Brian Rudman: The morning chorus is no more: where have all the sparrows gone?

Reading the other day that Britain's - and New Zealand's - most familiar bird, the sparrow, seems on the fast track to extinction in its homeland, my first reaction was that they were welcome to repatriate a few dozen from my front yard.

Then it dawned on me that my early morning chorus had all but disappeared of late.

Just to make certain, I tested this suspicion with a quick slam of the bedroom window early yesterday morning. It was as I feared. Just three of my feathered friends managed to rouse themselves out of their nests and chatter off to the safety of the nearby power lines.

In past years there would have been dozens fighting one another for a new perch, while other, more bolder birds, would have stayed put, shouting defiance from their nests.

Not that it needed the slam test to tell me something was wrong. With a large colony of sparrows living in the ivy running up the front of my house, at times it's been like living in a tree house.

They used to wake me up in the morning, which was certainly more pleasant than a radio alarm, and signal the arrival of the neighbourhood cats. But this summer it's been very quiet.

Where have they gone? And does anyone care? I drew a blank at the university, the SPCA and the zoo.

Pam Howlett, the indefatigable bird rescuer on the Tamaki River, didn't have any definitive answers either, though she did reassure me I wasn't delusional. She'd had calls for years from people noting there weren't as many sparrows as there used to be.

Searching further afield I came across a torrid debate about the subject a month ago in the Bay of Plenty. A woman wrote to her local newspaper putting the absence of sparrows from her garden down to electro-magnetic fields from burgeoning cellphone towers.

A grape grower wrote back suggesting she relax, that the birds hadn't been zapped with hidden rays, they'd just gone on vacation to his vineyard. With no vineyards nearby, I fear that's not the answer to my problem.

Neither are the neighbourhood cats. Sure, for years they've been knocking off the halt and the careless of the colony, but never before have their activities threatened its existence.

A more likely, at least part explanation is a strain of animal salmonella typhimurium DT160 infection which has spread up the country from the South Island, decimating sparrow populations as it went.

Most scientific interest seems to have concentrated on the effect of this strain of salmonella on humans, not birds.

A spokesman for the Ministry of Agriculture and Forestry said last August that there was now a reservoir of the salmonella strain in the sparrow population and probably other birds.

But whether salmonella is the cause of my missing sparrows - or even part of the cause - I have no idea. Certainly I haven't spotted a writhing body during the course of the great disappearance, but perhaps the four-legged vacuum cleaners got to the stricken birds before I did.

In Britain, outbreaks of death among sparrows and greenfinches were first reported in the 1960s when the general public started putting out bags of peanuts for the wild birds. The birds were found infected with either a strain of salmonella DT40 or another bacterium, E coli 086. The infection doesn't come from the feed put out for the birds, but the fact that the birds congregate together at feeding tables and infect one another.

A report by the Royal Society for the Protection of Birds on the state of Britain's birds in 1999 says the number of house sparrows are down by 58 per cent compared with the mid-1970s and tree sparrows down 87 per cent.

The decline has been so dramatic that recently the British Trust for Ornithology placed the house sparrow on its red list of endangered species. It said that between 1994 and 2001 house sparrow numbers in London fell 70 per cent - and there was no sign of recovery.

Falling numbers are stopping breeding and - once below a crucial threshold - causing colonies to dissolve.

That certainly seems to be the case in my once-thriving sparrow colony. The shame is, by the time the politicians and the experts get their act into gear, both here and in Britain, it could be too late.

Which will be a shame.

I'll have to wake to the raucous noise of radio instead.