The stack has never been inhabited, but has contributed considerably to the local economy by supplying the St Kildans with sea birds and their eggs.

He wrote of Stack-donn[Note 4]that: It is much of the form and height of a steeple; there is a very great dexterity, and it is reckoned no small gallantry to climb this rock, especially that part of it called the Thumb, which is so little, that of all the parts of a man’s body, the thumb only can lay hold on it... and having a rope about his middle, that he casts down to the boat, by the help of which he carries up as many persons as are designed for fowling at this time; the foreman, or principal climber, has the reward of four fowls bestowed upon him above his proportion; and, perhaps, one might think four thousand too little to compensate so great a danger as this man incurs; he has this advantage by it, that he is recorded among their greatest heroes; as are all the foremen who lead the van in getting up this mischievous rock.

This was almost the trickiest part of any expedition to those stacs like Lee, Armin or Biorach, which to the inexperienced eye seem to rise sheer from the water, smooth and unapproachable as pencil leads.

[7] Today climbing in all of the St Kilda archipelago is subject to the permission of the National Trust for Scotland,[25] which rarely grants it.

In 2023 a small group of British climbers, including Robbie Phillips from Edinburgh, completed the climb of Stac Biorach, the first documented ascent in over 130 years.

It’s a testament to their bravery and mental fortitude; to climb onto that sea stack 70m above the raging Atlantic without even shoes is wild to imagine".

[8] Haswell-Smith states that landing is only possible on three days in a summer month on average and that sailing the narrow channel between Stac Soay and Hirta is "possible in good weather".

[26] Like the other stacks and islands of St Kilda, Stac Biorach is extraordinarily rich in birdlife, and boasts the largest colony of guillemots in the archipelago.