Power
Power is one of the main themes in the play. Peisetaerus and Euelpides have left Athens because the power-mongering over laws has become too much for them. But, they soon teach the birds how to become the new gods. Aristophanes shows how easily it is for power structures to be created through past tales revealing genealogy, impatience, and vanity.
New Gods
This theme has to do with the fact that men, once they learn of the new gods -- the birds, attempt to manipulate them to get an upper-hand in their schemes for money on earth. This theme reveals that man will follow whatever god will best suit their abilities to grow more wealthy and allow them more leniency in their acts.
Morality
Morality is a major theme of this play. Peisetaerus sets out to get away from all of the laws of Athens, and in turn sets up the new gods that will allow man and him to need not the necessity of denial, that all of their desires would come true. Worshiping the birds as gods has to do directly with the fact that man will follow any god that allows them to continue to do bad, rather than be transformed into right living.
