When Glint Hawk enters the battlefield, sacrifice it unless you return an artifact you control to its owner's hand.
1/1/2011 You may choose to sacrifice Glint Hawk as its triggered ability resolves even if you control an artifact.
1/1/2011 You choose which artifact to return to its owner's hand as the triggered ability resolves. If you control no artifacts at that time, you must sacrifice Glint Hawk. Although players can respond to the ability, once it starts to resolve and you choose an artifact you control to return to its owner's hand, it's too late for players to respond.