Here are Mr and Mrs House Sparrow chilling out in my front tree. I think it's hard for the public to get their heads around the fact that House Sparrows in the UK are in serious decline. They are still regarded as a fairly common and historically ubiquitous little bird by many. In fact they are a Red Listed bird. "But surely there are millions of House Sparrows breeding in the UK," people might argue. Well, yes there are. More important than the base number though are the actually rates of decline. The decline of the House Sparrow isn't a recent thing. Numbers of the bird have been falling since the end of the First World War. In the last 30 years or so it is estimated that the decline is over 68% in the UK and it is figures like this that has triggered the bird's Red List status. This is not just limited to our country either - numbers are in freefall all over Europe. Scientists like Kate Vincent have been studying the phenomenon for years, trying to formulate an answer to why this is happening. One of the most likely theories is the lack of small insects that are needed for the survival of chicks and young birds. These birds can't eat nuts, seeds or many of the other foods that adult birds survive on and so if the insects are scarce, the chicks starve. The possible root cause: the loss of green spaces in urban areas and increases of pollution from car exhausts. Green spaces, trees etc are needed to support the large numbers of insects that the young birds need but unfortunately such habitats are disappearing as housing developments, roads and car parks proliferate.