It is very common here in Bensonhurst to have in front of your house a Mourning Bird nest from pesach to sukkoth. In order to preform Sheluach Hakan, note that the mother sits on the eggs/chicks late evening/night hours so make sure to preform the mitsvah close to nightfall.

You must scare the mother away, then take the nest---raise it 3 tefahim--then you may return it, the mother will usually come back. If the tree is in your yard that can be considered a Hazer Hamishtameres, then it may be a problem, b/c you are Zoka the eggs and it is considered Mezuman. So you may say in front of 3 I am Mafkir the birds!

If the trunk is on the sidewalk and the nest is inside your yard, i suppose that we do not say "the branch follows the trunk" so whatever grows inside the yard belongs to the master of the house.

Please find a nice article on http://www.nergavriel.org/uploads/%D7%AA%D7%95%D7%A8%D7%94%20%D7%94%D7%A7%D7%93%D7%95%D7%A9%D7%94/kashrus/The%20Mitzvah%20of%20Shiluach%20Hakan.doc