There is an interesting thread (with links to sub thread) HERE on Birdforum, with some comments from yours truly (you will need to sign in or register to view the thread). It is funny how these things usually revert to Scottish Crossbills and whether they exist or not !
One of the latest posts questions can crossbills be identified by the depredated cones they drop ? Well, sometimes but it would be generalisation, albeit with over 90 odd percent confidence limits in my opinion. It really depends on the cone - is it a closed green cone, is it a 'dried' closed brown cone, how wet the weather has been etc.
A Scottish Crossbill 'worked' cone, with Commons it would tend to be the anterior portion of the cone that would be worked:
A female Parrot Crossbill, October 2006, Deeside, the cone showing the 'split' scales that can be diagnostic:
In another few weeks, depending how wet or dry it is, the Scots Pine cones will begin to partially open. Parrot Crossbill has it's breeding season synced in with this event, the young usually hatching to coincide with more easily available seeds. Here in Deeside in 2013 we had an almost 'year zero' with a very poor autumn 2012 Scots pine crop throughout much of the region and consequently breeding was nominal and numbers of crossbills have 'crashed'. At a study site in upper Deeside approximately only 1 in 10 Scots Pines produced a reasonable crop of cones, but in most cases the vast majority of cones were 'stunted', the cone directly below the 10 pence coin is 'normal' sized (Deeside, Feb 2013) :
With cones so small Parrot Crossbills would certainly find these too difficult to work as well as unprofitable. Abnormal weather patterns may have been partially responsible for this, but this is just speculation.
Looking ahead, I wonder if any of the English Parrot types will attempt breeding in late February through to April this year ? Sure fire signs are singing males, fighting males, courtship feeding and of course nest building (birds flying with twigs, grasses etc).