A Black Grouse and several groups of Red Grouse (totalling around 24 birds) were in roadside fields between Drumochter and Dalwhinnie (no doubt forced down from the hills by the lying snow). 
With limited time in Aviemore, a walk around Craigellachie NNR seemed a good idea. Birds were fairly thin on the ground but two tit flocks were encountered, the first containing twelve Long-tailed Tits, two Blue Tits, two Coal Tits, five Goldcrests, and one Treecreeper, and the second seven Goldcrests, three Blue Tits, two Coal Tits and two Treecreepers. A Raven flew over unseen and Bullfinches were at two sites. Several Wrens were seen including one singing strongly and one which disappeared into a hole in the snow, presumably to feed in the Heather underneath. Best birds at Craigellachie were around 60 Redpolls in a feeding flock next to the A9.

Two Redwings were calling from the back garden of the Cairngorm Hotel and birds overhead included Herring Gulls, Collared Doves, Rooks and Jackdaws.
A quick detour down to the Spey produced a drake Goldeneye (a pair were also under the Spey Bridge east of Kingussie) and a singing Dipper.

Impressions of Strathspey in December:
It's virtually monochrome, with bare trees silhouetted against the snow. However the result is that the colours of the small birds (Blue Tit, Long-tailed Tit, Redpoll etc) stand out all the more.
It's eerily quiet with the only sound from passing tit flocks (although in Aviemore, the Jackdaws and Herring Gulls produced a bit of noise).
Birds are concentrated around the villages (in this case Aviemore). In the countryside they are mostly in flocks.