In the 2021 Census of Population conducted by Statistics Canada, Birsay had a population of 40 living in 20 of its 35 total private dwellings, a change of  from its 2016 population of 46.
In the 2021 Census of Population conducted by Statistics Canada, Birsay had a population of 40 inhabitants residing in 20 out of its total 35 residential units, indicating a decline from its 2016 population of 46.