House sparrowThe BBC's week long focus on invasive species certainly got people talking, which is always good. Let me throw a brick into the debate. As our ancestors explored the globe and created new trade routes, they took house sparrows with them. The descendants of those early sparrow settlers are now invasive species in other countries.

House sparrows are probably the world's most successful introduced bird. Originally they were just found in Europe and bits of Asia and North Africa. Now, you'll come across them in the Falklands, South Africa, North America, Hawaii and New Zealand. In fact, they occupy a quarter of the earth's land surface. Pretty impressive for a tiny brown and grey thing.

Our UK house sparrows are vanishing. Will we one day have to re-introduce them from those colonies we established elsewhere? I hope it never comes to that. Would you miss them if they were gone? I certainly would and judging by the responses of people who've visited our sparrow-watch on the South Bank in London, many of you would too.

Our Aren't birds brilliant! event on the South Bank is incredibly timely. It's the golden anniversary of the sparrow being declared public enemy number one in China by Chairman Mao. In 1958, he declared war on the imperial invader and ordered peasants to bang and shout to prevent sparrows landing and colonising China. He wanted them to be kept in the air until, exhausted by constant flying, they dropped dead from the skies.

Does this make the commune living sparrow an emblem of market driven democracies? Is its fate linked to the success of our western economies? The answers are respectively no and sort of yes. Just because Mao didn't like tree sparrows nicking grain doesn't make it a capitalist emblem. As for being linked with the economy; sparrows, do fare better in poor areas. They've pretty much vanished from London's rich financial heart - The City. However, I doubt very much that the present financial crisis will result in soaring house sparrow numbers.

To achieve that, we need to convince planners, architects, land managers and gardeners to do more for wildlife. Sparrows need seeds, bugs and dense shrubbery for shelter to survive. Encouraging people to do more for them requires lots of campaigning and letter writing. We're conducting new research in London on how to save sparrows. It involves growing different types of grass in public parks to support them. Whatever the outcome of the study, the more articles and letters we write highlighting the actions we can all undertake, the faster we can bring about change. Another case of the pen being mightier than the sward.