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