Nuthatch
It is only in the last few years that Nuthatches have become common in the Rannoch area. It is almost certain that they are responding to climate change and are moving north. They are now frequent visitors to bird tables where they have a fondness for peanuts.
The RSPB fact page is somewhat out of date as it says they are found in England and Wales and sometimes in southern Scotland.
Their dagger-like bill is ideal for extracting whole peanuts from the bird feeder just as it is for getting insect larvae from under bark as they move down trunks of trees.
Nuthatches nest in holes in tree trunks and if a hole is too large they will close it down with mud until it is the right size.
The nuthatch has a very distinctive call and is more often heard than seen.
Creative Commons - credit Andy Morffew