Egilsay Community Association list on their history page that:
'As part of the Bishopric estate the whole of Egilsay was feued to the Monteith family in the 16th Century. On the marriage of Marjorie Monteith to William Douglas, Chamberlain of Orkney, commemorated in the initialled skewputt, the island passed to the Douglas family.' 
There remains the Douglas house on Egilsay, named Howan House, and the Buildings At Risk register notes the following: "The skewputt to the north east is initialled WD MM for William Douglas and his wife Marjorie Monteith, 17th century owners and heirs to the Island of Egilsay. The interior of the house retains a carved lintel on the south wall inscribed 16.AMICUS.ET.GENO.81., decorated with a heart and fleur-de-lis transforming into roses and thistles. A badly weathered stone fireplace with fluted jambs sits in the west gable"