Funnily enough, we just did the Perthshire drive yesterday (taken from "Best Birdwatching sites in the Scottish Highlands" by Gorodn Hamlett (see Amazon)). We started by heading from Dunkeld to Loch Freuchie and passed a field with 9 black grouse. Also loads of common gulls, oystercatchers, lapwings, curlews and jackdaws in the fields.
Heading into Glen Quaich were meadow pipits and red grouse. Stopped halfway along the loch and my wife spotted a large bird in the trees on the island. Turned out to be a white tailed sea eagle. Being harrassed by common gulls, it took off, circled the island and then flew straight over our heads. Also seen from here were red grouse, lapwings, curlew, meadow pipits, canada geese, greylag geese, goosander and tufted ducks. The road was closed near Garrow, so we doubled back to take the road to Aberfeldy (1 loch on this road - completely frozen and snow covered - but plenty of forest to explore).
We rejoined the route and headed for Ben Lawers visitor centre. We got to the Ben Lawers car park (it appears there may not be a visitor centre anymore) and the road was closed here too. Buzzards seen here with deer on the slopes.
With these 2 roads closed we thought we'd give Glen Lyon a miss as it was likely this may be closed too!