Through Birds’ Eyes: What does vision tell us about the aquatic foraging of Cormorants?

Moving swiftly on from Ancient DNA to the mysteries of foraging seabirds this week’s guest in the Second Nature events series is Professor Graham Martin from Birmingham University’s Centre for Ornithology.

Professor Martin is the Professor of Avian Sensory Science and will be telling us about his work on Great Cormorants:

Photo by Sławomir Staszczuk

Great Cormorants (Phalacrocorax carbo) show the highest known foraging yield for a marine predator and they are often perceived to be in conflict with human economic interests. They are regarded as visually-guided, pursuit-dive foragers, so it would be expected that they have excellent vision much like aerial predators, such as hawks which detect and pursue prey from a distance. However, research shows that underwater the visual acuity of Cormorants is surprisingly poor (in fact, similar or worse than unaided humans under water) and very inferior to that of aerial predatory birds.

I suggest that Cormorants are able to detect typical prey items only at close range and conclude that cormorants are not the aquatic equivalent of hawks. It seems that their efficient hunting involves the use of specialised foraging techniques which employ rapid neck extension to capture prey that cormorants flush from hiding places; much like the foraging techniques of herons. Cormorants seem to be hunting an “escaping blur”. Like herons, the eye movements and visual fields of cormorants allow visual scanning for escaping prey in a wide arc about the head. The ability of cormorants to see prey held in the mouth may help to aid its identification when it is brought to the surface before swallowing.