Links to help with identification of Winter Moth and Northern Winter Moth

I posted this as a comment to Steve Trigg's question below, but the links don't work in comments, so I'm repeating it here - these are links to comparison images for Winter Moth (Operophtera brumata) and Northern Winter Moth (Operophtera fagata).

Main thing to look for is that Northern Winter Moth is a bit larger and paler (especially on the hindwing) than Winter Moth (but as ever worn specimens can be confusing). Check the undersides as well. If you can find the females they a bit easier to distinguish: both have reduced wings but Northern Winter's wings are less reduced than Winter.

And as Dave said below, Northern Winter is more closely tied to Birch and Alder trees, while Winter Moth feeds on a wider range of trees and shrubs.

• Comparison by Jon Clifton via Norfolk Moths
• Chris Lewis's British Lepidoptera page on winter and November moths
• Comparison from Northumberland Moths
• Comparison from Hants Moths
• Comparison from the German Lepiforum site, which includes info on the females

The specimen images on Lepiforum suggest that the underside of Northern Winter is noticeably paler than the underside of 'normal' Winter Moth, which may be a useful clue for moths on windows!