It really depends on what species you want to see and what you’re up for. Some species (eg: crossbill spp, capercaillie, ptarmigan, dotterel) can require walking to get the best chance of a view. But the length and type of route can sometimes be matched to your ability, whilst still offering the chance for a sighting. See the Walking Grades page for an explanation of the different types of walking that may be encountered. The description for each activity will include the walking to be expected.
I can offer guiding via the Cairngorm funicular railway, which offers an alternative means of gaining views of ptarmigan and dotterel ( additional charge and conditions apply ).