Long necks enhance and constrain foraging capacity in aquatic vertebrates

RORY P. WILSON; GIACOMO DELLOMO; JUAN EMILIO SALA; AGUSTINA GÓMEZ-LAICH; FLAVIO QUINTANA; HOLTON, MARK D.

Puerto Iguazú

Congreso; I Ornithological Congress of the Americas; 2017

Association of Field Ornithologists, Sociedade Brasileira de Ornitologia y Aves Argentinas

Highly specialised diving birds display substantial dichotomy in neck length with, for example, cormorants and anhingas having extreme necks while penguins and auks have minimized necks. We attached acceleration loggers to Imperial Cormorants Phalacrocorax atriceps and Magellanic Penguins Spheniscus magellanicus, both foraging in waters over the Patagonian shelf, to examine the difference in movement between their respective heads and bodies in an attempt to explain this dichotomy. 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 the descent and ascent phases of dives, 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 - VeDBA) was over 4 times greater. A simple model indicated that having the head on an extended neck would allow these cormorants to half the energy expenditure that they would expend if their body moved in the way their heads did. This apparently energy-saving solution is likely to lead to greater heat loss though and would seem tenable in slow-swimming species since the loss of streamlining that it engenders would make it detrimental for fast-swimming taxa such as penguins.