Madam, - Further to the letters from Ailbhe Logan (November 12th), Henry Grattan Bellew and Peter Pearson Evans (November 21st) I would like to note that despite the many and various theories, no-one has yet solved the mystery of the recent drastic reduction in house sparrow numbers. The London Independent newspaper's reward of £5,000 for a solution remains unclaimed to date.
Current theories include: air pollution, lack of nesting holes due to changes in building design, increased predation by cats and birds of prey in urban areas, changes in agricultural practice (e.g. autumn sowing), improved food storage/hygiene practices, increased competition from feral pigeons, or unknown pathogens and/or parasites. Adding to the mystery is the fact that while sparrow numbers have plummeted in London, Glasgow and Hamburg, the populations in Paris and Berlin appear stable.
Denis Summers-Smith, an acknowledged worldwide expert on sparrows, has suggested that air pollution caused by the MTBE in unleaded petrol may have caused a decrease in insect numbers. Although as adults house sparrows are predominantly seed-eaters, their nestlings are fed almost exclusively on insects for the first week to ten days of life.
However tempting it may be to blame the ubiquitous magpie, research on their diet suggests they are more likely to prey upon the young of "cup" nesting birds than on "hole" nesters such as sparrows.
As I have noticed a decline in numbers in my home town of Donegal over recent years I would be very interested in any observations or comments from readers in other parts of the country. (As an ecologist I have a particular interest in sparrows and have been studying them in London for the past two years.) - Yours, etc.,