For fellow baby boomers, the demise of house sparrows is an obvious and distressing sign of the crisis in nature around us. In a week when we celebrated World Sparrow Day, it was sad to also see a stunning survey from France, showing a collapse in bird numbers generally there. Why have house sparrows, a ubiquitous and cheery part of my childhood, run into such hard times that they are now a "species of conservation concern" in the UK? Aspects of their story are entirely typical of many other species in trouble here. The first common characteristic is that people don't really know the answer. It's difficult to research even house sparrows - a pretty charismatic and high profile species. There's probably a combination of factors at work, so far as I can gather. Maybe there are fewer nest sites. Availability of food seems to be a problem. It could be that pollution impacts on them, although numbers in town seem to be declining at the same rate as their country cousins. Maybe it's rising numbers of predators. Disease might also be a factor. I've heard the same answers as to why almost anything is disappearing- bees, bats, butterflies, hedgehogs, crickets... There is rarely a smoking gun, that's the point. The environment is much more complicated, to the irritation of many campaign groups. Even if you have a relatively clear cut case - like albatrosses and long line fishing - you won't save them from extinction purely by banning it. There's much more going wrong. It's impossible to weigh different factors or to isolate them, even if you had the funding to try to. In an area I know more about - honeybees - it's tempting to point the finger exclusively at the ghastly neonicotinoids. However, honeybees are struggling for a variety of reasons, neonics among them. In no particular order and in combination there's weather, climate change, varroa, habitat loss, monocultures, fungicide use, pesticide use... Again typically, elements in the house sparrow story suggest we're missing a key piece of interpretation. Numbers in the south east seem to be under more pressure than in the south west - why's that? As usual, when we don't know, odder - and unproven - theories take hold. Apparently mobile phones - once held to be decimating honey bee populations - are now also potential culprits for falling sparrow numbers. Sigh. So what can we do? What we can. Better and more plants, more seeds and bugs in our gardens. Nestboxes, nice thick hedges. Clean feeders. No pesticides. Cross our fingers.