While taking a walk around Lake Temescal in the Berkeley, CA hills the other day, I noticed there were a few Cormorants in among the rest of the aquatic inhabitants of the lake.
The Cormorants must have just finished their morning meal because most of them were intent on spreading their wings to dry off.
That strange head positioning, like a person tilting their head to look out through the bottom of their bifocal lens got me to wondering why they maintain their heads at that angle. Is there something peculiar about Cormorant vision related to their prowess as underwater fish catchers?
Some researchers speculated that Cormorants might possess superior underwater vision because they are so successful in capturing prey in 70-80% of their attempts. But, in fact, their visual acuity is no better than ours (without a dive mask) underwater, so how do they do it?
Cormorant visual acuity is definitely poorer under conditions of low light, high turbidity, and in open water lacking any sort of underwater structures. In fact, they do far better in habitats where they can chase fish out of their hiding places. And they will strike at anything that moves — fish or other, moving objects — by lunging at the intended prey with a rapid neck extension, much like herons and egrets striking from above down into the water. So they are apparently cued by movement, not definitive shape of a prey item.
Once they have snatched something in one of their diving forays, they bring it up to the surface to inspect it, and powerful extra-ocular muscles move the eyes to focus on the tip of their bill to see what they have caught. If it’s edible, down the gullet it goes; if not, they spit it out.