How do you get the pieces of heart on the way to Zora's Domain?

As you guessed, the way to get them is to use the chicken.

http://www.ign.com/wikis/the-legend-of-zelda-ocarina-of-time-3d/Zora%27s_Domain

River Heart Pieces

There are two Heart Pieces to grab while en route to Zora's Domain. They are attainable only with the help of the lone cucco near the Magic Bean. Grab the cucco and jump to the other side of the river. Walk until you hit a wall, then make a short jump across the water to the left. Keep going higher by jumping across the small gap to the left. Take a right after the gap and keep walking. You'll see the heart piece sitting on a platform off to the right. Use the cucoo to flutter you over to the high platform in front of you, but when you're about to hit the ledge, toss the cucoo in order to make Link grab onto the ledge and pull himself up. Then make a daring leap toward the heart piece and Link will just barely latch on to the edge. Hoist him up to obtain this Heart Piece.

Retrieve your cucco friend. If you can't find him, exit and re-enter the area; he will return to his original location. With chicken in hand, work your way up along the river, watching out for Octoroks. When you get to the large waterfall, walk up as high as you can and look around. You should spot a Heart Piece on a ledge protruding from a wall. Jump and hover to it to receive another Heart Piece.