How did Sasuke get his hawk summoning technique? When Sasuke fights Danzo, on chapter 477 page 9, he uses summoning technique and a hawk appears.
How and when did he sign a contract with hawks, and thanks to whom did he get it?
To symbolise his ascension from snakes (i.e. Orochimaru's power) he
  changed his team's name from Hebi (snake) to Taka (hawk). It is
  revealed that his animal-oriented techniques have also changed from
  snakes to hawks as shown from him summoning a hawk that he used to fly
  around on during his fight with Danzō, evade his assaults and in the
  anime perform coordinated attacks with Sasuke. It is currently unknown
  when he made a contract with them.


This can be found here under "Summoning Technique"