case of highly specialised diving seabirds there seems a real dichotomy, with cormorants having extreme necks while penguins and auks have minimized necks. We attached acceleration loggers to 10 Imperial Cormorants Phalacrocorax atriceps and six Magellanic Penguins Spheniscus magellanicus to examine the difference in movement between their respective heads and bodies. The penguins had head and body attitudes and movements that broadly concurred throughout all phases of their dives. In contrast, although the cormorants followed this pattern during descent and ascent dive phases, during the bottom (foraging) phase of the dive, the head angle differed widely from that of the body and its dynamism (measured using vectorial dynamic acceleration) was over 4 times greater. It is suggested that having the head on an extended neck allows these cormorants to half the energy expenditure that they would otherwise expend if their body moved in the way their heads did. This energy-saving solution is, however, only tenable in slow-swimming species since the loss of streamlining that it engenders would make it detrimental for fast-swimming taxa such as penguins.