Sir – I write concerning the article by Christopher Gray last week, in which he suggested that declines in small birds are due to birds of prey.

This is a common reaction to the sight of a bird being killed by a sparrowhawk but there is compelling scientific evidence that small bird declines are due to food shortages, not predation. One of the most definitive studies was performed locally in Wytham Woods, where blue and great tit numbers have been monitored closely for over 60 years by Oxford University scientists. Sparrowhawks and other birds of prey were abundant initially but were entirely absent during the 1960s and early ‘70s, having been wiped out by agricultural pesticides (including DDT).

Following the banning of these chemicals, the birds of prey returned and have now built up to their former numbers. However, the numbers of blue and great tits have not been affected by either the loss or the return of the predators. The clear conclusion from this and many similar studies is that although sparrowhawks take small birds, they have no effect on their numbers which are limited mainly by the winter food supply. To put it crudely, the fewer small birds that are eaten by predators, the more die of starvation each year and vice versa.

It is disappointing that your journalist chose to base his piece on a newspaper article when there are scientists expert in this field right on his doorstep.

A final thought — many of our butterflies and moths have also declined in recent years — and small songbirds are known to eat huge numbers (many billions) of their caterpillars every year. Does Mr Gray think that the right way to conserve our butterflies is to cull our small songbirds?

Dr A. U. Larkman, Conservation officer, Oxford Ornithological Society, Bampton