PATRICK Stirling-Aird (Letters, November 26) kindly provides us with percentages of occupation of breeding pairs of peregrine falcons in relation to land usage but I am not quite certain what point he is trying to make

Research has clearly shown that in the last century peregrines were decimated by the use of DDT on agricultural land. This not only poisoned many birds but also made a high proportion of the remainder infertile. This would appear to be by far the most significant reason for the dramatic decline in breeding pairs.

As a species recovers it is logical to assume that they will repopulate the areas most conducive to protective cover, food supply and breeding success. This would obviously be the farmland and deer forests where food sources are much more readily available than on windswept heather-covered grouse moors. I would suggest that as overall numbers increase the percentages will even themselves out though this should be looked at in comparison to percentages prior to the impact of DDT.

Another factor which now effects peregrine numbers is the massive increase in competing raptors which is being encouraged by raptor groups at the expense of other species. Man has significantly altered the balance of nature in which peregrines thrived even to the extent of having artificial feeding stations turning the birds into tourist attractions. As an example, most people will have noticed that buzzards are now an everyday sighting in any part of the country.

I am sure Mr Sirling-Aird did not intend to suggest that grouse moors were culpable for the smaller percentage described. He is no doubt aware that there are many factors effecting peregrine numbers.

David Stubley

22 Templeton Crescent,

Prestwick.