In Matthew 13:31-32 Jesus talks about the kingdom of heaven and what it is
like. The mustard seed starting out small and growing into something big(a
tree that grows 10-15ft high). My question

is what do “the birds of the air” symbolize in this passage? Is

there any reference in scriptures that would help identify this?

A general rule of interpretation of parables is that one should be
careful not to read too much into the parable. It is a common mistake to
over-symbolize the parables of Jesus–to force them to say things that are
not justified by the text. In general, the parables have a very simple
message. In the case of Matthew 13:31-32, the message of the parable is
that the kingdom of heaven (which is synonimous with the kingdom of God in
the other gospels)may start small, but with the proper care and by the
power of God, it can become very large. The fact is that although mustard
seeds are very small, the plants which are produced from them are
sufficiently large for birds to perch on their branches. It is my opinion
that there is no symbolism implied in the birds which perch on the
branches in Jesus’ parable. This is just a natural part of Jesus’
illustration about the phenomenal growth of the kingdom of God. Jesus is
explaining that although his kingdom would start small, it would grow to
include many people. This is indeed what happened.

John Oakes