Contrary to wide held beliefs, bioscientists at the University of Birmingham have discovered that cormorants often expend more energy when hunting sedentary prey than when hunting fast moving prey.
Cormorants are extraordinarily diverse predators. At sea, they can chase down fast moving prey, but can also examine the sea floor, carefully checking between and under rocks for animals hiding in the shadows.
Dr Lewis Halsey, a researcher from the University’s School of Biosciences, says, ‘We believe that the cormorants typically expend more energy when diving for sedentary prey – simulated in our study by fish pieces - because they work particularly hard during the descent phase of the dive. The costs of accelerating quickly down through the water are high because these birds have air trapped in their bodies and their feathers.
‘We think that they choose to descend rapidly to limit the chances of such slow prey moving and hiding while the cormorant is at the water surface breathing. In contrast, we found that the cormorants descended more slowly when searching out motile prey.’
Dr Halsey continues, ‘No measurements have been made, up until now, to find out about energy expended when foraging and previously it might have been assumed that cormorants expend more energy when foraging for moving prey, because pursuit involves changes in speed which affects power requirements. We have, however, found the reverse to be true in all but dives of relatively long duration.’
Ends
Notes to Editors
1. For this research the double-crested cormorant was studied (Phalacrocorax auritus).
2. The paper is published in the Royal Society Journal. When cormorants go fishing: the differing cost of hunting for sedentary and motile prey by Lewis Halsey;
Craig White; Manfred Enstipp; Dave Jones; Graham Martin; Patrick Butler
(doi:10.1098/rsbl.2007.0121) Published online at 00.01 BST Wednesday 11 July 2007.
For further information
Kate Chapple, Press Officer, University of Birmingham, tel 0121 414 2772 or 07789 921164.