Crows

This is a little piece I wrote years ago and posted on my BDN blog. As an undergraduate I had dreams of becoming an ornithologist or animal physiologist. Being among the world's worst birders ended my ornithological aspirations, and, fortunately I feel, I ended up becoming fascinated with microbes (and am far better at recalling their names). Still, I find birds and animals interesting to observe. This piece also reveals a little about how, at least one scientist goes about thinking, and asking questions about, the natural world.

            At low tide the other day I observed an interesting sight, a pair of crows crabbing. Anyone who has gone down onto seaweed covered rocks in Maine and pulled back the rock weed has observed a menagerie of small intertidal creatures, amphipods wriggling around, mussels living in crevices, and often a crab or two suddenly exposed and then scuttling to get back under cover of a rock or more moist seaweed. The wily gull strolls its webbed feet over this potential cornucopia everyday with sharp eyes and a quick beak at the ready for an easy meal; eider ducks haul out in whole flocks to rest on the rock weed after a busy diving session just off shore to feast upon, among other things, crabs and mussels.

The crow is a less frequent visitor to the waterline. But there were these two crows crabbing. The technique was simple, grab a beak full of rock weed and pull it back with a flick of the head to expose the rocks underneath, and then a quick check to see if there was anything to eat. Within a few minutes each crow had found a small green crab. It was quite funny to watch because it was clear that a crow is not a bird well-designed for eating crabs. The crow would grab the crab with its bill, but the crab grabbed back, sharp pointed legs and grasping claws poking around the bird’s face and eyes. It took some quick juggling, including a few drops and retrievals, but the crow soon prevailed and down the hatch went the crab.  By contrast, a heron with its long thin bill can stab a crab and keep it at a safe distance while preparing it for dinner; likewise, the gull and eider have little problem with these sticky prey. But I have never seen any of these authentic crab hunters use the crow’s efficient technique.

Crow’s are known for their intelligence, but how had they figured this out. Is their hearing acute enough they can hear the movement of a crab muffled under several inches of seaweed? Is their brain wired to connect different pieces of information together in a logical context? A sound connected to a food source they rarely hunt, but removed from sight. We would refer to this as the ability to think in the abstract. This would be similar to what robin’s do when they hunt worms, but a worm is one of the robin’s primary food sources; whereas a crab for a crow would be kind of like bird’s nest soup to me (a dish I have never tasted).   Perhaps they use similar techniques to catch insects on land, and pulling up seaweed is not so different from pecking at a rotting log or pulling aside grass? Perhaps one of these crows had watched a crab crawling across the seaweed and then disappear underneath it and made the connection that way? Crow’s are also known for having remarkable memories. 

Another interesting observation is that several herring and black back gulls were standing on the railing of a nearby dock. I am not sure how much attention they were paying to these two crows, but as far as I can tell, a gull doesn’t miss much of what is going on around it. So why doesn’t a gull learn a hunting technique from a crow? If these had been other gulls hunting this way, would the observing gulls have learned the technique quickly? The way they learn to drop whelks, mussels and other hard-shelled food from a height onto the rocks to break them open.  This is the only time I have seen the crows doing this, so such a sticky meal may be only to their liking when they are really hungry. Or perhaps they just wanted to crow about their cleverness.