Thanks to Rab for identifying the song.

I listened to the Gaberlunzie recording on Spotify. Here's my attempt at a transcription. Note there are a couple of gaps (…) and there may be other errors.

It's often I dream
O the hills above bonny Wemyss
And Breadalbane sae fair.
I long to be there,
In the country o my kinsmen,
Oer the moor and mountain way
And the Tummel ever windin'
To the Tay.

I weel mind the day
I saddled and rode away
When muskets torch and sword
And my father's proud words
For I spurned the royal bounty
Of yon … German king
Just to listen to the bonny
Blackbird sing.

And I echoed each note
That sprang from his bonny throat
And I followed him well
To Drumossie's dark dell
Where the dream of Scotland's heroes
Fell before the southron host
With the dream of freedom trampled
In the dust.

Now they ravage our lands,
The kilt and the claymore banned.
The blackbird's away,
In exile to stay,
And the lowland shores of Holland
I must take to for my shame,
For I'm banished and forbidden
Frae my hame.

But Scots, should you hear
In some distant future here
The clear crystal tone
Of the blackbird's sweet song
And a fighting force of freedom
Will ascend the … glen
When the blackbird sings for Scotland
Once again,
When the blackbird sings for Scotland
Once again.