I want to post my thoughts on moth recording in general in Calderdale and hopefully start a discussion on the matter as I don't claim to be correct in all aspects of what I say, these are just my own personal thoughts on the matter
Its not surprising that more "new" species are being recorded in Calderdale each year. This is due to the fact that in the past (and I speak from personal experience here) there were maybe one or two people in any period regularly recording moths in Calderdale. When I started, apart from Brian Cain recording in his garden in the middle of Halifax, there was only me with help from Martin Todoff and Ian Kimber. Second point on this is that we probably have less pollution and a higher annual mean temperature that at any time in the past when moth recording was taking place. This is obviously going to increase the range of species if not the number of moths recorded.Third point on this is that much more of Calderdale is now being regularly light trapped and searched than at ANY time in its past so again more species are turning up. Fourth point is this, probably some of the "new" species to Calderdale are not new at all but have been here all along but no one looked in the right area for them before.
The facet I find most interesting personally is the comparison with Collinsons statement of realative abundance of each species. My own figures tended to tie in with Collinsons for the more common species which were recorded in numbers. This poses the question, why if we suffer much less pollution are these moth populations not growing ? This leads onto speculation that "improvements" in agricultural methods, vastly increased road traffic (just check how many moths are stuck on your radiator grill when you drive at night),the huge increase in light pollution and lastly the vast areas of Calderdale that have been built on in the last 60 years have all played their part. One can only conclude that despite the drop in atmospheric pollution and cleaner rivers, many species are just about hanging on and if the "progress" of the last 60 years continues then ours might be the last generation to be able to record moths in Calderdale in any meaningful way, especially in lowland habitat. This in turn makes every record of every species vital in the fight to try and preserve habitat in Calderdale now, so that hopefully we will not be the last generation to record these marvelous insects