House Martin Delichon urbica, Hirondelle de fenêtre.
MV 2 9 28 Which pries not to th'interior but, like the martlet,
MAC 1 6 4 The temple-haunting martlet, does approve,
The martlet originally nested on cliffs and crags, and was likely to be confined to the coast, hill and mountain areas. The eaves of buildings provided it with ideal sites to which it has progressively moved, with continuing limited use of more natural sites. It must have increased and spread enormously over the centuries, as human settlement building increased.
From the detailed description Shakespeare makes of the nesting habits of the martlet, we can be fairly sure that it is the species we call now House Martin that he is talking about. The Swift Apus apus, Martinet noir, does not make a "pendant" nest while the Swallow Hirundo rustica, mentioned elsewhere under this name by Shakespeare (see SWALLOW), prefers not to build on the outside, "on the outward wall".
This habit of building its nest in places which look inviting, but are in fact dangerous provides Shakespeare with an illustration "to emphasise the irony of the deceptiveness of appearances" (SPURGEON, p. 187). This is evident in the Merchant of Venice where Arragon, who has to choose which casket to open, explains that he does not belong to
[...] the fool multitude that choose by show,
Not learning more than the fond eye doth teach,
Which pries not to th'interior, but like the martlet
Builds in the weather on the outward wall,
Even in the force and road of casualty.
(2 9 26-30)
The other occurrence of the martlet is found in Macbeth. Duncan, upon arriving at Macbeth's castle, engages the following dialogues with Banquo:
This castle hath a pleasant seat; the air
Nimbly and sweetly recommends itself
Unto our gentle senses.
This guest of summer,
The temple-haunting martlet, does approve,
By his loved mansionry, that the heavens' 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.
(1 6 1-10)
These casual remarks about the sweetness of the air and the bird create a strong dramatic contrast with the events that follow.
SPURGEON concludes her analysis of the martlet image by commenting that:
In each case a guest arrives, Arragon or Duncan, a guest who is to be 'fooled' or deceived, Arragon to find a fool's head instead of his bride, Duncan to be foully murdered by his thane and kinsman. A possible reason for the connection in Shakespeare's mind between the house martin and someone who is fooled or duped is that in the sixteenth and seventeenth centuries a kind of slang term for a 'dupe' was 'martin', and the word is so used by Greene and Fletcher.