What are the symbols and their significance in Macbeth Act 4 Scene 2?What are the effects of the symbols in macbeth act 4 scene 2

A symbol is something concrete that stands for a more
abstract characteristic or concept.  In this scene, one of the most obvious symbol is
that of birds.  Birds symbolize different things depending on the type of bird with
birds of prey generally representing evil or danger while smaller birds represent
freedom and innocence.

Lady Macduff uses a bird to describe
her feelings about her husband and his quick departure.  She notes
that

The most
diminutive of birds, will fight  Her young ones in her nest, against the
owl.

She intends to make the
audience feel as if Macduff has shirked his duty, leaving his young ones in danger.  He
has no courage, according to his wife, and no drive to save his
family. 

The effect of this symbol is to further the idea
of flight in the play.  Malcolm and Donalbain have "flown" to England and Ireland. 
Macduff has now "flown" as well.  Lady Macduff is warned to flee but choses not to,
asking "whither should I fly?"  She does not understand that she is in danger, thinking
instead only of her anger at her
husband.