Who killed Cock Robin? Or more accurately, who killed Mock Robin? This is the question US virologists have been asking recently, and the answer could be critical to the understanding of the spread of that enigmatic disease that has started colonising various parts of the world, West Nile virus. The trouble is, vital though the answer may be, there are some who don’t like the question in the first place. And when people don’t like a question, it’s usually got a back-story.
This particular story began several centuries ago when the first hopeful and undoubtedly homesick colonists set foot on the shores of North America to begin life in their brave new world. Now, brave new worlds are all well and good, but you can’t visit them without bringing some nostalgic baggage from your old world. You left a town called Plymouth, so why not call your new landing place Plymouth, too? For good measure, you decide to name the land New England, and get rid of anyone already there who doesn’t look much like the folks back home. And when a friendly little bird turns up and you notice its red breast, you smile and think of those distant fields and woods, and immediately call it a robin. Even though it acts like a thrush, is the same size and shape as a thrush, and, in fact, is a thrush… Well, it’s a robin now.
The American robin became very popular across the continent as the colonialists took hold and spread. They listened to its sweet song, they caged it to listen to it at close range, they shot and ate it and enjoyed its tasty flesh. Then, like the rest of us, they changed tack and admired it as it called from woodlands and wandered around the garden looking for earthworms. Today, it’s the state bird not only of Michigan, but also of Connecticut. Oh, and Wisconsin, too. Only three birds represent more states than the American robin, which is still a very popular friend.
So the news that it might be partly responsible for the spread of West Nile virus has not gone down very well. To date, some 200 species of bird have been found to contain the virus, which is then transmitted to humans by mosquitoes in search of fresh blood. In most cases, the symptoms are flu-like and pass through the system relatively harmlessly. But the virus can kill: 667 Americans have died from it so far. Many believe that crows are the main hosts of the virus, but recent research carried out in Connecticut has shown that no less than 40 per cent of viruscarrying mozzies also carry blood containing DNA of the iconic robin; whereas only 1 per cent had been feeding on crows. In fact, crows, which started dying in great numbers when the disease first struck, are now making a comeback. Could it be that they’ve developed an immunity? Or could the virus have subtly changed?
The news of the robin’s complicity with West Nile virus swept the nation. Even though other common birds, such as the house sparrow, gray catbird and mourning dove, were also implicated in the study, it was the beloved robin that hit the headlines. Local and national press picked up on the story at the end of July, and a spokesman for the government agency the Centers for Disease Control and Prevention was wheeled out to make a comforting statement: ‘I’d be surprised if the American robin would be very important,’ he said. ‘I wouldn’t jump to the conclusion that crows are not important. If this study analyses mosquitoes where there are lots of robins but no crows, that could be misleading.’ And all this before he’d even seen the Connecticut scientists’ data.
Now, of course, it could be that the Connecticut data is based in some way on a poor sample (although similar evidence is emerging from a New York-based study, too), but to dismiss it out of hand before you’ve even seen it is staggering. Any lead in a medical mystery that kills so many is surely worth investigating thoroughly before making pronouncements. And be in no doubt that this is a mystery: no one’s sure exactly which species of mosquito is the main carrying culprit, and there are some who think that the spread of the disease might not even be due to mosquitoes at all.
But then, perhaps this nervousness is unsurprising. It’s all due to that back-story. After all, to think that a deadly virus that arrived from overseas and quickly spread across the land might be hosted by a bird that welcomed the Pilgrim Fathers… Well, that could make for a very uncomfortable metaphor.
This article first appeared in the Ecologist September 2005
