House guests in the nonagon roof beams of the gazebo

Four mud nests built into the roof -
"This guest of summer,
The temple-haunting martlet, does approve
By his loved mansionry that the heaven's breath
Smells wooingly here. No jutty, frieze,
Buttress, nor coign of vantage, but this bird
Hath made his pendant bed and procreant cradle;
Where they most breed and haunt, I have observed
The air is delicate." (Macbeth, Act I, scene VI)