When birds are on territory how do they react to their neighbors' song?

They invariably get very excited and display and sing to them

They do not react to them even if they have ventured into their home territory

As long as they are where they are supposed to be $$they do not react very much

Invite them to brunch

They move to the edge of the territory and meet to reinforce their social position

Don't know how to get rid of this answer $-$ so don't choose it$!$